Vulnerabilities and opportunities of solar-hydro hybridization under climate change: a case study in the Swiss Alps

Many countries are increasing the share of variable renewable energy sources (VRES) in their energy mix, as part of their climate change (CC) mitigation strategy. Coupling solar photovoltaics (PV) with reservoir-based hydropower (HP) is a promising solution to facilitate the introduction of higher amounts of intermittent PV power in the electrical grid, thanks to storage capacity provided by HP. However, these resources are themselves vulnerable to CC: climate-induced modifications of the hydrological cycle may affect HP operations, whereas the projected air temperature increase badly impacts the efficiency of PV converters. Few research works focused on CC impacts on combined HP-PV operation, hence possible consequences for solar-hydro hybrids are still unclear for many regions, such as the Alps.
We evaluate the impacts of CC on a hybrid HP-PV plant in the Swiss pre-Alpine region, consisting of an existing pumped-storage HP plant, complemented by a fictional FPV plant. Simulations are run at hourly temporal resolution according to a top-down approach, involving an impact modelling chain forced by climate variables from a multi-model ensemble of 39 EURO-CORDEX-based GCM-RCM runs covering three emission scenarios; coherent projections for the reservoir inflows are obtained through a hydrological model, developed using the semi-distributed PREVAH modelling system.
We compare a reference setup (with no PV to support HP) to two hybrid setups: in the first one solar energy, if available, contributes to fulfil the demand and excess PV power is possibly stored through pumping; the second setup is similar, but it also includes the possibility to increase the legally prescribed environmental flow using part of the water which is not used for HP generation thanks to PV power contribution.
Simulations indicate an increase of HP production during winter and a decrease in spring and summer, resulting from a climate-induced shift in runoff seasonality. Annual PV energy yield might slightly decrease, mainly as a consequence of air temperature increase; the seasonal pattern of PV power available, instead, is projected not to undergo remarkable changes, the highest potential being concentrated in spring and summer. There exists a complementarity between changes in runoff seasonality in the study area and the seasonal pattern for PV power available, hence a properly designed PV plant might be able to compensate for most of the projected reduction in spring and summer HP generation. We also found that the introduction of PV might have a positive impact on reservoir management and might allow to increase downstream environmental flow without significantly affecting the performance of the power plant.