Value of Pumped-Hydro Storage in a Hybrid Energy Generation and Allocation System

Transition from fossil fuels to renewable sources is inevitable. In this direction, variation and intermittency of renewables can be integrated into the grid by means of hybrid systems which operate as a combination of alternative resources, energy storage and long distance transmission lines. In this study, we propose a two-stage stochastic mixed-integer programming model for sizing an integrated hybrid energy system, in which intermittent solar generation in demand points is supported by pumped hydro storage (PHES) systems and diesel is used as an expensive back-up source. PHES systems work as a combination of pumped storage and conventional hydropower stations since there is also natural streamflow coming to the upper reservoirs which shows significant seasonal and interannual variability and uncertainty. We propose the first model which help investigate the solar and PHES integration considering the streamflow uncertainty for large scale systems. With this model, we also study the benefit of pumped hydro storage systems comparing the results with that of conventional hydropower stations. We examine the role of pumped hydro systems in both isolated and connected systems (through inter-regional transmission lines) and show that the benefit of pumped hydro is more significant in isolated systems and resource-sharing in connected systems can help almost as good as a pumped hydro system. In addition, with the help of the proposed model, we show that the upper reservoir size of a pumped hydro system could be lower than the reservoir size of a conventional hydropower system depending on the demand scale and streamflow availability; that is, the most of the current conventional hydropower stations could be converted to a pumped hydro system in the expense of a small lower reservoir leading to a significantly reduced diesel contribution and lower system unit cost.