Category Archives: EuroSun2008-10

Demonstration system in a one family house

A new developed solar heating/natural gas heating system was installed in a one family house with three inhabitants in Helsinge, Denmark, latitude 56°N, in July 2006. The house is shown in figure 1 before the installation of the solar heating system.

Подпись: Fig. 1. Demonstration house before installation of the solar heating system. Left: From the south. Right: Non condensing natural gas boiler and separate hot water tank.

Before the installation of the solar heating system the house was supplied with heat from a Vaillant non condensing natural gas boiler from 1990 with a nominal power of 22 kW. For domestic hot water preparation the natural gas boiler heated a 50 l hot water tank, see figure 2.

image151

Fig. 2. Schematic sketch of the energy system before installation of the solar heating system.

The solar heating system installed in the house has 5 Velux solar collectors, type S08 with a total collector area of 6.75 m2. The collector orientation is 15° towards east from south and the collector tilt is 45°. The collectors have a start efficiency of 0.79, a first order heat loss coefficient of 3.76 W/m2K, a second order heat loss coefficient of 0.0073 W/m2K and an incidence angle modifier of 1 — tan3 9 (9 / 2), where 0 is the incidence angle.

The solar heating system is based on a technical unit and a heat storage unit produced by METRO THERM A/S. The technical unit includes a modulating condensing natural gas boiler from Milton A/S, type Milton Smart Line HR24, with a nominal power for space heating of 5.7-23 kW and a nominal power for hot water preparation of 5.7-28.5 kW, a heat exchanger producing domestic hot water, and all equipment needed to operate the solar collectors, the natural gas boiler and the heating system. The heat storage unit includes a 360 l solar tank which can be charged by means of the solar collectors and the natural gas boiler [5]. The tank insulation is partly PUR foam, partly vacuum panels.

Both the technical unit and the heat storage unit are built into 60 x 60 cm units by METRO THERM A/S. Due to this prefabrication, the installation of the system is easy and the risk of installation mistakes is reduced. The design of the units provides good operation conditions for the condensing natural gas boiler and for the solar collectors.

Figure 3 shows a schematic sketch of the two units as well as the solar collector loop and space heating system.

Figure 4 shows the house after installation of the solar heating system.

Fig. 4. Demonstration house after installation of the solar heating system. Left: From the south. Right: Solar

tank and technical unit in the basement.

The Solartwin zero carbon solar thermal solar controller in use

This solar controller potentially allows most types of pumped solar thermal system to become zero carbon. As used with Solartwin, upstream of the controller is a PV panel and downstream of it is a pump with a brushless DC motor. The controller will provide differential pump control plus additional functionality. Energy is stored for the processor and display at night but not for the pump, although this can be added as an option. The controller will operate DC pumps up to 25W and 22V. On the Solartwin solar thermal system we use a 12V DC brushless DC motor on a diaphragm pump with an 18 Cell Crystalline PV.

image039

Fig. 1. Simplified solar water heating from Solartwin

The design of the controller provides the end user with an attractive housing displaying temperatures, operation display and 5 cables: 2 for power and 3 sensors. The consumer is provided with onboard customisable aspects of program including:

• temperature differentials

• pump overrun time

• choice of 3 overheat options: pump on, off and differential.

The overall design is user friendly, and suitable for DIY solar heating panels for home use, sensor cables are colour coded for example.

image040Fig. 2. The Solartwin zero carbon solar powered solar controller

When the system is used with a non Solartwin solar thermal system there may be small adjustments to be made on the temperature differentials when solar water heating incorporates a long pipe run (this is not as important with the Solartwin system because Solartwin utilises low volume flexible microbore silicone rubber piping rather than the larger copper pipes of traditional solar thermal). The following table displays the suggested adjustments.

TOTAL length (i. e. there

and back added together)

of unheated pipes (e. g. in

lofts and on roofs PLUS HALF the length of heated

pipes (e. g. in the airing cupboard and in heated rooms)

Suggested

pump

overrun time setting in seconds

Suggested start difference (over the bottom of cylinder temperature) in degrees C

Suggested stop difference (over the bottom of cylinder temperature) in degrees C

up to 10m

30-90 sec

4C

2C

10.1 to 15m

120 sec

6C

3C

15.1 to 20m

180 sec

8C

4C

20.1 to 25m

240 sec

10C

5C

25.1 to 30m

300 sec

12C

6C

Table 2. Temperature differential adjustment for longer pipe runs.

Function description of the system

Numbers in the following paragraph refer to numbers in the Fig. 1. When the temperature difference between the top of the SHC 1 and the pit 9 is at least 3°C and the heat pump 6 does not work, the valve 2 is opened between P and B ports. The warm brine circulates between SHC, preaheater for the domestic hot water tank 7a, the ground heat exchanger 9, backflush valve 11, flowmeter 10 and circulation pump 4. When the temperature difference falls to less than 2°C, the pump 4 stops the brine circulation When thermostats, controlling the hot water or room temperature activate the heat pump, the valve 2 opens the path P to A and the circulation pump 4, as long as the atmospheric temperature is higher than the temperature of the cold brine, starts to work.. The brine flows then between SHC 1, valve 2, flat heat exchanger 3 and through pump 4 back to SHC. The brine is cooled down in the heat exchanger 3 to low temperature. At the cold surface of the SHC condenses the water vapour in the air and releases both the sensible heat of the air and the latent heat of the water vapour. The expanded, cold (< -5°C) heat transfer fluid in the heat pump circuit receives the heat from the brine and transports it to the loop 5 in the pit. Depending on the temperature difference between the fluid and the soil surrounding the loop, the fluid either loads the storage magazine or consumes the stored heat.

The heat capacity of the pit is dependent on the moisture content of the soil. Therefore all rainwater from the roof of the house is lead to the drainage tube system 12.

image093

2. Results and discussion.

An existing family house in the northern or middle Europe does not need to consume more than 10000 kWh/year. Solar energy distribution and energy requirements in such a house over one year can be seen in the Fig. 2.

Fig 2. Energy distribution during one year.

image094

The solar energy values in the diagram are calculated from measurements of solar irradiation, air temperatures and humidity The values are based on the SHC area 12 m2 and -5°C cold surface.

The air volume passing the collector during each night is calculated to 500m3. The electrical current consumption was daily recorded from the wattmeter of the house. The diagram shows, that energy demand of the house can be covered by solar energy between weeks 11 and 43. Between

weeks 1-10 ( 40 % of the year energy consumption) and 44-52 (26 % of the total energy consumption, totally 3400 kWh), has the energy for heating of the house be retrieved from a heat storage magazine.

About 1200 kWh electric energy consumes the heat pump for transfer of the energy from the pit to the house. The heating season begins in Stockholm area (59° 27’N) in the middle of September. The temperature of the moist soil, 0,5 m below the surface (Fig. 3) was at that time 12°C and the water content of the soil was 50%. The calculated heat capacity of the pit was in the middle of September 50 kWh/m3, inclusive the latent heat of the soil humidity.

Fig. 3. Temperature in the pit during the heating season 2006/2007.

image095

The heating system was not in the full drift during this winter season. The soil layer was only 50 cm above the heat collecting loop and the SHC was not yet functioning. The mean air temperature between the 10th and 28th February was -4,7°C with the minimum -6,1°C between the 22nd and 25th February. The relatively thin layer of the soil above the heat collecting loop did not prevent measurable influence of the air temperature on the temperature at the bottom of the pit. See Fig. 4. That explains the temperature depression in the pit during the last third of February. In spite of that, the heat pump could still keep the adjusted room temperature.

The effect of the latent heat of high soil humidity could be observed in the Fig.3 from the horizontal parts of the diagram. In January 2007, the most of energy for the heat pump was delivered by the freezing water. And in April, the sun radiation supplied heat for melting of the ice. The 25th of April melted the last ice crystal in the pit. On May 14th, the bottom of the pit reached the reference temperature of the ground. According to our measurements, the average insolation in April 2007 was 175 W/m2 and the sun radiation time was 348 hours. This corresponds to 1948 kWh energy theoretically absorbed by the dark surface of the pit.

The disadvantage of the shallow soil layer is the dependence of the soil temperature in the pit on the temperature of the air and hence the energy losses in the cold weather. The advantage is, that the ice in the ground, which originates from the short distance between parallel sections of the heat collection loop, does not result in permanently frozen pit bottom.

image096image097

During the autumn 2007 the pit was filled with the soil up to 1 m depth. The SHC remained still closed, so that all energy for heating of the house was taken from the humid soil. The results can be observed in the fig. 5.

Fig. 5 Temperatures in the pit during the heating season 2007/2008

10 —

Reference soil temperature

Подпись: Start of SHCBottom temperature of the pit

Подпись: Sep Подпись: Oct Подпись: Hou Dec Jan Feb Mar Apr May Jun Jul

0 —

From the midle of December to 10th of February remains the temperature in the pit within temperature +1 to -1°C. The average air temperature in this period is 1,1°C. The lowest temperature in the storage magazine coincides with the lowest air temperature in spring, -7,8°C on March 24th. The regression analysis of the correlation between the air temperature and the temperature at the bottom of the pit between 10th of March and the end of the month returned the magnitude of the proportional term 0,086°C/°C and the regression coefficient R2 = 0,494. The

direct influence of the outside temperature is therefore minimal. But the heat pump was running with full capacity and the magazine was almost empty.

The minimal influence of the air temperature on the temperature at the bottom of the pit kept the soil frozen even at the end of May. The ice in the pit started to melt first after the start of the brine circulation through the ground heating loop. The tight placement of the energy collection loop could not be used without active heating of the frozen soil.

4. Conclusions.

1. Cooling of the brine flowing through the SHC with the cold heat transfer fluid in the heat pump circuit makes it possible utilization of the SHC even during nights and cloudy, cold days.

2. Using of energy wells as heat source for the heat pumps is possible only in landscapes, where the soil depth is only few meters. An alternative solution, the digging of the loop for energy collection into the soil, required so far large ground areas, because the formation of permanent groundfrost has to be avoided. The coupling of the SHC to the heat pump, described in this contribution demonstrated, that the ground area needed for the energy storage can be diminished to 10-12 m2/ kWh. The expected energy content of the storage volume can be equal or higher than 40 kWh/m3.

5. Literature References:

[1]George A. Olah et al: Beyond Oil and Gas: The Methanol Economy; Wiley-VCH Verlag & Co. KGaA.

[2] http://www. parc. com/research/publications/files/5706.pdf.

[3] http://ep. espacenet. com

[4]M. Semadeni, Energy Storage as an Essential Part of Sustainable Energy Systems. Working Paper No 24, May 2003; CEPE ETH Zentrum WEC Zurich;

(www. cepe. ethz. ch)

[5]Simone Raoux and Matthias Wuttig Editors, Phase Change Materials: Science and Applications, Amazon N. Y.

[6] www. texsun. se

[7] www. megatherm. se

[8] Model VV from EMS Brno, CzechRepublic; www. emsbrno. cz

[9] www. kippzonen. com

Aims, scope and method

The aim of the project was to find the economic feasibility of using solar thermal energy as a complementing energy source in small scale (0.5-2 MWth) DH plants in north european conditions. Considered fuels saved are wood pellets or light heating oil. Also, the feasibility of moving the solar thermal plant was to be estimated, if possible.

Only short term thermal energy storage and ground mounted collector arrays were considered. Thermal load profiles for domestic hot water (DHW) and space heating (SH) on an hourly basis were created based on measured data from several sites. For the simulation studies the number of cases had to be limited; a “bad case” and a “good case” scenarios for solar were studied, assuming that most of other cases fall in between. Yearly energy balances and system sizings were obtained by simulations.

The feasibilities of the studied sizings were calculated with the Net Present Value (NPV) method. As sensitivity analysis different scenarios in fuel price increase and interest rates were considered.

Monitoring results

Подпись: Fig. 2. REBUS system schematic with sensor positions for the REBUS controller (blue with subscript c) and the monitoring system (red with subscript d).

In Figure 3 the heating energy supply for the building is presented from January 2006 to June 2007. The data before the installation of the REBUS system are calculated from the readings of the house owner from the main electrical meter and his records of wood use. The electricity for heating has been calculated based on measured household electricity in 2007. It can be seen that almost all bought electricity for heating was replaced by pellet and solar energy. About 200 kWh electricity were used by the electrical back up heater in the standby store in October 2006. The pellet stove was installed in the middle of October and not enough solar radiation was available, which explains the use of the electrical heater that month. Some electricity was also used in December 2007. Reason here was that the 80 litre standby volume heated by the pellet stove was too little to cover the peak heat demand so that the electrical heater in the standby store was backing up the heating.

Подпись: Fig. 3. Monthly heat supply for space heating and domestic hot water, *Electricity SH + DHW is the calculated electricity use for SH + DHW before the detailed monitoring.

This has also caused a high number of starts and stops with stove run times often not more than one hour. Consequently in the end of December 2006, the hydraulics have been modified so that also the upper third of the solar store, which is connected in serial with the standby store, is heated by the boiler.

This increases the standby volume to in total 200 litres. As a result of this modification it can be seen that the number of starts and stops have decreased drastically (Figure 4). The average run time increased to about 3 to 4 hours per start. Due to the longer run time of the stove also the proportion of the useful heat delivered from the stove to the water jacket has increased from 61% in December to 67% in January. This is still lower than the average 80% for the combustion range that is has been measured for the stove at the Austrian test institute BfL [1].

3000

Подпись:Подпись:Подпись:Подпись: 2Подпись: 174Подпись: 291Подпись: okt-06 nov-06 dec-06 jan-07 feb-07 mar-07 apr-07 maj-07 jun-07Подпись: Fig. 4. Monthly heat delivery of the pellet stove and number of starts and stops.image0732500

Подпись:
In figure 5 the energy use for the monitored time period is presented. The monthly hot water demand varies between 240 and 400 kWh. The annual space heating demand is about 7400 kWh, which is relatively low for a building with a heated area of approximately 130 m2 and indicates a good thermal insulation.

During one year the solar collectors have delivered about 2529 kWh which is a reasonable value considering the small solar store volume, the non-optimal orientation of the solar collectors and the low heat demand. In terms of bought energy this gives a solar fraction of 19%.

Table 1: Annual heat supply and useful heat

Annual heat supply (kWh)

Annual useful heat

(kWh)

Pellet

9319

Space heating

7611

Wood

1434

Hot water

3673

Solar

2543

Electricity

278

Total

13574

11284

2. Discussion and Conclusion

The newly developed solar combisystem has been monitored for one year. For the most part the system is working as expected. All loops and components are properly controlled by the new controller software. Only some fine adjustments of some parameters were necessary. Most adjustments were necessary for the settings of the pellet stove controller to ensure a proper interaction with the main system. A modification of the hydraulic connections was done to increase

the buffer volume of the pellet stove. Using only the 80 litre volume of the standby store led to very short run times and many starts of the stove. After the change the run times of the stove increased and the number of starts and stops decreased drastically. Similar findings have been reported also in other studies (3; 5).

From the annual energy values in Table 1 the system efficiency can be calculated using the following equation:

_ annual useful heat

sys annualsupplied primary energy for heating

With a primary energy factor of 0.4 for electricity the total system efficiency is 0.83. Including also the parasitic electricity consumption of pumps, valves etc. decreases the system efficiency to 0.74. The parasitic electricity of 680 kWh accounts for almost 5 % or the total energy input to the system. It is obvious that the parasitic electricity consumption should be reduced e. g. by the use of more efficient pumps which stand for the main part of the parasitic consumption.

3. Acknowledgement

We are grateful to the Nordic Energy Research and the Dalarna University College for their financial support for this work within the REBUS project.

4. References

[1] BfL, "Prufbericht Pelletskaminofen EVO AQUA." BLT Aktzahl: 053/04, Bundesanstalt fur Landtechnik, Wieselburg, Austria. 2003.

[2] F. Fiedler, "Combined solar and pellet heating systems — Study of energy use and CO-emissions," PhD thesis, Malardalen University, Vasteras. 2006.

[3] F. Fiedler, C. Bales, and T. Persson, "Optimisation Method for Solar Heating Systems in Combination with Pellet Boilers/Stoves." International Journal of Green Energy, 4[3], 325 — 337. 2007.

[4] S. Furbo, A. Thur, C. Bales, F. Fiedler, J. Rekstad, M. Meir, D. Blumberga, C. Rochas, T. Schifter — Holm, and K. Lorenz, "Competitive Solar Heating Systems for Residential Buildings (REBUS)." Byg, DTU, Copenhagen, Denmark. 2006.

[5] A. Heinz, "Fortschrittliche Warmespeicher zur Erhohung von solarem Deckungsgrad und Kesselnutzungsgrad sowie Emissionsverringerung durch verringertes Takten." Technische Universitat Graz, Institut fur Warmetechnik, Graz, Austria. 2006.

[6] IEA, "International Energy Agency — Solar Heating and Cooling Program." IEA-Task 26. 2002.

The air-cooled heat exchanger

The air-cooled heat exchanger, also known as dry cooler, air-cooler or fin-fan cooler, essentially consists of a finned tube heat exchanger bundle arranged above a fan plenum chamber. An induced draft fan respectively draws air across the finned tube bundles. The cooling water flows through the finned tubes, and heat is transferred from the water to the ambient air. With air-cooled heat exchangers, it is not possible to cool the medium below the ambient dry bulb temperature. In this case the difference between the medium outlet temperature and the air inlet temperature is generally referred to as the terminal temperature difference (TTD) or the approach temperature and values in the range of 7-8°C are considered economically feasible [4].

image124

Fig. 2. Air-cooled heat exchanger

The dry-cooler is an air-cooled compact, finned-tube heat exchanger. The type of surface selected is a finned circular tubes, surface 8.0-3/8T [8], the surface geometric characteristics are:

• Tube outside diameter = 0.0102 m

• Fin pitch = 315 per meter

• Flow passage hydraulic diameter = 0.00363 m

• Fin thickness = 0.00033

• Free-flow area/frontal area, ct = 0.534

• Heat transfer area/total volume, a = 587 m2/m3

• Fin area/total area = 0.913

• Number of tubes = 120

• Number of rows = 6

• Number of passes = 10

The heat transfer from a bank of circular finned tubes in counter flow with both fluids unmixed is considered here. The air and the fluid outlet conditions as well as the fans consumption are calculated with the EES code. The finned-tube rows are staggered in the direction of the fluid velocity.

The heat transfer characteristics of the finned-tube heat exchanger are:

• Heat exchanger effectiveness = 0.68

• NTU (Number of Transfer Units) = 1.893

• Water-side heat transfer coefficient = 12.75 (kW m-2 K-1)

• Air-side heat transfer coefficient = 0.14 (kW m-2 K-1), [9]

The dimensions of the dry-cooler were supplied by the manufacturer, 1.050 m x 2.725 m x 0.15 m for 40 kW nominal cooling capacity. Three fans are installed above the compact heat exchanger and the maximum power of each fan is 0.9 kW.

Future Utilisation Potential Factor (FUPF)

In order to translate the technical results of efficiency into an easy-to-understand term, which would not alarm the users but give a proactive impression of their system, a new term had to be defined as:

FUPF = n-~nmonth, for nrnonh >0 Equation (2)

Tjmonth

Where, FUPF = Future Utilisation Potential Factor, which gives the ratio of hot water reserved for future use to current hot water consumption, for a specific period.

Птах = maximum attainable efficiency for the specific solar technology under local

operating conditions (found to be 81.7% for these systems under local climatic condition), and

nmonth = mean efficiency for a specific period (a month for this case).

Подпись: Jan Mar May Jul Sep Nov Fig. 5. Future Utilisation Potential Factor (FUPF) for Flats 3 and 6.

A comparison was made between the FUPF values of Flats 3 and 6, which had complete data sets of at least 1 year each. Figure 5 showed that even though both owners were satisfied with the performance of their systems, it was apparent that Flat No. 6 had virtually no extra hot water storage during most months, while Flat No. 3 had up to almost twice the amount of hot water used, in reserve. This is a direct result of proper management of hot water usage, which was facilitated by the electronic control unit and the interest of the users to follow the daily weather forecast. The FUPF values for summer have little significance, since Flat No. 3 had fully covered the evacuated-tubes, in order to avoid overheating, while Flat No. 6 did not cover the tubes fully. As a result, one could notice that for July, the FUPF for Flat No. 6 was higher than Flat No. 3. This also translated into alarmingly high temperatures in the solar tank, which could be a potential hazard for skin burns and for a reduction in the lifetime of plastic hot water pipes of the apartment..

Solar CombiSystems Promotion and Standardisation (COMBISOL project)

M. ALBARIC1*, C. BALES2, H. DRUECK3, B. GAGNEPAIN4, G. KUHNESS5, T. LETZ6,
B. METTE3, A. THUR5, J. E. NIELSEN7, P. PAPILLON1

1 CEA, LITEN, INES 50 avenue du Lac Leman, 73377 Le Bourget du Lac, France.

2 SERC, Hogskolan Dalarna, 78188, Borlange, Sweden.

3 ITW, University of Stuttgart, Keplerstrasse, 70174, Stuttgart, Germany.

4 ADEME, 500 route des Lucioles, 06560, Sophia Antipolis, France.

5 AEE INTEC, Feldgasse 19, 8200 Gleisdorf, Austria.

6 INES Education, 50 avenue du Lac Leman, 73375Le Bourget du Lac, France.

7 Plan Energi, Jyllandsgade 1, 9520 Skoerping, Denmark.

* Corresponding Author, mickael. albaric@cea. fr

Abstract

Solar combisystems (SCS) are solar heating installations providing space heating as well as domestic hot water in buildings. Within a global solar thermal energy strategy, SCS are a key element to decrease the fossil energy demand for heating in existing and new buildings. This project will help to reduce the use of fossil fuels and hence also the emission of greenhouse gases. During 3 years (December 2007 — December 2010), experts from research, testing institutes and industry will work in the aim to encourage an accelerated deployment of SCS market — hence a higher share of heat produced by solar energy — and promote an improved quality of the installed systems.

Keywords: Solar CombiSystems, Performance, Standardisation, Promotion

1. Introduction

Solar combisystems are solar heating installations providing space heating as well as domestic hot water in buildings. Within a global solar thermal energy strategy, SCS are key elements to decrease the fossil energy demand for heating needs in existing and new buildings. From that point of view, their further market deployment will contribute to achieve the objectives of the White Paper on Renewable Energy Sources, of the Green Paper on Energy Efficiency, and of the Directive on the Energy Performance of Buildings.

2. The context

The large number of existing hydraulic layouts, the differences in storage volume and the various degrees of prefabrication make the installation difficult for installers and increase the risk for mistakes during installations.

Standards are well defined for solar collectors (EN 12975) and for small domestic water heaters (EN 12976), but not for SCS. For them, some standards are available (ENV 12977) but not already validated and not able to deal with all systems available on the market.

In France, only for one-family houses, approximately 90 different systems are available from 38 manufacturers [7]. This leads to a large difficulty both for the installers and consumers to know

image091

exactly which system is the best (with regard to cost and performances) adapted to a specific house, with specific equipments for auxiliary (oil, gas, electricity, wood, …) and specific heating devices (radiators, floor and wall heating or a combination of all).

Fig. 2. Heating floor storage and hydraulic storage.

Although the market share of SCS is increasing in most European countries, it is still quite small. CombiSol project, which is supported by Intelligent Energy Europe program, should encourage an accelerated SCS market deployment — and thus, a higher share of heat produced by solar energy.

This project will encourage quality improvements of the systems installed, by:

• promoting best practices for solar combisystems, both for new and existing buildings,

• promoting standardised systems and cost-effective solutions,

• recommending solar combisystem designs to manufacturers,

• training installers,

• developing specific dimensioning tools in order to facilitate the recommendation for solar combisystems based on the Energy Performance of Buildings Directive methodology,

• increasing consumers confidence with information on energy efficiency of solar combisystems, based on in-situ monitoring and test labs.

In order to achieve these goals, the consortium includes the main institutes in Europe dealing with this subject: SERC, AEE Intec, PlanEnergy, ITW, ADEME, INES Education and INES-CEA. It has a wide experience of solar combisystems since many years. Professional associations from France, Germany and Austria are also involved in this project, firstly as relay for the dissemination of project results to the relevant actors, and secondly, for providing valuable feed-back from manufacturers and installers.

Energy measurements

1.1. Monitoring systems

The space heating demand, the hot water consumption, the heat loss of the circulation pipe, the natural gas consumption and the electricity consumption of the natural gas boiler and the heating system were measured in periods before and after installation of the solar heating system. Further, the heat transferred from the natural gas boiler to the hot water tank was measured before installation of the solar heating system. Furthermore, the heat produced by the solar collectors, the heat produced by the boiler, and the electricity consumption of the solar heating system were measured in the period after installation of the solar heating system. The monitoring system is described in details in [5].

Based on the measurements it is possible to estimate the energy savings of the solar heating system.

Benefits of zero carbon solar thermal control to the wider solar thermal industry

Our aim in developing this controller is to offer the solar thermal industry the opportunity to zero carbonise all solar thermal systems. It is becoming accepted that zero carbon design is the gold standard in European housing design. The UK government consultation document3 published in December 2006 and entitled, Building A Greener Future: TowardsZero Carbon Development, discusses this in some detail and states that,“developing new homes to low and zerocarbon standards on a large scale, we can promote technologies and innovation which will help drive down emissions from the existing stock too. Our key goal is to achieve zero carbon new homes within a decade.”. Further, a recent life cycle analysis paper2 of three micro generators, states that “The UK domestic building sector, which contributes around 30% of final energy demand, and about 23% of greenhouse gas emissions, can play an important role in CO2 abatement. An uptake of low or zero carbon (LZC) distributed energy resources would help this sector to reduce fossil fuel energy use and CO2 emissions.”

3. Conclusions

Zero Carbon PV powered controllers and pumping for solar thermal systems should be seen as the new gold standard. These solar energy systems offer greater sustainability for the solar thermal industry avoiding the potential energy claw-back of up to 33% on conventional solar thermal. The opportunity for solar thermal manufactures and their customers to fully embrace zero carbon solar thermal technology has now become a simple reality.

Since the technology is now available to achieve this step change, it can be argued that all new solar thermal systems in Europe should be PV pumped by an agreed target date (such as 2012) and the industry’s current somewhat atomised approach on component efficiency should soon be

replaced by focussing on system sustainability. This should require zero carbon operation of solar thermal systems as mandatory in all domestic scale solar thermal installations.

References

[1] Martin C, Watson M. Side by side testing of eight solar water heating systems. ETSU S/P3/00275/REP/2, DTI/Pub URN 01/1292

[2] Allen, S. R., G. P. Hammond, H. Harajili, C. I. Jones, M. C. McManus, and A. B. Winnett, 2008. Integrated appraisal of micro-generators: methods and applications. Proc. Micro-Cogen 2008, Ottowa, Canada, 29 April — 1 May, Paper MG2008-SG-005, 8pp

[3] Building A Greener Future: TowardsZero Carbon Development 07HC04711, report available on download on 1st July 2007 at the following location

http://www. communities. gov. uk/publications/planningandbuilding/futuretowardszerocarbon