Citizen solar initiatives as an opportunity for decentralized energy supply

Authors: Sacha Hammes, Oliver Mayer As of May 2019 A citizen solar power system is a photovoltaic (PV) system operated collectively by several private individuals. Colloquially, a citizen solar system is also referred to as a citizen power plant. The private individuals who decide to invest in a collective photovoltaic system and join together form a participation community. Each of these participants, often citizens of the same municipality, invest contributions that are used for the acquisition of the photovoltaic system as well as for subsequent maintenance work.

How does a citizen solar power plant work?

Motivation of this collective investment is primarily with the yield thrown off the capital contribution made to exceed. The feed-in of the generated electricity, in this case by the photovoltaic plant, is legally guaranteed according to §21 of the law for the priority of renewable energies, in short EEG, with a fixed remuneration rate over 20 years. As of 2017, the compensation rate is limited to those plants that generate a nominal output of less than 100kW. Larger plants must market the generated electricity themselves. In addition to the fact of making a long-term and well-secured capital investment, it is often the desire and motivation of the participants to promote the use of renewable energy. Because the investors of a citizen solar system are usually located in the same municipality, it is highly likely that the jointly acquired photovoltaic system will be installed on the roof of a property operated by the municipality. Nearly all participating investors participated in a solar project installed in their own municipality. The maximum rated power P_Nominal of citizen solar power plants ranges from several kilowatts (kW) to several megawatts (MW). <7P>

How is the power of a photovoltaic system measured?

A colloquial, but non-standard term for the electrical power of a photovoltaic system is "watt peak", or "kilowatt peak". The peak power, translated peak power, corresponds to the standard-compliant nominal power at defined ambient parameters. For photovoltaic systems, the generated electrical nominal power is specified under standardized test conditions. In photovoltaics, the standardized test conditions are used to be able to compare and evaluate solar modules independently. For this reason, globally uniform operating conditions have been defined for this condition. The power specifications are based on an irradiance E of 1,000, on a module temperature T_PV of 25° C and on a sunlight spectrum at astronomical air mass AM of 1.5. This is specified in the standard DIN EN 60904-3. Per kW of output power is calculated under standard test condition with an average module area of 6 to 10 m² . Depending on the available roof area and the demand of the population, different system sizes and solution concepts result. In order to describe from now on in this article the plant size on the basis of the nominal power under standard test conditions, the non-standard but nevertheless much more common designation kWp is used.

Example of a citizen solar plant

As a typical case study of an average plant size and design of a citizen solar plant, the plant Geretsried I of the Solarkraftwerke München-Land GmbH in the town of the same name can be mentioned. The plant in Geretsried generates an output of 60.76 kWp, i.e. 60.76 kW nominal output under standard test conditions. The nationwide performance average of community solar investments is around 55 kWp . The photovoltaic system in Geretsried was installed on the roof of a commercial facility. 24 citizens of the small town in Upper Bavaria have taken over the investment of this plant. With 24 actors, the plant Geretsried I corresponds exactly to the arithmetic mean in comparison with other citizen solar initiatives in Germany. According to a data collection of the RWTH Aachen, this was about 24 persons per solar initiative . The total nominal power of these plants amounts to about 850 kWp . As a comparison, the citizen solar park in Wachenbrunn with P_Nenn=8.7MWp is one of the largest citizen solar plants in Germany. This solar park is operated by BürgerEnergie Thüringen e.V. and managed by EnergieGenossenschaft Inn-Salzach eG (EGIS). Due to the size of the plant with 34,000 PV modules, i.e. a module area of around 70,000 m², this power plant is classified as a ground-mounted plant. In contrast to the plant in Geretsried, the allocation of shares took place nationwide. Around 5,000 investors from all over Germany participated in the project in Wachenbrunn. Citizen solar initiatives as an opportunity for decentralized energy supplyWhat can be learned from this example? If a very suitable and at the same time very large area exists, like the roof area of the Oberland-Werkstätten GmbH in Geretsried, and if there are enough interested investors in the local circle, nothing stands in the way of the realization of the community plant. If, on the other hand, there are not enough investors in the local area with a suitable area, as is the case in Wachenbrunn, the option of a nationwide investment model can come into play. Potential investors who cannot realize their own projects locally, for economic reasons, or for reasons of physical geography and meteorology, can still do their part for the energy turnaround by participating in projects run by other communities.

How sensible are solar plants in Germany?

A look at Germany from a climatology perspective confirms the assumption that not all regions offer the same economic opportunities for solar plant operators. For example, the northern German lowlands and the German low mountain range threshold are less suitable locations than the south of the Federal Republic. This is illustrated in the following graph (Fig. 1). The graphic is based on the measurement data of the German Weather Service of the year 2013.

There are thus demonstrable yield differences depending on the region. It should be noted that a meaningful comparison cannot be made solely on the basis of the number of hours of sunshine, as other factors play a decisive role in this relationship. In summer, for example, the sun's radiation is about five times greater than in winter. Furthermore, the solar radiation depends on the degree of cloud cover, the length of the day and the altitude above sea level. The intensity of the sun, or the resulting nominal power of the photovoltaic system, is also influenced by the position of the sun, which is determined by the different seasons and by the geographical latitude. The proportionality between sunshine hours and generated power can therefore only be reliably described by taking into account the external parameters of the system. In addition, disturbing influences such as shading must be taken into account, as well as the influence of risk factors that vary from region to region, such as that of hail. Hail can lead to module damage and module destruction, which in turn means a reduction in yield for the system operator.

In this context, the advantage of citizen solar initiatives based on nationwide investment models can be highlighted once again in conclusion, that solar projects can be implemented in climatologically more suitable regions with an influx of capital from regions that are less suitable for the construction of photovoltaic systems. For example, investors from Saxony and North Rhine-Westphalia could be attracted to implement solar power plants in Baden-Württemberg and Bavaria. However, the supra-regional investment model for PV plants is not limited to the national level. Projects of Gigawatt Global®, Sustainable Energy Services International® or of Kronos Solar® confirm the previously described advantage on an international level. In countries such as Rwanda, Burundi, Tunisia, Algeria, Mexico and Afghanistan, which all offer good conditions for high PV yields from a climatological point of view, the aforementioned Western solar initiatives already rely on the international investment model. The disadvantage is that many of those countries that are particularly well suited for the construction of photovoltaic plants are considered politically unstable. Volatile and crisis-prone domestic politics have a direct impact on the use and operation of current plants, as well as on the decision to build new projects. For example, numerous Desertec Foundation® solar power plant projects failed due to the Arab Spring. Numerous private investors rejected the project because of the tense situations at the time.

How can citizen solar plants be financed?

But because of the comparative and demonstrably high yield advantages, supraregional investment models should be adhered to, with PV sites in climatologically suitable regions. Be it on a national level, such as the example of the citizen solar plant in Wachenbrunn, or on an international level using the example of the Gigawatt Global® projects. The goal and task of the financiers and initiators should not only be the marketing and use of electricity, but also the support and promotion of those countries that provide the location and are considered domestically unstable. Only effective political and economic support for the target regions can ensure continued and secure operation of the photovoltaic systems. In collective investment projects, such as that of a citizen solar system, the administrative burden increases with the number of investors. A higher administrative effort leads to higher administrative costs, which in turn means a lower return for the participants. Investment models in which everyone can choose for themselves the amount with which they wish to participate are also associated with an increased administrative burden. Such investment models are often used for larger plants. The prospective customers can buy themselves thereby often into certain classes, for example 200 €, 500 €, 1,000 € or 2,000 €. Furthermore, there is the model of cooperative shares to acquire, for example, 50 € per cooperative share, as it offers the Energiegewinner eG . The higher the investment class or the more cooperative shares acquired, the greater the yield. Consequently, the second aspect of the above case studies can be defined as follows: The more confusing the organizational structure, the greater the administrative costs and, consequently, the smaller the return on capital. The advantage associated with such investment models is that the general public is enabled to actively participate in the energy transition. Above all, financially weaker persons are offered the option of participation through such models. In citizen solar projects, an attempt is made to avoid social inequality by setting the minimum participation amount relatively low . In this context, it may be possible to create a socially mixed clientele of participants. This would clearly serve the fight against social class differences and strengthen the "we-feeling" in the communities. From the advantages and disadvantages mentioned above, the personal recommendation therefore follows that a balance should be found between the maximum number of participants and the administrative burden. Since the administrative costs are comparatively small with larger plants, a direct dependence results between the plant size and the maximum suitable investor number with an acceptable administrative expenditure. Not only in completely Germany, but world-wide among other things with the initiative of the citizen solar plant, a process is set in motion, which rejects the past concept of few large central power stations. With citizen solar plants, private photovoltaic plants, biogas plants and communal wind power plants, many small power plants are emerging everywhere, which take over the task of power generation from the large centrally located coal and nuclear power plants. This development trend in power generation is supported by numerous literature sources.

Example of decentralization in energy policy

As an example of the proven success of decentralization in energy policy, the offshore wind farms in the North Sea should be listed. As of June 30, 2016, a total of around 800 offshore wind turbines with a total rated output of just under 3 GW were in operation in Germany's northeastern high seas. This is almost equivalent to the nominal output generated by the nuclear power plants on the North Sea that have already been shut down. The nuclear power plants at Unterweser (1.41 GW), Stade (0.67 GW) and Brunsbüttel (0.8 GW) , which are part of the central energy policy, have been replaced by a large number of small-scale renewable power plants in the North Sea. Part of the cost of these wind farms comes from money from citizens' initiatives. A comparison with photovoltaics can be made between the nuclear reactors operating in Bavaria until 2014 and the installed nominal PV capacity in the same year. 484,000 individual photovoltaic systems ranging in size from a few kWp to several MWp generated 10,310 million kWh of electrical energy in Bavaria in 2014. An installed capacity of 10.8 GWp of solar power plants compares to only 5.5 GW of nominal capacity of four nuclear power plants currently still operating until 2022. Here again, the mass distribution becomes unmistakable. A few central power plant units are being replaced by a large number of smaller plants.

Citizen solar power plants: a conclusion

It can be stated that the process of decentralized energy management is already underway far away from broad public interest. The restructuring, away from a few large centralized power plants to a plethora of diverse small power plants has thus successfully started. It therefore only remains to analyze to what degree decentralization can and should progress in the future. The adopted energy transition also requires a radical paradigm shift in terms of energy accounting and control procedures, grid infrastructure, storage and environmental impact. In conclusion, it can be stated that citizen solar plants, due to their diverse design options of investment models, offer the necessary flexibility to address a diverse and broad clientele. The high flexibility of implementation options also allows small power plants, such as the citizen solar plant, to essentially drive the meaningful process of decentralization and the energy transition.

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