i

Declaration of originality

I certify that this is my own work, and it has not previously been submitted for

any assessed qualification. I certify that the use of material from other

sources has been properly and fully acknowledged in the text. I understand

that the normal consequences of cheating in any element of an examination, if

proven and in the absence of mitigating circumstances, is that the Examiners’

Meeting be directed to fail the candidate in the examination as a whole.

Signed:

……..………………………………………………………………………………

Date:

……………………….……………………………………………………………….

ii

Abstract The current situation and prospects for small wind turbines (<50kW) in the UK urban

environment are examined. Technical information was obtained from British and

Irish manufacturers & designers of small wind turbines to assess the state of the art.

The number & types of UK installations were collected, and a detailed questionnaire

was designed and distributed to them. Models were created and information was

collected to assess the economic viability. 31 turbines (including prototypes) were

assessed, 92 installations were found of which 19 returned completed questionnaires,

and economics for four situations were assessed in detail. The technology is

promising, as are the experiences of wind turbine owners (although significant issues

remain), but economic viability depends on a combination of factors including grants

and good average wind speeds (the latter could be rare in the urban environment).

The work was conducted with IT Power for the EC co-funded WINEUR project.

iii

Executive summary

This report examines the current situation and prospects for small wind turbines

(<50kW) in the UK urban environment. It focuses on the state of the art, installations

& installation experiences, and the economics.

To assess the state of the art, technical information was obtained from all 16 British

and 3 Irish manufacturers & designers of small wind turbines to assess the state of the

art. There are 31 small turbines being manufactured or designed that could be

installed in the urban environment, 18 of which are specifically marketed for it. There

are no VAWTs currently being manufactured, but 7 are being designed for the urban

environment. The turbines presently being manufactured are categorised: there are 6

“micro HAWTs”, 3 “small HAWTs not aimed at the urban market”, 4 “small HAWTs

aimed at the urban market”, and 6 “larger HAWTs”. The latter two categories are

aimed at the urban environment.

A small wind turbine test centre would be useful to corroborate the data supplied by

manufacturers, which would help in making objective technical comparisons of the

turbines. The importance of a low cut-in wind speed of 2 or 2.5m/s where AMWSs

(Annual Mean Wind Speeds) are ≤4m/s, and the energy a turbine theoretically loses if

it cuts-out at 15m/s where AMWSs are ≥7m/s is demonstrated.

Internet research revealed 92 installations of wind turbines in the urban environment

in the UK. They are categorised according to who installed them (i.e. school or

housing association), type of turbine, urban or semi-urban, and building-mounted or

ground-based. Most of the installations are of Proven 2.5 and 6kW turbines, and they

are mostly installed at schools or environment centres.

A detailed questionnaire was created from scratch which covered sociological &

technical aspects, barriers to installation, and economics. It was distributed to the

installations found, and 19 responses were received. The results show that although

turbine owners tend to have high levels of satisfaction, and that the perceptions of

neighbours and the local communities significantly improved after the installations

compared with before; a high proportion of owners have had technical problems with

iv

their turbines, suffered from poor after sales service, and overrate the economics. The

most significant obstacles to installation encountered were planning and connecting to

the grid (neighbours and the local community had comparatively little effect). A

significant proportion of those who responded had also depended on grants.

Installed costs for the turbines are estimated based on data collected, and by £/kW are

found to approximately corroborate with the Clear Skies estimate of £2,500-5,000 per

kW. Economic estimates for building-mounted installations are not significantly

more expensive than ground-based installations for turbines of the same type.

Initial economic modelling is completed for turbines at a school in Glasgow, a house

in Reading, and the RIBA (Royal Institute of British Architects) and Aylesbury Estate

buildings in London. The last three sites all have measured wind speed data which is

why they have been chosen, because NOABL (a wind speed database widely used by

the industry) does not make accurate predictions where the local topography has a

large effect (e.g. in the urban environment). The economic analysis for the school is

for ground-based turbines, for the London buildings building-mounted turbines, and

for the house both kinds. The economics for all of the installations are found to be

poor, apart from the Aylesbury Estate where a payback of 5 years could be achieved

with a building-mounted Proven 6kW if 50% of installation costs are grant-funded

and ROCs are collected. This is due to the high AMWS of 8m/s on the rooftops of

the Estate’s tower blocks. AMWSs in the other measured areas are much lower,

2.8m/s in central Reading, and 3.4m/s on RIBA’s rooftop, and leads to paybacks >20

years. Installations in all the areas are shown to be predominantly sensitive to

changes in wind speed, followed by level of initial investment, (other variables

measured included ROCs, discount rate, and annual maintenance costs).

The research has been carried out with IT Power as part of the EC-funded WINEUR

project. This work focuses on the UK & Ireland, while the WINEUR project is

covering technologies and the state of the market in Europe.

v

SMALL WIND TURBINES FOR THE URBAN ENVIRONMENT: STATE OF THE ART, CASE STUDIES, & ECONOMIC ANALYSIS

TABLE OF CONTENTS Declaration of originality i

iiiii

Abstract Executive Summary Table of Contents vList of figures and tables viiGlossary of terminology ixAcknowledgements x Chapter 1 INTRODUCTION 1.1 Renewable energy & microgeneration targets 11.2 Possible benefits of urban µgeneration, and small wind 1.3 The WINEUR project 1.4 Aims & objectives of this project

2 2 3

Chapter 2 METHODOLOGY 2.1 Methodology 42.2 Note on references 5 Chapter 3 STATE OF THE ART – UK & IRELAND 3.1 The urban wind regime 63.2 HAWT vs. VAWT, lift vs. drag 3.3 Building-mounting 3.4 Categorising small wind turbines with respect to the urban

environment 3.5 State of the art summary 3.6 Technical comparisons of similar turbines

3.61 Power & efficiency comparisons on the “small HAWTs aimed at the urban market” 3.62 Power & efficiency comparisons on “the larger HAWTs” 3.63 The importance of low cut-in wind speeds 3.64 Cut-out wind speeds 3.65 Weight per swept area – turbine robustness 3.66 RPM (Revolutions Per Minute) & TSR (Tip Speed Ratio)

6 8

9 10 14

14 16 18 21 23 24

Chapter 4 UK INSTALLATIONS 4.1 Limitations to the study 254.2 Installations found - results 4.3 The returned questionnaires

4.31 Demographics

25 27 28

4.32 Turbine details 294.33 Location type 304.34 People’s perspectives of the turbine 314.35 Economics & lack of knowledge of turbine operators 344.36 Reasons for installation 364.37 Obstacles to installation 37

vi

4.38 Turbine problems & after sales service 384.39 With hindsight, would they install a small wind turbine again? 38

4.4 Analysis of results 394.41 Of all the installations found 394.42 Of the returned questionnaires 40

Chapter 5 ECONOMICS 5.1 Methodology 435.2 Estimated installed costs per kWe for turbines 445.3 St. John Bosco School, Renfrewshire 5.4 A traditional house in central Reading, Berkshire 5.5 Large buildings in London – RIBA, and the Aylesbury Estate 5.6 Analysis

46 50 55 59

Chapter 6 CONCLUSIONS 61 REFERENCES 64 APPENDICES Appendix A Wind turbine details Appendix B Catalogue of wind turbines on the market Appendix C Catalogue of prototype wind turbines Appendix D Permanent magnet or induction generators? Appendix E Full list of known installations Appendix F Blank sample case study questionnaire Appendix G Raw questionnaire data Appendix H Additional installation results Appendix I The variables for economic analysis Appendix J Approximate installed turbine costs Appendix K Full installation costs for different turbines at John Bosco School Appendix L Important conversations and emails Appendix M Economic questionnaires

vii

List of figures and tables Figure 1– the HAWT categories and their rotor diameter ...........................................10 Figure 2 – Power vs. wind speed for the “small HAWTs aimed at the urban market”15 Figure 3 – Power per m2 of swept area vs. wind speed for the “small HAWTs aimed at the urban market”.........................................................................................................15 Figure 4 – Fraction of the Betz limit attained by the “small HAWTs aimed at the urban market” vs. wind speed......................................................................................16 Figure 5 – Power vs. wind speed for “the larger HAWTs” .........................................17 Figure 6 – Power per m2 of swept area vs. wind speed for “the larger HAWTs” .......17 Figure 7 – Fraction of the Betz limit attained by “the larger HAWTs” vs. wind speed......................................................................................................................................18 Figure 8 – kWh the D400 generates due to wind speeds in the ‘bins’ of 3m/s and 3 & 4m/s at different AMWSs ............................................................................................19 Figure 9 – Percentage of the total annual energy capture of the D400 due to wind speeds in the ‘bins’ of 3m/s and 3 & 4m/s at different AMWSs .................................20 Figure 10 – kWh the Proven 15kW generates due to wind speeds in the ‘bins’ of 3m/s and 3 & 4m/s at different AMWSs ..............................................................................20 Figure 11 – Percentage of the total annual energy capture of the Proven 15kW due to wind speeds in the ‘bins’ of 3m/s and 3 & 4m/s at different AMWSs ........................21 Figure 12 - kWh the Proven 0.6kW and the Swift generate due to wind speeds in the ‘bins’ ≥15m/s at different AMWSs..............................................................................22 Figure 13 – Percentage of the total annual energy capture that the Proven 0.6kW and the Swift generate due to wind speeds ≥15m/s or ≥20m/s at different AMWSs.........23 Figure 14 – Weight per swept area of the turbines ......................................................24 Figure 15 – Locations of all 92 installed turbines........................................................26 Figure 16 – Turbine models chosen.............................................................................27 Figure 17 – Turbine models chosen.............................................................................29 Figure 18 – Locations of installed turbines..................................................................30 Figure 19– Owner’s overall happiness with their turbine............................................31 Figure 20– Owner’s rating of the visual appearance of their turbine ..........................32 Figure 21 – Neighbours’ and local communities’ perceptions before the installation 33 Figure 22 – Neighbours’ and local communities’ perceptions after the installation ...33 Figure 23 – Owner’s estimates of the turbine’s paybacks ...........................................35 Figure 24 – Reasons listed for installing the turbine ...................................................36 Figure 25 – Owner’s rating of the difficulty in overcoming obstacles ........................37 Figure 26 – Estimated turbine installed costs in £/kW ................................................44 Figure 27 – John Bosco School’s turbine and its location...........................................46 Figure 28 – LPC sensitivity analysis for John Bosco School ......................................48 Figure 29 – Estimated LPCs for different turbines installed at John Bosco School....49 Figure 30 – Map of central Reading ............................................................................51 Figure 31 – LPC sensitivity analysis for the installation of a Swift on a house in Reading ........................................................................................................................54 Figure 32 – Map of RIBA’s location in London..........................................................55 Figure 33 – Map of Aylesbury Estate’s location in London........................................56 Figure 34 – LPC sensitivity analysis for a roof-mounted Proven 6kW on the Aylesbury Estate ..........................................................................................................59

viii

Table 1– the DTI’s definition of microgeneration.........................................................1 Table 2 – Advantages & disadvantages of HAWTs, Lift VAWTs, & Drag VAWTs...7 Table 3 – Summary of manufacturers..........................................................................11 Table 4 – Turbines being manufactured for the urban environment ...........................12 Table 5 – Prototypes being 12designed for the urban environment ............................12 Table 6 – Turbines on the market which are suitable for building-mounting 13 Table 7 – Prototypes which should be suitable for building-mounting .......................13 Table 8 – Breakdown of total number of installations.................................................25 Table 9 – Number of known rooftop installations .......................................................27 Table 10 – Locations of installed turbines...................................................................28 Table 11– base case of the school for LPC sensitivity analysis ..................................47 Table 12 – estimated installed costs for turbines at John Bosco School .....................49 Table 13 – Estimated economics of residential turbine installations in Reading ........52 Table 14 – Base case for residential Swift installation in Reading, for LPC sensitivity analysis.........................................................................................................................53 Table 15 – Economics of roof-mounted turbines on RIBA & the Aylesbury Estate ..57 Table 16 – Base case for roof-mounted Proven 6kW on the Aylesbury Estate, for LPC sensitivity analysis .......................................................................................................58

ix

Glossary AMWS Annual Mean Wind Speed BEAMA British Electrotechnical and Allied Manufacturers’ Association. With

respect to microgeneration, they are interested in how exports could be metered.

Betz limit Theoretical maximum limit to the amount of energy that can be extracted from an airflow, for either HAWTs or VAWTs. The limit is 59.3% of the energy in the wind.

CREDIT Centre for Renewable Energy, at Dundalk Institute of Technology CREST Centre for Renewable Energy Systems Technology, at Loughborough

University DTI Department of Trade and Industry EERU Energy and Environment Research Unit, at the Open University in

Milton Keynes G59 & G83 grid connection standards. When a renewable energy generator

connects to the grid, they must ensure that they meet these standards. GLA Greater London Authority HAWT Horizontal Axis Wind Turbine LPC Levelised Production Cost is the present cost of the energy from e.g. a

turbine given the costs and income it provides over its lifecycle (normally assumed as a 20 year period).

µgenerator (Microgenerator) DTI’s definition, is: < 50kWe, or < 45kW heat, from a low carbon source.

NOABL DTI database on estimates of AMWSs throughout Britain, to a 1km square 10, 25, or 45m above ground-level

ODPM Office of the Deputy Prime Minister PPS22 Planning Policy Statement 22, issued by the ODPM. Guidance aimed

at encouraging local planning departments to view renewable energy installations favourably.

Rayleigh Wind speed distribution. Special case of the Weibull where the shape factor k = 2. The scale factor c depends on the mean wind speed, therefore the whole shape of the curve can be determined by the mean wind speed.

ROC Renewable Obligation Certificate RPM Revolutions Per Minute (of the turbine’s rotor) SCHRI Scottish Community and Household Renewables Initiative. This is

essentially Clear Skies, but in Scotland. They seem to have more money to spend on projects than Clear Skies, and their website is more comprehensive.

SEI Sustainable Energy Installations. A sister company of IT Power that conducts renewable energy installations.

TSR Tip Speed Ratio VAWT Vertical Axis Wind Turbine Weibull Wind speed distribution. Shape of the curve depends on shape factor k,

scale factor c, and the mean wind speed.

x

Acknowledgements I would like to thank my supervisor, Tim Cockerill, for his interest and excellent advice. Special thanks to Katerina Syngellakis, Project Engineer at IT Power, without whom this project would never have gone ahead, and whose project management skills and help were invaluable. Many other members of staff at IT Power were extremely helpful. Particularly Kavita Rai who analyzed some of the data of the installation questionnaires looking for trends (although most of her work is not included in this project), and Duncan Brewer whose knowledge and experience in the subject from an installer’s perspective resulted in frequent conversations and much help & guidance. Thanks also to Sarah Davidson and Warren Hicks for their knowledge, and Rolf Oldach for his knowledge of roof-mounting turbines. The resources that were already available at IT Power – the library of knowledge around the office and on their computer system collected through their years of work – was invaluable. My fellow MSc student from Loughborough University, Steve Carroll, who was working in parallel with me on the project was also of great helping in broadening my knowledge of the subject, providing frequent conversations, and solicit responses to the case study questionnaire. I would also like to thank the other members of the WINEUR project – primarily for designing the technical questionnaire which I utilized for obtaining technical data on the turbines, and also for their research into the wind turbines and state of the market in other countries around the world, that helped me to gauge the UK’s global position in this field. They also provided the principal economic questionnaire, which I used to interview manufacturers, and Steve Carroll and I modified to send to case studies.

1

1. INTRODUCTION

1.1 Renewable energy & microgeneration targets

Britain has a target to source 10% of its electricity from renewables by 2010, and

“aspires” to source 20% by 2020. Although the Energy White Paper assumes this will

mostly be met by large-scale wind turbines, it also believes that microgeneration will

provide an important contribution and is worth pursuing. (DTI, 2003)

Some local planning authorities’ Unitary Development Plans (so far Merton, Croydon,

and North Devon) now demand that a percentage of energy for all major

developments 1 must be sourced from onsite renewables (SolarCentury, 2005a).

Influence from National planning document PPS22 (ODPM, 2004a) and the Greater

London Authority (GLA, 2004) is strongly encouraging other Local Authorities to

follow suit.2 Small wind generators are already being used to meet these local targets

(Merton 2004, and SolarCentury 2005b).

Table 1– the DTI’s definition of microgeneration For heat, < 45 kW

For electricity, < 50 kWe

Low net carbon emissions

(Resouce05, 2005)

The DTI also call microgeneration µgeneration. This is convenient, and hereon it is

used in this project.

1 Definition of a major development. With dwellings: >10 or total area > 0.5 hectares. Other uses: floor space >1,000m2, or site > 1 hectare. (Solar Century, 2005a) 2 The Energy Performance of Buildings Directive, when it comes into force, may also have some impact (ODPM 2004b), but it remains to be seen how much.

2

1.2 Possible benefits of urban µgeneration, and small wind

This research is worthwhile because of the possible benefits of urban µgeneration.

They can be summarised as:

1. Additional untapped source of renewable energy

2. At point of use and thus eliminating transmission losses

3. Potentially leading to strengthening of the grid (Martin Bradley conversation,

24/5/05) and distribution networks (DTI, 2005), reducing the need for

upgrades

4. Raises awareness of sustainability

In addition, compared to the other µgeneration technologies wind is among the most

economic where wind speeds are reasonable (DTI 2005), and will probably have a

higher Energy Payback Ratio (EPR) and emit less CO2 over its lifecycle (Boyle et al.

2003, Resource05 2005). Depending on where it is sited, it can be highly visible

making it very appropriate for making a green statement or raising awareness. Small

wind can also complement PV because it generates most of its energy in the winter,

while PV generates most of its energy in the summer. (SolarCentury, 2005b)

1.3 The WINEUR project

Despite the relative potential importance of small scale wind generation in urban areas,

there is as yet very little comprehensive information on the subject, covering both

building-integrated and mast-mounted installations. The EC co-funded WINEUR

project (Wind Integration in the Urban Environment) will fill this information gap by

collecting, analysing and disseminating information on the technical, economic,

planning, policy, and sociological aspects of small wind energy for the urban

environment. One of the main aims of the project is to provide comprehensive

information that will encourage the further development of urban wind µgeneration.

More information on the WINEUR project is available at the project website

www.urbanwind.org.

3

1.4 Aims & objectives of this project

This report covers the following work that forms part of the WINEUR project:

Aims

1. Cover the state of the art of turbines being manufactured and designed in the

UK & Ireland

2. Assess the situation with regards to installations, and analyse detailed

experiences of wind turbine owners & operators

3. Analyse the economics

Objectives

1. Technology inventory for the UK & Ireland, containing technical details and

comparing technologies

2. UK installations assessment, estimating the number and kinds of installations,

and analysing some detailed experiences

3. Economic assessment, of the viability of small wind turbines in urban areas

By itself, this work is sufficient to give an insight into the state of urban wind in

Britain today.

It is worth noting that the UK is among the most advanced countries in the world in

this field. Only the Netherlands and Japan are on a comparable level with regards to

developing urban wind turbines and attempting roof-mounted installations.

(WINEUR, 2005)

4

2. METHODOLOGY

2.1 Methodology

To obtain technical details on the British & Irish turbines suitable for the urban

environment:

1. Adapted & utilised a standard technical questionnaire prepared by the

WINEUR partners to interview manufacturers & designers of small wind

turbines (in addition to the questionnaire answers comprehensive notes were

made on any additional comments)

2. Going beyond the requirements of WINEUR, the turbines were then split into

broad categories depending on their intended use (i.e. urban or non urban) and

design (power, rotor diameter, and axis), and then analysed & compared

To summarise the situation with regards to urban installations, and find some detailed

experiences:

1. Researched installations using the internet. Useful websites included: Clear

Skies, SCHRI, Wind & Sun, EcoArc, Community Environmental Networks

(CEN), SEE Stats, BWEA, Action Renewables, and BBC. Ensured

installations identified were urban by locating them on a map.

2. Some analysis of these known urban installations was made – popularity of

types of turbine, who are installing them, percentage which are roof-mounted.

3. Created a standard questionnaire from scratch for distribution to small wind

turbine owners & operators. Covering sociological, technical, and economic

aspects.

4. Input the data received into a spreadsheet, and analysed it with regards to the

sociological, technical, and economic aspects. Kavita Rai of IT Power also

used specialist to make further comparisons according to my suggestions (and

some of her own).

This second task provided some valuable information for the sociological and

economic aspects of the WINEUR project.

5

To analyse the economics:

1. Utilised a standard economic questionnaire prepared by the WINEUR partners

to interview turbine manufacturers.

2. Modified the questionnaire, and emailed it to those who had returned

installation questionnaires and who had agreed to answer further economic

questions.

3. Utilised economic data from the returned case study questionnaires, & other

sources

4. Obtained a spreadsheet of 151 turbine installations (economic breakdown,

AMWS, and generation estimates) made through the Clear Skies program.

5. Accessed economic information from the case studies available on the SCHRI

and Clear Skies websites, and the other studies available.

6. Obtained AMWS data

7. Utilised the turbine power curves obtained from the turbine manufacturers,

with AMWS estimates & a Rayleigh distribution to produce generation

estimates.

Further details on the methodology are in Chapter 5 below.

2.2 Note on References

As much of the research completed was first-hand, many of the references are

discussions and emails with people. These references are contained in Appendix L in

the back of the project, and they are referred to with the name of the person

communicated with, the way the communication was made (i.e. conversation or

email), and the date. In Appendix L they are ordered by date.

6

3 STATE OF THE ART – UK & IRELAND

3.1 The urban wind regime

Two things particularly characterise the urban wind regime – lower AMWSs (Annual

Mean Wind Speeds) compared to rural areas, and more turbulent flow. The lower

AMWSs are caused by the “rough uneven ground” (i.e. a higher roughness length z0)

which causes wind to increase with height more slowly. The turbulent flow is a result

of the wind interacting with the buildings.

Despite the advantages in bringing local wind generation to cities, the low AMWSs

and turbulent flow have discouraged many people who may otherwise have been

interested, as wind economics are totally dependent on the available resource. (Gipe,

2004)

Turbulent flow presents challenges in two ways – rapidly changing wind direction,

and buffeting the turbine blades. The options are to find a machine that copes well

with turbulence, or to find the least turbulent areas of the urban environment. Of the

latter, building-tops could show a great deal of promise, partly because the wind flow

there could be substantially greater as it gets concentrated by passing around the

building. Other less turbulent areas are open areas on the ground such as school

playing fields or parks.

3.2 HAWT vs. VAWT, and lift vs. drag

There is some debate about which of the different kinds of turbine are most suitable

for the urban environment, which would be best for building-mounting, and even

whether building-mounting is a good idea.

The advantages and disadvantages of the main different designs of machine are

summarised in table 2 below.

7

Table 2 – Advantages & disadvantages of HAWTs, Lift VAWTs, & Drag VAWTs

HAWTs Lift VAWTs Drag VAWTs

Advantages 1. Efficient

2. Proven product

3. Widely used

4. Most economic

5. Many products

available

1. Quite efficient

2. Wind direction

immaterial

3. Less sensitive to

turbulence than a

HAWT

4. Create fewer

vibrations

1. Proven product

(globally)

2. Silent

3. Reliable& robust

4. Wind direction

immaterial

5. Can benefit from

turbulent flows

6. Create fewer

vibrations

Disadvantages 1. Does not cope well

with frequently

changing wind

direction

2. Does not cope well

with buffeting

1. Not yet proven

2. More sensitive to

turbulence than

drag VAWT

1. Not efficient

2. Comparatively

uneconomic

(Randall 2003, Timmers 2001, and Clear Skies 2003)

An unmodified HAWT will work well where the air flow is less turbulent, on top of

high buildings or near open spaces, but in more turbulent areas HAWTs would need

to be made robustly in order to cope with blade-buffeting. Detrimentally, this will

increase the turbine’s weight and cost (John Balson conversation, 18/5/05). In fact,

many of the HAWTs aimed at the urban market are heavy with respect to surface area,

probably for this reason. However this would not solve the issue of them being

unable to orient themselves quickly enough to catch all the energy when the wind

direction is prone to change frequently.

8

Other, less certain issues are that:

1. Lift VAWTs may not be able to cope with strong turbulence either, because

they also rely on lift and so their blades would frequently stall (Ken England

conversation, 19/5/05)

2. VAWTs should be easier to maintain, as the generator is below the rotor,

normally on the ground. (Timmers 2001 & Clear Skies 2003)

3.3 Building-mounting

Some respected people within the small wind turbine industry such as Paul Gipe and

Mick Sagrillo are against rooftop mounting. They are concerned over vibrations

being transmitted to the structure, and the turbulence caused by the roof. (Gipe, 2003)

In addition, Larry Staudt (formerly Engineering Manager of Enertech) found that it

was very difficult to get a rotor diameter on a roof big enough to get a significant

amount of power. (Larry Staudt conversation, 19/5/05)

Indeed, structural integrity due to vibrations and dynamic loads is a significant current

concern in building-mounting turbines. Hiring a structural engineer to assess the

suitability of the buildings is a major cost, as is altering the structure (e.g. by adding

steel frames). (Rolf Oldach conversation 16/6/05, Clear Skies 2003) In addition,

Gipe, Sagrillo, & Staudt’s experiences are predominantly with HAWTs, and VAWTs

create less vibrations, exert smaller dynamic loads on the building, and can cope

better with turbulence. (However, they are also currently less economic.) (Clear

Skies, 2003)

Advantages of building-mounting are:

• potentially much higher wind speeds (depending on relative height

of the building compared to surrounding buildings – see Chapter 5

below)

• less turbulence

9

3.4 Categorising small wind turbines with respect to the urban environment

For the purposes of this report small wind turbines are placed into five principal

categories:

• micro HAWTs

• small HAWTs not aimed at the urban market

• small HAWTs aimed at the urban market

• larger HAWTs

• VAWTs

The definitions of these categories are as following:

Micro HAWTs – very small HAWTs designed and marketed for remote locations or

boats, which in normal conditions would produce too little power to noticeably reduce

an ordinary domestic (or other) electricity bill.3 In addition, G83-certified inverters

that could grid-connect the tiny amounts of power they produce cost more than the

turbines in August 2005. (Peter Anderson conversation, 9/8/05)

Small HAWTs not aimed at the urban market – HAWTs that would produce a

significant amount of power, but are still aimed at remote locations.

Small HAWTs aimed at the urban market – HAWTs that are designed & marketed for

the urban market and should produce enough power to noticeably reduce a normal

domestic (or other) electricity bill.

Larger HAWTs – the larger HAWTs with a rotor diameter >2m, aimed at either the

urban or rural markets.

VAWTs – currently, the VAWTs can all be conveniently grouped together.

3 Gipe defines micro turbines as being those with a rotor diameter of under 1.25m (Gipe, 2004), which correlates with this definition.

10

Figure 1– the HAWT categories and their rotor diameter

0

2

4

6

8

10

12

1 2 3 4

Turbine type

Rot

or d

iam

eter

, m

1 = Micro HAWTs

2 = Small HAWTs notaimed at the urbanmarket3 = Small HAWTs thatare aimed at the urbanmarket4 = Larger HAWTs

Figure 1 above compares the categories of the HAWTs, with the rotor diameters of

the turbines, to see if there is any correlation. Category 3 overlaps slightly with

categories 1 and 2 because it is primarily defined by the fact that these turbines are

aimed at the urban market, and not by their rotor diameter.

3.5 State of the art summary

There are 11 companies (2 of which are Irish) manufacturing 19 small wind turbines

(all HAWTs). There are 12 organisations (1 of which is Irish) designing and

developing small wind turbines (5 HAWTs & 7 VAWTs). Of these 12, 4 are also

manufacturers, so 19 organisations in total are either manufacturing or designing 31

small wind turbines, all of which could theoretically be placed in the urban

environment.

The proven products that generate a substantial amount of energy and are available

now for the built environment are the “larger HAWTs” made by Proven, Iskra, and

Gazelle. These products are almost always ground-based, with the exception of

Proven who have recently started building-mounting their turbines. Other proven

products that could be used in the urban environment are the “micro HAWTs”,

although they generate so little power their applications would be limited.

Products which are just emerging (or have emerged recently) onto the market which

are specifically intended to be building-mounted on domestic properties (and other

11

buildings) are the “small HAWTs aimed at the urban market” made by Eclectic

Energy, Renewable Devices, and Windsave. (There is one other recent product in this

category – Surface Power’s turbine – but it can’t be building-mounted.)

There are no VAWTs currently on the market,4 but many VAWTs designed for the

built environment (and that should be suitable for building-mounting) are prototypes

currently being tested, and should be available in 2006/2007.

Table 3 below summarises the different companies, the categories of turbines they

manufacture, and how long they have been manufacturing them for.

Table 3 – Summary of manufacturers Turbine type Company Years manufacturing,

in 2005

Micro HAWTs

Marlec

LVM

Ampair

> 25

≥ 25

≥ 25

Small HAWTs not aimed

at the urban market

Marlec

Atlantic Power Master (Irish)

> 25

2

Small HAWTs that are

aimed at the urban market

Eclectic Energy

Surface Power Technology

(Irish)

Windsave

Renewable Devices

≥ 3 (other turbines)5

This year

This year

This year

Larger HAWTs

Iskra

Proven

Gazelle

This year

14

7

(George Durrant email 8/7/05, Marlec 2005, LVM 2005, Atlantic Power Master 2005,

Eclectic Energy 2005, Surface Power Technology 2005, Windsave 2005, Renewable

Devices 2005, Iskra 2005, Proven 2005, MKW 2005)

4 Although Ampair used to make a Savonius VAWT for boats called the “Dolphin”, it was withdrawn due to its extremely low efficiency and power rating. (George Durrant conversation, 16/5/05) 5 Meaning that Eclectic Energy have been making a product which is both wind & water turbine for use on boats for at least 3 years. However, their new urban wind turbine product is new in 2005.

12

Tables 4 & 5 below summarise the turbines currently being directed at the urban

environment. In table 5, some turbines may be unfairly excluded, due to a lack of

knowledge.

Table 4 – Turbines being Table 5 – Prototypes being manufactured for the urban designed for the urban environment environment Model & Manufacturer

Rated power, kW

Model & designer/developer

Rated power, kW

D400 (Eclectic Energy) Surface Power Technologies Windsave Swift (Renewable Devices) Proven WT600 Proven WT2500 Iskra Proven WT6000 Proven WT15000 Gazelle

0.4 0.46 1 1.5 0.6 2.5 5 6 15 20

CREDIT Rugged Renewables Eurowind FreeGEN Posh Power Swift, smaller version (Renewable Devices) XCO2 Wind Dam

1.5 0.4 Many (1.3 to 30) Unknown ~2-2.5 Unknown 6 2 (also in stackable modular design)

(Resource05 2005, (Larry Staudt conversation 19/5/05,

John Quinn email 21/5/05, Ken England conversation 19/5/05,

Renewable Devices 2005, Eurowind 2005, Posh Power 2005,

Iskra 2005, MKW 2005) Richard Cochrane conversation 11/7/05,

Julie Trevithick conversation 16/5/05)

(Although some turbines are being manufactured for the urban environment and

others are not, it is possible that any of them can be found in the urban environment

somewhere.)

From table 4 it can be seen that the three most experienced manufacturers of small

turbines in Britain & Ireland – Marlec, LVM, & Ampair – presently show no interest

in the urban market. This is due to poor wind conditions, and the tiny amounts of

power their products produce. (Graham Hill conversation 13/5/05, George Durrant

conversation 16/5/05, & Stuart James conversation 18/5/05)

13

All the turbines in table 4, and the CREDIT & smaller Swift turbines in table 5 are

HAWTs, which should therefore be designed in a robust manner. All the other

turbines in table 5 are VAWTs.

Of the turbines being made for the urban environment, tables 6 and 7 list those aimed

at building-mounting.

Table 6 – Turbines on the market Table 7 – Prototypes which which are suitable for building- should be suitable for mounting building-mounting Model & Manufacturer

Rated power, kW

Model & designer/developer

Rated power, kW

D400 (Eclectic Energy) Windsave Swift (Renewable Devices) Proven WT600 ??6 Proven WT2500 Proven WT6000 Proven WT15000 ??7

0.4 1 1.5 0.6 2.5 6 15

Rugged Renewables Eurowind Swift, smaller version (Renewable Devices) XCO2 Wind Dam

0.4 Many (1.3 to 30) Unknown 6 2 (also in stackable modular design)

(Resource05 2005, (Ken England conversation 19/5/05,

Renewable Devices 2005) Richard Cochrane conversation 11/7/05,

Julie Trevithick conversation 16/5/05,

Eurowind 2005)

As can be seen from table 6, Surface Power Technologies are absent due to their

concern about vibrations (Jenny email, 11/7/05). Iskra are absent as although they are

interested they believe they would need to design a new turbine, and they are not in

table 7 as it seems this has not begun yet (John Balson conversation, 3/6/05).

Gazelle’s intentions are not certain, but their turbine is probably too big.

In table 7, CREDIT are absent due to their concerns over generating enough energy

and vibrations (Larry Staudt conversation, 19/5/05), while FreeGEN and Posh Power

have been removed as it is not clear if they are intending for their turbines to be 6 Although there are no known examples involving the Proven 0.6kW, it probably could be as the larger 2.5 & 6kW Provens are being building-mounted. 7 Proven haven’t excluded the possibility of building-mounting their 15kW turbine, but it has not been done yet, and it has not been possible to confirm that any installations will go ahead.

14

building-mounted. Apart from the smaller Swift, all of the turbines in table 7 are

VAWTs.

For individual descriptions of the turbines see Appendix A.

For pictures and technical details of the turbines, please see the catalogues –

Appendices B and C.

3.6 Technical comparisons of similar turbines

This section will focus on the turbines being aimed at the urban market - the “small

HAWTs being aimed at the urban market”, and the “larger HAWTs”. The machines

that are being designed and developed will not be analysed, as their technical

specifications (where available) will probably change.

As mentioned at the beginning of Appendices B & C, there is a need for a small wind

turbine test centre, that will test and independently verify the technical data supplied

by manufacturers. This is particularly the case with data such as power curves.

3.61 Power & efficiency comparisons for the “small HAWTs aimed at the urban

market”

Power curve data for the Windsave is still classified in August 2005, so it can’t be

compared.

15

Figure 2 – Power vs. wind speed for the “small HAWTs aimed at the urban market”

0

200

400

600

800

1000

1200

1400

1600

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Wind speed (m/s)

Pow

er (W

)D400

SPT

Sw ift

Given that the Swift is rated at 1.5kW, while Surface Power’s turbine is rated at

0.46kW and Eclecitc’s D400 at 0.4kW, it is not surprising that in figure 2 the Swift is

shown to produce far more energy than the other two turbines at all wind speeds.

Figure 3 – Power per m2 of swept area vs. wind speed for the “small HAWTs aimed at the urban market”

0

100

200

300

400

500

600

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Wind speed (m/s)

Pow

er p

er m

2 of

sw

ept a

rea

(W/m

2)

D400

SPT

Sw ift

16

It is much more interesting to compare the products by power per m2 of swept area as

in figure 3. Surface Power’s turbine cuts-in at a lower wind speed, but the turbines

are broadly similar until 7 and 8 m/s, when the Swift is shown to produce the most

power/m2, followed by the D400, and lastly by Surface Power’s.

Figure 4 – Fraction of the Betz limit attained by the “small HAWTs aimed at the urban market” vs. wind speed

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Wind speed (m/s)

Frac

tion

of B

etz

limit

atta

ined

D400

SPT

Sw ift

Figure 4 shows how all three turbines apparently break the Betz limit at 3m/s, but the

Swift is notably for extravagantly breaking the Betz limit at 4 and 5m/s. For many of

the other wind speeds it is also extraordinarily efficient, while this is also the case for

the D400 at 6m/s and below.

The Swift has a ring around it, which could partially concentrate the airflow (Larry

Staudt conversation, 19/5/05) or reduce blade tip losses – but as it is only a few inches

wide (see picture in Appendix B) it is more likely that the power curve supplied is

erroneous.

3.62 Power & efficiency comparisons on “the larger HAWTs”

It should be noted that the power curve data for the Gazelle is based on very old data,

and derived theoretically. (Garry Jenkins email, 12/7/05) Therefore it may not

represent the machines actual performance in the field very well.

17

Figure 5 – Power vs. wind speed for “the larger HAWTs”

0

5000

10000

15000

20000

25000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Wind speed (m/s)

Pow

er (W

)

Proven 0.6kW

Proven 2.5kW

Iskra 5kW

Proven 6kW

Proven 15kW

Gazelle 20kW

In figure 5 above, it can be seen that the turbines generate quite different amounts of

power. The most comparable machines are the Iskra 5kW and the Proven 6kW.

Figure 6 – Power per m2 of swept area vs. wind speed for “the larger HAWTs”

0

50

100

150

200

250

300

350

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Wind speed (m/s)

Pow

er p

er s

wep

t are

a (W

/m2)

Proven 0.6kW

Proven 2.5kW

Iskra 5kW

Proven 6kW

Proven 15kW

Gazelle 20kW

In figure 6 above, the Proven 0.6kW stands out for producing the least power/m2, and

the Gazelle the second least amount, for wind speeds ≥5m/s. It is difficult to

differentiate the other four turbines, except ≥13m/s where the Proven 2.5kW is

sharply ahead.

18

Figure 7 – Fraction of the Betz limit attained by “the larger HAWTs” vs. wind speed

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Wind speed (m/s)

Frac

tion

of B

etz

limit

atta

ined

Proven 0.6kW

Proven 2.5kW

Iskra 5kW

Proven 6kW

Proven 15kW

Gazelle 20kW

As might be expected from figure 6, in figure 7 the Proven 0.6kW is predominantly

the least efficient, followed by the Gazelle. This is the case except where wind speeds

are ≤ 4m/s, where the Proven 0.6kW is more efficient than the Gazelle. All the other

turbines are broadly similar. It is interesting to compare this figure with figure 4 for

the “small HAWTs being aimed at the urban market” – none of these turbines break

the Betz limit, or have such extraordinary efficiencies for such wide bands of wind

speed. This indicates again that the power curves for the smaller HAWTs could be

erroneous, especially for the Swift.

3.63 The importance of low cut-in wind speeds

Figures 8, 9, 10, and 11 below demonstrate the importance of a low cut-in wind speed

at different AMWSs, for two machines – Eclectic’s D400 and the Proven 15kW.

These machines have been chosen because they are of completely different sizes. The

D400 cuts-in at ~2m/s, the Proven 15kW at 2.5m/s, and they first generate measurable

amounts of energy at 3m/s.

A Rayleigh distribution assigns probabilities that the wind will have different wind

speeds given the AMWS. It splits the range of wind speeds into different wind speed

19

‘bins’, of 1, 2, 3, etc. m/s. These probabilities can be multiplied by the number of

hours in a year to assess the number of hours in a year that the wind speed will blow

at that wind speed, given the AMWS. These figures can then be multiplied by a

turbine’s power curve, to give an estimate for a turbine’s annual energy generation.

Figures 8 and 10 compare the energy that the turbines generate due to wind speeds in

the ‘bins’ of 3 and 3 & 4 m/s, while figures 9 and 11 show the percentage that wind

speeds in these ‘bins’ contribute to the total annual energy capture. So these graphs

show how much energy these turbines would lose if they cut-in at higher wind speeds.

Figures 8 and 10 correlate approximately with money lost (approximately due to

complications with ROCs, see Chapter 5, but as a rough method use £0.06/kWh).

Figures 9 and 11 show the percentage of total annual energy capture that would be

lost.

For the D400

Figure 8 – kWh the D400 generates due to wind speeds in the ‘bins’ of 3m/s and 3 & 4m/s at different AMWSs

0

10

20

30

40

50

60

0 1 2 3 4 5 6 7 8 9 10

AMWS, m/s

Ener

gy g

ener

ated

per

yea

r, kW

h At 3 m/s

At 3 & 4 m/s

20

Figure 9 – Percentage of the total annual energy capture of the D400 due to wind speeds in the ‘bins’ of 3m/s and 3 & 4m/s at different AMWSs

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7 8 9 10

AMWS, m/s

Perc

enta

ge o

f ann

ual e

nerg

y ge

nera

tion,

% At 3 m/s

At 3 & 4 m/s

Proven 15kW

Figure 10 – kWh the Proven 15kW generates due to wind speeds in the ‘bins’ of 3m/s and 3 & 4m/s at different AMWSs

0

500

1000

1500

2000

2500

3000

0 1 2 3 4 5 6 7 8 9 10

AMWS, m/s

Ener

gy g

ener

ated

per

yea

r, kW

h At 3 m/s

At 3 & 4 m/s

21

Figure 11 – Percentage of the total annual energy capture of the Proven 15kW due to wind speeds in the ‘bins’ of 3m/s and 3 & 4m/s at different AMWSs

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7 8 9 10

AMWS, m/s

Perc

enta

ge o

f ann

ual e

nerg

y ge

nera

tion,

% At 3 m/s

At 3 & 4 m/s

In summary, from figures 8-11 above, a low cut-in wind speed would make a

noticeable difference to the annual energy capture for AMWSs ≤ 4m/s, and a crucial

difference with AMWSs ≤ 2m/s. There may be many settings in the urban

environment with such small AMWSs (see Chapter 5).

Also, as turbines with induction generators require a gearbox, which results in a

higher cut-in wind speed (see Appendices A & D), they should be avoided where

AMWSs are very low.

However, there is a question of whether the Weibull distribution is an accurate

representation of wind regimes in the urban environment. And it may not be,

according to Tim Cockerill of Reading University.

3.64 Cut-out wind speeds

None of these wind turbines have a cut-out wind speed, apart from the Windsave

which cuts-out at ~15m/s, and the Gazelle which cuts-out at 20m/s.

It is possible to theoretically compare a turbine to what it’s energy capture might be

like if it did not cut-out – by taking the power curves of wind turbines which don’t

22

cut-out, and seeing how much of the annual energy capture at different AMWSs is

generated by wind speeds at and over those cut-out wind speeds.

Figure 12 below tries to estimate how many kWh the Windsave 1kW is losing by

cutting-out at 15m/s, by using the power curves of its nearest equivalents in terms of

rated power – the Proven 0.6kW and the Swift 1.5kW. (Recall that Windsave’s

power curve is not currently available.) The amount of energy that the Windsave

theoretically loses should lie somewhere between the curves for the two turbines.

Figure 13 below tries to estimate what percentage of the annual energy capture these

turbines are losing. The Swift & Proven 0.6kW >15m/s curves should be useful to

make estimates for the Windsave. The Gazelle is more difficult given that it cuts-out

at 20m/s, and only one power curve is available which extends for wind speeds

beyond this – the Swift’s. Therefore, the Swift >20m/s curve is used to make an

estimate for the Gazelle.

The graphs show that a cut-out wind speed of 15m/s only makes a significant

difference to the annual energy generated at AMWSs ≥7m/s, while a cut-out of 20m/s

only makes a difference where AMWSs ≥9m/s.

Figure 12 - kWh the Proven 0.6kW and the Swift generate due to wind speeds in the ‘bins’ ≥15m/s at different AMWSs

0

500

1000

1500

2000

2500

0 1 2 3 4 5 6 7 8 9 10

AMWS, m/s

Ene

rgy

that

wou

ld b

e lo

st a

nnua

lly, k

Wh

SwiftProven 0.6kW

23

Figure 13 – Percentage of the total annual energy capture that the Proven 0.6kW and the Swift generate due to wind speeds ≥15m/s or ≥20m/s at different AMWSs

0

5

10

15

20

25

30

35

0 1 2 3 4 5 6 7 8 9 10

AMWS, m/s

Per

cent

age

of a

nnua

l ene

rgy

capt

ure

that

wou

ld b

e lo

st, %

Swift, 15m/s & greaterProven 0.6kW, 15m/s & greaterSwift, 20m/s & greater

3.65 Weight per swept area – turbine robustness

This is a way of estimating a turbine’s robustness. Sagrillo says that engineers design

turbines for survival wind speeds on paper, but rarely test the machines at these

speeds. Besides, a wind turbine is more likely to be destroyed by turbulence than

survival rated wind speeds. Therefore, he recommends that one divides the weight of

the full rotor/nacelle assembly, with the swept area. Lightweight turbines can’t

handle sites with strong winds or turbulence. Heavyweight turbines should last longer,

but are more expensive. (Sagrillo, 2002)

His approximate rule is:

>10 kg / m2 = heavyweight

5-10 kg / m2 = medium weight

<5 kg / m2 = lightweight

(Sagrillo, 2002)

It should be noted that as Sagrillo’s experience is limited to HAWTs, so is the

analysis below.

24

Weight/swept area figures for all the HAWTs are in Appendices B & C, and none of

the machines “lightweight”, and only two are “medium weight” – Surface Power

Technologies’ turbine and Windsave’s. Therefore they may not cope as well at a

turbulent or very windy site as the rest.

Figure 14 below compares the weight per swept area for the turbines being

manufactured which are aimed at the urban environment.

Figure 14 – Weight per swept area of the turbines

0.00

5.00

10.00

15.00

20.00

25.00

D400

Surfac

e Pow

er

Windsa

veSwift

Proven

0.6k

W

Proven

2.5k

WIsk

ra

Proven

6kW

Proven

15kW

Gazell

e

Wei

ght p

er s

wep

t are

a, k

g/m

2

3.66 RPM (Revolutions Per Minute) & TSR (Tip Speed Ratio)

Although a high RPM/TSR makes a turbine noisier, and more prone to wear & tear,

(Sagrillo 2002), there is only RPM data for a few turbines – not enough to make

comparisons with.

25

4. UK INSTALLATIONS

For this section as many examples of small & micro urban wind turbine installations

in the UK were found as possible. The research was mainly conducted on the internet.

4.1 Limitations to the study

There can only be an approximate relationship between the frequency with which

installations have been detected on the internet, and their actual occurrence in the field.

Some organisations are more likely than others to highlight that they have wind

turbines on the internet e.g. schools & environmental centres, while individual

householders are unlikely to do this. So there is a bias towards some kinds of

installations, and against others such as domestic installations and turbines aimed at

that market like: the D400, Surface Power’s, and the Windsave. The extent of the

effect of these biases on the present work is unknown.

4.2 Installations found – Results

Table 8 – Breakdown of total number of installations <0.5kW 80kW >0.5kW & <50kW Total

Planned 0 0 21 21

Built 8 1 62 71

Total 8 1 83 92

Appendix E contains a full list of the installations. It should be noted that some

examples will have been inevitably missed during the research for this report (due to

the limited time available). Therefore, at a minimum there could be 100 installations

in total.

91 turbines fit our definition of a µgenerator (excluding the 80kW turbine).

Of the 21 (23%) which have not been installed yet it is known that 9 will imminently

start building, 2 require planning permission, and 1 requires fundraising – there is no

detailed information on the state of progress of the other 9.

26

Case studies have been split among urban and semi-urban, which were loosely

defined as follows:

• Urban – where a turbine appears to be in or within 1 km of a densely

populated area (town or city).

• Semi-urban – where a turbine appears to be in or within 500m of a less

populated area (e.g. tightly-knit village, but not a loose scattering of houses).

Of the 92 installations, 71 are urban (77%), and 21 semi-urban (23%).

Figure 15 below shows that 31 of the installations are schools & colleges (34%), and

21 are environmental centres of some type (23%).

Figure 15 – Locations of all 92 installed turbines

0

5

10

15

20

25

30

35

Govern

ment re

searc

h lab

Housin

g Ass

ociat

ion prop

erties

Univers

ities

Communit

y cen

tres (

non e

nviro

)

Loca

l Auth

oritie

s

Indivi

dual

domes

tic pr

opert

ies

Private

compa

nies

Enviro

nmen

tal ce

ntres

Schoo

ls & C

olleg

es

Where installed

Num

ber o

f ins

talla

tions

Figure 16 below shows all the kinds of wind turbines that have been chosen to be

installed. Where more than one model of turbine was chosen at a site, this is

represented. But if more than one turbine of a model was installed at a site, this is not

represented – and counts as one. The idea of the graph is to gauge the popularity of

turbines among people choosing them. As most of the installations are of one turbine,

it would correlate quite well with a graph of the total number of turbines. The most

popular turbine is the Proven 6kW, followed by the Proven 2.5kW.

27

Two wind turbines are notably absent – the Proven 0.6kW, and Surface Power

Technologies.

Figure 16 – Turbine models chosen

0

2

4

6

8

10

12

14

16

18

Aerody

n

Wind D

am

Lage

rwey

80kW

Wind H

arveste

r 60k

W

Wind H

arveste

r 45k

W

Eoltec

Wind R

unne

r

Ropate

c

Windsid

e

Ampair

Eclecti

c's D

400

Jaco

bs 29

-20

Proven

15kW Isk

ra

Windsa

ve

Gazell

e

Proven

unkn

ownMarl

ecSwift

Proven

2.5k

W

Unkno

wn

Proven

6kW

Type of turbine chosen

No.

of t

imes

cho

sen

Table 9 shows that rooftop installations represent 27% of the 92 installations. (22 of

them are urban.)

Table 9 – Number of known rooftop installations Built Planned Total

19 6 25

4.3 The returned questionnaires

Most of the built installations above were contacted, and asked to complete a case

study questionnaire. An example case study questionnaire is in Appendix F. 19

responses were received out of a possible 71, which is a response rate of 27%. The

raw data of the questionnaires is in Appendix G.

28

There are some limitations to the responses received. The accuracy of the answers

can only be as good as the knowledge of the person responding. Some of the

responses were obviously inaccurate, e.g. with payback times, and generation

estimates. Where identified, inaccuracies have been taken account of.

There are only a limited number of conclusions that can be drawn with 19 responses.

With more responses, perhaps more trends would be apparent. Kavita Rai’s work

consisted of cross-tabulating many results. A selection of these are shown in the

section below and Appendix H, however the majority of them did not show any

correlation and due to the size of her work it has not been included as part of this

report.

4.31 Demographics

Turbine locations

Table 10 – Locations of installed turbines Frequency Percent School 5 26.3College 1 5.3Environment centre 4 21.05Local Authority 1 5.26Environment centre and University 1 5.26Environment centre and Local Authority 2 10.53School and Local Authority 1 5.26Other 4 21.05Total 19 100

© Kavita Rai, IT Power, 2005

As would be expected, the case studies are dominated by educational establishments

(42%), and environment centres (37%). Local authorities own 4 of the sites above

(21%). The remaining 4 (“other”), are: a housing association, a charitable

organisation, and 2 businesses.

29

Environmental consciousness

One person wasn’t able to reply on behalf of their organisation, but of the rest 13

thought their organisation was “very environmentally conscious” (72%) and 5 thought

it was “fairly environmentally conscious” (28%). An option nobody selected was

“indifferent to the environment”.

4.32 Turbine details

Wind turbines chosen

Figure 17 below broadly correlates with figure 16 above. The most popular turbines

are still the Proven 6kW & 2.5kW.

Figure 17 – Turbine models chosen

0

1

2

3

4

5

6

7

Ropate

c

Jaco

bs 29

-20

Lage

rwey

80kW

Proven

15kW

Marlec 9

10F

Gazell

e

Proven

2.5k

W

Proven

6kW

Turbine choice

No.

of s

ites

at w

hich

cho

sen

Number of installations

Of the 19 sites, 15 had only one turbine (79%), two had two, one had three, and one

had four.

30

Ground or roof-mounted, and open space

17 of the responses (89%) were from ground-based turbines, but Heeley City Farm

has a wall-mounted Marlec 910F (as well as a ground-based Proven), and Bradford

West City Community Housing Trust has at least 2 Ropatecs on the roof of a

residential tower block (see Clear Skies 2003).

4.33 Location type

Figure 18 – Locations of installed turbines

0

1

2

3

4

5

Dense

inner-

city

Typica

l town/c

ity re

siden

tial a

rea

Indus

trial d

evelo

pmen

t

Commerci

al de

velop

ment

Small to

wn

Suburb

an

Village

Countr

y park

Type of area

Freq

uenc

y

6 of the installations (32%) are in a village/country park, and can be considered as

“semi-urban”.

31

4.34 People’s perceptions of the turbine

Owner satisfaction

Figure 19– Owner’s overall happiness with their turbine

0

1

2

3

4

5

6

7

8

9

10

Very happy Happy Ambivalent "Awaitingresults"

Unhappy Veryunhappy

Overall happiness with turbine

Freq

uenc

y

One person was not able to answer the question above on behalf of their organisation.

This result is a good sign for the small wind industry. 14 people (78%) are “happy”

or “very happy” with their turbine.

The people who were ambivalent, “awaiting results”, and very unhappy, had all had

problems with their turbines (the latter have had severe and ongoing problems). The

ambivalent owns a Proven 6kW, “awaiting results” a Proven 15kW, and the very

unhappy people own a Gazelle and Jacobs turbines.

The very happy people own a Gazelle, Lagerwey, Proven 6kW, and two of them own

Proven 2.5kW’s. Three of them had also had problems with their turbines, although

only two of the happy people had had turbine problems.

32

Owner’s feeling of visual appearance of turbine

One person felt unable to answer this question on behalf of their organisation.

Figure 20– Owner’s rating of the visual appearance of their turbine

0

2

4

6

8

10

12

14

Beautiful Pretty Okay Quite ugly Very ugly

Owner's rating of turbine's visual appearance

Freq

uenc

y op

inio

n ex

pres

sed

12 people (67%) felt indifferent about their turbine’s visual appearance, 5 were

positive (28%), and only one was negative.

A Gazelle, Proven 6kW & Proven 2.5kW were all rated as “beautiful”, while the

Jacobs and Marlec were rated as “pretty”. The Proven 15kW was described as “quite

ugly”. Of course, these opinions are highly subjective.

Safety

Out of the 19, 6 rated their turbine as “very safe” (32%), 12 rated it as “safe” (63%),

and the last rated his 5 year-old Gazelle as “about acceptable”.

Owner’s perception of the turbine’s noise level

With the limited data there is very little correlation between the turbine type or

location as shown in Appendix H.

33

Change in neighbours’ and local communities’ perceptions

Opinions of the neighbours and local communities overwhelmingly veered towards

the positive after the installation compared with before, only a few stayed the same,

and none became negative.

Two people were not able to answer these questions, and one simply said that for both

groups “opinion varied” before & after.

Figure 21 – Neighbours’ and local communities’ perceptions before the installation

0

1

2

3

4

5

6

7

Very negative Negative Indif ferent Positive Very positive

Their opinion

Freq

uenc

y ex

pres

sed

NeighboursLocal community

Figure 22 – Neighbours’ and local communities’ perceptions after the installation

0

1

2

3

4

5

6

7

8

Very negative Negative Indifferent Positive Very positive

Their opinion

Freq

uenc

y ex

pres

sed

NeighboursLocal community

34

4.35 Economics & lack of knowledge of turbine operators

Grants & loans

Two people were unable to answer this question.

4 organisations (24%) did not have any financial help at all (a school, a business, and

two environmental centres). Only one took out a loan (a business).

Of the 13 which had received grants, 8 (62%) mentioned Clear Skies / SCHRI, 4

mentioned an electricity supplier’s grant stream (31%), 2 their local support team for

Community Renewables Initiative (15%). Other funding sources included: European

Commission; Department of Enterprise, Trade, and Investment (DETI); and

Buckinghamshire County Council. 2 people who had received grants neglected to say

from where. 5 (38%) received grants from more than one source.

Out of the 13 organisations which had received financial support, 8 (62%) said they

would not have been able to proceed without it, and 5 (38%) were not sure. Not a

single one said they would have proceeded anyway.

ROCs

Two people were unable to answer this question.

Only 5 organisations are collecting ROCs (29%), 2 of which found the paperwork

difficult, one had the paperwork completed by their local renewable energy agency,

one did not know, and one disagreed that the paperwork was difficult.

2 people are in the process of completing the ROC paperwork, one of which is finding

it difficult.

10 are not collecting ROCs, none of which said anything about the paperwork.

Generation estimates

One other interesting fact is the lack of knowledge many people have regarding their

small turbines. Of the 14 that were in a position to know how many kWh their turbine

produced, 5 did not know, and at least 2 seemed far too low and 1 far too high. This

is >50% of respondents that did not know how much energy their turbine generates.

35

Therefore many people did not know if this was the same, more or less than they had

originally anticipated. Of the 14 that should have known, 3 did not answer, 2 wrote

that they did not know, 6 wrote “the same” (1 of which had overestimated kWh

generated), and 3 wrote “less”. An interesting result is that not a single person wrote

that it was generating “more” than expected.

Payback

With regards to payback, of the 17 people that should have known 4 did not. Given

the answers provided for energy generated the answers given have been checked

using the data from the returned questionnaires, and/or NOABL and power curves.

The responses are shown in figure 23 below.

Figure 23 – Owner’s estimates of the turbine’s paybacks

0

1

2

3

4

5

5 9 10 12 13 14 15 20 >20

Payback period

Freq

uenc

y

It was possible to check 10 of these, and the results are,

• probably over optimistic: 5, 10, 12, 13, 15, 20 years,

• probably correct: 9, 14, and two of the “>20 years”.

(There is insufficient data to determine what the payback figures actually are.)

36

It is significant that the 9 year payback is the 80kW Lagerwey, and the 14 year

payback is the 4 x 20 Jacobs 29-20 turbines – these are the largest installations in

terms of total rated power out of all the ones that returned questionnaires. Both of

these received grants, and the Lagerwey is also claiming ROCs.

4.36 Reasons for installation

Figure 24 – Reasons listed for installing the turbine

0

2

4

6

8

10

12

14

Salesm

an

"Cou

nty in

itiat iv

e"

Network

effect

Financia

l reas

ons

To tes

t the t

urbine

Genera

l educ

ation

Organis

ation

's im

age

Enviro

nmen

tal re

ason

s

Enviro

nmen

tal edu

catio

n

Reasons for installation

No.

of o

rgan

isat

ions

list

ing

the

reas

on

Two organisations were unable to provide answers.

“Network effect” means that they knew somebody who had one. “County initiative”

presumably means the decision was mandated from the county council (this person

did not list any other reasons).

Given that the majority of the institutions are educational in some way (including the

environment centres), it is not surprising that 13 of them (76%) list “environmental

education”. Given that they are all environmentally conscious, neither is it surprising

that 12 (71%) list “environmental reasons”. (Only one organisation did not list either

37

“environmental education” or “environmental reasons”, and that was the one that

listed “county initiative”.)

Relevant to the economics in Chapter 5, only 2 (12%) listed financial reasons.

The fact that nobody selected “salesman”, might tell us that up to now wind turbines

have been marketing themselves, without the need for initiative from manufacturers.

4.37 Obstacles to installation

Figure 25 – Owner’s rating of the difficulty in overcoming obstacles

0

2

4

6

8

10

12

14

16

Planning issues Connecting to the grid Neighbours Rest of localcommunity

Potential obstacle

Freq

uenc

y

Almost insurmountableDifficultSmall problemNo ProblemActually helped

8

7 people (44%) had some problem with planning, 7 (50%) had a problem in

connecting to the grid, 5 (29%) had a problem with neighbours, and 2 (12%) had a

problem with the rest of the local community. Only planning and the local

community managed to help installations.

8 With graph LMU above, it is important to note that 3 people did not answer planning, 5 did not answer regarding grid-connection (2 because their turbines are off-grid), 2 did not answer neighbours or local community.

38

4.38 Turbine problems & after sales service

8 of the 19 installations (42%) suffered a technical problem.

It should be noted that all of the problems were different. They were:

• blade broke off

• tail fell off

• problems with a power supply unit

• gearbox problems

• generator problems

• inverter problems

• mast was badly finished and turbine kept sticking in one position

• lightning strike put it out of commission for 2 weeks

There is insufficient data to draw conclusions on the quality of any of the individual

products.

In total 5 people (26%) complained about the after sales service they had received. 4

of these had had problems that’d needed fixing, so 50% of those who had had

problems complained about delays in getting them fixed. This is despite the fact that

no question on “after sales service” was asked.

4.39 With hindsight, would they install a small wind turbine again?

Of the 16 people who were able to answer this question, 100% said that they would

make the same decision again – although 2 (13%) said they would choose a different

turbine (without the questionnaire prompting them). Both of these customers had had

technical problems with the turbine and had experienced poor after sales service.

39

4.4 Analysis of results

4.41 Of all the installations found

BRE estimates there are 700 odd mini (>0.5kW & <50kW) wind turbines in the UK

(DTI, 2005). Table 8 shows 62 in urban areas. Therefore at a minimum ~10% of the

mini-wind installations in the UK are in the urban or semi-urban environment, in

August 2005. For total wind installations (including planned) there should be at least

100.

Figure 15 shows that the majority of installations are limited to schools &

environment centres (but bear in mind the limitations of the study above).

Figure 15 does not accurately represent the contribution made by local authorities, as

both schools & environment centres are often local authority controlled. In addition,

the planning departments of local authorities must be considered. Therefore, local

authorities play an important role in all small wind turbine installations.

From figure 16, the popularity of Provens is obvious (33% of all turbines chosen –

which makes the unpopularity of their 0.6kW model all the more surprising), as is the

high number of Unknown turbines (17%), and the percentage of turbines which are

British (74%)9. The lack of micro turbines either supports, or is because of, the

viewpoints of Marlec, LVM, and Ampair. The most popular turbines are the Provens

2.5 and 6kW.

There are a surprising number & proportion of rooftop installations because they have

only been occurring for approximately the past 2 years. They are probably expanding

rapidly – e.g. 9 of the 25 rooftop installations are Swifts (36%) and 4 are Windsaves

(16%), which have only been available in 2005.

9 This can be compared favourably against the proportion of large wind turbines installed which are British.

40

4.42 Of the returned questionnaires

Demographics

So far, most installations have been made by people who are environmentally

conscious. Nobody is installing them solely because of financial reasons.

Turbine locations

The urban sites with open spaces are being developed first. This is unsurprising, as

this kind of installation is well-established, and there are relatively good wind regimes.

People’s perceptions of the turbine

Few people find these small wind turbines visually stunning. Although it is possible

that some people will prefer the design of the newer models, e.g. Swift, XCO2, Wind

Dam, etc, and this could potentially help the small wind industry. Nevertheless, the

results show that visual appearance need not be an obstacle to installation of small

wind turbines.

The vast majority of people are happy with their wind turbines.

It is fortunate that the turbines are believed to be safe, but it is hard to say on what

basis the people rated their turbines as safe. At present there is limited health and

safety guidance for small wind turbines.

There are a wide variety of opinions on the amount of noise these turbines make, and

no apparent correlations with turbine type or location. There could be several reasons

for this – relative background noise, distance the owner is accustomed to being from

their turbine, or differences in the owner’s hearing.

The change in perception for neighbours & community between before and after an

installation is remarkable, and very good news for the industry. Such evidence could

truly help the small wind industry, showing that their products are ‘popular’.

Therefore, negative feedback from a community or neighbours before an installation

may well be due to an overreaction or lack of knowledge. Taking them to see a

working small wind turbine could be an excellent way to assuage their fears.

Economics & lack of knowledge of turbine operators

To date, the existence of grants has been very important for the installation of small

wind turbines. It is likely that without grants the number of installations would

41

significantly drop. This is to be borne in mind given that Clear Skies will end in

March 2006, and that there is no guarantee of a smooth transition period to the Low

Carbon Buildings Program or of its form.

With regards to generation estimates, it is interesting that not a single person wrote

that the turbine was generating more than expected – this would have been the case

with large wind turbines, where manufacturers often underestimate their performance

so as to please customers (Gipe, 2004). Small wind turbine manufacturers may be

overestimating performance or relying on incorrect wind speed data for those

locations (e.g. NOABL data is widely used by the industry, but see comments on it in

Chapter 5).

Over optimism on payback times shows lack of knowledge once again, but it also

shows that the economics are worse than people anticipate/calculate. Whether or not

this will lead to disappointment remains to be seen.

It is hard to tell if making the paperwork for claiming ROCs easier could significantly

impact on the number of installations made.

Obstacles to installation

Connecting to the grid and planning are the biggest potential obstacles to installing

small wind turbines. Neighbours and local community tend not to be much of a

problem. (There is not enough data to see if initiatives like PPS22 have had an impact

yet.)

Hindsight

Despite the complexity of installing a small wind turbine, or the expense, or the

technical / after sales problems many of these people have had, they would make the

same decision again with hindsight. Exactly why is unclear from this data.

Overall

Overall the results are positive for the small wind turbine industry, but it has serious

issues to contend with:

• their products need to appeal to people who are not just

environmentally conscious, or interested in environmental

education

42

• the industry needs to be able to survive any potential hiatus in

Government grant programs

• connecting to the grid and planning need to be easier

• the finished products need to be less problem-prone

• after sales service needs to be improved

43

5. ECONOMICS

This section of the report covers the economics of small urban wind turbines for a

school in Scotland, a typical domestic situation in the south east of England, and some

large buildings in London. It gives an assessment of the economic viability of small

urban wind.

All of the economic assessments in this chapter should be used as a guide only.

5.1 Methodology

A spreadsheet was created to model the economic data. It uses standard discount

analysis to calculate the net present value and payback. It also estimates the energy

the turbine could produce using the power curve and a Rayleigh distribution. Power

curves are assumed to be accurate.10

Appendix I shows the variables included in the model.

Sensitivity analysis is also used to determine the sensitivity of the economic situations

to the variables. To do this it is necessary to pick a base case where the values of all

the variables are taken to be equal to 1, and then the effect that different fractions (say

0 to 5) of each variables has on the Levelised Production Cost (LPC) of energy is

shown. The result is a ‘spider diagram’, with the lines converging on the base case.

The LPC is the present cost of the energy from the turbine given the costs it has and

income it provides over its lifecycle (assumed as a 20 year period). LPC does not

need to make any assumptions about the electricity tariffs, including the future

evolution of electricity prices – but in assessing economics one can consider those

factors once the LPC is calculated.

10 Recall that power curves are from manufacturers and not from independent testing.

44

Although 7 of the people who returned questionnaires on their installation agreed to

answer more questions on the economics, only 1 person did. This means that limited

data is available on the real breakdown of costs of actual installations.11

No modelling can be done on the Windsave, as neither the power curve nor

generation estimates at different AMWSs are available in August 2005.

5.2 Estimated installed costs per kWe for turbines

Based on the information sources, estimates for installation costs of turbines are

shown in Appendix J. Figure 26 below is the graphical representation of this data.

Clear Skies say that a typical system cost is 2500-5000 £/kW (Clear Skies, 2005). As

can be seen, many estimates of turbine costs fall within this band. In figure 26 below

the Clear Skies estimate is next to the y-axis.

Figure 26 – Estimated turbine installed costs in £/kW

0

2000

4000

6000

8000

10000

12000

Clear S

kies e

stimate D40

0

Surfac

e Pow

er

Windsa

ve

Swift (no

w)

Swift (pr

ojecte

d)

Proven

2.5k

W (grou

nd)

Proven

2.5k

W (buil

ding)

Iskra

Proven

6kW (g

round

)

Proven

6kW (b

uildin

g)

Proven

15kW

Gazell

e

Turbine type

Est

imat

ed c

ost p

er in

stal

led

kW, £

/kW

In figure 26 above the error bars show the full range of installed costs that the

research has found for each kind of installation, and the heights of the columns

11 However, many other sources of data were utilised, as outlined in Chapter 2.

45

represent the average of the extremes of those ranges. There was insufficient data to

try and gauge the probability that an installation might have a given cost.

There is more data for some installations such as the Proven 2.5kW (ground-mounted),

than others, meaning the extremes for installed price are broader. This is because the

installed cost of a turbine depends a great deal on individual site factors. Some of the

other installation costs might show the same range of extremes if more data were

available.

Building-mounting Proven 2.5 and 6kW turbines is not significantly more expensive

than ground-mounting them.

The Windsave is the cheapest turbine per installed kW, but this is the manufacturer’s

estimate and it is not yet being sold at this price. Very few installations exist, so the

price cannot be confirmed and may be subject to change.

Surface Power’s turbine is a do-it-yourself kit which may explain the low cost, but as

with the Windsave there is very limited data available apart from that supplied by the

manufacturer.

Plotting a graph of £/kW against rotor diameter shows no significant correlation, due

to a lack of data (particularly with turbines of a higher rotor diameter).

46

5.3 St. John Bosco School, Renfrewshire

Figure 27 – John Bosco School’s turbine and its location

© St John Bosco School © www.multimap.com

This analysis is based on an actual installation of a Proven 2.5kW at St. John Bosco

School. The school can be seen on the map in figure 27. It is in “Erskine”, the

westernmost part of Glasgow.

AMWS

The school estimates their annual energy production at 8,600kWh per year (Appendix

G). This corresponds to an AMWS of 7.15 m/s.

At 45m above ground level, NOABL estimates an AMWS of 6.50m/s, at 25m 5.8m/s,

and at 10m 5m/s. The turbine’s mast is 11m high but it is also on a hill, and the

location is near the sea which might make it windier than NOABL predicts. However,

considering how local topography affects NOABL, 8,600kWh should be regarded as

an optimistic estimate. (BWEA, 2005)

Tariff

The school have a net metering arrangement with Scottish Power, so they buy and sell

electricity at 6.15p/kWh. Net metering is the equivalent of offsetting 100% of

imported electricity costs.

47

Economics

They do not claim ROCs (Appendix G).

Total project costs were £25,000, but grants worth £18,000 were obtained from two

sources. (EST, 2005a) The remaining £7,000 was shared with the Local Authority.

The school estimated the payback time of their Proven 2.5kW to be 13 years.

Assuming the school paid £5,000, and a 4% discount rate, and 0% annual change in

electricity prices, gives the same payback as the school estimated.

Figure 28 below analyses the sensitivity of the economic situation the school believes

they are in to changes in various parameters.

Table 11– base case of the school for LPC sensitivity analysis Energy generated 8,600kWh

School’s investment £5,000

Discount rate 4%

Annual maintenance

costs

£180

ROCs claimed? No

48

Figure 28 – LPC sensitivity analysis for John Bosco School

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.1 0.4 0.7 1 1.3 1.6 1.9 2.2 2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9

Fraction of case study's situation

Leve

lised

Ene

rgy

Cos

t £/k

Wh

Energy generatedSchool's investmentDiscount rateMaintenance costsROC value

In figure 28 above, the school’s LPC is most sensitive to changes in energy produced.

If the turbine generates less than they believe (which is likely), they will effectively

be paying more for their energy.

The LPC is also quite sensitive to the investment that the school made (5 on the x-axis

is equivalent to the school paying the full cost of the turbine 5 x £5,000 = £25,000).

The LPC is less sensitive to the effects of discount rates and annual maintenance.

As the school is not claiming ROCs these have been calculated in a different way.

Where the fraction is ≤1 then ROCs = 0, then it is increased proportionally until at 4

ROCs = £45. If the school started claiming ROCs today, then it would be the

equivalent of the LPC being at 4 on the ROC graph. But if the value of ROCs were to

then fluctuate the effect this would have on the LPC is also shown.

Changes in turbine model also affect the economics significantly. Below, in table 12

and in figure 29 the LPCs for different turbine types at this location are shown.

Given the grant situation with the school is complex and would have changed had

they opted for a different turbine, represent the full costs of the turbines are

represented here.

49

Table 12 – estimated installed costs & LPCs for turbines at John Bosco School

Proven 2.5kW

Iskra 5kW

Proven 6kW

Proven 15kW

Initial cost, £ 25000 27510 32570 53602 yield, kWh 8600 18221 22539 56576 LPC, £/kWh 0.214 0.111 0.106 0.070

The reasoning behind the estimates for the different turbine costs for this situation can

be found in Appendix J.

Figure 29 – Estimated LPCs for different turbines installed at John Bosco School

0

0.05

0.1

0.15

0.2

0.25

Proven 2.5kW Iskra 5kW Proven 6kW Proven 15kW

Turbine type

LPC

, p/k

Wh

Assumptions made in calculating the LPCs:

• Project lifetime of 20 years

• No grants

• No maintenance costs

• No ROCs claimed

• Discount rate of 4%

• AMWS of 7.15m/s

The overall economics would have been significantly better if the school had opted

for a larger turbine. The improvement in LPC from a Proven 2.5kW to the other

turbines exceeds the bounds of error, and so may the improvement from a Proven

6kW and a Proven 15kW. However, from the results obtained, no difference can be

assumed in the economics of an Iskra 5kW and a Proven 6kW.

50

5.4 A traditional house in central Reading, Berkshire

This analysis is to assess the feasibility for domestic small wind turbines in a typical

inland urban site in the South East of England – the large town of Reading, in

Berkshire. Reading has been chosen because wind speed data is available for it.12

The turbines (for which data is available) that might be appropriate for an inner-city

house are:

• Eclectic’s D400

• Surface Power’s

• the Swift

The highest point of a typical house in central Reading is ~12m high. Therefore, the

rooftop turbines could have a hub height of ~13-14 metres above ground.

As Surface Power turbines cannot be roof-mounted (Appendix A), it is assumed that

they could be installed on a 13 or 14m mast (or higher) provided potential owners

have a large enough garden. However, this is much less convenient than a roof-

mounted installation.

12 It has also been chosen because it is based on a real situation. Dr. Jonathan Gregory – who works in climate change science – is interested in installing a small wind turbine on his house at this location.

51

Location

Below is a map of central Reading. The residential areas principally consist of

closely built houses, where buildings rarely exceed 12m in height.

Figure 30 – Map of central Reading

© www.multimap.com

AMWS

The Meteorology Department of Reading University (based in the Whiteknights

campus visible on the map) have collected extensive data from an 8m mast and

estimate an AMWS of 2.8m/s (Ken Spiers email, 18/8/05).

However:

• 8m is lower than a turbine would probably be placed

• the mast is (effectively) in a field in the middle of Reading

• most houses are surrounded by houses of the same height

On balance, 2.8m/s is a relatively good guess for a turbine in this area, given that the

first of these factors should mean that the turbine receives more wind while the next

two should mean it receives less wind, and given that there is no other data available

apart from NOABL.

52

NOABL estimates that the wind speed 10m above ground would be 4.8m/s here –

indicating its unreliability where local topography is complex.

Tariffs

A green electricity tariff might be 7.56p/kWh.13

Electricity consumption

Typical annual electricity consumption might be 2,900 kWh/year.14

Economics

Table 13 – Estimated economics of residential turbine installations in Reading Turbine type Annual

energy yield,

kWh

Installed

cost

Payback

w/out

grant, years

Possible

grant

Payback

with grant,

years

D400 110 £2,200 63 Not eligible XXXXX

Surface Power

Technologies

178 £1,518 44 Not eligible XXXXX

Swift 474 £5,000 49 £1,500 41

Assuming conditions synonymous with best case scenario conditions:

• none of the electricity is exported

• annual maintenance costs are zero

• discount rate of 0%

• 4% annual increase in energy costs

• Best case installation costs for each turbine

None of the turbines are exporting enough energy to qualify for ROCs.

13 Based on Jonathan Gregory’s bills. 14 Based on Jonathan Gregory’s electricity consumption.

53

The Swift is the only one that could qualify for a grant as the D400 and Surface

Power’s turbines produce too little power. (Clear Skies, 2005)

Even with a grant, the Swift payback is 41 years. This is considerably greater than the

expected lifetime of the turbine.

Therefore, it would be uneconomic for the homeowner of a typical house in Reading

to install any of these turbines.

To raise public awareness one could install a D400 relatively cheaply, but it would

only reduce their annual energy bill by £8.32 (at these tariffs).

For the D400 to payback within 10 years at this location under the highly favourable

conditions above, it would need to cost £99 or less. While at £2,200 the D400 takes

13 years to payback, even with an AMWS of 10m/s and including ROCs at £45/MWh.

Surface Power’s turbine generates its maximum amount of energy at an AMWS of

about 9.5m/s, and in the best case conditions above, it can payback in 11 years. It can

not benefit from ROCs as it is intended to be an independent off-grid supply.15

With the best case cost price for the Swift of £3,500 after grant, and including ROCs

at £45/MWh, it can payback within 10 years with an AMWS of 5.5m/s.

But with the current cost of the Swift of £8,500 after grant, including ROCs, to

payback within 10 years requires an AMWS of 9m/s.

Figure 31 below is LPC sensitivity analysis, for a Swift, where the base case of 1 is:

Table 14 – Base case for residential Swift installation in Reading, for LPC sensitivity analysis

Energy generated 474kWh

Amount invested £3,500

Discount rate 4%

Annual maintenance

costs

£75

15 As explained in Appendix A, Surface Power market their turbine (and solar panels) with a deep-cycle battery, inverter, and plug sockets, and intend for this arrangement to be off-grid – so that a homeowner may operate some of their appliances from it whilst leaving the rest of their appliances connected to the grid, thus reducing their bills.

54

Figure 31 – LPC sensitivity analysis for the installation of a Swift on a house in Reading

0

1

2

3

4

5

6

7

8

0.1 0.4 0.7 1 1.3 1.6 1.9 2.2 2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9

Fraction of base case parameters

Leve

lised

Ene

rgy

Cos

t £/k

Wh

Energy generatedAmount investedDiscount rateMaintenance costs

The LPC is most sensitive to changes in the energy generated, and the installation cost.

Even a small improvement in either can significantly improve the economics. The

line for ‘amount invested’ could stop where the fraction is 3.43, because that reflects

£12,000. The furthest extent for the line of ‘energy generated’, reflects an AMWS of

5.2m/s.

The annual maintenance cost of £75 has been guessed, but once the maintenance costs

for the Swift are known (whether they are £0 or £375) the LPC can be deduced from

this graph.

In the base case the Swift generates insufficient energy to qualify for ROCs, hence

there is no graph for it.

55

5.5 Large buildings in London – RIBA and the Aylesbury Estate

This analysis looks at theoretical costs of two projects in London. The RIBA (Royal

Institute of British Architects) who were interested in installing a wind turbine on

their roof,16 and the Aylesbury Estate in Southwark should have some wind turbines

installed on the rooftops of their tall tower blocks. They have also been chosen

because wind speed data is available for them.

Locations

Figure 32 – Map of RIBA’s location in London

© www.multimap.com

In the map above, the RIBA building is just off the A4201, W1B 1AD. It is slightly

taller than the buildings in the surrounding area.

16 They were refused planning permission for such a project prior to PPS22 and the GLA’s support, but may try again.

56

Figure 33 – Map of Aylesbury Estate’s location in London

© www.multimap.com

The Aylesbury Estate comprises much of the area south of East Street, e.g. around

Thurlow Street, SE17 2UZ. It is Europe’s largest estate.

AMWS

Data measured from the rooftops of the RIBA building and a tower block of Portland

Estate (near Aylesbury Estate) found the AMWSs to be 3.4m/s (Thomas, 2003) and

8m/s respectively.17 (Nick Banks email, 4/8/05)

The difference in wind speeds could be due to differences in the relative height of the

RIBA building and its surroundings, and the Portland Estate tower and its

surroundings. The Portland Estate tower could also be much higher.

At RIBA NOABL estimates the AMWS to be 5.7m/s at 25m height (the RIBA

anemometer was 36.5m high – Thomas 2003), and at Aylesbury Estate at 45m height

it finds it to be 6.1m/s – although the towers could be higher than this.

17 Southwark Council who conducted the measurements take no responsibility for any conclusions that might be drawn from the use of this data.

57

Tariffs

A tariff of £0.06/kWh is used. Although the Aylesbury Estate towers are residential

the electricity may be used by the landlord, and if not then it will underestimate the

turbine economics as domestic tariffs are higher (e.g. £0.07/kWh).

As both buildings are large it is unlikely any electricity would be exported.

Turbines chosen

The D400 is too small, and Surface Power’s turbine cannot be roof-mounted. Even if

there were data the Windsave would not be a good choice for the Aylesbury Estate

given its low cut-out wind speed (see Chapter 3). The Swift and Proven 2.5kW are

appropriate. The Proven 6kW might be too large, but this would depend on the

outcome of a structural survey, so it will be considered.

Economics

Installation costs for building-mounting the three turbines can be found in Appendix J.

For the Proven 2.5kW & 6kW the most expensive estimates of £21,000 and £26,000

will be used. Swift estimates show a far greater variation in price: £5,000-12,000 due

to the projected price decrease over the next 12-24 months. Both of these prices shall

be assessed as it is uncertain if their target price will be achieved.

Table 15 – Economics of roof-mounted turbines on RIBA & the Aylesbury Estate

RIBA Aylesbury Estate

Annual

energy yield,

kWh

Payback,

years

Annual

energy yield,

kWh

Payback,

years

Proven 2.5kW 1,497 82 10,188 10

Proven 6kW 4,183 32 26,140 5

Swift 1.5kW,

best £ case

33 5

Swift 1.5kW,

worst £ case

798

89

5,466

11

58

Assumptions:

• grants cover 50% of the total installed cost

• collecting ROCs at £45/MWh

• only offsetting imports

• discount rate 4%

• annual increase in electricity price 1%

• no annual maintenance costs

Altering these conditions slightly, if the Proven 6kW for Aylesbury Estate didn’t

collect ROCs it would payback in 10 years, if it didn’t receive any grants it would

payback in 12 years, and if it didn’t receive any grants or ROCs it would payback in

24 years.18

Figure 34 below is a sensitivity analysis for some parameters for the base case of a

Proven 6kW on one of the towers of the Aylesbury Estate. The base case of 1 is:

Table 16 – Base case for roof-mounted Proven 6kW on the Aylesbury Estate, for LPC sensitivity analysis

Energy generated 26,140kWh

Amount invested £13,000

Discount rate 4%

Annual maintenance

costs

£180

ROC value £45/MWh

18 The expected lifetime of a Proven 6kW is 20-25 years (Appendix B).

59

Figure 34 – LPC sensitivity analysis for a roof-mounted Proven 6kW on the Aylesbury Estate

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.1 0.4 0.7 1 1.3 1.6 1.9 2.2 2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9

Fraction of base case parameters

Leve

lised

Ene

rgy

Cos

t £/k

Wh

Energy generatedAmount investedDiscount rateMaintenance costsROC value

Any large increase in electricity generation or ROC value from the base case is

unlikely so should be ignored. Negative LPCs shown in these instances are a result of

large amounts of money being made from ROCs.

From the base case’s proximity to an LPC of 0p/kWh, it can be seen that it is

economic.

For the base case, £180 was chosen for the maintenance costs as that is the known

maintenance cost for a Proven 2.5kW (see John Bosco School in Appendix M), and

the maintenance cost for a building-mounted Proven 6kW will be at least as large.

Effects of an increased maintenance cost on the LPC will be slight.

5.6 Analysis

All of the sensitivity analyses show a greater sensitivity to changes in AMWS than for

any other variable. Therefore this is the most important consideration in siting an

urban wind turbine. The amount invested is also highly important, and therefore

grants should be sought whenever possible.

60

In the urban environment one is far more likely to encounter a good AMWS at the top

of a tall building which is considerably taller than the surrounding buildings, e.g. the

tall tower block of Southwark’s Portland estate. In this kind of location urban wind is

economic – although it still requires grants and/or ROCs. These are the locations in

any city that need to be taken advantage of.

Given the comparison with RIBA, tall tower blocks may be the only windy locations

in a place like London, although windier cities (e.g. Edinburgh) may have many more.

Wind turbines for houses in places such as Reading (and probably also London) won’t

be successful on the basis of economics, and won’t generate a significant portion of

energy either because of the low AMWSs. And at present, the only wind turbine (for

which figures are available for) which will be economic with an achievable AMWS

(5.5m/s), is the Swift at its projected price (and assuming a grant). The other turbines

aimed at the domestic market (D400 and Surface Power’s) need to drop in price

and/or other economic factors need to change.

With regards to wind data, more work needs to be done to determine what an AMWS

will be at a particular urban site. The difference between the RIBA and Portland

Estate figures indicates an extremely high degree of variability in the urban

environment. More data could be collected, and computer models could be developed

that would make predictions. One should not rely on NOABL in the urban

environment because it does not take into account local topography, and will very

likely give overestimates for wind turbines.

To help put small wind into context, SEA estimate that there are ~4000 or so tower

blocks in the UK. If on average 10kW were installed per block, that gives a rated

capacity of 40MW. The equivalent of about 20 large wind turbines.

Although it would be interesting to compare the economics of the turbines with their

cut-in wind speeds, there is insufficient data to do so.

61

6. CONCLUSIONS

State of the art

1. While “the larger HAWTs” have urban and rural uses, the 4 “smaller HAWTs

aimed at the urban market” all came on the market in 2005, while there are

another 8 prototypes being designed for the urban market. Therefore, many in

the industry in the UK & Ireland believe small wind turbines in the urban

environment (especially building-mounted ones) have great potential. As the

majority of these are VAWTs, many of them also believe that the advantages

of VAWTs (particularly ones that use the lift force) will outweigh their

disadvantages. It is hard to tell if so many new products are justified; it will

depend on the ultimate development of the market. The success of VAWTs

also depends on how successful the HAWTs are at cornering the market in the

intervening time – although VAWTs may always find a niche where buildings

have focussed the airflow and made it extremely turbulent.

2. Cut-in and cut-out wind speeds should be considered given the turbine’s

environment. Turbines with a high cut-in (e.g. the Gazelle) should not be

placed in sites with a low AMWS (e.g. ground-level of central Reading).

Turbines with a low cut-out (e.g. Windsave) should not be placed in sites with

a high AMWS (e.g. on high rooftops).

3. Judging from Sagrillo’s method, the HAWTs intended for the urban

environment are built to withstand turbulent conditions. It remains to be seen

if they can withstand the levels of turbulence found in such sites.

4. It is not certain that manufacturers can be trusted to provide impartial technical

data on their products. An independent small wind turbine testing centre (as

there is with larger wind turbines) would be useful. A standard rating for

small wind turbines similar to that with photovoltaics would be useful for

customers. The rating could potentially have the form of energy generated per

year at different AMWSs. This can be derived from power curves, but this is

not a customer-friendly format.

62

Installations

5. There are probably at least 100 installations of wind turbines <50kW in the

urban/semi-urban environment in the UK. Given the number of products this

figure is low, possibly reflecting the immaturity of the small urban wind

market.

6. Rooftop installations are increasing rapidly. This indicates a demand for

building-mounting turbines, and therefore corroborates the industry’s chosen

direction. Despite this, the majority of urban/semi-urban turbines already

installed at the time of writing (August 2005) are ground-mounted Provens.

7. The results from detailed experiences are:

• Positive for the small wind turbine industry with respect to owner’s

overall satisfaction, the perceptions of neighbours and the local

community before & after, and safety.

• Satisfactory with respect to visual appearance.

• Unclear with respect to noise level.

• Negative with respect to dependency on grants, owners overestimating

economics, quality of the finished product, and after sales service.

Policy makers and implementers (& the industry) need to overcome the limited

numbers of people claiming ROCs, and difficulties with planning & connecting to

the grid.

Economics/Installations

8. The vast majority of installations already installed belong to environmentally

conscious organisations/people. The economics of small urban wind turbines

are not currently good enough to attract those who would see it as an

investment, and unfortunately also make the industry over dependent on grants.

This makes it vulnerable to any potential hiatus in the grant programs. It is

necessary for the economics to improve for the market to significantly expand.

Currently machines are being hand assembled in small numbers; mass

63

production or new manufacturing techniques would improve the economics.

Other components such as inverters would also need to drop in price.

9. A combination of factors is necessary to make economics viable in most

situations. The economics are especially sensitive to changes in the AMWS.

10. The evidence suggests that NOABL wind speeds are overestimates for the

urban environment. It is possible that reliance on NOABL is one aspect that

has led to so many turbine owners overestimating the economics. Remedies

for this include more publicly available wind measurements from urban areas

(especially rooftops), or wider use/development of reliable software.

11. At current prices, the wind turbines for the domestic market are uneconomic.

It is hard to envisage how this market will be successful unless prices drop

and/or other conditions change (e.g. tariffs).

12. Given the AMWS measured on the Portland Estate, rooftop installations on

high tower blocks could be extremely promising. Some more research and

experience of roof-mounted installations is required, but if grants and/or ROCs

remain available and high AMWSs are found to be widespread on tower

blocks, then installations of this type could rapidly become a feature of the

urban landscape.

13. However, given the measured Reading & RIBA wind speeds much of the

urban environment may be unsuitable for small wind turbines to be

economically successful.

14. Micro turbines may find applications where they are more economic than

alternatives as is happening with photovoltaics – e.g. temporary road works

signs, bus stops.

15. It is uncertain if manufacturers can be trusted with economic information until

their product is actually for sale at that price, e.g. comparing the price of the

Windsave to Eclectic’s D400, and their rated powers.

64

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