Aharon Roy/Department of Chemical Engineering/Ben-Gurion University, P. O. Box 653, Beer-Sheva 84105, Israel. <rovaaron@.baumail. bgu. ac. il>

Phone: +(972)8-646-1484; Fax: +(972)8-647-2916.

Introduction

The hybridization of PV with a diesel or other types of fuel-fired generators is one of the ways for creating new markets, accelerating PV deployment and driving the cost down. The hybridization is a practical way for enabling the PV hybrid plant to supply uniform power and operate for a long time throughout the year. However, in order to meet environmental goals some fundamental considerations should be applied. If a renewable hybrid system is not appropriately designed, environmental achievements could diminish. So much so, that in some cases the absolute quantity of the environmental benefits of the PV subsystem (prior to fuel hybridization) may undergo a significant decline or even annihilation by the fuel used in the PV-hybrid plant. There is an immediate, acute problem to solve, how and why it happens, and to help perfect technologies amenable to a global strategy of integrating renewable energy in sustainability policies.

Green energy and sustainability

The term "green power” has come to signify electricity generated from renewable energy sources like wind, solar, geothermal and biomass. The key point is that every kilo-Watt-hour electricity (kWhe) generated from a renewable energy source is a kWhe that need not be generated from fossil or nuclear sources [1]. Namely, every green kWhe output replaces a fossil-derived kWhe; and thus must decrease the use of fuel by the amount needed for producing one kWhe. The task of green power is to mitigate pollution and global greenhouse gases and consequent future hazards; also, to decelerate world fossil reserves depletion. Thus, green power contributes to world sustainability. Various technologies are being developed worldwide for enhancing PV systems effectiveness and marketability.

In case of road lighting, a stand alone PV system is basically constituted by PV modules, batteries, charge regulator, DC/AC converter and AC load constituted by arc lamps. The main specifications of a commercial system, reported in fig. 1, includes two PV modules (for each 80 Wp), two lead-acid batteries (for each 12 V — 110 Ah at 100 h discharge rate), a charge regulator (24 V — 8 A) and a lamp (26 W) equipped with its ballast. Normally the lamp illumination does not last for all the night, in the worst months, but only for 6-8 hours.

Peder Vejsig Pedersen,

Cenergia Energy Consultants
Sct. Jacobs Vej 4
2750 Ballerup
Denmark

Tel.: +45 4466 0099
Fax: +45 4466 0136
Mail.: cenergia@cenergia. dk
Web: www. cenergia. dk

Introduction

The city of Copenhagen has already agreed on a very ambitious CO2 reduction plan and concerning support to renewables around one Mio. EURO of funding have recently been allocated for implementation of building integrated PV, at the same time supporting the ambitious PV implementation plan for the city area Valby where it is aimed to have installed 300.000 m2 of PV-modules (30 MWp) for a city with

45.0 inhabitants by 2025

An important partner in these activities is the electricity, gas and district heating utility, Copenhagen Energy which is owned by the Municipality of Copenhagen and which has now launched a Solar Stock Exchange for the whole Copenhagen area where it is aimed yearly to have installed around 200-300 kWp of PV-modules based on a feed-in tariff of approximately 0.55 EURO/kWh which will be financed by green electricity sales to environmentally concerned citizens. Installation of the PV projects for the Solar Stock Exchange will be made by private companies based on a 20 year contract with Copenhagen Energy. In connection to this a Copenhagen PV-Coop has been established based on the idea to secure investments in shares of PV installations from private people along the same lines as the “Middelgrunden” windmill park which has been erected in The Copenhagen Habour.

Besides Copenhagen Energy also the Urban Renewal Copenhagen company and Cenergia is deeply involved in the here mentioned PV implementation plans.

Besides it has been agreed to establish a “Solar City Copenhagen” organisation which shall function as a stakeholder association promoting use of PV and energy efficient building in connection to foreseen urban development projects in Copenhagen not only focussing on Valby but on Copenhagen as a whole.

This initiative is also related to the European Solar Cities initiative, ESCI.

See www. eu-solarcities. org and http//sc. ises. org.

In total four rather different systems have been investigated, two systems with a pellet stove (system 1 and 2), one with a store integrated pellet burner (system 3) and one with a pellet boiler (system 4) (see also figure 2 and table 1).

System 1 is the simplest system using separate units to provide domestic hot water and space heating. A pellet stove transfers the heat to the building by convection and radiation. This requires a building with open interior design in order to allow a good heat distribution to the building. The power of the stove is automatically and continuously modulated according to the room temperature, but has a limiting minimal power. In the specified power operation range between 2 and 6 kW the stove reaches efficiencies between 83 and 89 % under stationary conditions (Persson, 2004). The domestic hot water is provided by a solar hot water system comprising a 280 liter store and 5m2 of solar collectors. The solar circuit is coupled to the storage by an immersed heat exchanger in the bottom of the store. The auxiliary heat is provided by a electrical heater in the top third of the store.

Figure 1. Simulated performance of the water mantled stove in system 2 with constant room temperature of 22°C, water return temperature of 55°C, mass flow of 0,111 kg/s and air factor of 6

(Pmin) and 4 (Pmax).

System 2 is rather similar to system 1 but the pellet stove delivers heat to the building in two ways: directly by convection and radiation as in system 1; and indirectly through an inbuilt heat exchanger to the water based radiator system. Approximately 80% of the produced heat can be transferred to the radiator system
when the stove is operated under stationary conditions with the maximum combustion power (figure 1). The stove is on/off controlled by the room temperature, operating by default with the maximum power.

System 3 is a solar combisystem with a store integrated pellet burner and a water based radiator system. All required heat for hot water and space heating is taken from the combistore, the water for space heating directly and the domestic hot water by two immersed heat exchangers placed in the bottom and the top of the combistore. The heat from the solar heating circuit is transferred by another immersed heat exchanger to the bottom of the store. The store integrated pellet burner delivers heat by a water to air heat exchanger consisting of horizontal pipes in the upper part of the store. The burner is on/off controlled by a sensor placed in the storage tank above the burner. The pellet burner has a maximum power of 25 kW, enough capacity even for single family houses with a rather high space heating demand. The burner can be adjusted for summer operation to half of the maximum combustion power. The collector area for system 3 and 4 is about 10 m2 which somewhat typical for Swedish solar combisystems.

System 4 is also a combisystem but uses an external pellet boiler as the main auxiliary heat source. The pellet boiler is coupled to the store by another immersed heat exchanger in the upper part of the store. The boiler is on/off controlled and has an internal water volume of 140 liter. The boiler contains an integrated heat exchangers for hot water preparation, but his was not used. No connections are available to couple the boiler to a solar circuit. Consequently only the space heating part of the boiler was used and connected to a combistore.

Lighting of roads, non-illuminated traffic and road signs at crossroads, along certain sections of highways is another, very important segment of the market of solar cells application in Yugoslavia.

For lighting of roads and road signs at crossroads, special systems of solar cells of an average power of 150 W will be used. For lighting of individual traffic signs, mini-systems of 20 W will be used. Exeptionally, on particularly dangereous spots (black points, sharp curves, rockslides, gusts of wind, large ascents, slippery road, etc.) even more powerful solar lights of 200 W and more may be installed for lighting of traffic signs of warning.

Among them, one of the more perspective ways for solar cells application is a parking service. In that sense, some steps are made recently. As a part of introducing the new car­parking system in the centre of the city (November 2003), Parking-service Utility of Belgrade installed 30 parkomats with solar cells (70 Wp each). [3] Fig.1.

The analysis has been based on an estimate that, during the first observed year (2006), about 160 kW photovoltaic power will be installed for this purpose. In next four years, number of installed solar systems for lighting of crossroads and traffic signs would grow at an annual rate of about 78, 24,19 and 11% respectively. (Table 2.)

Balance of growth rate relative to planned dynamics of irrigation solar pumps is explained by the fact that is the matter of a market segment of the public sector, which is low-dependent on supply-and-demand variations.

1. Supply of remote villages and weekend houses with energy

More than 50,000 households in Serbia and Montenegro are not connected to power grid. Calculating with an average power of solar system for household electrification of 600 W, potential of this market segment exceeds 30 MW! In this sense, our country is similar to Spain, and Spanish experience ought to be wery usefull. [4]

Similarly, about 55,000 weekend houses in our country are not connected to power grid. As electric-power requirements in the weekend houses are two times lower, we shall calculate with an average electric power of solar systems of 300 W for the one weekend house. Especially if their owners use some type of hybrid collectors, with simultaneous generation of electric power and low temperature heat energy. [5], [6]. Total potential of solar electrification of weekend houses is about 15 MW!

According to our forecast, during the first observed year, somewhat below 0.3% of total number of observed weekend and family houses will be electrified by solar systems, reaching power of about 140 kW. With optimal combination of PV area and storage capacity [7], for next four years, planned dynamics of growth of solar electrification of weekend and family houses is about 64, 28, 15 and 12% respectively (Table 3.).

Medium high and moderately lowering annual growth rates are the result of low starting basis, as well as of market stimulus. These are mainly the owners of private weekend houses that belong to the more-wealthy social layer and, willing to emulate, they want to afford themselves the luxury of energetic independence.

4.1 General information

Kollektivhuset is a building for disabled people, and located close to one of the busiest roads to the centre of Copenhagen. The building works along the principle of commune living, with mutual services in the lower floors. In this project, 12 kWp have been installed as part of a fagade renovation. The renovation of the open balconies to glazed balconies with integrated PV-systems, have dramatically improved the comfort and reduced the energy consumption of the building. This specific building has a panoramic view and is a good example of buildings from the early 70’s. Kollektivhuset is a valuable building, worth the effort of remodelling and improving. With its location the project can be expected to be one of the most visible and well-known PV projects of Copenhagen.

The main objective of the demonstration project Kollektivhuset is to demonstrate how BIPV can be utilised in a fagade renovation of a housing block. The principle is that PV-modules are fully integrated in the new glazed balconies of the building, allowing the possibility to individually expand the PV-modules to cover the whole parapet area of the fagade

Kollektivhuset, Hans Knudsens Plads Copenhagen, Denmark.

4.2 Innovative BIPV Architecture

The renovation of the building was initiated in order to extend the lifetime of the open concrete balconies and at the same time enlarge the balconies to allow access by wheel chairs. By glazing the balconies the heavy traffic noise problems from the main road can be reduced significantly.

The new concept developed within the project focuses on the integration of the climate envelope of the building and individually AC — modules. The new facade profile system allows for opening of the windows in the glazed balcony and in the parapet of the balcony, a flexible system for individually sliding back — plates behind the PV-modules are installed to provide flexible utilisation of the heat generated by the PV-modules.

Mostly disabled tenants are occupying the house, many in wheel chairs, and an ordinary installation of PV-panels in the parapet would have radiated a large fraction of heat directly to the legs of the tenants. The solar cell installations in effect work as radiators for the balconies. The moveable back-plates invented here, provide a flexible way of controlling this heat emission from the panels and even support the controlled airflow around the panel in order to remove the excess heat. Hereby a dynamical control of the heat emission is provided without the use of advanced ductwork for ventilation air, with cleaning and regular maintenance needs.

The front glass of the parapet is a normal glazed balcony glazing, ensuring water tightness and sound protection from the main road in front of the building. The PV modules are laminated directly to the back of the parapet glass. The flexible sliding back-plate moves in the same mounting profile as the glass. Hereby the users of each dwelling can decide whether or not utilise the solar heating, which builds up on the PV-panel. In the summer case, the users will be most interested in ventilating the heat from the PV-panels to the outside. This is done by sliding the moveable back-panel in a position just behind the PV-panel (top picture). Hereby the heat will be forced to leave the parapet-zone through the ventilation slits at the top and bottom of the PV-panel. In case the user wants to have the heat to enter the glazed balcony, the back plate is moved to the side

(middle picture). In this position, the PV-panel will radiate heat to the balcony. In the spring and fall, the heat from the solar cells can thus extend the possibilities to use the balcony.

PV-module with open regulator — spring / fall.

The system is prepared for the addition of another solar module in each balcony. The current economy only allowed for one module per balcony. In order to use the sun to maximum effect, the modules are put to the left on the balcony (as seen from the outside,
bottom picture), where they avoid shading from the structure.

The solar cell aesthetics are worked through thoroughly, especially when it comes to semi­transparency, effects of layers and so on. Mono-crystalline cells were chosen for the beauty of their deep-blue colour. The glass fapade on the balcony lets light through to the inside. A low opaque part (the hand-rail, approximately 70 cm) gives a sense of safety, while still giving the opportunity to look down from a sitting position (which is important for handicapped tenants). An interesting, deliberate effect is that the moving of the regulators will create a living, dynamic fapade. This brings the spark of life to a strict building.

4.3 Innovative electrical connections

In ordinary projects the electrical wiring of the systems would be based on string wiring, where each floor of the building would be connected to one string inverter. In order to provide more flexibility in the future expansion of the system, the approach is different in this project. The string wiring is established in vertical zones fully integrated in the facade construction collecting the power from each panel. All electrical connections are based on the Multicontact® PV-cables, which allow the connectors to be accessed directly at each balcony without any risk of electrical shocks. The sliding system of the panels described above is designed so that further panels can be inserted at each balcony and directly connected to the string wiring, allowing flexible expansion of the system.

Furthermore the installation is also very easy to carry out, since all manual installation work and expansion of the system can be done from the balcony and does not require expensive scaffolding of the building. Hereby the relative installation costs of the system will be relatively low compared to traditional installations of PV in high-rise buildings.

4.4 Energy and environmental performance

Through the carefully designed PV-system an

electrical yield of approximately 85 kWh/sqm is expected from the system. Due to the net- metering possibility in Denmark, the value of the power produced will be equal to the amount the tenants would have paid for the electricity
including environmental taxes and VAT. The installation costs were approximately 11.2 Euro per Wp. This amount must be seen in connection with the high degree of flexibility and large potential of replication.

4.5 Kollektivhuset in summary

Kollektivhuset is a very visible housing block located at the Hans Knudsen Square. More than 30.000 citizens of Copenhagen pass the building during rush hours. The facade of the building is likely to be one of the most visible and well-known demonstration projects with building integrated photovoltaic systems in Denmark. The individual wiring of the PV — panels, and combination of sliding back-panels and fixed front glazing is a unique concept in Europe. It is very likely that the system will mark a new standard for providing PV to Scandinavian housing block tradition, where the tenants can be expected to have individual priorities and possibilities to further expanding their solar system.

2. Conclusions

PV-NORD is the first step towards the widespread exploitation of building integrated photovoltaics in the Northern Dimension of the European Union. All the building owners, construction companies, PV manufacturers and designers involved in PV-NORD believe BIPV to be an important area of work for the future energy supply for society. It is clear from the early results, that the cost of the solar modules still is too high for BIPV to be a realistic alternative in the open market. It is also clear that the added values, inherent in BIPV, can be a feature better utilized for the increased use of BIPV, as shown by the Kollektivhuset building. The use of BIPV in high-profile buildings requires financial support. Limits, imposed by the authorities, on the design values of the energy use in the buildings are supportive incentives.

The programme was formally launched by Canara Bank in January 2003 and actual implementation started only in April 2003 when all the contract formalities had been completed. The Syndicate Bank formally launched the programme in February and actual implementation began in June 2003. To date four solar vendors have met the qualification criteria (Selco, Shell Solar, Tata BP and Kotak Urja), and therefore can now send their customers to either Canara or Syndicate bank branches for SHS financing.

A target was set of 5,000 systems financed over the first two years, and 18,000 over the 4-year programme.

Programme progress to date has been quite promising. From the period April-September 2003 (6 months of Canara Bank and about 4 months of Syndicate Bank’s operation), 1672 SHS loans were approved and disbursed. Furthermore, during an audit of bank branches in January 2004, it was apparent that loan disbursement has picked up, indicating increased sales. According to tentative estimates, by March 30, 2004, Syndicate Bank alone has financed about 2000 SHS. The banks had set ambitious targets for themselves and although they were not unhappy with the outcome so far, they are keen to take steps to improve performance further. Considering that this is still the initial period of loan programme stabilization, it is expected that the programme will surpass the two-year 5000 target ahead of schedule, possibly in the first year.

In terms of comparing these figures with a baseline, before the launch of the UNEP programme in Karnataka a total of only 1380 loans had been approved in the state for SHS over the previous 5 years. These were through Syndicate Bank (300 units), Malaprabha Grameen Bank (1,016 units), and Varada Grameen Bank (64 units).

Another heartening development has been the interest shown by some other banks, notably Vijaya Bank and Corporation Bank to implement an initiative along similar lines. Although it has not been possible to include them in the programme in order to avoid crowding for the limited programme funds, Vijaya Bank has launched the loan programme without any subsidy. Corporation Bank is also considering launching the loan programme without any subsidy. UNEP has assured them of the technical support, if required.

The partner banks are also considering launching the loan scheme in other states after some experience has been accumulated. Replication will be easy due to their reach across India.

2. Conclusions

RE has tremendous potential to provide energy and electricity to the people in developing countries who lack access to modern energy sources. In India, the high cost of RE compared to conventional energy is still a matter of concern but with the right packaging and approach, Solar Home Systems can fill the gap and provide access to modern energy to a large number of households, particularly those in rural areas who lack access to electricity. A properly designed programme, involving stakeholders during design as well as execution stage, can help develop markets for RE, as evident from early indications from UNEP’s SHS Financing Programme in India. Continuous monitoring and involvement of stakeholders at all stages of execution remains key to good programme progress. Eventually though, the success of the programme will be assessed in its ability to transition the market from a subsidised to commercial market. The programme design has considered this by gradually increasing the interest rate to market rates. The expanded market for vendors, coupled with confidence of the financing institution is expected to ensure that consumers benefit as the effective cost to them may remain same even after the programme has ended.

Acknowledgements: The UNEP programme on PV Solar Home System Financing in Southern India has been supported by funds from UN Foundation and Shell Foundation. The data on SHS sales and other items has been provided by partner banks in India; Canara and Syndicate Bank, and the vendors, viz., Selco Solar Light India, Shell Solar India, Tata BP Solar India and Kotak Urja, India. The programme support in India has been provided by Crestar Consultants, India. Authors would like to thank Andrew Smith for support with paper preparation.

Cooling problems are found in other areas than photovoltaics. Extensive research has been performed on the issue of cooling of electronic devices. Large cooling loads and strict temperature limitations are also found in the nuclear energy and gas turbine industries. These applications generally deal with larger areas and different geometries from the electronics industry. Research from these three fields should provide a broad base for finding better options for cooling of photovoltaics.

1.3 Passive systems

There is a wide variety of passive cooling options available. The simplest ones involve solids of high thermal conductivity, like aluminum or copper, and an array of fins or other extruded surface to suit the application. An good overview of these systems is give in [24]. More complex systems involve phase changes and various methods for natural circulation. The use of heat pipes, which is a very efficient way of passively transporting heat, is thoroughly described by Dunn and Reay [25]. The use of heat pipes is not feasible for high concentrations because heat pipe performance is limited by the working fluid saturation temperature and the point at which all liquid evaporates (burnout). It should be noted that passive cooling is just a way of transporting heat from where it is generated (in the PV cells) to where it can be dissipated (the ambient). Complex passive systems reduce the temperature difference between the cells and the ambient, or they can allow a greater distance between the cells and the dissipation area. However, if the area available for heat spreading is small and shading is an issue, no complex solutions will help avoid the use of active cooling. Heat dissipation is still limited by the contact point between the terminal heat sink and the ambient, where the convective heat transfer coefficient, and less so the radiative heat transfer (except at very high temperatures), are the limiting factors.

Prof. D. S. Strebkov, Dr. A. E. Irodionov.

All-Russian Research Institute for Electrification of Agriculture
VIESH, 1-st. Veshnyakovsky proezd, 2, Moscow, 109456, Russia
viesh@dol. ru

Basic principles of national, international and global solar power system designs and some results of computer simulation are considered. Rational siting of solar power generating units allows appreciably improving the diagram of the electric power generation, largely approaching to requirements of the consumer. The specified effect is reached by distribution of solar power stations in meridional direction so that the ending of insolation of a photoactive surface of one power station coincides with the beginning of insolation of panels of another, the nearest sunwise, station.

Principles of development and functioning of power engineering were designed in middle of 20-th century when a main problem was increase of energy generation with use of mineral fuel. The era of cheap energy on the basis of mineral fuel is coming to the end, and already today it is necessary to change approaches and directions of development of world power engineering to provide sustainable future development. It is obviously, that tendencies and prospects of development of energetics cannot be viewed in a separation from use of renewable clean energy sources what are the sun, wind, geothermal waters, biomass, energy of water-currents and series of others [1, 2, 3].

Despite its irregularity of operation as a result of known periodic and stochastic processes, solar photovoltaic generators on set of properties are most perspective for use in power industry. Thus in a number of countries solar power stations are used not only in an autonomous mode, but also directly connected to national electric power systems.

However, connection of high capacity solar stations to energy distribution networks may seriously complicate problems of power output and load matching and electromagnetic stability — which are the major tasks at designing and operation of reliable and effective electric power supply. Really, the power output of solar stations may vary dynamically and unpredictably for a control service of a distribution network. If the share of solar stations capacity in an electric power system is great, it will be difficult to compensate such fast power fluctuation and it may give rise to negative consequences both for generators of an electric power system, and for load.

The offered approach allows to not restrict the part of an installed power but to create a global electric power system in which solar stations will play the basic role.

Rational siting of solar power generating units allows appreciably improving the power output curve, largely approaching it to requirements of the consumer. The specified effect is reached by distribution of solar power stations in meridional direction so that the ending of insolation of a photoactive surface of one power station coincides with the beginning of insolation of panels of another, the nearest sunwise, station.

The distance between the adjacent solar stations in degrees of longitude should be no more than

15fhl + h) ,

where h1 and h2 — durations of daytime in latitudes in which stations are located, expressed in hours.

For a year-round and day-and-night operation it is durations of daytime in the winter solstice.

Changing an installed power and distance between stations in longitude, it is possible, in known limits, to correct a diurnal variations of an average system power output. If necessary, additional solar power substations may be included in the system for covering maximums of daily demand. The longitude, in which the substation should be located, is defined by time of passage of the corresponding maximum — at this time in desired longitude there should be midday. Siting of system solar power stations on either side of the equator will allow eliminating seasonal changes in an electricity generating — winter decrease in one hemisphere is compensated by summer growth of generation in the other.

Unique geographical features of Russia allow creating the solar power system with continuous and enough uniform electric power generating in a summer period. In the summer the sun does not sets on Russia, and the similar system generates energy day — and-night — the sun in succession illuminates photoactive surfaces.

Figure 1 shows the siting of two solar stations of the Russian national electric power system. One of stations is located on Chukot at 66°N and 173°W, second — in the Pskov region in the point with coordinates 57°30’N and 28°E. The probable need of the Russian Federation for the electric power by 2010 may will come up to 1100 Terawatt-hour (TWh). The system providing monthly electricity generation from March to August at a level 80 — 140 TWh may consist of two equal in power solar stations, 0.3 TW each. The diurnal variations of average power output of such electric power system are showed in Fig. 2. Computation is carried out for panels with polar axis tracking.

Solar panels of system generate electricity day-and-night during five months from April to August. During two more months — in March and September — interruptions are no more than 2 hours per day with a little bit greater irregularity of diurnal variations (Fig.2).

Fig. 2. Day variations of a mean power output (TW h) for national system consisting of two PV plants located in Chukot and Pskov region (0.3 TW each) with polar axis tracking panels.

It is possible to expand calendar duration of day-and-night work of the solar power system, as much as possible by increasing distance between its solar stations. For this purpose, for example, one of the solar stations may be located in the east of Russia, second in the West of Europe or in Africa. Figure 3 shows the solar power system with stations located in Russia (village Markovo, 64°40’N and 170°23’E) and in Mauritania in the point with coordinates 20°N and 10°W. The Afro-Eurasian solar power system, using panels with polar axis tracking, during seven months from March to September, day-and — night generates the electric power (Fig. 5). With station capacities in Mauritania is equal 1.0 TW and in Russia — 1.5 tW, the system annual power output is 6400 TWh.

For a year-round and day-and-night operation, longitudinal extent of one Russia or even whole continent is not enough — only the global solar power system is capable of such operation.

Figure 4 shows variant of stations siting of the global solar power system. Three solar stations evenly distributed in the meridional direction, the first power station is located in Bolson de Mapimi desert region (Mexico, 28°N and 104°W), second — in Libyan Desert (Libya, 25°N and 16°E), and the third — in Simpson Desert (Northern Territory of Australia, 25°N and 136°E). The electric power system is capable year-round and day-and-night to supply customers with "solar electricity".

The system consists of three each 2.5 TW-generating solar power stations with stationary panels, and its total annual power output is about 17800 TWh with high uniform of average diurnal variations (Fig. 6).

For placing of each such station with efficiency of photovoltaic cells of 20%, the territory with the area 44000 km2 (210 km x 210 km) is required. Naturally, there is no necessity to arrange compactly the panels of each station — the single requirement is proximity to the given meridian.

There is very high insolation level in Australia, but it is the remote continent, therefore instead of Australia the solar power station may be located in the same longitude in South Siberia, Russia. Because of short winter daytime, irregularity of a diurnal variations of

average power output of such system will be a little bit higher, and because of smaller insolation level, peak power of the Siberian solar station should be increased by 40%.

It is impossible to avoid influence of weather factors on a power output of solar stations. In stand-alone solar power supply for compensation of power fluctuation, standby generators and buffer energy storage units are successfully used. The modern buffer storages (electrochemical accumulators, capacitive stores, etc.) have excellent maneuverable performances — they automatically and very quickly pass from charge to discharge mode, but to create in a large electric power system the storage battery of sufficient capacity it is practically impossible.

The control system with space monitoring will allow using with global solar power system existing traditional power stations as standby generators. Depending on the type, traditional power stations have different maneuverable characteristics — for starting it is required from 2 — 3 minutes till several hours. More powerful power stations require, as a rule, the greater starting time.

Observation of a cloudy cover in vicinities of limited number extra-high-power solar plants by satellites will allow to predict a power output level and, if necessary, to specify the moment of starting for those or another standby generators. Such system will allow using traditional fuel or other renewable (biomass, hydro) power stations for compensation of solar array power output fluctuations.

Moreover, the global electric power system organized in a similar way is capable to operate generally without standby generators and buffer storages.

In the global solar power system some of a photoactive surfaces are always insolated, it generates the electricity continuously — depending on solar irradiance, the level of a power output varies only. Special interest represents time variations of a power output at worst-case conditions of insolation. Its minimal value in an annual cycle is the basis level of the diagram of the electricity generation, a warranted lower limit of a system power output.

).

With the specified probability all possible fluctuations of a system power output are higher than this level, and, as result, a part of reserve power stations, with equivalent installed capacity, may be completely put out from operation without damage to load.

Obviously, that the basis level of a power output depends not only on the lower level of insolation, but also on installed capacities of solar power stations. In principle, it is possible to create a global electric power system with stations of such peak power that even at worst-case conditions of solar irradiance the potential power output in each time interval will exceed needs of load. The most part of time, such system will generate excess energy, but exclusive maneuverable performances and ability of solar arrays to work uncertainly long in any modes — from idle up to maximum power — allow supporting a power output of PV system precisely at that level which is required and, that it is more important, without additional energy sources.

Practical realization of the project will demand solution on interdependent scientific, technical and economic problems. Some of them:

• Construction of solar global system with common control center;

• Interconnection of national electric power grids with the solar global power system;

• Providing Terrawatt capacity intercontinental flow of electric power [4].

Non-profit corporation Global Energy Network Institute (GENI), registered in USA is

actively engaged in similar projects, with an emphasis on linking local and remote renewable energy sources (wind, solar, hydro, geothermal, tidal and biomass). But build­up of the global solar power system will demand new approach to solution of these tasks. A serious problem may be intercontinental transfer of super-power energy fluxes on thousands kilometers, including underwater, with the minimal losses. Moreover, change of generating units siting and routes of power trunk may demand reorganization of national distribution grids.

As to photovoltaic generators, here efforts should be guided on solution of usual tasks — lowering of a specific cost, increase efficiency and resource of photovoltaic modules. Additionally, pace of production of unified photovoltaic modules should be enlarged on some orders.

It is obvious, that realization of the global photovoltaic project will demand long-term combination of efforts and mobilization of resources of all world community.

Conclusions

Solar power stations may be a basis of global electric power system — at rational siting of power stations, the system generate the electric power in year-round and day — and-night mode.

With use of a satellite monitoring a cloudy cover and a transparency of an atmosphere, the part of world system of traditional fuel power stations may be used for compensation of power output fluctuations as a result of the weather phenomena.

The global solar power system, with adequate peak power of solar stations, is capable to power supply all load demand under any conditions of insolation without use of buffer stores and standby generators.

1.

Long-term measurements are only available from few PVSs. Figures 5 and 6 illustrate the monthly yields for two typical cases.

The PVS Kirnitzschtal consists of two 20 kW PV power plants, equipped with a total of 756 Siemens M55 modules. In each plant, four inverters PVS-5000 are being used in master — slave operation. The generator plane is optimally oriented (37 degree slope, orientation 12 degrees SW). Because of the location of the PVS in the Kirnitzsch valley, shadows appear in the winter months in the morning and evening hours, which lead to a yield loss of approximately 10%. The results shown in figure 5 nonetheless clarify the reliability of the installed grid connected PV plants since 1994. Aside for the defects in inverters that occurred between May and August of 1997, there have been no problems. The highest yield was reached in the high-radiation year of 2003.

The PVS in Zehren, also brought online in 1994, was equipped with 90 modules of model MQ36 (DASA). The generator plane is well oriented (49 degree slope, orientation 15 degrees SE), a SOLWEX 4090 inverter has been used. The first five years of operation show a normal behaviour of monthly yields according to the corresponding radiation levels; annual yields range between 750 and 840 kWh/kW. After 1999 the yield amount clearly decreased, as a result of the breakdown of several modules. Switching out individual modules did not have far-ranging success, since other modules continued to break down.

Only after a comprehensive replacement of all modules (activated guarantee) in July of 2003 did the PVS once again attain normal yield levels as of August 2003.