CONSUMER SOLAR

THERMAL POWER

Manuel Nascimento – 52294

Introdução à Investigação 18 Dezembro 2012

Overview

Collectors – flat panel and CPC

Solar thermal water heating setups

Solar irradiation availability

Commercially available solutions

Energy calculations

Case Study – energetic and economic results

Conclusions

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Collectors

“Capture" the sun and absorb its energy, heating the HTFs (heat transfer fluids)

HTFs can be water or glicol-water mixtures (help prevent freezing)

Water is cheaper and easier to use

Glicol-water mixtures are more expensive, but more efficient and help prevent

freezing

HTFs transfer heat to potable water via heat exchanger elements

Two types of collectors: flat plate and CPC (compound parabolic collector)

Flat plate collector Compound parabolic collector

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Flat Plate Collectors - overview

Simplest design: insulated box with absorber tubes and glass surface on top

Glass (can be ordinary or special glass) lets solar "rays" through

HTF flows along crisscross-shaped absorber tubes, absorbing heat from the sun

Box provides "hot house" effect and protection from the outside

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Flat Plate Collectors - detail

Losses of energy must be considered

Reflection of incident rays ρ

Glass absorption α

Transmission to the inside tau (what we're interested in)

Recent designs provide optical efficiencies of around 80%, sometimes more

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CPC’s - overview

For radiation within a certain angle, rays are concentrated on the absorber

More expensive compared to flat panel collectors, but potentially greater efficiency

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Collectors - comparision

Tradeoff in performance: choose for high ΔT or small ΔT regimes (ΔT= TC – Tamb)

Obvious conclusion: CPC better for higher heating temperatures (greater ΔT)

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Solar Thermal Setups

Termosyphon (natural) Circulation

Forced Circulation

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Termosyphon Circulation

Sun heats up HTF liquid inside absorber tubes

Hotter fluid decreases in density and travels up towards water tank

Inside the water tank, HTF heats up potable water via heat exchanger

Cooled down HTF returns to the lower part of the collector, continuing the cycle

Possibility of having an electrical resistance inside the tank in order to compensate for insufficient

solar power

Otherwise, traditional boilers (gas, electrical) can be used further along the piping for that effect

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Termosyphon - considerations

Simplest and cheapest setup, but has limited heating power

Tank on the outside is subject to energy losses (colder outside)

Impossible to control HTF flux and heat exchange: if solar power is not enough, HTF

will still be in contact with the water and can even cool it (worst case scenario)

Best used in situations where there’s a low demand of hot water (< 200 litres) and/or

solar radiation is abundant

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Forced Circulation

Automatic control: HTF is pumped only if HTF temperature is larger than tank temperature

HTF flux control increases efficiency, controlling ΔT on the collector and/or heat exchanger

Tank inside the building further reduces energy losses (not so cold inside)

If additional heating power is needed, water can be heated with an auxiliary system of conventional technologies (gas or electrical boiler, electrical resistance, etc.)

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Forced Circulation - extensions

More complex but more powerful and versatile solution

Increased space for tank, if available, provides scalability (tanks usually from 200L to 1000L)

Bigger systems provide additional hot water for house heating and cooling (via walls, floor, radiators, AC…)

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Forced Circulation - photos

Water tank and piping Piping, control and expansion vessel

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World Solar Irradiation 15

Portugal is relatively good...

Solar Irradiation in Europe 16

...especially within

Europe

The energy is there for

the taking

Commercially available panels by Rigsun

Sani line Poli line

Water heating Water and ambient heating

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Costs and characteristics

Sani line

Rated solar fraction: from 60% to 80%

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Costs and characteristics

Poli line

Rated solar fraction: from 80% to 90% for water heating and from 30% to 50% for ambient heating

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Calculating supplied power

Lots of things to consider…

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Easier solution? Software!

Has all the equations necessary for lots of setups in solar thermal and photovoltaic

Has all the necessary radiation data for Portugal

Presents Energy and Economics analysis of project setup

1 to 4 Licenses: 130€ + VAT + mail expenses (per license)

There are other, more powerful software, like Polysun

Polysun has data from all over the world

Many more house customizing options

More expensive: 1 License = 779€

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General Considerations

Optimal placing of panels: facing directly South; inclination equal to location latitude

Small offsets from these (<10º) don't present significant loss in efficiency

Sizing a solar system correctly: try to get > 90% solar fraction in the Summer

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Case Study – parameters

Sani 300-2 setup by Rigsun (2 solar panels, 300L tank)

4 person family

Total turn-key cost: 4200€ (VAT included)

Custom water consumption plan

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Case Study – consumption

Studies show ~95L /p.day of hot

water

Example: shower 6L/min x 15 mins

= 90L ! (remaining 5 L/p.day)

Considered 2 showers in the

morning (not good for solar

panels...) and 2 late in the afternoon

Remaining water for cooking / dish

washing, etc.

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Energy Results

3974 kWh per year (average) supplied by solar system

5300 kWh per year of natural gas saved! (that’s 1.3 ton of equivalent CO2)

Solar Fraction 81.8% - slightly better than advertised

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Economics Results – 5y bank loan

Saving 572.4 €/year in

natural gas bill

(47.7€/month) over 20 years

Real profit of 4711€

(earnings + residual value)

First 5 years: expenses of

about 50 €/month (bank bill

about 93€/month)

Years 6-20: savings of

42.7€/month

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Economics Results – own capital

If done with own capital (no

bank loan, no interest

rates), profit increase to

6136€

That’s 146% of the system

initial cost…

…meaning profitability of

7% per year for 20 years

Recover invested capital in

12 years (following 8 years:

profit)

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Additional savings in space heating

Average energy spent on ambient heating in a US household: 12 MWh/year

Solar energy provided if solar fraction for space heating is about 50%: 2.429 MWh/year

It's a crude overestimation, during half the year probably ambient heaters aren't used

Even so, if electrical resistances are being used to heat the house: 1214.5 kWh x 0.21

€/kWh = 255€ of savings on electrical bill

Don't forget, however, a system for water AND space heating has higher initial cost

Household energy consumption in the EU-27

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Conclusions

Solar thermal setups for water heating are effective, efficient and profitable...

... especially in places with high solar irradiation (South of Europe is more than enough)

In larger households or even entire buildings, additional savings can be achieved by using ambient heating as well

Furthermore, savings in natural gas also contribute to reduce C02 emissions, lowering ecological footprint and energy imports

Software solutions are complete tools for designing solar thermal power projects for water (and space) heating and predicting results

Oh! How good this is! The touch of gold on one’s skin is invigorating!

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Thank you for your attention

Time for questions

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Bibliography

Manuel Collares-Pereira e Maria João Carvalho, “Dimensionamento de Sistemas Solares – Sistemas de aquecimento de água com armazenamento acoplado”, Laboratório Nacional de Engenharia e Tecnologia Industrial, Departamento de Energias Renováveis, 1983

Luís Roriz, João Rosendo et al., "Energia Solar em Edifícios – Edições Orion, 2010

SolTerm software user manual

http://www.fc.up.pt/pessoas/psimeao/#recursos

http://energy.gov/energysaver/articles/active-solar-heating

http://www.rigsun.pt/

http://www.creditopaineissolares.com/credito-pessoal-paineis-solares-bpi/

http://www.painelsolartermico.com/incentivos-2010/

http://www.erse.pt/pt/electricidade/tarifaseprecos/tarifas2012/Documents/PrecosTVCF%20PTCont_2012.pdf

http://www.erse.pt/pt/gasnatural/tarifaseprecos/201207a201306/Documents/Tarifas%20GN%202012-2013_Final.pdf

http://en.wikipedia.org/wiki/Domestic_energy_consumption

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