East to west - The optimal tilt angle and orientation of photovoltaic panels from an electricity system perspective

The integration of photovoltaic as a fluctuating renewable energy source has raised concerns about additional costs for the electricity system due to the variable nature of power output leading to more frequent and steeper ramping of conventional power plants and the need for backup capacity. One way to reduce those costs can be the variation of installation angles of PV panels at different locations to smoothen out the total production from PV in the whole system. To a certain extent steeper tilt angles can shift the production from summer months to winter months and the variation of the azimuth from east to west can partly shift production during the day increasing the production in morning or afternoon hours. However, for fixed mounted PV panels, there is one angle combination that maximizes the total output of the PV panel throughout the year and each deviation from this angle combination results in losses of total output. This paper evaluates the trade-off between annual energy losses and possible electricity generation cost reductions through adapting PV installation angles for the current electricity system and for potentially higher PV penetration levels in the future. A theoretical explanation why the annual maximum output of a PV system is not always the optimal solution from a system perspective is presented. To assess the effects of deviations from output maximizing angles at present, the wholesale market value of PV for various tilt angles and orientations in 23 regions of Austria and Germany using historic data on solar radiation and hourly electricity prices is calculated. For the analysis of future system states with potentially high shares of PV in the market, a linear optimization model representing the German and Austrian electricity wholesale market is applied. Furthermore the article provides additional insights on the market value of PV and CO2 emission reduction potential at high PV penetration levels from the model. Both, the historic analyses and the model results for Austria and Germany suggest that at present PV penetration levels, the angle combination that maximizes the output of a PV system also provides the highest spot market value and consequently minimal total system costs. For higher shares of PV in the system the model suggests deviations from those angle combinations to be optimal. For additional PV capacity of up to 40 GW (72 GW in total) a slight shift to easterly orientated PV modules is observed. For very high penetration levels of more than additional 100 GW optimal deviation angles deviate strongly from the output maximizing angles and the model shows optimal angles to be up to 20 steeper and orientations from east to west. However, the impact on total electricity generation costs is very low even for extremely high shares of PV in the system (<1% change in total costs). It is also found that despite of optimized installation angles, the average market value of electricity production from PV drops significantly from 41 (sic)/MW h at the base year 2012 to below 24 (sic)/MW h for additional 40 GW which has strong implications for the competitiveness of PV in the future. Marginal CO2 emission reductions however decline slower than the market values as PV cuts into production from coal power plants. (C) 2015 Elsevier Ltd. All rights reserved.