Using cascaded hydropower like a battery to firm variable wind generation

This paper presents a case study on using a cascaded hydropower system to firm wind generation. We have designed a real-time, sub-hourly optimization scheme for the coordinated control of a hydropower system. The receding horizon control scheme models the nonlinear hydropower production function and system hydraulics. We consider a coordinated hydro-wind system in which hydropower is used to firm wind generation at multiple time scales (multi-day, daily, intra-day, and hourly), balancing deviations from the average production schedule of the wind generation. We use hydro and wind power in the Pacific Northwest region of the United States as a test system, and we evaluate the balancing performance of the hydropower cascade as if it were a battery. The primary contribution of this paper is to introduce methods for estimating the power capacity, energy storage capacity, and efficiency of a hydropower battery, and to give example calculations for all three metrics.