Browsing by Subject "Streamflow rate"

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    Operational benefit of transforming cascade hydropower stations into pumped hydro energy storage systems
    (Elsevier, 2022-07) Toufani, Parinaz; Nadar, Emre; Kocaman, Ayse Selin
    This study evaluates the potential benefit of retrofitting existing conventional cascade hydropower stations (CCHSs) with reversible turbines so as to operate them as pumped hydro energy storage (PHES) systems. We examine the energy generation and storage problem for a CCHS with two connected reservoirs that can be transformed into a PHES system in a market setting where the electricity price can be negative. We formulate this problem as a stochastic dynamic program (SDP) under uncertainty in the streamflow rate and electricity price. We analytically derive an upper bound on the profit improvement that can be obtained from the PHES transformation. We conduct numerical experiments with data-calibrated time series models and observe that the PHES system provides a greater benefit under more limited streamflow conditions or more frequently observed negative prices.
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    ItemOpen Access
    Short-term assessment of pumped hydro energy storage configurations: Up, down, or closed?
    (Elsevier Ltd, 2022-11-09) Toufani, Parinaz; Nadar, Emre; Kocaman, Ayşe Selin
    We study the energy generation and storage problem for various types of two-reservoir pumped hydro energy storage facilities: open-loop facilities with the upper or lower reservoir fed by a natural inflow and closed-loop facilities. We formulate this problem as a stochastic dynamic program under uncertainty in the streamflow rate and electricity price. We include the streamflow rate and electricity price as exogenous state variables in our formulation. We compare the short-term total cash flows obtained by running different pumped hydro energy storage configurations in a market setting where the electricity price can be negative. We first derive theoretical bounds on the revenue gains and losses from switching from one configuration to another. We then conduct numerical experiments by employing time-series models to formulate the evolution of our exogenous state variables. We consider three distinct seasons with different streamflow rates, different negative price occurrence frequencies, and different reservoir capacities. Our results show that: (1) The open-loop facility with the upstream flow can yield cash flows that are up to four times as large as those of the closed-loop facility; (2) The cash flow from operating a large closed-loop facility can be achieved by operating an open-loop facility with 10 times smaller reservoirs; and (3) The open-loop facility with the downstream flow can be more advantageous than the open-loop facility with the upstream flow (with an improvement of more than 10% in the cash flow) if the negative electricity price occurs more than 30% of the time.