Integrating wind and photovoltaic power with dual hydro-reservoir systems

Abstract

Hydropower facilities can be dispatched to offset wind and photovoltaic energy variability in power systems. But the abrupt water discharges needed to cope with wind and photovoltaic intermittency causes harmful riverine disruptions with significant environmental costs. In systems with hydropower cascade consisting of two or more reservoirs, the river flow disruptions created by the upstream hydro-reservoir can be mitigated by dispatching the downstream hydro-reservoir in a restorative way. The hypothesis of this paper is that it is possible to operate cascaded hydropower reservoirs to integrate wind and photovoltaic power in a way that reduces total power output variability and downstream water flow disruptions. The upstream hydro-reservoir is operated in such a way that it complements the variable power (from photovoltaic and wind), while the downstream hydro-reservoir runs mitigating runoff disruption (i.e., re-regulating). An optimization model finds the hydro-wind-photovoltaic power’s operational strategy that minimizes the variability in total power output and the river flow’s alteration. The results of a case study of the world largest hydro-junction, Three Gorges Dam - Gezhouba Dam, illustrate that 1) the proposed strategy is feasible; 2) the water head and reservoir storage capacity are the two key features for determining the hydropower facility’s re-regulation capacity; 3) the upstream hydro-reservoir alone can integrate up to 1.7 GW of wind and 1.7 GW of photovoltaic -i.e., about 15% of the upstream hydro-reservoir's 22.5 GW of capacity- without altering the river's flow, and the downstream hydro-reservoir can integrate an additional 2.8 GW from wind and 2.8 GW of photovoltaic, hence the dual hydro-reservoir can integrate 9 GW of wind plus photovoltaic -i.e., 35% of the upstream + downstream hydro-reservoir capacity; 4) increasing the upstream hydro-reservoir's water-head and/or downstream hydro-reservoir's storage capacity would increase the size of wind and photovoltaic they can integrate. The strategy proposed is helpful to power system managers planning and operating systems with high penetration of variable renewable energy.