domestic renewable energy supply technology review: current status

Domestic Renewable Energy Supply Technology Review: Domestic Renewable Energy Supply Technology Review: Domestic Renewable Energy Supply Technology Review: Domestic Renewable Energy Supply Technology Review: Current Status and Future PotentialCurrent Status and Future PotentialCurrent Status and Future PotentialCurrent Status and Future Potential

EEEEnergy Policy Research in Domestic Buildingsnergy Policy Research in Domestic Buildingsnergy Policy Research in Domestic Buildingsnergy Policy Research in Domestic Buildings

Research Project funded under Technological Sector Research (2006) Strand III

Faculty of Business Faculty of Engineering

Faculty of the Built Environment Futures Academy

Dublin Energy Laboratory Focas Institute

Deliverable No. 2, WP3. Deliverable No. 2, WP3. Deliverable No. 2, WP3. Deliverable No. 2, WP3.

Ref: WP3Ref: WP3Ref: WP3Ref: WP3----Del02Del02Del02Del02

May 2008

Domestic RES Technology Review Dublin Institute of Technology

Energy Policy Research in Domestic Buildings i

CONTENTSCONTENTSCONTENTSCONTENTS

1111 OverviewOverviewOverviewOverview ................................................................................................................................................................................................................................................................................................................................................................................................................................ 3333

1.1 Introduction .............................................................................................. 3

1.2 Methodology ............................................................................................. 4

1.3 Summary of Findings ............................................................................... 5

1.4 Conclusions ............................................................................................... 7

1.5 References ................................................................................................. 8

2222 PhotovoltaicsPhotovoltaicsPhotovoltaicsPhotovoltaics ........................................................................................................................................................................................................................................................................................................................................................................................................ 9999

2.1 Technology Overview ............................................................................... 9

2.2 Capital Costs .......................................................................................... 10

2.3 Financial Viability .................................................................................. 10

2.4 Conclusions ............................................................................................. 12

2.5 References ............................................................................................... 12

3333 MicroMicroMicroMicro----CHPCHPCHPCHP ............................................................................................................................................................................................................................................................................................................................................................................................................ 13131313

3.1 Technology Overview ............................................................................. 13

3.2 Micro CHP technologies ......................................................................... 14

3.3 Micro CHP applications ......................................................................... 17

3.4 Benefits of Micro CHP ............................................................................ 18

3.5 Market Status ......................................................................................... 19

3.6 Conclusions ............................................................................................. 20

3.7 References ............................................................................................... 21

4444 Solar ThermalSolar ThermalSolar ThermalSolar Thermal ........................................................................................................................................................................................................................................................................................................................................................................................ 23232323


4.2 Capital Costs .......................................................................................... 28


4.4 CO2 Reduction Performance ................................................................... 30

4.5 References ............................................................................................... 31

5555 Micro Wind TurbinesMicro Wind TurbinesMicro Wind TurbinesMicro Wind Turbines ............................................................................................................................................................................................................................................................................................................................................ 32323232


5.2 Capital Costs .......................................................................................... 38


5.4 Financial Viabililty & Emissions Benefits ............................................. 45

6666 Ground Source Heat PumpsGround Source Heat PumpsGround Source Heat PumpsGround Source Heat Pumps .................................................................................................................................................................................................................................................................................................... 47474747



Energy Policy Research in Domestic Buildings ii

6.2 Capital Costs .......................................................................................... 49



6.5 References ............................................................................................... 51

7777 Wood Pellet Boilers & StovesWood Pellet Boilers & StovesWood Pellet Boilers & StovesWood Pellet Boilers & Stoves ............................................................................................................................................................................................................................................................................................ 52525252


7.2 Capital Costs .......................................................................................... 53



7.5 References ............................................................................................... 54


Energy Policy Research in Domestic Buildings 3

1111 OVERVIEWOVERVIEWOVERVIEWOVERVIEW

Aidan Duffy

School of Civil & Building Services Engineering

1.11.11.11.1 IntroductionIntroductionIntroductionIntroduction

1.1.1 Background

Policies in the areas of energy efficiency (EE) and renewable energy supply (RES) have taken centre stage at regional, national, European and global levels. Increasing oil prices, political volatility in fossil fuel-producing countries and global warming have impacted competitiveness, security of supply and environmental change in almost all countries around the world. Ireland is no exception – indeed, because of its heavy dependence on fuel imports (approximately 90% of total requirements) it is more exposed than most to problems of security of supply and competiveness. In addition, Ireland’s greenhouse gas (GHG) emissions’ are poor by comparison with other wealthy European states: per capita 2005 emissions were 22% higher than the EU15 average (EEA, 2008).

In January 2008 the European Commission published the Directive on the promotion of energy from renewable sources which commits the EU27 to increasing its share of renewable energy production to 20% by 2020. Ireland’s national RES target within this Directive is 16% of energy supply, increasing from 3.1% in 2005. At a national policy level Ireland’s 2007 Energy White Paper is more aggressive, committing the country to achieving:

“33% of our electricity consumption from renewable sources by 2020 with 15% the target for 2010”.

These targets present challenges for policymakers in allocating scarce resources to promote RES technology uptake, particularly when considering the range and complexity of solutions available. This report represents work in progress in addressing this issue at a residential sectoral level.

In 2005, the residential sector accounted for 25% of primary energy consumption (EPA, 2007). Rapid developments in RES technologies for new and existing domestic dwellings mean that there is significant potential to switch energy production in this sector to renewable sources of energy, reduce GHG emissions, improve Ireland’s security of supply and competitiveness.

This report forms part of an inter-disciplinary research project ‘Energy Policy Research in Domestic Buildings’ undertaken at the Dublin Institute of Technology and funded under the Technological Sector Reseach (2006) Strand III research programme.

1.1.2 Objectives

The main objective of this report is to identify domestic RES technologies which have the potential for widespread deployment in the Irish market. The



technologies will be included in detailed appraisals in the remainder of the research project.

1.1.3 Technologies

An appraisal of existing technologies was carried by means of literature survey, expert and supplier interview as well as a review of other technologies promoted internationally. The following RES technologies were considered to have potential within the residential sector in Ireland:

• photovoltaics (PV);

• micro combined heat and power (Micro CHP);

• solar thermal systems;

• micro wind turbines;

• geothermal energy using ground source heat pumps (GSHP); and

• wood pellet boilers and stoves.

Mini CHP or biomass boilers linked to district heating systems were also identified as having potential but will be considered in a separate report.

1.21.21.21.2 MethodologyMethodologyMethodologyMethodology

This report deals only with the technical feasibility, economic viability and CO2 abatement potential of the chosen technologies. It does not consider other factors which are essential for technology uptake and success such as: market conditions, supply chain issues and buyer/user behaviour; these will be dealt with in other project reports.

1.2.1 Technology Overview

Technologies were assessed using academic literature, official and NGO reports, industry body information, product data sheets and expert opinion to determine:

• the range and characteristics available;

• infrastructural requirements;

• efficiencies and emissions;

• key technical barriers to uptake;

• capital and running costs; and

• trends in all of the above parameters (where available).

1.2.2 Economic Viability

The economic viability of each technology was calculated for typical residential dwellings in two steps: determining the operational energy balance; and calculating life cycle cash flows and economic viability.

Operational energy balances were assessed based on efficiency and other information gathered during the technology overview process. Energy inputs and



outputs as well as the form of energy involved (gas, heat or electricity for example) were determined in each instance.

Based on the estimated technology lifespan, life cycle cash flows were then calculated. These included:

• capital costs based on the technology overview information;

• energy input costs based on operational data and current domestic gas and/or electricity tariffs;

• energy output values based on operational data and current domestic gas and/or electricity tariffs; and

• maintenance costs based on technology overview information.

These cash flows were then discounted to present values (using a 6% discount rate) and summed over the life cycle to give a net present value (NPV) associated with investing in the technology.

It is important to note that this economic appraisal did not include externalities. For example, PV, micro CHP and micro wind may require special input/output or smart metering; or intermittent or variable technologies (PV, micro wind) which do not decrease conventional installed capacity will result in higher national electricity prices.

1.2.3 CO2 Abatement Potential

The CO2 abatement potential for each technology was calculated using the operational energy balances referred to above. A CO2 intensity was applied to the RES technology energy inputs as well as to the energy requirements of the displaced technology and these were subtracted to determine the reduction in annual CO2 emissions associated with switching to the RES technology. For example, if a house switches from a gas boiler to a GSHP, then the boiler gas consumption is multiplied by the CO2 intensity for gas (0.18kg/kWh) and subtracted from the GSHP electricity consumption multiplied by the CO2 intensity for electricity (0.64kg/kWh).

The cost of CO2 abatement was then calculated for each technology by dividing the NPV of the technology by the total CO2 avoided over its lifespan (assuming constant CO2 intensities for gas and electricity).

1.31.31.31.3 Summary of Summary of Summary of Summary of FindingsFindingsFindingsFindings

1.3.1 Technologies

All of the domestic RES technologies considered in the report – with the exception of micro CHP – have been commercialised and are in mass production.

The PV market is growing rapidly and experience curves suggest that unit costs will continue to fall significantly in the future. A number of alternative PV technologies are emerging which focus on low cost, high efficiency or both, but these technologies are not sufficiently advanced to evaluate their long-term market potential.

Micro CHP appears to be at an ‘early adopter’ stage in the product life cycle and unit costs should decrease significantly if full market potential is realised.



Although fuel cell technologies appear promising in the medium term (10-20 years) and internal combustion technologies are undergoing development, Stirling engine solutions appear to be the most likely dominant technology in the short-medium term. A number of trials have been undertaken recently in the UK and are currently underway in Ireland.

Solar thermal technologies are well developed and widely deployed internationally, although the market in Ireland is in its infancy. No significant technology developments are envisaged in the medium term although with greater market penetration, installed costs may fall. There is potential for combining the technology with other RES systems such as GSHP.

Although technically well understood, micro wind is a financially unproven technology with high capital costs. However, with changing regulation (e.g. easing of planning and grid connection requirements) this market may grow and unit costs decrease.

GSHP technology has recently become popular in Ireland relative to other RES technologies. It is more widely used on Continental Europe where its environmental credentials are improved by low CO2-intensity grid electricity. The technology is well understood and developed technologically.

Wood pellet boilers and stoves are widely used in Scandinavia, Austria and Germany and can be relatively easily retrofitted to existing dwellings with wet-based central heating systems. The technology continues to evolve to provide a low-maintenance, visually attractive product although space requirements may present challenges. Fuel supply chains have become established in Ireland where the technology has proved popular since its promotion under the ‘Greener Homes Scheme’.

1.3.2 Financial Performance & CO2 Abatement Potential

Table 1 summarises the current financial performance and CO2 abatement potential for each of the technologies considered. It can be seen that all of the technologies returned negative NPVs meaning that it is more economically rational to invest in a conventional system (here a gas fired boiler and mains electricity) than in any of the RES technologies considered. It can be seen that the most attractive RES technologies from an NPV perspective are solar thermal and GSHP. The least attractive are micro wind turbines and wood pellet boilers.

However, the technologies which show the greatest per-dwelling reductions in CO2 emissions are micro wind turbines and wood pellet boilers. Micro CHP and GSHP technologies have the lease impact in this regard.

From a policy perspective it is important that government identify where scarce resources would be best allocated. For this reason a CO2 abatement cost is calculated which shows that solar thermal technologies have the lowest cost at €59/tonne – an order of magnitude less than the highest cost technology, micro CHP and considerably lower than the next lowest cost of €305/tonne for wood pellet boilers.



Technology Specification System Cost Lifetime NPV CO2 Avoided CO2 Abatement

Cost

(€) (€) (kg) (€/tonne)

PV 1kWp Solar System 7,950 (6,301) 14,368 439

Micro CHP 8kW(t) Sterling Engine 6,000 (5,407) 9,201 588

Solar Thermal 8.5m2 Evacuated Tube 5,000 (1,211) 20,500 59

Micro Wind 2.5kW Horizontal Axis

Building Mounted

27,500 (19,271) 54,810 352

GSHP 4kW Closed Horizontal

Loop

8,690 (2,408) 5,230 460

Wood Pellet Boiler 15kW Boiler 11,000 (14,201) 46,617 305

Table 1: Summary of financial and emissions findings.

1.41.41.41.4 ConclusionsConclusionsConclusionsConclusions

1.4.1 Potential RES Technologies

Six forms of RES technologies were identified and assessed under current conditions for economic viability, CO2 abatement potential and CO2 abatement cost. No technologies were found to be economically viable when compared to existing, conventional energy sources (natural gas and grid electricity). However, projected experience curves indicates that there is significant scope for capital cost reductions for many technologies, most notably PV and micro wind. This projection, when combined with increasing energy costs and the certainty of carbon taxes indicates that many RES technologies will become finically viable in the near-to-medium term. PV, for example, may become viable within the next ten years or so.

Wood pellet boilers and wind were found to have significant abatement potential and would reduce national energy-related CO2 emissions by 8% and 7% respectively if deployed in the entire housing stock in the Republic of Ireland. The cost of abatement was lowest by far for solar thermal systems and these costs are expected to fall with falling capital costs and rising energy prices.

All of the technologies show some form of potential and warrant inclusion in the phase of the project, with a particular focus on those which have the potential to be cost-effective in the short-medium term (solar thermal, GSHP, PV) or which have significant, cost-effective CO2 abatement potential (solar thermal, wood pellet boilers).

1.4.2 Further Research

This report represents work in progress. It relies on lumped models using aggregate annual energy inputs and outputs which do not capture the dynamic, diurnal complexities of domestic energy supply and demand interactions. The development of robust and credible dynamic models is a key deliverable of this project and will necessitate the collection of more detailed, reliable data both for domestic energy consumption profiles and the techno-economic performances of the various technologies.



A further area requiring development is that of externalities. The costs of smart metering, grid stability and displacing conventional power sources should be determined and included where appropriate.

Although it is easy to calculate an abatement cost per tonne of CO2 under current conditions, this does not necessarily reflect the long-term potential of a particular technology. For example, the German government’s significant subsidisation of domestic PV technology in recent years has had a significant impact on reducing abatement costs for this technology. Micro CHP and micro wind are two technologies where significant market development would substantially reduce capital costs and, therefore, the cost of CO2 abatement.

Some measure of the deployment potential for each technology must be included in the mix of factors influencing policy direction. For example, a promising technology with little deployment potential will not offer significant CO2 abatement benefits at a national level, whereas one with a lower individual impact but greater deployment potential may make significant inroads into national GHG emissions.

In summary, the next stage in the development of this work will be the creation, validation and projection into the future of dynamic energy balance models linked to project viability, externalities and CO2 abatement costs. This will be undertaken for each of the technologies listed in this report.

1.51.51.51.5 ReferencesReferencesReferencesReferences

EEA (2008) Greenhouse gas emission trends and projections in Europe 2007: Greenhouse gas emission trends and projections in Europe 2007: Greenhouse gas emission trends and projections in Europe 2007: Greenhouse gas emission trends and projections in Europe 2007: Tracking Tracking Tracking Tracking pppprogress rogress rogress rogress ttttowards Kyoto owards Kyoto owards Kyoto owards Kyoto ttttargetsargetsargetsargets. EEA Report No 5/2007.

EPA (2007) Environment in Focus 2006: Environmental Indicators for IrelandEnvironment in Focus 2006: Environmental Indicators for IrelandEnvironment in Focus 2006: Environmental Indicators for IrelandEnvironment in Focus 2006: Environmental Indicators for Ireland. Environmental Protection Agency.



2222 PHOTOVOLTAICSPHOTOVOLTAICSPHOTOVOLTAICSPHOTOVOLTAICS

Aidan Duffy

School of Civil and Building Services Engineering

2.12.12.12.1 Technology OverviewTechnology OverviewTechnology OverviewTechnology Overview

2.1.1 Principles

Photovoltaic (PV) installations comprise cells of semiconducting materials which release electrons when they absorb incident photons of light. Collections of cells are connected to form individual ‘modules’, any number of which may be installed in an ‘array’ to produce appropriate amounts of renewable energy for the installation in question (Queisser and Werner, 1995).

A PV system comprises the array as well as a balance of system (BOS) which includes: array support frames, wiring, inverters and circuit breakers; the BOS may also include batteries and metering (where required). The system is normally maintenance-free, although arrays may require cleaning to ensure that they continue to function at optimum efficiencies. Life expectancies are in the order of twenty to twenty five years.

2.1.2 Types

There are two basic types of PV cell material:

- wafer-based silicon; and

- thin films.

Single crystal and polycrystalline wafer-based silicon (Si) is the most common material used in the manufacture of PV cells and accounted for some 85% of total production in 2004; thin film technologies which include copper-indium-diselenide (CIS) and cadmium telluride (CdTe) accounted for 3.9% of global production in the same year (Maycock, 2005). High-efficiency thin-film technologies such as those employing gallium arsenide (GaAs) do not yet account for a significant proportion of world-wide production due to cost constraints.

The efficiencies of these technologies range from 5 to 15%.

2.1.3 Trends

The market for PV technologies is global and growing rapidly. Resulting economies of scale , combined with ongoing research are leading to increases in efficiencies and reductions in capital costs. In the EU-27 for example, total installed PV capacity has grown from 69.1MWp in 1993 to 3,733.0 in 2007 (Photovoltaic Energy Barometer, 2007). Annual installed capacity in 2007 was 57% greater than in the preceding year. World PV production increased from 716MWp in 2003 to 1,195MWp in 2004 (Maycock, 2005).



Thin film technologies are still not financially-viable in the mass-market and it is anticipated that wafer-based technologies will continue to dominate the market for the foreseeable future. It is estimated that efficiencies in wafer-based technologies will increase to 15-20% over the next 20 years or so. Efficiencies of up to 30% may be possible in the longer-term, but this will require technology step changes (PV-TRAC, 2005).

A number of alternative PV technologies are emerging which focus on low cost, high efficiency or both, but these technologies are not sufficiently advanced to evaluate their long-term market potential (PV-TRAC, 2005).

2.22.22.22.2 Capital CostsCapital CostsCapital CostsCapital Costs

2.2.1 Module Costs

The installed costs of PV systems have decreased consistently from approximately €100 per Watt peak (Wp) since their first commercial adoption in the 1980s to approximately €3/Wp in 2005. Module cost curve projections are based on a 20% reduction for every doubling in global sales; on this basis module prices are expected to fall to €2/Wp in 2010, €1/Wp in 2020 and 50cent/Wp in 2030 (PV-TRAC, 2005).

2.2.2 Balance of System (BOS) Costs

The total installed costs of residential PV systems in 2004 were approximately $7/Wp and $6/Wp in the US and Japan respectively (Maycock, 2005), suggesting that BOS represents more than 50% of the total cost of a system. Research in the Netherlands has indicates that cost-curves similar to PV module production apply to BOS costs also: between 1991 and 2000, BOS costs dropped from almost €20/Wp to €5/Wp (Schaeffer et al., 2004).

2.32.32.32.3 Financial ViabilityFinancial ViabilityFinancial ViabilityFinancial Viability

2.3.1 Methodology

The financial viability of a 1kWp domestic installation was undertaken in the following manner:

1. The annual electrical production was calculated using RETScreen4 software (http://www.retscreen.net/) based on Dublin Airport insolation levels and an array of 5 Poly-Si BP Solar modules (BP 365) with the following characteristics:

• 11m2 collector area;

• 9.0% module efficiency;

• 5.0% miscellaneous array losses (dirt, shading etc)

• average 90% inverter efficiency.

The collector was calculated to produce 898kWh per annum.

2. All prices are quoted in 2005 €.



-€7,000.00

-€6,000.00

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3. All electricity produced was valued at 14.4cent/kWh in 2005 increasing at 2% per annum in real terms thereafter.

4. System capital costs were €2.90/Wp in 2005 decreasing to €2.10, €0.90 and €0.50 in 2010, 2020 and 2030 respectively.

5. The net present value (NPV) was calculated based on a discount rate of 6% over 25 years since this is a typical life expectancy of a PV module.

6. Twenty six NPV calculations were undertaken assuming that an investment in a new system is undertaken each year for all years up to and including 2030.

2.3.2 Results

Even assuming a generous cash flow based on applying the Irish domestic tariff to all energy produced, the NPVs for domestic-scale PVs are very poor for the foreseeable future. Figure 1 shows that a 2005 investment in the 1kWp BP Solar PV system would have a negative NPV of approximately €6,300, falling to -€1,825 in 2015. Based on the stated assumptions, it would not be worth investing in this technology until 2022 if a positive NPV is required.

Figure 1: Projected net present values (NPVs) and system costs associated with investing in a PV system in any of the years between 2005 and 2030.

This financial model is not particularly sensitive to the electricity revenues. For example, if a carbon levy of 3c/kWh is added to the unit prices of electricity (inflated in the same way), then the neutral NPV year is brought back from 2022 to 2020. On the other hand, it is very sensitive to capital cost assumptions: if system costs are €1/Wp higher than anticipated, then the NPV for a project undertaken in 2030 is -€1,400.




A simple lumped financial model which assesses domestic-scale PV technology suggests that the technology is a very poor performer. Current cost curve projections indicated that the technology will not become financially-viable until the 2020s when judged a NPV basis.

The critical driver is capital cost which includes both module and BOS costs. In domestic applications – particularly in ‘retro-fit’ situations – BOS costs may be greater than module costs. Although there is a large body of literature available on module costs and cost-trends, there is limited similar BOS information available.

Finally, no attempt has been made to address the externalities associated with back up to small-scale variable supply such as PV. This would need to be addressed as part of a more comprehensive financial study.


Maycock, P. (2005) PV review: World Solar PV market continues explosive growth, RefocusRefocusRefocusRefocus,,,, 6666, Issue 5, September-October 2005, pp. 18-22.

Photovoltaic Barometer (2008) Photovoltaic Energy Barometer, Systèmes Systèmes Systèmes Systèmes SolairesSolairesSolairesSolaires le journal des énergies renouvelables, 184184184184-2008.

Photovoltaic Technology Research Advisory Council (PV-TRAC) (2005) A Vision A Vision A Vision A Vision for Pfor Pfor Pfor Photovoltaic Technologyhotovoltaic Technologyhotovoltaic Technologyhotovoltaic Technology, European Commission, Office for Official Publications of the European Communities, Luxembourg.

Queisser, H. and Werner, J. (1995) Principles and technology of photovoltaic energy conversion in Proceedings of the 4th Int. Conf on SoProceedings of the 4th Int. Conf on SoProceedings of the 4th Int. Conf on SoProceedings of the 4th Int. Conf on Solidlidlidlid----State and State and State and State and Integrated Circuit Technology 1995Integrated Circuit Technology 1995Integrated Circuit Technology 1995Integrated Circuit Technology 1995, pg. 146-150, Eds.: G.L. Baldwin et al., New York.

Schaeffer, G, Alsema, E, Seebregts, A, Beurskens, L, do Moor, H, van Sark, W, Durstewitz, M, Perrin, M, Boulanger, P, Laukamp, J and Zuccaro, C (2004) LearLearLearLearning from the Sun: Analysis of the use of experience curves for energy policy ning from the Sun: Analysis of the use of experience curves for energy policy ning from the Sun: Analysis of the use of experience curves for energy policy ning from the Sun: Analysis of the use of experience curves for energy policy purposes: the case for photovoltaic powerpurposes: the case for photovoltaic powerpurposes: the case for photovoltaic powerpurposes: the case for photovoltaic power. Final Report for the Photex Project. ECN-C-04-035.



3333 MICROMICROMICROMICRO----CHPCHPCHPCHP

Gerry Conroy


3.13.13.13.1 TechnologTechnologTechnologTechnology Overviewy Overviewy Overviewy Overview

3.1.1 Principles

Micro combined heat and power (Micro CHP) is the simultaneous production of heat and power in the home. It is distinct from Community Heating-based CHP systems which rely either on large centralised plant linked to district heating systems or on ‘block’ CHP where a unit serves a single apartment block. It is intended that Micro CHP unit replaces a conventional boiler in a central heating system.

Fig ??: Schematic energy flows in Micro CHP system (Ref??)

Commercially-available micro CHP systems typically comprise a small gas engine which drives an electrical generator the waste heat from which is used in the domestic heating system and the electricity generated is either used in the house or exported to the network to be consumed by neighbours.

The system has a similar thermal efficiency to that of a conventional gas boiler - typically in the region of 80%. However, in addition, around 10-15% of the calorific value of the fuel is converted to electrical energy which has a significantly higher value both in carbon abatement and economic terms than the heat which could be gained by simply burning it.

3.1.2 Technological Challenges

The technical and economic challenges impeding widespread adoption of Micro CHP systems are significantly more onerous than those faced by larger scale systems. However, once these challenges are overcome, the potential environmental, social and economic benefits are substantial because of the technology’s potential for retrofitting to existing dwellings.

In order to achieve economic viability, it is essential that the product can be manufactured at a cost that can be recovered from the savings in operating costs.



Manufacturing cost per unit power output tends to rise exponentially as size decreases. Only through the economies of scale can costs be reduced to a viable level for Micro systems. This presupposes that significant market potential exists.

Operation costs include service costs which can be a significant life-cycle cost and represents a significant challenge to the implementation of CHP below around 30kWe. Micro CHP technologies and supply chains therefore need to deliver significantly lower maintenance costs than those currently charged. The challenge for manufacturers is to achieve service intervals, reliabilities and life expectancies which are in line with those of current gas boilers.

In order to meet customer expectations a number of further criteria must be met:

• units must be unobtrusive (similar in size to the gas boilers they replace), quiet and free from excessive vibration;

• they must have low emissions; and

• they must be compatible with the operational characteristics of existing central heating systems, such as flow rates, temperatures and ease of installation.

3.1.3 The role of Micro CHP in sustainability

In general terms, Micro CHP is little more than an attractive, cost-effective energy efficiency (as opposed to renewable energy) measure. As such it must stand the test of comparison with other measures. With a cost effectiveness of 2c/kWh saved, it rates well against cavity wall insulation and substantially better than double-glazing. However, it is less effective than loft insulation or wall insulation installed during construction. The logical conclusion then is that Micro CHP is an effective measure for existing homes, particularly when for example, there is no cavity to insulate.

3.1.4 Domestic Energy Consumption by End Use

In Ireland, over 60% of energy in a typical home is used for space heating, with an additional 23% for water heating. Only 15% in total is for appliances and lighting which require electricity. These proportions are similar for other N European countries (e.g. France with 60% space heating, 19% water, 21% other). It is thus significantly more effective to invest in targeting the 85% thermal energy demand rather than the relatively small potential in electricity, particularly bearing in mind the high cost and poor generation profile of PV generation.

It is perhaps also worth bearing in mind that Stirling engines are fuel flexible and, whilst they can make use of the current natural gas infrastructure, they could in the future make use of biogas or hydrogen when those fuels become widely available. They thus represent both a transitional technology and a potential Renewable Energy converter.

3.23.23.23.2 Micro CHP technologiesMicro CHP technologiesMicro CHP technologiesMicro CHP technologies

A number of prime mover technologies have been proposed for Micro CHP applications, based on ICE (Internal Combustion Engine), Stirling engines,



Rankine cycles and Fuel Cells. Early attempts to apply converted automotive ICE units led to high service costs and poor life expectancy. However, more recent products such as the Baxi/Dachs unit in Germany and the Honda/Ecowill unit in Japan both applied purpose designed engines to overcome the considerable challenges of emissions and noise reduction and to achieve realistic service intervals. In both cases this has been achieved at considerable cost and it is questionable whether they will ever become truly competitive in normal domestic applications.

3.2.1 Internal Combustion Engine

The internal combustion engine (ICE) has been continuously developed for over a century and has achieved particular success in applications where power flexibility is required. However, the internal combustion process is inherently difficult to control so that emissions are high as is the noise emanating directly from the "explosion" in the working space. The need for oil lubrication and regular, frequent servicing indicate that this technology is poorly suited to Micro CHP applications. However, there are products (most notably Senertec 5.5kWe) which achieve relatively low emissions and noise levels, as well as service intervals of 3500 hours. These attributes are achieved by, amongst other measures, incorporation of substantial acoustic attenuators, catalytic converters and a substantial oil reservoir. Naturally, this results in a very expensive engine and a very large product unsuitable for installation in an individual home. It is believed that Honda are developing a 1kWe unit, but it is unlikely that all the desirable parameters for Micro CHP can be achieved with ICE technology. It is interesting to note that the relatively low heat to power ratio (and high electrical efficiency) achieved by ICE has implications for the gas supply infrastructure and makes this technology more sensitive to changes in gas prices.

3.2.2 Fuel cells

Fuel cells are under development by a number of companies, but all face cost and service life challenges. Leading exemplars include Vaillant/Plugpower with a 5kWe PEM (Polymer Exchange Membrane) unit suitable for small apartment blocks and the Sulzer Hexis SOFC (Solid Oxide Fuel Cell) 1kWe unit with integral gas burner to provide flexible thermal output.

Fuel cells, which convert fuel directly into electricity, appear to offer very low emissions, high efficiency and very low noise levels. Heat is produced as a by-product of the electrochemical process, with water as a waste product. Although, in theory, there are no moving parts, the reality is somewhat different. Firstly the natural gas needs to be reformed into hydrogen, requiring additional components and implying parasitic energy consumption. The exhaust gas also needs to be treated to eliminate CO and the gas supply may also need to be cleaned to remove sulphur. Although the electrical conversion itself may be quite efficient, the need to convert the DC output to AC requires power electronics and implies further costs and losses.

Current prototypes are thus too noisy, bulky, inefficient and expensive to be viable. Indeed, there is only one product (Sulzer Hexis 1kWe) specifically targeted at individual homes and this is recognised as being several orders of magnitude too expensive. However, it is believed that continued development will enable them to compete within a ten year timescale.



3.2.3 Stirling engines

Stirling engines, with their potential for low noise and vibration, low emissions and service life in line with gas boilers are the closest to fulfilling the demands of the mass domestic market and two UK energy companies Powergen and British Gas have teamed up with WhisperTech and BG Microgen respectively to introduce Stirling based Micro CHP in the near future. Powergen recently announced a commercial launch of their product and the technology is described in further detail below.

Stirling engines are external combustion engines, which allow continuous, controlled combustion resulting in very low pollutant emissions and high combustion efficiency. They can operate without valves or an ignition system, thus permitting long service intervals and low running costs.

In its simplest form the Stirling engine comprises cylinder, regenerator, piston and displacer. Fuel is burned continuously outside the engine to maintain one end of the cylinder at high temperature while the opposite end is cooled by circulating water around it. Power is derived from the pressure fluctuations acting on the working piston, as a fixed volume of working gas (sealed within the engine) is alternately heated and cooled, forcing it back and forth between the two temperature zones via the regenerator. The working gas is moved by the displacer, which is 90° in advance of the working piston. The sinusoidal waveform of the power output results in low vibration and noise levels.

Thermal efficiency is enhanced by the regenerator, a heavy matrix of fine wires that acts as a repository for heat extracted from the working gas during the cooling pass to be returned on the heating pass.

One significant difference between ICE and Stirling engines is that, in an ICE, it is possible to adjust power virtually instantaneously by controlling the fuel supply. This makes ICE ideal for automotive applications where rapid variations in power are required. However, there is a significant time delay between fuel input and power output in a Stirling engine, as there is usually a substantial amount of heat stored in the hot end, which continues to transfer energy to the working gas long after the fuel supply to the burner is cut. Although this is not a concern in stationary applications, which do not require instantaneous power variation, it is a consideration for control that there is a delay of the order of minutes between a thermostat calling for heat, the availability of heat and finally the output of power. In addition, the stored energy must be passed to the heat distribution system before the engine shuts down at the end of a heating cycle.

A recent technological development is the Organic Rankine unit from Inergen, now also part of Baxi Technologies in the UK. This is based on conventional refrigeration components and, although having rather low electrical efficiency, is well matched to many domestic applications and appears to offer relatively low manufacturing costs and good service life characteristics.

3.2.4 The Whispergen Micro CHP unit

The Whispergen Micro CHP unit uses Stirling engine technology. Developed in New Zealand by WhisperTech Limited, it has its origins as a battery charger for marine applications fuelled by diesel and is still commercially available in this configuration as well as with other fuels. It thus has a long pedigree demonstrating extensive running hours in numerous installations in addition to the units installed in field trials in the UK.



The unit has a thermal output of 8kWt and a peak electrical output of 1.2kWe. It is used in conjunction either with a thermal store or an optimising controller to maximise the thermal output and match it to the thermal demands of the home. It is similar in size to a domestic fridge and has similar noise levels to a large freezer. However, due to its weight (around 140kg) it must be installed on a solid ground floor and is normally installed in a utility room.

3.33.33.33.3 Micro CHP applicationsMicro CHP applicationsMicro CHP applicationsMicro CHP applications

The economic and environmental benefits of Micro CHP are discussed below, but it is clear that, although Micro CHP does offer considerable advantages over conventional solutions in many applications, there are others where it is not the optimum solution.

The cost effectiveness of Micro CHP is broadly in line with cavity wall insulation. In this case it provides a solution where such measures are not possible (e.g. in homes with solid walls). Generally speaking, Micro CHP can be considered an ideal solution for the majority of existing homes where other energy efficiency measures are either not possible or where they have already been implemented.

It can also be applied to new homes, but improved levels of insulation represent a better overall investment and should always be considered first.

For homes with very small heat loss, multi- storey flats and extremely high density urban housing, Community Heating may be more appropriate particularly if the fuel being consumed is renewable.

3.3.1 Integration with home energy systems

In order to be viable in domestic installations it is essential that Micro CHP is compatible with the operational parameters of central heating, such as water flow rates and temperatures, and that it does not require the addition of, for example, large storage tanks to provide thermal buffering.

3.3.2 Electrical

Several trial systems so far installed have been wired back to a point upstream of the consumer unit, with a cable rated to take the full starting current of the generator. This is an expensive item and is physically intrusive. It is desirable to both minimise the rating of this cable and, ideally connect it to either a high current circuit (such as cooker spur) or even the ring main. Although this no longer appears to be an obstacle, the implications for cable and fuse ratings for ring mains are still under review for Micro CHP.

3.3.3 System design

There has been much discussion of the range of homes for which Stirling engine systems are appropriate. Although the thermal output is significantly lower than the boiler it replaces, this does not necessarily imply inadequate performance. Intelligent controls, with or without thermal buffering, can significantly enhance the effective output, although there are implications for extended preheat periods rating. However, this also enhances comfort and it is not improbable that homes will begin to follow European practice of having "set-back" rather than "on-off controls. It is also important to bear in mind that Micro CHP dos not respond



well to rapid on-off cycling and that engines (as is the case for heat pumps) are normally designed to meet about 60% of the peak design load. This maximises useful run hours under average winter conditions, and normally leads to the bulk of annual demands being met by the primary system.

However, some form of supplementary heating may be required in severe weather conditions and to achieve rapid heat up, for example, after the home has been unoccupied for some time. The BG Microgen units are expected to incorporate some form of flow boiler, although this does have implications for the annual run hours achievable during which electricity is produced.

3.3.4 Installation

As Micro CHP nears mass introduction into real homes, it is becoming apparent that the level of skills required, both electrical and plumbing, are significantly more advanced than for installation of a conventional boiler and are even a step change from condensing boilers. It is widely believed that the current route to market through the installer network has been one of the major reasons why condensing boilers have failed to achieve significant market penetration and this remains a key challenge to Micro CHP companies.

As a practical solution, Powergen have set up training courses for approved installers and are gradually developing an installer network across the UK. These installers also undertake to provide ongoing service and maintenance for the life of the systems, providing the essential customer reassurance for such a novel technology and aiming to overcome the obstacles which hindered the widespread adoption of condensing boilers for so long.

3.43.43.43.4 Benefits of Micro CHPBenefits of Micro CHPBenefits of Micro CHPBenefits of Micro CHP

3.4.1 Environmental benefits

Micro CHP operation, as for a gas boiler, is thermally led, i.e. running when there is a demand for heat. Effectively the electricity generated as a by-product imposes no additional carbon burden and could be considered zero carbon electricity. However, compared with a condensing boiler with an equivalent total fuel to heat conversion factor (92%), the electricity has a carbon impact equal to that of gas (i.e. it is equivalent to gas fired central generation operating at 100% efficiency and ignoring the transmission and distribution losses of central generation). The actual savings in CO2 as well as SOx, NOx depend on the annual operating hours and, an often overlooked fact, the time of day when electricity is produced. That is, it produces power principally on cold winter days in the early morning and evening when grid demand is at its highest. Thus Micro CHP displaces relatively carbon intensive generation.

3.4.2 Economic benefits

As outlined earlier, the economic viability of Micro CHP depends on both the marginal capital investment (compared with a gas boiler) and the value of electricity produced by the unit. For any given system, therefore, the payback relies on the unit's operating hours and consequently the total kWh produced annually. Table 2 illustrates the economics for a typical home with 18,000kWh annual thermal demand. It can be seen that the value of the electricity is also



dependent on whether it is consumed within the home (avoiding purchase at 6.5p/kWh) or exported and sold to the energy supplier, where it is worth less than half this amount.

The financial and emissions performance of a commercially-available Micro CHP is illustrated in Table 2 based on data from a field trial in Northern Ireland. The net present value of the investment over an expected 15 year life span was calculated to be €-5,407 annual avoided CO2 emissions to be 613kg. Clearly, the capital cost is a significant economic barrier to the uptake of the technology.

Energy Balance

Micro CHP Installed Capacity 8 kW(t)

Efficiency 76.5 %

Heat/Hot Water Produced 20,095 kWh/annum

Electricity Production 2,063 kWh/annum

Gas Consumption 26,255 kWh/annum

Economics

Capital Cost (6,000) €

Heat Unit Value 7.6 c/kWh

Value of Heat Produced 1,532 €/annum

Electricity Unit Value 14.4 c/kWh

Value of Electricity Produced 297 €/annum

Gas Unit Cost 6.86 c/kWh

Cost of Gas (1,801) €/annum

Net Saving by Micro-CHP 28 €/annum

NPV (15yr @ 6%) (5,407) €

CO2 Emissions

Natural Gas CO2 Intensity 0.18 kg/kWh

Natural Gas System CO2 Output 4,726 kg/annum

Electricity CO2 Intensity 0.64 kg/kWh

CO2 Avoided 5,339 kg/annum

CO2 Saving by Micro CHP 613 kg

Table 2: Financial and emissions summary for a Micro CHP system.

3.53.53.53.5 Market StatusMarket StatusMarket StatusMarket Status

3.5.1 Potential impacts of Micro CHP

Although the impact of any one Micro CHP system is insignificant on a global scale, the cumulative impact of large numbers of installations expected will have considerable impacts on the energy supply industry and the environment. It is claimed that units can save up to 1.5 tonnes CO2 and generate 3000kWh of electricity annually, although the findings above do not support this. The ultimate market for this technology is estimated at 500 thousand installations in Ireland, possibly more when other fuels and prime movers are considered. At the same time, annual CO2 emissions could be reduced by 1.5 million tonnes making a considerable contribution to Ireland’s Kyoto commitment.

However, one attraction of Micro CHP in this context is that its impact is incremental and unlike conventional capacity for example can be implemented with staged investment, incremental risk and minimal detrimental



environmental or other impact. It also avoids the long delay between investment and generation; each kWe capacity is available as soon as it is paid for.

Clearly, the positive benefits identified above do have a downside. Current participants in the energy industry will be faced with a substantial reduction in electrical demand, so that generators, suppliers and network operators will lose out if they are unable to actively participate in the emerging Micro CHP market.

3.5.2 Installation Issues & Failures from Assessing Field Data

Whilst the installation of commercially-available Micro CHP unit (such as the WhisperGen) into a house is technically very similar to a boiler installation although there are various differences indicated below and these mean that the installation can only be carried out by fully trained staff. This means that the units cannot be sold off the shelf at DIY stores or Plumbers merchants and a network of trained installers needs to be established. ,

• Electrical wiring - this is different from the conventional systems currently installed for boilers and although does not require extra cabling it needs a greater understanding

• PIC - the Programmable Intelligent Controller is very different to a standard two channel time-clock and is programmed not to when you want the CHP running but when you want the house at your selected/inputted temperature. This can be very confusing initially and with too many menu screens most householders find it difficult to programme. The MkV will work with off-the-shelf CH/DHW controllers so it will simplify wiring where this is desirable

• Commissioning of the unit is more complicated and must be carried out by a qualified and suitably trained installer

• The unit is too large to be installed within the home and therefore it is more difficult to install in homes which do not have a garage or separate boiler house compared to wall hung gas boilers.

This unit has proven to be more problematic and has had the following issues:

• The wall mounted controller (PIC) has failed several times although switching the power off & on to the unit temporarily solves this problem.

• Core Engine failure related to bearing problems within the "wobble yoke", which resulted in the unit being replaced, this was a known failure by Whisper Tech and has been rectified on future units.

• Installation of TRV's on site and new central heating pump with a software modification as the unit would continue to heat the house in summer months instead of shutting down when it gets up to temperature.

• Corrosion problems - this lead to a leak in the nitrogen gas and resulted in the unit being replaced again. This was put down to low boiler water quality and may have resulted in poor system flushing as much of the installation was originally plumbed in Micro bore piping.


The following are general conclusions which require further development:



• Cost - With annual savings currently in the region of €200.00, this indicates that the unit should not be €1,000.00 more than a conventional condensing boiler or approximately €1,500.00 (assuming a 5 year payback). With current pre-production units at circa €7,500.00 Whisper Tech have a significant challenge before them to reduce these costs, and are currently seeking a mass manufacturer although Government initiatives such as VAT reduction to 5% will partially assist with this.

• The current unit has a maximum heat output of approx 8 kWth and therefore is only suitable for smaller house types of approximately 3 bedrooms, which in addition may require an upgrade of insulation installed to maximise thermal retention within the dwelling. Although this may change in future with the MK5 unit which has an extra burner to increase the thermal output.

• Export Value - the DCHP unit does export electricity at various times throughout the day whilst running (approx 30-40%). The vast majority of the electricity exported is in the morning as the unit needs to start earlier than a conventional boiler to achieve the set point temperature and therefore the value of exported units at this time would need to be explored as to what value they would have to the network operator. It may be better to divert the electricity to a boost electric water heater

• Life expectancy of the unit is still unclear. Several breakdowns including a bearing failure (a known failure to Whisper Tech which has led to subsequent system modifications) and corrosion problems (as a result of poor central heating water quality) leading to loss of nitrogen gas pressure should be noted.

• Fully trained staff will be a key requirement to any future much larger scheme as the installation, service and repair are more involved than could be provided by the average plumber or electrician that currently installs typical oil and gas boiler systems. Experience has shown that failures will occur at the most inopportune times and spare parts need to be available locally, so that repairs can be carried out quickly without the need to have parts brought in from across the water.

• The faults that have appeared to date do not suggest that they are quite ready to be made more widely available. Whilst it is understood that this is a pilot scheme and organisations can take the risk associated with a small pilot, it will be an entirely different matter when they go onto the open market. Domestic dwellers could not absorb the maintenance costs associated with unreliable units, not to mention potential tenant dissatisfaction. Nor will the general public subscribe to costly heating systems with question marks on reliability.


3rd International Conference on Sustainable Energy Technologies, Nottingham, UK, 28-30 June 2004.

Domestic CHP Report for Northern Ireland Electricity, Phoenix Natural Gas and Energy Saving Trust prepared by Steven Lyle Energy Consultancy.

Energy Saving Trust Web Site (http:/www.est.org.uk).



Harrison, J. Micro CHP – The Implications for Energy Companies, March 2000.

Harrison, J. Micro CHP for Housing, Micro Energy Systems for the 21st Century, June 2002.



4444 SOLAR THERMALSOLAR THERMALSOLAR THERMALSOLAR THERMAL

Lacour Ayompe



The use of renewable energy sources such as solar energy instead of conventional ones when they are available is now a global concern. Although the sun radiates much energy on the earth’s surface, systems to harness and convert this energy to heat are not utilized because of the high initial investment needed to install them.

Solar energy is abundant in the summer period and represents an interesting solution to limit usage and consumption of fossil fuel during the summer. Solar thermal systems can greatly decrease fuel consumption for water and space heating.

Heat for comfort in buildings can be provided from systems similar to those used for water heating. Water and air are the two types of commonly used fluids. In temperate climates, the basic components comprise of the collector, storage unit, the load (i.e., the house to be heated) and an auxiliary energy source [1]. Space heating systems are either active or passive but active systems are mostly used in temperate climates.

In Ireland, a horizontal surface of 1m2 receives an average of between 1,000 and 1,200 kWh of solar energy per year. Considering that a solar collector with an efficiency of 50% is used, it will be able to collect between 500 and 600 kWh. This energy is equivalent to between 4.3 x 10-5 ktoe and 5.2 x 10-5 ktoe or 100 to 120 litres of oil. If all of Ireland’s land mass of 70,280 km2 is used to harness solar energy it would be able to produce 3 x 106 – 3.6 x 106 ktoe. The total primary energy consumption in Ireland in 2006 including non-energy was 16,200 ktoe. The potential for solar energy is 186.5 to 223.9 times the annual total primary energy requirement for 2006.

Ireland had over 1.5 million domestic dwellings in 2007, of which 89.3% are not apartments [2] and the average floor space was 159 m2 in 2006 [3]. This represents an accessible resource of over 40 million m2 (28.8 GWth) for installation of solar thermal collectors Ireland’s. The installed and projected solar thermal capacity in 2007 was about 20 MWth [4]. The installed solar thermal capacity within the Irish domestic sector therefore represents about 0.1% of the available capacity. This highlights the need for more ambitious policies to encourage large-scale uptake of this technology.

4.1.1 Principles

Solar Thermal systems comprise a collector, working fluid, circulation system, storage, and controls. These components function together to convert solar radiation into heat, which can be used in various applications. Although the solar fluid can be circulated by natural or forced means, the forced circulations



systems are most appropriate in the Irish climate. Solar collectors are the most important component of solar thermal systems.

Solar collectors are heat exchangers that transform solar radiation energy to internal energy of the transport medium. These are devices which absorb the incoming solar radiation, convert it into heat, and transfer this heat to a fluid (usually air, water, oil or a mixture) flowing through the collector. The solar energy thus collected is carried from the circulating fluid either directly to hot water or space conditioning equipment, or to a thermal energy storage tank from which it can be drawn for use at night and/or cloudy days [5].

Collectors applicable to the Irish domestic sector include:

• Flat plates

• Evacuated tubes

Flat Plate Collectors

A typical flat plate solar collector is shown in Figure 2. Solar radiation passes through the transparent cover and impinges on the blackened absorber surface of high absorptivity. A large portion of this energy is absorbed by the plate and then transferred to the transport medium to be carried away for storage or use. The underside of the absorber plate and sides of the casing are well insulated to reduce conduction losses.

The transparent cover reduces convection losses from the absorber by restraining the stagnant air layer between the absorber plate and the glass. It also reduces radiation losses from the collector since glass is transparent to short wave radiation received from the sun but is nearly opaque to long-wave thermal radiation emitted by the absorber plate. The optimum tilt angle of the collector is equal to the latitude of the location with angle variations of 10–15o more or less depending on the application [6].

Figure 2. Schematic diagram of a flat plate collector [5]

Evacuated Tube Collectors

Evacuated tube collectors use liquid–vapour phase change materials to transfer heat at high efficiency. These collectors have a heat pipe placed inside a vacuum-sealed tube. The absorber is made up of a pipe attached to a black copper fin that fills the tube. The condenser is made up of a metal tip protruding from the top of each tube attached to the sealed pipe. The heat pipe contains a small amount of fluid that undergoes an evaporating-condensing cycle. Solar heat evaporates the liquid, and the vapour travels to the heat sink region where it condenses and



releases its latent heat. The condensed fluid return back to the solar collector and the process is repeated. When these tubes are mounted, the metal tips up, into a heat exchanger (manifold) as shown in Figure 3. Water, or water/glycol mixture, flows through the manifold and picks up the heat from the tubes. The heated liquid circulates through another heat exchanger and gives off its heat to a process or to water that is stored in a solar storage tank [5].

Figure 3: Schematic diagram of an evacuated tube collector [5]

4.1.2 Water Heating

Solar hot water systems used in temperate climates employ a solar collector that converts both direct and diffuse solar radiation to heat. A solar fluid comprising a mixture of water and glycol is circulated through the collector using a pump operated by a controller. This enables the solar fluid to collect heat when it is available and transfer it to a hot water tank via a solar coil. This cycle continues as long as there is a sufficient temperature difference between the inlet and outlet temperature of the collector. The system’s auxiliary heating system takes over when more hot water is needed than can be supplied by the solar collector. The hot water tank has two coils, the solar coil being at the bottom and the auxiliary heating coil at the middle. Auxiliary heat can be supplied by electricity or a conventional fuel fired boiler. Figure 4 shows a schematic diagram of a typical solar water heating system used in Ireland. Some solar water heaters use a small photovoltaic panel to power the pump. They do not need a solar controller since the pump operates only when solar energy is available.

Figure 4: Schematic diagram of a typical solar hot water system used in Ireland

4.1.3 Space heating

Active systems

Pump

Sol

ar c

olle

ctor

Hot water out to demand

Hot water tank

Boiler coil

Solar coil

Solar controller

Antifreeze fluid Cold

water in

Pump

Sol

ar c

olle

ctor

Hot water out to demand

Hot water tank

Boiler coil

Solar coil

Solar controller

Antifreeze fluid Cold

water in



In active solar heating systems, collectors are used to heat a fluid, the collected energy is then stored, a distribution system and control system provides the stored energy when needed for space heating. Solar thermal systems in combination with an auxiliary heating system then provide the required levels of comfort, stability and reliability.

Figure 5 shows a schematic diagram of a basic solar air heating system with pebble bed storage and an auxiliary heater. The auxiliary heater is used to supplement the air temperature in case that supplied by the solar collector is not enough. Air systems have advantages over water heating systems in terms of freezing and boiling in the collectors and corrosion. High degree of stratification in the collector bed leads to lower collector inlet fluid temperature. Major disadvantages include high storage volume and pumping cost. They are leak prone and high energy losses are possible along ducts.

Figure 5: Schematic diagram of a basic hot air system [1]

Figure 6 shows a schematic diagram of a basic solar hot water system. It consists of a solar collector with a hot water storage tank and an auxiliary heater. The hot water is supplied to radiators which are used for space heating. The by-pass around the storage tank is used to avoid heating the storage tank with auxiliary energy.

Figure 6: Schematic diagram of a basic hot water system [1]

Passive systems

Collectors and storage systems are integrated into the building structure and movable insulation is used to control thermal losses. In temperate climate, auxiliary heating sources are employed to improve on the system’s reliability. Mechanical energy is usually required to move insulation such as window blinds or distribute heat throughout the building.

In the northern hemisphere, south facades of large windows or storage wall elements are used while shading is provided to control overheating in summer. Adequate insulation is needed to heat loss while energy conservation methods

Colle

ctor

Pebble bed

storage unit

Storage by-pass

From cold

AuxiliaryAir ducts

To warm

Air returns

3-way dampers

Colle

ctor

Pebble bed

storage unit

Storage by-pass

From cold

AuxiliaryAir ducts

To warm

Air returns

3-way dampers

Collect

orWater tank

storage unit

Tank

by-pass

From building

Auxiliaryradiators

To building

radiators

3-way dampersPump Pump



are necessary [1]. Passive heating is achieved through direct gain where the window acts as a collector and the building the storage. Collector storage walls can be used which combine both energy collection and storage as one unit. Greenhouse or conservatories attached to buildings can be used as solar energy collection and storage units.

4.1.4 Cooling systems

Solar energy can be used to provide refrigeration for food preservation and comfort cooling. Cooling in buildings is an attractive idea as cooling loads and the availability of solar energy are almost in phase. Solar air conditioning can be accomplished by three classes of systems namely desiccant cycles, solar-mechanical processes and absorption cycles [1].

Solar cooling is expensive, as is solar heating. Reduction in cooling loads through careful building design and insulation will certainly be warranted and, within limits, will be less expensive than providing additional solar cooling. For an air conditioning and heating system, good building design and construction are needed [1].

A growing number of demonstration projects show the huge potential for solar assisted cooling. Thermally driven chillers use solar energy to produce cold and/or dehumidification. When backed up by biomass boilers, 100% Renewable Cooling Systems are possible. Solar cooling is on the edge of wide market introduction and substantial cost reductions can be expected in the next few years [7].

4.1.5 Trends

Over the years, solar thermal systems have witnessed tremendous increase in performance as well as reduction in cost. These have been attributed to

• Improved methods of production

• Modularization and optimization of components

• Improved pump designs adapted to suit different flow regimes

• Developments in coating materials used for absorbers

• Reduced heat losses at the collectors and hot water tank due to better insulating materials

• Improved collector designs

• Integration of different auxiliary heating systems in the storage tank

• New tank designs with enhanced stratification mechanisms that enable hot water to be easily available

Many hybrid configurations of solar thermal systems are currently available in the market for water and space heating. These systems provide two different systems in one product, i.e. a traditional system and a solar one. Despite attempts to optimize hybrid systems in terms of performance improvements while lowering their investment costs to make them more desirable, they usually tend to be inaccessible and unattractive for home or low request usage. The above mentioned problem alongside high efficiency of traditional heating systems, does not encourage investment in hybrid systems [8].



Floor heating is one of the current innovations in space heating. Rooms are heated by lukewarm water circulating in continuous pipe loops embedded in concrete or under wooden floors. To ensure total reliability, there are no joints in the pipes in the floors. The floors reach a pleasant temperature of around 27°C, and produce a wonderful even heat at all points in the room.

Solar Assisted Heat Pump (SAHP) systems combine heat pump technology and solar thermal energy application in mutual beneficial ways. This combination, to some extent, improves the COP of the heat pump unit and reduces the consumption of fossil energy resource. They are used for both water and space heating. According to different heat transfer mediums filled in the solar collector, the SAHP systems can be divided into direct expanded solar assisted heat pump (DX-SAHP) system and indirect expanded SAHP system. In the DX-SAHP system, the refrigerant works as the heat transfer medium. For the indirect expanded SAHP system, which includes the solar assisted air source heat pump (SA-ASHP) system and the solar assisted water source heat pump (SA-WSHP) system, the heat transfer medium is usually water, air or antifreeze solutions etc [9].


4.2.1 Today

Table 3 gives the size and cost of a standard solar water heater based on the number of people in a household installed in Ireland. The prices are for complete solar water heating systems excluding value added tax (VAT) and installation cost. Evacuated tube collectors are more expensive than their flat plate counterparts. They are however more efficient than flat plate collectors in cold climates like Ireland and would therefore require smaller collector sizes for the same application.

Table 1: Flat plate collector size and cost based on household size [10]

Number of people in the household

Area of solar collectors m2

Volume of the solar hot water tank (litres)

Indicative initial investment (€)

2 - 3 2 - 4 100 - 200 2,540 - 3,175

4 - 5 4 - 6 200 - 300 3,175 - 3,809

6 - 7 6 - 8 300 - 400 3,809 - 5,079

Table 3 gives the size and cost of an average combisystem based on the number of people in a household. The prices are for complete solar package excluding VAT and installation cost.

Table 4: Flat plate collector size and cost based on household size [10]

Number of people in the household

Area of solar collectors m2

Volume of the solar hot water tank (litres)

Indicative initial investment (€)



2 - 3 4 – 6 200 - 350 3,809 - 5,079

4 - 5 8 – 10 350 - 600 5,709 - 7,618

6 - 7 10 – 12 600 – 1,000 7,618 - 8,888

4.2.2 Projections

In previous years, the price of solar thermal systems for single family houses, which have a market share of more than 80% in Europe, decreased continually. In all European markets the trend has been equal, although the system costs vary a lot according the typical size, type and quality.

The learning curve of the costs for a typical DHW system in Central Europe as shown in Figure 7 indicates the past cost development as a function of time and increasing installed capacity. The estimates as to further cost development are based on typical learning curve theories, depending on the expected growth of installed capacity. Within the next 20 years, costs are expected to reduce by more than 50%.

Fig. 7: Development of specific costs and installed capacity for small solar

thermal systems with forced circulation in Europe [11]


Where possible, the combination of solar cooling and heating should improve the economics, compared to heating alone [1]. However, this is not widely applicable in Ireland and will not be considered further here.

In the average size house the bulk of domestic energy consumption is used in water and space heating (85%). Three quarters of this energy is used for space heating, a quarter is used for domestic hot water. The remaining portion of the total energy (15%) is the electric portion. There are two ways of using solar thermal heat. Firstly a system for hot water provision can give savings of around 5 - 15% of the total annual energy (60% plus of the hot water). Alternatively a system combining hot water and heating support can give savings of 15 - 40% of the annual hot water and space heating costs. Even greater percentage savings can be made in low energy or passive solar heated houses.



4.3.1 Costs

A typical 8m2 evacuated tube collector installation with a capital cost in the order of €5,000 is used for the purposes of illustrating the technology’s financial and environmental performance. It is assumed that there are no running costs – that electrical parasitic loads are minimal and that the system is maintenance-free.

4.3.2 Revenues

For the purposes of net present value calculations (NPV), revenues are taken to the avoided cost of gas which would have been employed, corrected for a seasonally-adjusted condensing gas boiler efficiency of 90%.

4.3.3 Value

Table 4 illustrates the financial performance of the evacuated tube solar thermal system where it can be seen that the 25-year (estimated system lifespan) NPV at a discount rate of 6% is €-1,200 (negative) when compared to an equivalent gas system.

The combination of tax breaks, government incentives, mass production due to attainment of a critical mass, the learning curve, and improvements in manufacturing processes have led to a drop in capital cost trends over the years. Increase in the cost of conventional fuels as well as imminent introduction of carbon taxes in some countries is making solar thermal systems more attractive.

Retrofitting constitutes one of the major areas where significant savings in energy can be achieved within the domestic sector. Since energy use is greatest in older buildings, solar thermal systems would be of more economic and environmental value in them than in new buildings.

Energy Balance

Solar Thermal Installed Capacity

8.56 m2


Economics



Value of Heat Produced 313 €/annum

NPV (25yr @ 6%) (1,211) €

CO2 Emissions


CO2 Saving by Solar System 820 kg

Table 4: Summary of financial and emissions performance of the solar thermal system.

4.44.44.44.4 COCOCOCO2222 Reduction PerformanceReduction PerformanceReduction PerformanceReduction Performance

Based on the avoided gas burned, the system will reduce emissions from the dwelling by 820kg per annum. This figure is conservative since it assumes that all hot water would be generated using gas if the solar system were not installed:



in reality some electicity would be used in the immersion coil and the CO2 emissions reduction would be greater.


1. Duffie, J.A. and Beckman W.A. Solar engineering of thermal processes. New York: Wiley; 1991.

2. Central Statistics Office of Ireland, www.cso.ie

3. M. Howley, F. O’Leary and B. Gallachoir, Sustainable Energy Ireland, Energy Statistics 1990 – 2006: 2007 report, Sustainable Energy Ireland, Energy Policy Statistical Support Unit, December 2007.

4. European Solar Thermal Industry Foundation Solar Thermal Markets in Europe

(Trends and market statistics 2006), June 2007. Available at: http://www.estif.org/fileadmin/downloads/Solar_Thermal_Markets_in_Europe_2006.pdf

5. Kalogirou, S.A. Solar thermal collectors and applications. Progress in Energy and Combustion Science 30 (2004) pp 231-295.

6. Kalogirou, S. The potential of solar industrial process heat applications. Appl Energy 2003;76:337–61.

7. European Renewable Energy Council, Renewable Heating: Action Plan for Europe, Brussels, January 2007.

8. Carboni, C. and Montanari, R. Solar thermal systems: Advantages in domestic integration. Renewable Energy 33 (2008) 1364-1373.

9. Li, H. and Yang, H. Potential application of solar thermal systems for hot water production in Hong Kong. Appl Energ (2008), doi: 10.1016/j.apenergy.2007.12.005

10. Sustainable Energy Ireland. Solar water heaters: A cost-effective and sustainable alternative. http://www.sei.ie/reio.htm

11. Solar Thermal Vision 2030. European Solar Thermal Technology Platform, May 2006. http://esttp.org/cms/upload/pdf/Solar_Thermal_Vision_2030_060530.pdf



5555 MICRO WIND TURBINESMICRO WIND TURBINESMICRO WIND TURBINESMICRO WIND TURBINES

Keith Sunderland & Michael Conlon

School of Electrical Engineering Systems


An investigation was instigated into the availability and performance of technologies pertaining to micro/mini wind generation. As recently as March, A Building Research Establishment (BRE) event: ‘Low Carbon Technology Briefings: Small Scale Wind’ was attended; out of which, insight into the viability of the sector was considered. There is significant work and progress required if the Irish context is to acquire parity a fact verified at the recent Irish Wind Energy Conference (IWEC) ‘2020 and beyond’ (18th April, 2008). However in light of the recent announcement by Energy Minister, Eamon Ryan (16th April, 2008), who spoke at the annual SEI Energy Show at the RDS of a pilot grant scheme which will allow users to generate electricity for their own use, Ireland Inc. might actually be beginning to “… focus on small scale generation in commercial sites and

domestic dwellings”.

5.1.1 Principles

Wind turbines extract kinetic energy from moving air, converting it into mechanical energy via the turbine rotor and then into electrical energy through the generator.

The kinetic energy of the wind, flowing through the turbine rotor is described by Pwind as:

( )3

windbladesairwind v..A.ρ2

1P =

With:

ρair - the mass density of air;

Arotor - the propeller area;

Vwind - the wind speed.

The mechanical energy Pmech that is taken by the wind is equal to:

( )3

windbladesairpmech v..A)ρ,(.c2

1P βλ= [W]

Where:

- Pmech = Mechanical output power of the turbine [W] - cp = Performance coefficient of the turbine – i.e. the fraction of the kinetic energy of the air captured as rotational energy by the turbine blades



- ρair = Air density [kg.m-3] - Arotor = Turbine swept area [m2] - vwind = wind speed [m.s-1] - λ = Tip speed ratio of the rotor blade tip speed to the wind speed - β = Blade pitch angle [deg] Cp is a function of blade design, tip-speed ratio (λ) and the blade pitch angle (β).

The tip-speed ratio is defined by:

wind

turbineblades

v

R ωλ

.=

A generic equation is used to model cp(λ, β) as it cannot be analytically described.

λβλ

βλ λ643

21

5

),( ceccc

cc i

c

i

p+

−−=

−

With

1

035.0

08.0

113 +

−+

=ββλλ

i

Where:

C1 = 0.5176 C2 = 116 C3 = 0.4 C4 = 5 C5 = 21 C6 = 0.0068

The theoretical upper limit for Cp is 59%, i.e. the ‘Betz limit’.

Figure 8: Power in terms of coefficient (Cp) and mechanical output with respect to wind-speed and blade orientation



5.1.2 Wind Turbine Characteristics

A number of parameters are involved in ascertaining the performance of wind turbines with respect to the environment they will be situated. Table 5 illustrates the parameters involved.

Power (unit)

Rated Power kW

Rated Wind Speed

Cut-in Wind Speed

Cut-out Wind Speed

Maximum wind speed

Dimensions

Rotor Weight kg

Rotor Diameter m

Hotor Height (VAWT) m

Swept Area m2

Height of mast m

Other Information

Number of Blades ?

Brake System ?

Operation Temperature Range0C

Acoustic Levels (at 5m/s at 20m) dB

Lifetime of machine yrs

Up/Down-wind ?

Generator type ?

Self Starting? ?

m/s

Table 5: Parameters are involved in ascertaining the performance of wind turbines

• Cut-in speed: lowest wind speed at which the turbine can produce net electrical power (typical value being 3-5m/s)

• Rated wind speed: lowest wind speed that the turbine produces its rated electrical power (13-16m/s)

• Cut-out speed: highest wind speed at which the turbine produces power (25-30m/s, HAWT). Speeds in excess of this will cause the machine to shut down. Four principles are control and minimize rotor speed:

o Passive stall control

o Blades are designed to naturally stall at excess wind speeds

o Active pitch control

o Blade pitch is altered so as to reduce the energy captured

o Yaw or tilt control

o The rotor axis is either actively or passively shifted out of the wind by rotating the nacelle

o Placing the turbines profile out of the wind.

o No control

o Mechanical/electrical designs robust enough to tolerate extremes.



5.1.3 Types

There are three main design types of wind turbine:

• Horizontal axes

• Vertical axes (Lift or Drag)

The advantages of the three tare summarized below

Table 6: HAWTs vs VAWTs [http://www.urban-wind.org/pdf/technological_analysis.pdf]

In a built/urban environment where the wind flow is frequently turbulent, the vertical axes machines have the advantage of not needing to be directed into the wind. Conversely however, horizontal axes turbines are inherently more efficient in terms of energy conversion from wind into electricity.

In more turbulent areas, HAWTs need to be made robustly in order to cope with blade-buffeting. The negative aspect of increasing the ‘sturdiness’ of the wind turbine is the additional weight accrued by the technology resulting in increased cost implications.

A selection of technologies available to the Irish market was scrutinized in terms of potential for research. As Table 7 illustrates, the manufacturers guidelines could be construed as somewhat ambitious’ when considering the power coefficients of some of the technologies.



The ratings being considered to realistically represent generating capacities appropriate to an average household’s annual consumption (5-7kWh) were in excess of 0.75kW1:

kWannumhrs

57.0/8769

5000=

Model

Grid

Connect

Diameter

(m2)

Swept Area

(m2)

Cut-in Speed

(ms-1

)

Rated Speed*

(ms-1

)

Rated

Power (W)

Output at

Rated

Speed

Power

Coefficient

(Cp) Weight (kg)

Jetstream II

(SP750W)No 3 7.07 2.8 8 1500 900 0.41 40

Espada Yes 2.2 3.80 3 10 800 480 0.21 52

Passaat Yes 3.12 7.65 3 10 1400 950 0.20 75

Whisper

200Yes 2.7 5.73 3.1 11.6 1000 0.18 39.46

Whisper

500Yes 4.5 15.90 3.4 10.5 3000 0.27 70

Proven 2.5 Yes 3.5 9.62 2.5 12 2500 2200 0.22 190

WES5

TulipoYes 5 19.63 3 9 2500 2100 0.24

Skystream

3.7Yes 3.7 10.75 3.5 9.4 1800 975 0.18 77

Swift Yes 2.1 3.46 2.3 14 1500 0.26

Inclin 1500 Yes 2.7 5.73 3.5 12 1500 0.25 42

Windsave Yes 1.75 2.41 3.5 12.5 1100 1000 0.35 25

Microwind Turbines available on the European (UK) Market [Horizontal Axes] - CURRENTLY AVAILABLE TECHNOLOGIES

* = Output for rated speed stated

Table 7: Technology Comparison (based on disseminated manufacturer data)

5.1.4 Trends

There have been a number of initiatives of late relating to the connection of microgeneration to the planning considerations and metering involved.

Connection

As directed by CER2 to connect to the grid, an “inform, consent and fit” process will apply to the installation of micro generation. Owners must inform ESB Networks (ESBN) of any planned installation and follow a formal application process. ESBN is required to respond to an application within 20 business days. An approved list or register of type approved micro generation units will be maintained by ESBN. Micro generators will be included as a priority group in the smart metering implementation programme. In the interim, micro generators can apply to ESBN for an interval meter to be installed. The standard employed for the technologies will be EN50438 (due to be ratified in 2008) and in the interim, ESBN require that technologies apply by their standard: 'Conditions

Governing the Connection and Operation of Micro-generation’

Planning

1 Appendix A illustrates an energy calculator for an average house holds electrical consumption. 2 Arrangements for Micro Generation (CER/07/208)



Wind Turbines with a mast height of 10 metres and a rotor diameter of 6 meters will be exempt from planning permission requirements subject to the following conditions:

The rotor diameter should be 6 metres or less

� There should be a 3 metre minimum clearance between the lower tip of the rotor and the ground

� The minimum distance of a wind turbine from its nearest neighbouring boundary would equal the total height of the turbine plus 1 metre

� Noise levels at the nearest neighbouring inhabited dwelling should be <43dB(A), or <5d(B) above background noise

� Only one turbine is permitted within the curtilage of a house

� The turbine must be situated behind the front wall of the house

� All turbine components shall have a matt, non-reflective finish and the blade shall be made of material that does not deflect telecommunication signals.

� No advertising or logos may be placed or appear on turbines.

In the main, the conditions attached to the exemption for micro wind turbines are designed to ensure their safe installation and use. Issues such as visual amenity, noise, vibration, possible structural damage, safety and poor installation mitigate against the inclusion of building mounted turbines as exempted development. Nevertheless, it will still be possible to apply for planning permission for such turbines in the normal way.

There are proposed exemptions for turbines3 but on the whole, for domestic installations, no further concession (other than what is highlighted above will be likely.

It is not proposed to provide exemptions for building mounted turbines on the basis that the absence of an applicable building standards for such turbines means that the planning code is the only process by which safety considerations relating to these turbines can currently be addressed.

Metering

The current standard for the connection of microgeneration in Ireland4 does not warrant a mechanism for the sale and export of excess electricity from microgeneration. Indeed, EN50438, the European Standard (due for final voting in 2007) dealing with “Requirements for the connection of micro-generators in parallel with public low-voltage distribution networks is more concerned with the technical aspects such as PQ, safety and interface protection than the mode of metering.

In relation to microgeneration, there are no current estimates pertaining to the amount of microgeneration being installed in Ireland and the amount of electricity provided from this source of power, but according to Tony Hearne of ESBN, there is documentation for 16 Wind Turbine installations and 65 PV installations. Indeed, if such technologies are to be encouraged, a form of smart

3 Department of the Environment, Heritage and Local Government: Consultation Paper on the proposed planning exemptions for certain Renewable Energy Technologies 4 Conditions Governing the Connection and Operation of Micro-Generation (DTIS-230206-BRL), May 2006



metering and the means to accurately ascertain the import/export patterns is of paramount importance. A recent Energy Savings Trust study5 suggests that 30-40% of the UKs electricity demands could be met through microgeneration technologies by 2050.

The Commission for Energy Regulation (CER) on the 5th of November published an information paper6 7 on the back of a consultation paper in the area of smart metering.

The Commission decided to work with ESB Networks, suppliers and other stakeholders in structuring and implementing the role out of an optimally designed universal smart metering programme that will embrace all aspects of smart metering relevant to the Irish electricity market. The Commission has also decided that micro-generators will be included in the assessment of the optimal design of a smart meter and its attendant processes (albeit the infrastructure for gathering their data may not be fully established).

John Quinn of Surface Power pointed out at the recent IWEA Conference that whilst net metering has a very positive effect on CO2 abatement, it is not such a positive force on wind energy. A reversing meter at peak times implies that someone else pays. Demand side management is more prudent going forward. Indeed, he drew on the examples of Germany and Italy in the context of wind generation spill payment:

Wind payment (Wind payment (Wind payment (Wind payment (€)€)€)€) PV payment (PV payment (PV payment (PV payment (€)€)€)€)

GermanyGermanyGermanyGermany 0.46/kWhr 0.07/kWhr

ItalyItalyItalyItaly 0.60/kWhr 0. 0/kWhr


The capital outlay for a wind turbine installation includes:

� Required information costs

o Detailed structural drawings of the proposed location

o Structural Details affecting installation

o Planning information compliance

o Permission from the owner/manager of proposed location

o Detailed photographs

� Technology specific costs

o Turbine

o Mounting – support towers

o Rectifier/Meters

o Inverter

For the Proven Turbine being considered, a general costing is illustrated below:

5 Energy Savings Trust: “Potential for Microgeneration Study and Analysis (Final Report)”,14th November 2005

6 Smart Metering The next step in implementation (CER/07/198)

7 Demand Side Management and Smart Metering (CER/07/038)



Turbine

Model Origin

Rated

Capacity

(kW)

Total cost

per kW (€)

Energy Yield

per year

(kWH)

Warantee

(yrs)

Turbine

Lifetime

(yrs)

Proven UK 2.5 (ground) 5220-14500

4282 (@5.0

m/s) 10 20-25

Proven UK 2.5 (building)

10440 -

12180

4282 (@5.0

m/s) 10 20-25

Table 8: [http://www.urban-wind.org/index.php?rub=6&srub=21]

Figure 9: Estimated turbine installed costs for a sample of technologies (UK) [http://www.urban-

wind.org/index.php?rub=6&srub=21]

It is worthy of note here that the above data has some limitations in accuracy. Where more data is available (e.g. Proven 2.5kW) means the greater chance of cost variation based on the fact that coat is further dependent on individual site factors.

5.2.1 Today

Preliminary discussions with respect to the procurement of a Proven 2.5kW and the ancillary equipment indicated the following.

£(stlg) £(stlg) - incl. VAT

PROVEN-2.5/300 Proven 2.5kW grid connect turbine 300V 4020.5 4724.09

ECM2504ME/300 Rectifier & meters for Proven-2.5/300 418 491.15

TM-1100/2500 Proven 2.5 11m self supporting tower 3338.5 3922.74

WB-3000 Windy Boy inverter 3000W 1351.04 1587.47

TM-150/2500F Proven 2.5 flanged tower mount adapter

for use with own mast382.5 449.44

£11,174.89

€16,753.96

€33,507.92

PROVEN 2.5 ASSOCIATED EQUIPM ENT

Roof-mounted Consideration



It is felt however, that a Proven 2.5kW might not be the most viable technology for the sector being scrutinized due to it’s significant mounting requirements as well as the preclusive nature of the cost. The SWIFT turbine was investigated and from discussions with Cell Energy Ireland Ltd. (CEI). The proce (cost) quoted was €11,175.77 (VAT incl.) – which includes consideration towards monitoring (MET and turbine performance).

Appendix 2 provides an illustration of the proposed positioning of the SWIFT turbine.

5.2.2 Projections

In terms of improving the economics of small wind turbines, areas which are likely to see short to medium improvements include:

� Reliability and energy yields

o Maturity of the technologies should assure this

� Technology positioning intelligence

o As the available quantity of (accurate) wind data grows, energy predictions will become more accurate and site installation



experiences will provide the knowledge to place technologies in the locations guaranteeing maximum wind capture

� Feed-in tariff structure(s)

The UK Government and the Department for Business, Enterprise and Regulatory Reform (BERR)8, offer a range of incentives attempting to encourage and develop the sector. Indeed, in March 2006, the BERR published its Micro generation Strategy through which the Government outlined its ambition to “create the conditions under which micro generation becomes a realistic alternative or supplementary energy generation source for the householder, the community and for small businesses”. It envisages that to realise such an endeavour actions on constraints pertaining to cost, information, technical development and regulatory control are required. To date progress has been made in terms of planning, export tariffs, ROCs9 (Renewable Obligation Certificates) and the development of the ‘Microgeneration Certification Scheme10’.

In the UK, there is an intention for all new homes to be zero carbon by 2016 with a major progressive tightening of the energy efficiency building regulations - by 25% in 2010 and by 44% in 2013 - up to the zero carbon targets in 2016. In conjunction with this, the proposal for a European Directive on the promotion of the use of energy from renewable sources (23rd January, 2008)11 requires the BERR to devise a cross-Governmental strategy to realise the aspirations of such a Directive by 2009 that will meet the UK’s share of the EU 2020 Renewable Energy target. In particular the areas concerning Energy Efficiency, Distributed Electricity and Heat will require innovative are being considered.

The Low Carbon Buildings Programme (UK)12 for the installation of microgeneration

technologies in a range of buildings to include households, community organisations,

public, private and the non-profit sectors has been put in place. This is an £86m grant programme for microgeneration technologies, launched in April 2006 offering capital grants over 3 years to successful applicants. As well as this,

Phase 2 of the Low Carbon Buildings Programme (LCBP) concerns the non-private home dwelling sector. Through it, BERR hopes to achieve reductions in the cost of microgeneration technologies; increase public awareness leading to a better understanding by the general public as a result of their installation in a wide range of buildings.

The grant must be used to fund the supply and installation of a renewable energy scheme at a permanent building located in the United Kingdom. In general, only costs directly related to the installed equipment and work is eligible. Projects where installation of microgeneration measures has already started are not eligible for funding.

The Grant levels involved include13:

� Solar photovoltaic 50%

� Solar thermal hot water 30% 8 formally the Department of Trade and Industry, Dti 9http://www.berr.gov.uk/energy/sources/sustainable/microgeneration/strategy/implementation/certificates/page39834.html 10 Which will provide consumers with independent certification of microgeneration products and installers, together with a consumer Code of Practice, to ensure that consumer complaints are handled properly. 11 http://ec.europa.eu/energy/climate_actions/doc/2008_res_directive_en.pdf 12 http://www.berr.gov.uk/energy/sources/sustainable/microgeneration/lcbp/page30472.html 13 http://www.lowcarbonbuildingsphase2.org.uk/



� Wind turbines 30%

� Ground source heat pumps 35%

� Automated wood pellet stoves 35%

� Wood fuelled boilers 35%

� Size limits: Electricity 50kW; Heat 45kW

Benchmarks in terms of £/tCO2 also apply and may act as a cap on grant.

The European position with the technology was investigated via The Wind Energy Integration in the Urban Environment (Wineur14) Project was set up with the following objectives:

� Identify the conditions that need to be established for the integration of

small wind turbines into the urban environment

� Promote the emergence of this technology as a real option for electricity

supply in towns and cities across Europe

� Raise awareness amongst municipal authorities and decision-makers, because the promotion of wind energy technology in the city clearly rests on the involvement and take-up of this option by decision-makers at the local, city-wide level.

� Assess and improve the prospects for social, aesthetical, architectural and urban planning acceptability of such wind energy applications by raising public awareness, defining performance and technical guidelines

The proposed project was established to support the EU and its Member States in achieving their renewable energy target : to increase the utilisation of renewable energies from the present 6% to 12% by 2010.

In the Irish context, the announcement by the Minister for Communications, Energy and Natural Resources Eamon Ryan that businesses and individual householders will be encouraged to generate their own electricity using wind and solar power under a trial programme is very encouraging. The ‘microgeneration’ programme allowed the potential to sell excess power back to the national grid.

A 50 per cent start-up grant will be made available to cover the installation costs of microgeneration systems in about 50 trials to be conducted throughout the State. €2 million will be provided by the department in 2008 to fund the grant scheme, which will be administered by SEI, the national energey agency and other bodies such as the Commission for Energy Regulation, ESB Networks. It is intended that such a “… scheme will empower electricity users to take action”.


Currently, the viability of wind turbine installation in urban environments is not considered (by industry consensus) cost viable due to the lack of available data to influence installation and also the embryonic development of site-specific wind turbines. However it must be acknowledged that economic factors are often not the primary reason for installing wind turbines.

14

http://www.urban-wind.org/index.php?rub=3



Indeed Wineur data suggests that there are a number of drivers for urban wind turbines, as illustrated below:

Figure 10: 1st European Windy Cities Meeting, Amsterdam, The Netherlands, 26th & 27th October 2006 [http://www.urban-wind.org/admin/FCKeditor/import/File/Status_Techno_Costs_UK.pdf]

5.3.1 Costs

� The factors which mostly affect the economics of wind turbine installation include:

o Applied discount rate

� This discount rate is the rate by which benefits that accrues in some future time period must be adjusted so that they can be compared with values in the present.

� Grant funding

� Wind speed and energy yield

� Ground conditions

� Maintenance costs

� Tariff structures

� Demand/consumption patterns

In terms of costs, HAWTs are currently much cheaper than VATs and have better energy yield. However, HAWTs present three particular issues: noise, vibration and safety which arise less frequently with VAWTs.

5.3.2 Revenues

At the moment, for micro (and mini) wind turbines, there are no government incentives other than the relative leniency shown with regard to planning (up to 2.5kW) and the ease at which the technologies can be grid-tied – albeit for no financial benefit. With the Minister of Energy’s announcement, the potential(s) are just beginning to be explored.



5.3.3 Value

There are very few studies available looking at the value (economic) that can be attained by increased penetration of microgeneration in the Irish context. SEI commissioned PB Power in 2004 to investigate the costs and benefits of embedded generation in Ireland with an addendum on microgeneration. PB Power were required to perform a detailed assessment of the costs and benefits to all parties involved in the connection of embedded generation to the electricity networks, including analysis of generic sections of the Irish electricity distribution network.

The report found that the benefits that accrue for larger embedded generators with direct connections to the MV and HV distribution network will also accrue for SSEG connected to LV networks. The cumulative benefit for multiple SSEG’s could actually be higher than for an equivalent size larger generator, given the additional energy and losses savings.

The report also suggested a series of steps required to facilitate this goal:

� Determine the standard interface arrangements, connection terms and costs to facilitate connection of micro- and small-scale embedded generation to the Irish distribution network, taking into consideration the draft European Norm;

o With the recent announcement of the pilot scheme, this work is only commencing

� Determine the load profile for typical SSEG installations associated with domestic, small commercial and small industrial customer categories. These profiles can then be adopted within the planning process for new LV networks;

o With the consumer standard, the myths associated with the performance of the technologies can be tackled

o Installers need also to be trained to a standard appropriate to the sectors requirement

� Determine the levels of SSEG that can be connected to different designs and types of ESB distribution network without requiring changes to the network

o Ongoing research involving PQ investigations as well as proportionality of grid topologies

� Determine the longer-term costs and benefits associated with multiple SSEG connections, based on market forecasts for different technologies.

� Determine the best mechanisms for apportioning costs and benefits, given the likely ownership of SSEG

In 2004, there was also a study commissioned by The Department for Business, Enterprise and Regulatory Reform (formally the DTI) commission Mott McDonald to carry out a study: System Integration of Additional Microgeneration (SIAM)15. This study was commissioned by the DTI in April 2004 to provide an analysis of the costs and benefits of integrating additional micro-generation on the low voltage (LV) electricity networks towards 2020. The project has been

15 http://www.berr.gov.uk/files/file15192.pdf



steered by members of Work Stream Four (WS4) of the Distributed Generation Co-ordinating Group (DGCG).

The analysis in the report demonstrated that the network costs of integrating microgeneration into the GB networks are comparatively small and that they would be outweighed by the benefits as summarised in Figures below.

Figure 11: Mott McDonald (SIAM) comparison of Network and System Costs/Benefits with additional microgeneration

Lawrence Staudt of the Centre of Renewable Energy, Dundalk It in his recent paper reports the results of preliminary computer modeling of energy production and economics of domestic grid-connected wind energy in Ireland. In it he integrates domestic electricity consumption profiles with wind turbine power curves (for Proven (2.5/6kW) and Air Dolphin models). Modelling is performed to derive the economic performance - in terms of either being afforded no value for exports or 8c/kWhr for exports - for the three technologies in terms of three different average hub-height wind speeds for three different domestic demand levels.

The report concluded that grif-connected wind turbines can produce much of a home’s electricity needs. However, the mismatch between supply and demand means that a significant percentage of production will typically be exported’ Therefore, value must be given to these exports as well as CO2 abatement for domestic wind turbines to be economically viable and the cost associated with wind turbines also needs to decline more rapidly in order to encourage the market.

5.45.45.45.4 FinanFinanFinanFinancial Viabililty & Ecial Viabililty & Ecial Viabililty & Ecial Viabililty & Emissions Benefitsmissions Benefitsmissions Benefitsmissions Benefits

Table 9 summarises the financial and emissions performance of the building-mounted Proven 2.5kW horizontal axis turbine. The unit produces electricity with a value of €617 per annum and has a negative NPV of €19,271. The displaced conventional electricity would have emitted 2,740 kg of CO2 per annum.



Energy Balance

Wind Installed Capacity 2.5 kW

Electrical Output 4,282 kWh/annum

Economics


Electricity Unit Cost

14.4 c/kWh

Value of Electricity Produced 617 €/annum

NPV (20yr @ 6%) (19,271) €

CO2 Emissions


CO2 Savings 2,740 kg/annum

Table 9: Financial and emissions performance of a micro wind turbine.



6666 GROUND SOURCE HEAT PGROUND SOURCE HEAT PGROUND SOURCE HEAT PGROUND SOURCE HEAT PUMPSUMPSUMPSUMPS

Aidan Duffy



Geothermal technologies are widely promoted as energy-efficient, cost-effective and environmentally-friendly. The area covers a large variety of technologies exploiting a wide range of heat sources including:

• high temperature sources such as geysers, hot springs, steam vents; and

• lower temperature sources such as aquifers, bedrock and the soil.

High temperature heat sources are highly location-specific and do not generally have widespread potential. Lower temperature sources, however, have widespread application and are therefore the subject of the remainder of this section. Systems utilising low-grade heat will be referred to here as ‘ground source heat pumps’ (GSHP).

6.1.1 Principles

GSHPs collect and transfer heat locally from the ground, upgrade or concentrate this to heat to a higher temperature using a heat pump which is then used for space heating and/or hot water in a building. Heat collection may be by means of an ‘open’ or ‘closed’ system. An example of the former is where groundwater is abstracted from which heat is extracted and the cold water the runs to waste or is reinjected downstream. Such systems require the presence of sufficient groundwater flow rates and often have significant maintenance requirements due to the presence of impurities. For these reasons closed systems are much more common (and will be the focus of this section of the report) where lengths of pipe are buried in the ground through which a fluid flows and collects heat from the ground.

GSHPs typically comprise the following three components:

• a ground loop where pipes are buried either vertically or horizontally in the ground through which a water/glycol or refrigerant is pumped;

• the heat pump which extracts heat from the ground loop circuit and concentrates it to a higher temperature (much in the same way as a fridge or freezer extracts heat from inside and dumps it to the outside); and

• a heat distribution system for transferring heat from the heat pump into the dwelling. Because heat pumps produce low grade heat (to maintain high efficiencies), they cannot use typical ‘radiatior’ perimeter heating systems and instead rely on underfloor systems (typically embedded in a concrete screed).



6.1.2 Types

Closed loop GSHP systems can be classified in two main ways:

• whether direct or indirect; and

• by ground loop configuration.

Indirect systems (which are most common) have a water/glycol (antifreeze) mixture circulating in a sealed buried pipe which collects heat from the soil; this fluid is transferred to the heat pump through a heat exchanger. Direct systems involve the circulation of the heat pump refrigerant through the soil, thus eliminating the need for an additional heat exchanger and consequently increasing system efficiency.

Ground loop can be configured in two main ways:

• horizontally where the pipework is buried in the ground at a depth of between 1 and 2 metres;

• vertically in backfilled boreholes where sufficient land area for a horizontal system is not available.

Vertical systems are more costly than horizontal ones.

The term ‘coefficient of performance’ (COP) is used to describe the efficiency of a GSHP system and is defined as the ratio of total heat output to total electrical consumption (Mustafa, 2007). COPs are a function of the ground loop water temperature (this being dependent on ground temperature, flow rate, pipe characteristics, etc.) and the output temperature (see Figure).

Figure 12: Coefficients of Performance (COPs) of typical small GSHPs (BRESEC, 2000)

Maximum COPs in the range of 3-4 are typical for GSHP systems (Mustafa, 2007) although figures as high as 5 have been obtained for newer technologies (Sanner et al., 2003) - direct systems performing slightly better than closed systems for reasons already discussed. However, typical seasonally adjusted



COPs lie in the rance 3.0-3.8 although a well designed system can achieve 4.0 (Sanner et al., 2003). The US Energy Star website (a joint initiative between the US Environmental Protection Agency and Department of Energy) quotes COPs of 3.3 and 3.5 for closed and open loop domestic systems respectively (EnergyStar, 2008).


Capital costs of GSHP systems vary significantly depending on a variety of factors including:

• whether it is a new-build or retro-fit project;

• ground conditions;

• whether a vertical or horizontal ground loop system is chosen;

• complexity of control strategies;

• degree of back-up.

Some indicative costs from literature are shown in Table 10. These exclude the cost of the underfloor heating system which may cost up to 20% more than a conventional system (€35/m2 extra).

GSHP Capital Cost Exclusions Source Year Note

1,000-1,200 €/kW heating distribution

Greenspec.co.uk 2008 Converted from Stg to Euro

845 €/kW none BRECSU 2000 Converted from Stg to Euro; Converted to 2008 prices

320-630 €/kW not stated Mustafa 2008 Converted from USD to Euro

Table 10: GSHP system capital costs from a variety of literature sources.

6.36.36.36.3 Financial ViabFinancial ViabFinancial ViabFinancial Viabilityilityilityility

The GSHP financial viability assessment outlined here is based on the installation of a 4kW unit in a 200m2 detached residential dwelling which is sized to provide 90% of space heating and 55% of hot water requirements. Figure 13 illustrates annual heat and hot water consumption and GSHP production data.



15,539

2,309

13,985

1,270

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

Space Heating Hot Water

Co

ns

um

pti

on

(k

Wh

/an

nu

m)

Total

Produced by GSHP

Figure 13: Annual total heat and hot water consumption and GSHP production for a typical domestic dwelling.

A base case of a gas-fired condensing boiler linked to a traditional perimeter heating system was taken for comparative purposes. The additional cost of a GSHP when compared to this system was estimated to be €8,690 allowing for the heat pump, horizontal ground loops and the additional cost of the underfloor heating system; a credit was included for the omitted gas boiler.

6.3.1 Running Costs

A COP of 3.5 was used to estimate total electricity consumption by the GSHP system and a unit electricity price of 14.4 cent was used to calculate annual running costs. No maintenance charges were included.

6.3.2 Revenues

Revenues are based on the value of the avoided cost of gas, charged at a unit price of 6.86 cent and corrected for a modern condensing boiler efficiency of 90% (hcv).

6.3.3 Value

Table 11 summarises the financial performance of the GSHP system and shows that it would have a negative net present value (NPV) of €2,408 using a discount rate of 6% over 20 years when compared to the gas system.

Energy Balance

GSHP Installed Capacity 4 kW

COP 3.5


GSHP Electrical Consumption 4,359 kWh/annum

Economics






Electricity Unit Cost 14.4 c/kWh

Cost of Electricity Consumed (628) €/annum

Net Saving by GSHP 535 €/annum

NPV (20yr @ 6%) (2,408) €

CO2 Emissions




GSHP System CO2 Output 2,789 kg/annum

CO2 Saving by GSHP 262 kg

Table 11: GSHP net present value and CO2 emissions impact.

6.46.46.46.4 COCOCOCO2222 Reduction PerformanceReduction PerformanceReduction PerformanceReduction Performance

The annual reduction in CO2 emissions from the GSHP system were found to be 262kg/annum when compared to the base gas-boiler case. This represents a 9% reduction in emissions. This reduction is low by international standards and highlights the high CO2 intensity of electricity produced in Ireland when compared to that of natural gas (640g/kWh and 180g/kWh respectively).


EnergyStar (2008) Geothermal Heat Pumps Key Product Criteria. Website accessed 13th May 2008 http://www.energystar.gov/index.cfm?c=geo_heat.pr_crit_geo_heat_pumps

BRECSU (2000) Heat Pumps in the UK – a monitoring report. General Information Report 72, Energy Efficiency Best Practice Programme, HMSO, UK.

BRESEC (2004) Domestic Ground Source Heat Pumps: Design and installation of closed-loop systems, Energy Efficiency Best Practice Programme, HMSO< UK.

Mustafa Omer, A (2008) Ground-source heat pumps systems and applications, Renewable and Sustainable Energy Reviews. Volume 12, Issue 2, Pages 344-371.

Sanner, B., Karytsas, C., Mendrinos, D. and Rybach, L. (2003) Current status of ground source heat pumps and underground thermal energy storage in Europe, Geothermics, Volume 32, Pages 579-588.



7777 WOOD PELLET BOILERSWOOD PELLET BOILERSWOOD PELLET BOILERSWOOD PELLET BOILERS & STOVES& STOVES& STOVES& STOVES

Aidan Duffy



7.1.1 Principles

Wood pellet boiler and stoves provide domestic space heating through the combustion of compressed sawdust which is regarded as a carbon neutral waste product. Stoves provide space heating directly by radiation and convection. Boilers deliver space heating to a dwelling through a conventional wet-based perimeter heating system of radiators and pipework; they have the added advantage of providing hot water also.

These technologies are favoured by policy makers due to their perceived carbon neutrality, relative ease of retrofitting to existing dwellings, the use of locally-sourced fuel and the proven nature of the technology.

7.1.2 Boilers & Stoves

Although standard oil boilers can be fitted with a pellet burner, the most common units available on the European market are integrated units where the burner is an integral part of the boiler. These units may have integrated pellet storage although in many instances the boiler and store a separate. In this case, a conveyor system (screw or suction) is used to feed fuel from the store to the boiler or stove (Fiedler, 2004).

Modern integrated wood pellet boilers and stoves have overcome many maintenance and reliability issues. However, cleaning and de-ashing is required between 1 and 3 times per annum. The large size of the boiler relative to gas- or oil-fired alternatives, together with the requirement for pellet storage (store volumes of 6-8m3 are required for an average house), mean that they require more space than alternatives (Fiedler, 2004).

Emissions from wood pellet boilers and stoves must comply with national and EU standards for emissions from small-scale wood combustion units (EN 303-5 in the case of the European Standard).

Modern boilers with state-of-the-art sensors and controls can reach maximum efficiencies of up to 94% although seasonally-adjusted efficiencies of 70% have been reported (Nova Scotia DoE, 2008). Stoves have reported efficiencies in the region of 55-80% (Natural Resources Canada, 2008).

7.1.3 Trends

The market for wood pellet heating systems appears to be growing quickly. For example, in German, Austria and Sweden the total number of installed residential pellet boilers and stoves grew from under 10,000 in 1997 to 52,000 in



2001 (Fiedler, 2004). In Ireland 1900 pellet boilers and 570 stoves were installed between April 2006 and August 2007 (SEI, ).

The technology is well established and commercialised although research and development is still continuing in a number of areas including: emissions; slagging; influences of physical and chemical fuel composition; efficiency optimisation (Vinterbäck, 2004).


The capital cost of installing a wood pellet boiler in a typical Irish house are estimated to be in the region of €10,000 to €16,000 (SEI, 2008a). Austrian and German figures lie in the range of €7,750 to €11,000 for a 10-20kW domestic boiler (Fiedler, 2004). There are no additional costs associated with the heating distribution system and a saving in the order of €2,000 for the avoided cost of a condensing gas boiler.


7.3.1 Running Costs

The costs involved in operating wood pellet boilers and stoves include:

• wood pellet fuel;

• electricity for fans, controls, pumps etc;

• maintenance.

The cost of wood pellet fuel is in the order of 4.58c/kWh (SEI, 2008b). This is close to prices quoted in the UK of 4.39c/kWh (Biomass Energy Centre, 2008). The delivered cost of heat is therefore taken to be 6.54c/kWh, using Irish costs and adjusting for seasonal boiler efficiency.

The cost of running parasitic electrical loads is assumed to be negligible and the annual cost of maintenance to be €150.

7.3.2 Revenues

Revenues are based on the value of the avoided cost of gas, charged at a unit price of 6.86 cent and corrected for a modern condensing boiler efficiency of 90% (hcv).

7.3.3 Value

Table 12 shows the net present value (NPV) of investing in a wood pellet boiler in a ‘typical’ 200m2 detached house based on the above capital costs, running costs and heat revenues. It can be seen that the installation has a negative NPV in the region of €14,000 over an operating life of 15 years.

Energy Balance

Pellet Boiler Installed Capacity 15 kW

Efficiency 0.7




Economics




Pellets Unit Cost 6.54 c/kWh

Cost of Pellet Fuel (1,452) €/annum

Maintenance (150) €/annum

Net Operating Surplus (417) €/annum

NPV (20yr @ 6%) (14,201) €

CO2 Emissions



Wood Pellet CO2 Intensity 0 kg/kWh

GSHP System CO2 Output 0 kg/annum

CO2 Saving by GSHP 3,108 kg

Table 12: Wood pellet boiler net present value and CO2 emissions impact.

7.47.47.47.4 COCOCOCO2222 ReduReduReduReduction Performancection Performancection Performancection Performance

The wood pellet boiler installation for the ‘typical’ house results in annual CO2 reductions of 3,108kg assuming that the fuel is ‘carbon neutral’. This assumption is, however, disputed due to the processing, packaging and transportation of the waste sawdust. The energy requirements associated these activities may result in emissions of up to 40g/kWh, equivalent to 22% of natural gas emissions (Duffy & Conroy, 2007).


Biomass Energy Centre (2008) Fuel costs per kWh: Typical domestic prices for fuels. Web site accesses 14th May 2008 http://www.biomassenergycentre.org.uk/portal/page?_pageid=75,59188&_dad=portal&_schema=PORTAL

Duffy, A. and Conroy, M. (2007) The Embodied Transport Energy Analysis of Imported Wood Pellets in Energy and SustainabilityEnergy and SustainabilityEnergy and SustainabilityEnergy and Sustainability (eds. C. Brebbia and V. Popov), Proceedings of a Conference held at Wessex Institute of Technology, UK, WIT Press, pp 299-308.

Fiedler, F. (2004) The sate of the art of small-scale pellet-based beating systems and relevant regulations in Sweden, Austria and Germans in Renewable and Renewable and Renewable and Renewable and Sustainable Energy ReviewsSustainable Energy ReviewsSustainable Energy ReviewsSustainable Energy Reviews, Elsevier, 8888, pp. 201-221.

Natural Resources Canada (2008) Office of Energy Efficiency: Heating with Gas. Web site accessed 14th May 2008 http://www.oee.nrcan.gc.ca/publications/infosource/pub/home/Heating_With_Gas_Chapter5.cfm?text=N&printview=N

Nova Scotia DoE (2008) EnerInfo Advisor: Introduction to Home Heating, Information leaflet accessed on-line, 14th May 2008. https://www.gov.ns.ca/energy



SEI (2008a) Greener Homes Scheme: Frequently Asked Questions. Web site accessed 13th May 2008 http://www.sei.ie/index.asp?locID=779&docID=-1

SEI (2008b) Fuel Cost Comparisons: Domestic Fuel Cost Comparisons. Web site accessed 13th May 2008 http://www.sei.ie/index.asp?locID=58&docID=-1

Vitnerbäck, J (2004) Pellets 2002: the first world conference on pellets in Biomass and BioenergyBiomass and BioenergyBiomass and BioenergyBiomass and Bioenergy, Elsevier, 22227777, pp. 513-520.

domestic renewable energy supply technology review: current status

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