M. Santamouris, K. Paraponiaris and G. Mihalakakpou

University of Athens, Department of Physics, Division of Applied Physics, Laboratory of
Meteorology, University Campus, Build. PHYS-V, Athens, GR 15784. Greece.

1. Introduction

The city of Athens is characterised by a strong heat island effect, mainly caused by the accelerated industrialisation and urbanisation during recent years. The urban heat island phenomenon has been investigated in 23 experimental stations located in the Greater Athens Area, (GAA). Hourly values of ambient air temperature and relative humidity were recorded at each station. Based on the above mentioned experiment, the influence of various climatic parameters and of the prevailing synoptic conditions on the heat island effect was studied in (Santamouris et al., 1999; Mihalakakou et al., 2002; Mihalakakou et al., 2003; Livada et al., 2002). In Santamouris et al. (2001) it can be seen the impact of the urban climate in the greater Athens area on the energy consumption of urban buildings during summer 1996. Moreover in Hassid et al. (2000) it can be observed the effect of the Athens heat island cooling energy consumption of another reference building in various stations of the western GaA and for the years 1997 and 1998.

Everybody has an impact on Earth, as they consume the products and services of nature. Their ecological impact corresponds to the amount of nature they occupy to keep them going. The ecological footprint is defined as the the land and water area that is required to support indefinitely the material standard of living of a given human population, using prevailing technology, (Rees, 1992). The ecological footprint is a measurement of the ecological sustainability, illustrating the reality of living in a world with finite resources, (Barett and Scott, 2001). It provides a final figure in land areas, (in hectares), which is necessary to support an individual, city, region, country or the entire world population. It provides a visual picture of the Earth’s carrying capacity. For that reason, the ecological footprint has become recently very popular as it can offer a representative idea of the ecological limits, which is one of the main topics of sustainable development. The ecological footprint can be regarded as a potential aggregated indicator for sustainable development. Each year the ecological footprint becomes more refined, portraying a more and more accurate figure of the appropriated land for humanity, (Wackernagel and Rees, 1996; Simmons and Chambers, 1998; Wackernagel et al., 2000).

Calculation of the additional ecological footprint is performed by simulating the additional energy consumption of buildings caused by the heat island effect. Simulations have been performed using experimental data from various urban climatic stations located in the Athens Urban area, for the summer period of the years 1997 and 1998. The ecological footprint of this energy cost is then calculated in the present study using the globally accepted CO2 sequestration pattern.

The direct current-voltage characteristic of glass-ITO-n-CdS-p-CdTe-graphite structure is shown in Fig.1 This dependence can be described as

I= I01 exp(eV/AikT) + I02 exp(eV/A2kT) (1)

Fig.1 The forward current-voltage characteristics at different temperatures: 1-193 K, 2-223 K, 3-243 K, 4-273 K, 5-293 K

where A1 = 2 at low voltages of kT/e < V < 0.1 -0.4 V and A2 = 1.0 — 1.5 at 0.1-0.4 < V < VD. While I0 reduces with decreasing of temperature. So, expression (1) can be written as

I = b1(T)exp(S1V) + I02(T)exp(S2V) (2)

The dependence of the direct current on temperature at different voltages is shown in Fig.2. It is seen that the slope of this dependence dI/dT does not depend on voltage.

Fig.1 and 2 allow us to conclude that the predominant mechanism of the direct current is the tunneling of carriers and can be described by the following empirical equation

I = bexp(aT + bV)

where, a and b are experimentally determined parameters which are typical for tunneling — recombination mechanism in heterostructures.

The reverse current-voltage characteristics at different temperatures are presented in Fig.3 and can be described as

Ir — V n (4)

Where n = 1.5 for kT/e < V < 0.8 — 1.0 V and n > 3.0 for 1.0 < V < 10.0 V. For low voltages value of n indicates on thermal generation of carriers in the space charge region. The reverse current mechanism is tunneling at high voltages.

Acknowledgement

The authors would like to thank Professor Y. Goswami and Dr. S.Vijayaraghavan for their support.

The considered scenario refers to an annual production of 500 000 modules with an average output power of 0.3 Wp per module at standard test conditions. Starting with this number of modules the investment into a production plant is worthwhile. If investment costs of 2.5 million Euro and a service life of the plant, which is shown in Fig. 7, of 10 years are assumed this will result in production costs of 5.12 Euro per module for the module production. The total module costs result from the sum of solar cell costs and the above mentioned module production costs. Additionally to the costs for the production plant the following costs were set: material unit costs: 0.70 EUR

manufacturing unit cost: 3.10 EUR

overhead unit costs: 0.13 EUR

The in Fig. 7 represented production plant consists of the dispensing and equipment unit, a hardening furnace for the SMD adhesive, a reflow oven to melt the solder paste, a roll laminator and an edge trimming unit. The dispensing and equipment unit can be taken over from the SMD manufacturing technology. It must control simultaneous dispensation and equipment, since after placing a solar cell their bus bar had to be covered with solder paste. The hardening and reflow oven are likewise standard production devices from the SMD technology. Only the roll laminator and the edge trimming unit are special devices for the production of solar modules. A roll laminator for module production is for example described in [HANOKA99]. For the edge trimming a water jet cutter is suitable.

Conclusions

The packaging and the contacting of high efficient solar cells was examined. In the first part of this work the function of electrically conductive adhesives in high efficient solar modules for device integration was tested. However no significant advantage resulted in relation to soldered contacts.

A new procedure for the shingle connection for solar cells on a printed circuit board was developed. The manufactured modules have a very small thickness of only 1.5 mm but are nevertheless mechanically so stable that they can be integrated into mobile devices. Additionally it is possible to use the economical manufacturing processes of the SMD manufacturing because of the use of printed circuit boards. By the use of PCBs the production of solar modules in an arbitrary form is possible. Almost no boundaries are set to the design of mobile devices. We have shown in our former work that it is possible to

integrate such high efficient modules in personal digital assistants (PDA) [Schmidhuber01 a]. With these solar powered PDAs a fully self-sufficient operation is possible.

Acknowledgement

We want to thank all colleges at Fraunhofer ISE for the support during this work.

B. Beier et al.; „Electrical Conductive Adhesives: A Novel Reliable Method for Interconnecting Crystalline Silicon Solar Cells“; 17th Photovoltaic Solar Energy Conference, Munich (2001)

D. W.K. Eikelboom et al.; „Conductive Adhesives for Interconnection of Busbarless Emitter Wrap-Through Solar Cells on a Structured Metal Foil“; 17th Photovoltaic Solar Energy Conference, Munich (2001)

D. W.K. Eikelboom et al.; „Conductive Adhesives for Low-Stress Interconnection of Thin Back-Contact Solar Cells“; 29th IEEE Photovoltaic Specialists Conference, New Orleans (2002) „European Union Directive on Waste Electrical and Electronic Equipment (WEEE), Restrictions on hazardous substances (RoS)“; European Parliament result 2. reading (10.04.2002)

L. Frisson et al.; „Conductive Adhesives as an Interconnection Technique for Very Thin Solar Cells“; 17th Photovoltaic Solar Energy Conference, Munich (2001)

A. Haines;

www3.gartner. com/5_about/press_releases/asset_53947_11.js (2003)

J. I. Hanoka; „Advanced Polymer PV System"; PVMaT 4A1 Final Report, September 1995 — December 1997 (1999)

O.-D. Hennemann et al.; „Entwicklung von neuen Klebetechnologien in der Elektronik“; ADHASION Buchreihe, Munich (1991) (German)

T. Loding; www. heise. de/mobil/newsticker/meldung/42219 (2003)

S. Mau et al.; „Kleben statt Loten: Eine neue Technologie fQr die Kontaktierung von Solarzellen“; 17. Symposium Photovoltaische Solarenergie, Bad Staffelstein (2002) (German)

S. Mau et al.; „Elektrisch leitfahige Klebstoffe fQr die Kontaktierung von Solarzellen: Ein neues industrielles Verfahren“; 18.

Symposium Photovoltaische Solarenergie, Bad Staffelstein (2003) (German)

H. Schmidhuber et al.; „First Experiences and Measurements with a Solar Powered Personal Digital Assistant (PDA)“; 17th Photovoltaic Solar Energy Conference, Munich (2001)

H. Schmidhuber et al.; „Why Using EVA for Module Encapsulation if There is a Much Better Choice“; 17th Photovoltaic Solar Energy Conference, Munich (2001)

H. Kergel et al.; „Elektrisch leitfahiges Kleben von SMT-Bauteilen zur Anwendung in der Mikrosystemtechnik“; Verbundprojekt 1996 — 1999, Abschlussbericht, VDI/VDE-Technologiezentrum Informationstechnik GmbH, Teltow (1999) (German)

J. Zhao, et al.; "22.7% Efficient PERL Silicon Solar Cell Module with a Textured Front Surface"; 26th Photovoltaic Solar Energy Conference, Anaheim (1997)

The same media are used in solar cell manufacturing processes, but the media sequence is different. So their evolution graphs and resulting solar cells differs appreciably.

For simulation was used fragment of SSC presented in Fig. 8. I(U) characteristic (Fig.

9) is close to theoretical for (m)Si SC.

Proposed model can be used for evaluation of characteristics of SSC.

Variation of geometrical parameters when other parameters are constant proved that only some of geometrical parameters influence SSC efficiency to large degree.

Constant parameters used in experiments: light absorption coefficient a = 0.1 1/ц, thickness D = 300 ц, a = 10 ц, diffusion length Ln = 100 ц, diffusion coefficient Dn = 25 cm2/s, recombination rate Sn =

1.0- 108 цЩ recombination rate S_Air =

1.0- 107 ^s, photon energy hv = 1.6 eV.

In Fig. 10 are presented example results enabling to predict optimized structure for Spatial Solar Cell.

Summary

Self-formation emerged as a method to increase the performance of products by using a simpler manufacturing process — with associated significant reduction of manufacturing costs — in the field of semiconductors (including PV cells manufacturing), fuel cells, molecular electronics, etc. Fundamental research, laboratory work and experiments, have already demonstrated the large technological potential for Self-formation. In this paper we presented self-formation possibilities for simplification and cost reduction in Spatial Solar Cell technology. As it was expected self-formation methods are fully applicable for such technology and can be used for production of highly efficient and lower-cost SSC.

Developed software for simulation of physical characteristics of Spatial Solar Cells depending on geometry and material properties can be used for evaluation of optimal characteristics of SSC and further optimization technological processes. First estimations demonstrate significant reduction of the production costs for SSC produced by Self­formation technology.

We also expect that proposed method for optimization of SSC performance can become a useful tool for technologists predicting and optimizing SSC properties and also in searching and predicting new SC

[1] .

The biofuel market inside Russia is currently week and limited mainly by firewood for heating in rural areas (about 325 TWh/year), and is not expected to grow within, at least, the next decade. The two major reasons for this are:

■ negative trends in Russia’s rural demographic situation leading to considerable decrease of population, as well as of industrial and economic activity in these areas,

■ low internal prices for fossil fuels that make biofuel production technologies unattractive for potential consumers and unprofitable for potential investors,

■ high world prices for oil, that in present-day transient economic situation in Russia make any technologies, other than oil extraction, primary petroleum products production and transportation, unattractive for potential investors,

■ intensive development of the gas pipeline network results in substitution of coal and wood, traditionally used for domestic and municipal heating, by natural gas.

The share of all renewables (biomass, solar, wind, geothermal, small hydro) in power and heat consumption was only 0.3% in 2000 and, even according to the optimistic scenario, was not expected to exceed 1.7% (i. e., 65 TWh/year) by 2010 [7]. It is only 7% of biomass resources of the European part of Russia.

Still less optimistic perspectives for biomass internal consumption in Russia for the coming years are in the field of use of biofuels in transport. Estimations made by the EU experts show that with the current biofuel technology level they can be price-competitive with petroleum derivatives at about 65 Euro per one barrel of crude oil. Therefore a substantial economic and legislative support of the state is needed to promote biofuels use in the transport segment. In Russia, such support programs are just in phase of initiation today, and a long period of time will be needed before the first perceptible results of their implementation are reaped. That is why the situation today will still remain rather favourable for those EU biomass market operators who decides to gain a foothold in this region.

In the following considerations, the regions previously identified both within the EU and in the expansive surrounding areas have been examined with regard to the local costs of production. For certain distant locations, the expected transmission costs to the city of Kassel, which has been selected arbitrarily, have also been included. The costs are comprised of the capital investments in all components calculated at a real interest rate of 5%, the outlays for maintenance and repairs, as well as additional expenditures such as insurance and operating expenses.

• 5.1 Costs of Wind Energy

Wind turbines have been calculated using a specific cost of 1000 € per Kilowatt. The expected costs for offshore wind farms are currently about 1850 €/kW, whereby locations in the North Sea promise a yearly equivalent output of 3500 FLH (s. [Pla. 00], [SEAS 97] and [CHK 98]). An assumed turbine service life of 20 years is used to calculate the annuity, and the yearly operating costs are set at 2% of the total capital investment.

If the full potential of electricity generation from wind power in Germany were to be realized, an equivalent average generation of 1600 FLH with electricity costs of 6.3 €ct/kWh could be achieved according to the computational method mentioned above. The costs for electricity generated by offshore wind turbines may be estimated at 5 €ct/kWh. Equal distribution of wind power throughout all EU countries (according to the yield anticipated in [Gie 00]) would likely result in an average cost of about 5 €ct/kWh, as well. With the concentration on particularly good sites proposed above, about 3.7 €ct/kWh could be achieved. Tab. 3 gives the calculated local electricity costs for northern Russia with western Siberia, southern Morocco, Mauritania, and Kazakhstan as well as the transmission distances, costs, and losses. It should be noted that local measurements in southern Morocco [ER 99] clearly indicate the existence of sites capable of achieving 2.2 €ct/kWh locally, while the Egyptian sites previously mentioned promise generating costs of only 1.7 €ct/kWh owing to expectable yields above 6000 FLH. The transmission line losses would be greater because of the high level of output, but costs of delivered electricity below 3.5 €ct/kWh may be expected for the Moroccan high-yield sites and even less for Egyptian wind power reaching central Europe. If the electrical energy from Morocco were to be transmitted initially only as far as Spain, the cost would probably lie below 3 €ct/kWh. As soon as the high-yield predictions have been verified, wind energy imports from Kazakhstan could likewise be considered possible at costs of less than 4 €ct/kWh. Yet because of systematic underestimations, these particularly good sites are not represented in ECMWF data, which form the meteorological basis of the scenarios. They are consequently omitted in the scenarios and will be accorded no further discussion in this paper.

Tab. 3 Anticipated local average costs of electricity (EC) and at arbitrary delivery point Kassel (ECK) for electricity generation from: a) land-based wind turbines, b) solar thermal electricity production with heat storage for 14 FLH (With St.), c) as b), but at half the current costs for the solar mirror field (With St. % FC), d) as b), but without storage (No St.) and e) PV. The transmission losses (L) include consideration of grid load variations with time due to changing infeed and the transmission distance to Kassel (DK) together with converter losses for the conversion from AC to HVDC.

Objectives

The Canton of Geneva has experienced a relatively strong growth of PV deployment in recent years with total installed capacity increasing from around 240 kW in 2000 up to 1300 kW in 2003. The long-term goals are a minimum share of solar power in the electricity mix, more precisely the solar share should cover 1% in 2020 and 10% in 2040 of the total electricity consumption. In the short term, the next goal is set at a total installed capacity of 6 MW by 2010, which is above the average level of 9 W per capita within the 3 gW target in EU15 by 2010. Interestingly, the multi-utility is even more ambitious and strives to achieve that target by the end of 2006.

Figure: Photovoltaic deployment in Geneva. Historical data from 2000 to 2003 with total capacity installed almost doubling from year to year. Target values of 6 MW for 2006, 25 MW for 2020 and 250 MW for 2040.

Energy Law, Planning and Market

The Energy Law in the Canton of Geneva prescribes energy conservation and efficiency as well as the development of renewable energy. The legal prescriptions are translated into working targets, to which both the public and private sector contribute. However it can be stated that "the law stands only for the limits to what is acceptable”. A pure application of the law seems to proove insufficient if the ambitious energy policy goals were really to be achieved. This is the reason why a set of actions has been put in place in order to incite the different stakeholders to improve their performance in terms of energy conservation, efficiency and a higher share of renewable energy.

Different sectors — called platforms — have been identified:

a) public bodies (“collectivites publiques”),

b) commercial actors and SMEs (“arts&metier”),

c) building and real estate sector (“immobilier”),

d) large consumers (“gros consommateurs”) and finally

e) global actions (“actions globales”).

Two major stakeholders (among the many actors) in the context of photovoltaics are the local utilities (Services Industriels de Geneve — SIG) and the Cantonal Service of Energy (ScanE). SIG are the energy producer and distributor, ScanE is responsible for the implementation of the energy policy. In June 2002, SIG implemented major changes in the offer of electricity products. Four basic types of products (see table below) were introduced together with a new price scheme. The new products were sold — in comparison to the old reference price per kWh — at 1 Swiss cent cheaper for Bleu, at 2 cents respectively 7 cents extra cost for Jaune respectively Vert.

The restructuring of the electricity offer can be considered a great success for the renewables (see table below). The Vitale products obtained the very large share of the power market. About 90% of the customers with an electricity consumption share of over 80% subscribed to SIG Vitale Bleu (customers not expressing any explicit subscriptions were automatically attributed to this product category). The very local product SIG Vitale Jaune had a particularly high share with the authorities/public bodies and the product with 2.5% new renewable power, SIG Vitale Vert, achieved a market share of 1.6% in terms of number of customers and 0.5% in terms of electricity consumption. Again authorities/public bodies and the private persons display an above-average concern and subscription to renewable power purchase.

Market share of SIG electricity products in terms of electricity consumption (figures in the cells) and number of customers (figures “inst” between the cells).

The positive market trends and energy policy adopted are likely to further support the deployment of renewable power in Geneva. The public multi-stakeholder strategy for the promotion of solar energy in the canton of Geneva summarises main elements in terms of actors and actions and framework of the electricity sector (see figure below).

The four key areas of the public multi-stakeholder strategy for the promotion of solar energy in the canton of Geneva

As the figure above clearly shows, the assessment of the solar energy resources is part of the public multi-stakeholder strategy for the promotion of solar energy in the canton of

Geneva by providing, for instance, the information on the suitable sites for photovoltaic power systems on roofs belonging to publicly owned buildings.

The newly edited energy plan of the canton of Geneva includes a set of about 20 actions being addressed to the five sectors / platforms mentioned above.

Action No 11 is focussing solar thermal energy. The action addresses three out of the five sectors / platforms, which are public bodies, SME’s and building sector. Especially, the building sector is expected to greatly contribute to the targets set with 44 out of 51 TJ of solar thermal energy production per year by 2015. One of the major challenges is the property structure as the very most people live in rental appartment buildings.

Action No 12 is dedicated to the deployment of solar photovoltaics within the sector / platform of global actions.

The objectives of the action are:

• Promotion and integration of solar power in the grid

• Promotion and integration of photovoltaic modules from the point of view of architecture

• Inventory of roofs suitable for solar photovoltaic use

In order to achieve the objectives, three main measures are considered:

• Budget from the cantonal Office of Energy dedicated to pilot projects and architectural measures

• Partnership with SIG distributing renewable power (SIG Vitale products) to 97% of the households

• Legal measure prescribing a cost-covering tariff for solar power produced and fed into the grid as well as setting up of a common promotion structure for the supply and demand of photovoltaic power together with SIG

Two quantitative targets are set:

• Production of 21 TJ per year by 2010 (installed capacity approx. 6 MW)

• Production of 43 TJ per year by 2015 (installed capacity approx. 12 MW)

With respect to the cantonal Service of Energy, five key tasks are identified:

• Development of supportive financial framework appropriate for the installation of photovoltaic systems

• Support for the architectural integration of photovoltaic installations in the city

• Promotion

• Information to the wider audience and professional stakeholders

• Technical skills and education

Results

The assessment of the solar energy resources in the Canton of Geneva will provide detailed information on the solar-architectural features in the (public) building stock. Aggregated and/or differentiated results can be generated according to, for instance, i) building typology, period of construction (dynamics!), planning relevant zones and areas, roof shape, roof size (size of installation), ownership, energy „metabolism" of the buildings,
potential reduction factors (construction elements, shading,) etc. Results are based mainly on statistics and data specifically collected and can be furthermore visualised thanks to the Geographic Information System, which also makes data and results accessible and available to a wider range of audience and users. Most important, the wealth of data collected and generated allows for drawing conclusions for future activities. Some of the activities are immediately launched. For instance, as an important result of the assessment of the solar energy resources, an inventory of roofs suitable for photovoltaic installations will be made available.

The assessment is part of a larger context of an energy policy based on a public multi­stakeholder strategy for the promotion of solar energy in the canton of Geneva. Solar thermal systems shall be strongly deployed, especially in the building sector addressing the difficulty of a very high share of rental appartment buildings. Solar photovoltaics is considered a key power technology that can be integrated in the urban environment. Solar energy is therefore given some priority via an action plan within the cantonal energy planning (with binding and indicative objectives).

Conclusions

The Canton of Geneva is renowned for a strong energy policy. The assessment of the solar energy resources is part of a public multi-stakeholder strategy for the promotion of solar energy in the canton of Geneva. It provides the authorities and relevant stakeholders with detailed and concise information, tools and networks as well as support with a long­term perspective that allows investors to act in a coherent and stable framework. Solar thermal and photovoltaics become part of sound strategies for a sustained development and deployment of a renewable energy sector. Solar energy is considered a particularly significant and realistic option as well as suitable and valuable solution to bring about sustainability in a highly urbanised area like the

Kenya covers an area of approximately 587,900 sq km of which 576,700 sq km is land surface while the rest is inland water covering 11,200 sq km. Kenya lies astride the equator, its entire land area is located within five degrees North and South latitude. Consequently solar radiation tends to be high (about 5 kwh/m2) over the entire region.

The total population of Kenya is about 32 million of which about 82% of this population lives in the rural areas. Kenya depends on three primary sources of energy namely:- wood-fuel, crude petroleum and hydro electric power. Geo-thermal energy is also being harnessed by the government at Ol Karia in the Rift Valley. Since independence, consumption of electricity has been growing steadily at 5.7% per annum. Currently, the combined hydro, geo-thermal and thermal generating capacities are capable of meeting the national peak demand (approx. 700 mW) for electric power. Approximately 45 mW geo-thermal electricity is generated in the Tana and the Turkwell river basins.

Kenya Power and Lighting Company (KPLC) is responsible for providing electricity to the Kenyans. Per capita electricity consumption in Kenya is estimated at 92 kwh. The main grid primarily serves the urban industry; commercial customers and residents. Less than 3% of the power supplied by the KPLC is consumed by rural Kenya, where the majority of Kenyans live.

Shortage of conventional power and non-availability of grid is responsible for poor coverage of rural people. High solar isolation level and excellent climatic conditions favours a wide usage of photovoltaic systems in many parts of Kenya. The PV in rural areas are mainly for private households use (home lighting system, school lighting, rural water pumping, solar refrigeration for health centres etc).

In terms of fuel quantities, the general equation for the green energy fraction (GREF) of a solar power plant system is, by definition,

GREF = (gr baseline — gr input)/ gr baseline (1)

i. e., GREF = 1 — (gr input)/(gr baseline)

Where,

gr input — — total fuel consumption in the hybrid system

in grams per 1kWhe net electrical plant-output (gr/kWhe)

gr baseline — — 160 gr/kWhe, the specific fuel consumption of the chosen reference (baseline standard), (i. e., a CC using fuel of around 9000 kcal/kg).

For simplicity, both the hybrid system and the reference power system here use the same fuel. It should be realised that the grams ratio expressions signify the inverse efficiencies ratio. The use of grams emphasises the requirement that any fuel used in the plant should be counted and included in the equation.

The concept of fuel avoidance requires comparing a fuel-blended, renewable hybrid system to a real, competing, efficient, non-renewable system for reference (as baseline standard). On circumstances where CC systems cannot be considered as a useful alternative fuel fired electricity generator, thence the 60% baseline is not practical. Therefore, another a locally competing, fuel-fired, efficient system is to be selected for reference standard. Thus, the 40% Rankine-cycle system may serve as a secondary reference against which solar systems will have to compete. In such a case, because by definition the green energy is a reference — dependent parameter, the resulting value for the green energy fraction will be different.

Transformation of a green energy fraction from one reference standard to another can be performed by

TOC o "1-5" h z GREF1/GREFF2 = (B2/B1) (B1-gr)/ (B2-gr)) (2)

Where,

GREF1 — — green energy fraction 1

GREF2 — — green energy fraction 2

B1 — — baseline 1- — in gr/kWhe, (reference standard 1)

B2 — — baseline 2- — in gr/kWhe, (reference standard 2)

gr — — the total fuel consumption in grams per 1kWhe net electrical plant-output

This equation converts a GREF 1 of baseline 1 to GREF 2 of baseline 2. It is significant for enabling comparison between technologies and systems.

Rudi Kaiser, Felix Kosack, Nils Reich, Andreas Steinhuser
Peter Adelmann1

Fraunhofer Institute for Solar Energy Systems ISE
Heidenhofstrasse 2, 79110 Freiburg, Germany
Tel.: +49 (0) 761/4588-5225, Fax + (0) 761/4588-9225
Andreas. Steinhueser@ise. fraunhofer. de
1Phocos AG Deutschland, Bergstrasse 2, 89171 Illerkirchberg, Germany

1. Introduction

The "Rappenecker Hof", a hikers’ inn on the Schauinsland mountain near Freiburg, Germany, was the first solar-powered inn in Europe. A hybrid system consisting of photovoltaics, a wind turbine and a diesel generator has supplied electricity since 1987. In addition, thermal solar collectors provide domestic hot water. Up to now, the system concept has been based on a battery with a rated voltage of 162 V. The solar generator, the wind turbine and the rectifier from the diesel generator have fed electricity directly to the DC circuit. The basic power supply concept is about 15 years old. Technical progress in systems technology and an increased energy demand resulting from changes in the inn’s catering concept forced to modernise the system.

2. Design of the new power supply system

The starting point in planning the new power supply concept was the decision to continue and reinforce the "Rappenecker Hof’s" character as a pioneering system for stand-alone power supplies. For this reason, a fuel cell was chosen as the auxiliary power supply for the "Rappenecker Hof". The photovoltaic generator and the wind turbine will continue to supply around 70 % of the annual energy consumption. A 48 V battery compensates for fluctuations in supply and demand.

The fuel cell guarantees a reliable power supply during periods when the contribution from the renewable energy sources is too low. To ensure that the system can supply electricity reliably at all times, particularly during the initial test phase, the existing diesel generator has been integrated into the power supply concept. If insufficient power was available or the fuel cell broke down, the diesel generator would ensure that the battery can be recharged.

The charge controller is responsible for the management of operation of the complete system. Depending on the prevailing state of charge of the batteries, the fuel cell and the diesel generator are automatically activated and then switched off again once a specified state of charge is reached. If the system should be not available due to maintenance work or a system breakdown, the system operator can still start the diesel generator manually and connect it directly to the domestic circuit, as indicated in the block circuit diagram. The information on the state of charge needed for operation management is determined by the battery management system described in section 4 and sent to the charge controller.

With the former power supply concept, where the inverter was dimensioned to be relatively small, the diesel generator had to be connected manually and the domestic circuit connected directly to the diesel generator whenever there was a high power demand, e. g.

when the dishwashers were operated. Now the complete energy demand can be met with the inverter and the battery. By this, optimal use of the regenerative energy sources, sun and wind, has been made feasible.