Highest Energy Yields per Area for PV Systems on Flat Roofs

A very common installation design of PV systems on flat roofs is an east/west orientation of modules under low tilt angles even though the specific energy yield in kWh/kWp ratio is higher for other system layouts. With the steadily decreasing share of module costs in the overall cost structure of PV systems on flat roofs, this type of installation has become the standard design for flat roofs. It enables high ground cover ratios (GCRs), the use of costeffective substructures and high total energy yields per roof area. This paper addresses the question whether the energy yield per area can be further enhanced by alternative system designs. Two system variants are analysed in this study: One axis, horizontally tracked east/west aligned modules, so-called HSAT systems with atypically high area utilisation ratios of over 90% and the use of additional reflectors next to the collector field, which can also be controlled in part on a time-dependent basis. HSAT systems are normally installed at ground mounted installation with much lower GCRs to suppress self-shading of neighboured module rows. Simulations and measurements show that area-related energy yield increases of the HSAT systems of 5% compared to the reference system are possible if a very small tilt angle range of ±5° is used. The use of reflectors enables area-specific yield increases of 30% on the days measured. It is now proposed to use time-dependent controllable reflectors in order to be able to enhance the energy yields as well as to adjust the temporal generation profile to a specific energy demand or to time-varying electricity prices.