Solar technology is spreading rapidly around the world. As a renewable energy source, PV-plants are currently on the top of the list of relevant research topics pertaining to the present energy transition (Energiewende). The installed photovoltaics are increasing annually in power capabilities plus, their costs are sinking. In Germany for example, the electricity generation costs of already established PV-plants are currently lower than other fossil or renewable energy sources and about the same as on-shore wind turbines. With the expansion of PV-plants, certain challenges develop however, making only certain locations suitable for their erection. Manufacturers and operators require plenty of information in order to better assess potential risks that could face the PV-plants. “As we at Fraunhofer ISE have been researching PV-technologies for many years, we understand naturally how important this topic is,” explains Christian Schill from the Fraunhofer Institute for Solar Energy Systems (ISE). He and his colleagues collaborated with researchers from the Chair of Remote Sensing and Landscape Information Systems of the University of Freiburg. In the pilot project “GloBe Solar: Global load classification system for solar technical materials” of the Sustainability Center Freiburg (LZN), they hoped to gather information on specific damaging mechanisms on a global scale in a geo-databank.
“Since the manufacturers of PV-modules and plants generally have projects in various locations around the world, our data pool had to be suitably large, in order to be of use for those actors,” explains Jan Herrmann from the University of Freiburg. The foundation of the team’s analyses was therefore amongst others, long-term satellite images and reanalysis data. These data sets are generally accessible in high quality, contain important information, and cover a wide geographical range. With these data, the GloBe Solar Team aimed to analyze the stresses facing PV-plants in the open and to model typical damages. Four damaging mechanisms were chosen: first UV-radiation, then temperature cycles, thirdly, corrosion or rusting of the four standard metals used for PV-components. Lastly, the dirtying or so-called “soiling” of the PV-modules was to be examined. The temperature cycle is particularly important in arid or dry areas of the world. During the day, temperatures can reach well beyond 40°C but plummet to the region of freezing during the night. The temperature change in the PV-modules can be even greater due to material characteristics. The components therefore need to be able to weather out these varying conditions. In terms of rust, the four metals most often used in PV-plants i.e. aluminum, copper, iron and zinc had to be examined for their location-dependent corrosion sensitivity. Corrosion is caused mainly due to high air humidity and great concentrations of sulfur dioxide and sea salt in the atmosphere. As a further damaging mechanism, soiling of PV-modules is important, particularly in the aforementioned arid zones. When sand or other dirt comes onto the surface of the module and remains there, significant loss in power can occur. UV-radiation highlights the fact that the damaging mechanisms can be seen from different perspectives: a mid-range UV-Index is not necessarily damaging to the modules but is damaging to human health. Consequently, the question of occupational safety comes into play. Ideally, the topic of damaging mechanisms should not be restricted to only technical aspects.
The extensive experience of the Fraunhofer ISE researchers at the various test locations was particularly helpful in this project. The test locations are alpine, arid, near to the coast, and in the temperate zone. They thereby represent a wide range of varying climatic factors and environments. The data collected in these areas can help boost the sometimes lacking resolution of images and models currently available. The small-scale effects can sometimes even modify certain established stresses. An example thereof is a test stand on the island of Gran Canaria. The island with its average nine sun hours per day in the summer seems to be ideal for solar panels but the spray of the surrounding water contributes greatly to the surrounding atmospheric sea salt concentration. The greater the distance between the PV-cells and the water, the less corrosion occurs; even a few 100 meter can make a difference. Despite the limitations in small-scale spatial resolution, the researchers gladly used the data provided by the European global observation program “Copernicus” or by NASA. These satellite images are particularly helpful as they are regularly updated and are open access.
The overarching goal of this collaborative work was the creation of a global map with information on the relevant stress factors within a geo databank. The access to these data would be limited and thereby not complete open access. “Three actors would be particularly interested in gaining access,” says Mr. Schill. “PV-module manufacturers, EPC companies, responsible for the planning and building of PV-plants, and reinsurance companies.” The module manufacturers need to obtain specific certifications for their products, among which is a certain resistance against hail strikes. “When a manufacturer wishes to build a PV-plant in an area in which hail storms regularly occur, then he will want to have that information beforehand,” clarifies Mr. Herrmann. Furthermore, the manufacturer can then decide based upon the received data, if it is ludicrous to build a plant in the chosen location. EPC companies require the information as well, in order to build and maintain the PV-plants according to regulations. Finally, the reinsurance companies are also interested to know what sort of costs might occur due to varying damaging mechanisms. All three actors thereby require a very good databank.
In the last weeks of the funding period, the researchers plan to classify the individual stress factors. All data are to be summarized into stress classes and then be formed into a general map. The researchers hope to form a future collaboration within the LZN. Particular research topics such as the effect of extreme weather events due to climate change on PV-materials need to be approached. Other important components of the location assessments such as small-scale soiling possibilities in large power stations, biodiversity or possible archaeological finds are other interesting research points. Furthermore, the researchers hope to continue their work on a larger scale, such as in an EU-funded project. The colleagues are on the lookout for possible future collaborations and are excited to continue their work.