Potentials and applications of solar energy in the decarbonized German energy system

This dissertation examines the techno-economic potential of rooftop and ground-mounted photovoltaics (PV) and their interaction with the energy system on the path to climate neutrality. By analyzing from the urban to the national level, it addresses questions of direct relevance for policy makers and actors in the energy sector. The key findings highlight the differences that limit the potential of rooftop and ground-mounted PV. The energy yield from rooftop PV is primarily limited by the available roof area and roof orientation. Solar irradiation and size-dependent economies of scale, which affect the specific investment costs, are the main factors for the levelized cost of electricity (LCOE) of rooftop PV. This leads to “hockey-stick” cost-potential curves. Once the best sites have been built on, the LCOE starts to rise significantly, while at the same time module price reductions mitigate this increase. Ground-mounted PV, on the other hand, is hardly subject to a technical upper limit, but is heavily dependent on the political and social will to make land available for energy generation. A major contribution of this work lies in the consideration of the system-wide consequences of extensive PV expansion. By combining various modeling results, it is shown that achieving the German climate targets requires both an appropriate expansion of ground-mounted PV through the allocation of sufficient land and ensuring that rooftop PV - since there is no competition with other land uses - can cover a larger share of the national electricity demand through stricter requirements for new buildings and renovations. At the same time, the strong national expansion of PV requires flexibility on the demand side, which is reflected, among other things, in storage and electrolysis accounting for up to 30 % of total system costs. These findings highlight the need for integrated policies that align green energy imports, land use policies and new build and refurbishment requirements.