Browsing by Subject "Pumped hydro energy storage"

Now showing 1 - 6 of 6

Open Access
A chance constrained approach to optimal sizing of renewable energy systems with pumped hydro energy storage
(2022-08) Kalkan, Nazlı
Burning fossil fuels is responsible for a large portion of the greenhouse gases released into the atmosphere. In addition to their negative impacts on the environment, fossil fuels are limited, which makes the integration of renewable energy sources into the grid inevitable. However, the intermittent nature of renewable energy sources makes it challenging to regulate energy output, resulting in low system flexibility. Adoption of an energy storage system, such as pumped hydro energy storage (PHES) and batteries, is necessary to fully utilize and integrate a larger proportion of variable renewable energy sources into the grid. On the other hand, in investment planning problems, satisfying the demand for certainty for even infrequently occurring events can lead to considerable cost increases. In this study, we propose a chance constrained two-stage stochastic program for designing a hybrid renewable energy system where the intermittent solar energy output is supported by a closed-loop PHES system. The aim of this study is to minimize the total investment cost while meeting the energy demand at a predetermined service level. For our computational study, we generate scenarios for solar radiation by using an Auto-Regressive Integrated Moving Average (ARIMA) based algorithm. In order to exactly solve our large scale problem, we utilize a Benders based branch and cut decomposition algorithm. We analize the efficiency of our proposed solution method by comparing the CPU times provided by the proposed algorithm and CPLEX. The findings indicate that the proposed algorithm solves the problem faster than CPLEX.
Open Access
Markov decision process formulations for management of pumped hydro energy storage systems
(2023-06) Toufani, Parinaz
Renewable energy sources have received much attention to mitigate the high dependence on fossil fuels and the resulting environmental impacts. Since the variability and intermittency of such renewable sources lower the reliability and security of energy systems, they should often be accompanied by efficient and flexible storage units. This dissertation focuses on pumped hydro energy storage (PHES) facilities, which are one of the most commonly used large-scale storage technologies. We study the energy generation and storage problem for PHES facilities with two connected reservoirs, where water is pumped from the lower reservoir to the upper reservoir to store energy during low-demand/low-electricity price periods, and released back to the lower reservoir to generate energy during high-demand/high-electricity price periods. The first part of this dissertation investigates the potential benefits of transforming conventional cascading hydropower stations into PHES facilities by replacing turbines with reversible ones. The second part compares the short-term cash flows obtained from different PHES configurations (cascading vs. non-cascading facilities, upstream vs. downstream inflows, and closed-loop facilities). We formulate both problems as Markov decision processes 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 analytically derive bounds on the profit improvement obtained from PHES transformation in the first part and bounds on the revenue differences obtained from different configurations in the second part. In the last part, we establish several structural properties of the optimal profit function for general two-reservoir PHES systems. We show the optimality of a state-dependent threshold policy for non-cascading PHES facilities when the electricity price is always positive. Leveraging our structural results, we construct a heuristic solution method for more general settings when the electricity price can also be negative. In this dissertation, we also conduct comprehensive numerical experiments with data-calibrated time series models to provide insights into the optimal operation of PHES facilities, considering distinct seasons with different streamflow rates, different negative electricity price occurrence frequencies, and different system parameters.
Open Access
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.
Embargo
Optimization of pumped hydro energy storage systems under uncertainty: A review
(Elsevier, 2023-12-20) Toufani, P.; Karakoyun, E. Ç.; Nadar, Emre; Fasso, O. B.; Kocaman, Ayşe Selin
This paper provides an overview of the research dealing with optimization of pumped hydro energy storage (PHES) systems under uncertainty. This overview can potentially stimulate the scientific community’s interest and facilitate future research on this topic. We review the literature from various perspectives, including the optimization problem type, objective function, physical characteristics of the PHES facility, paradigm used to capture uncertainty, and solution method adopted. We then identify several research gaps and future research directions for energy researchers. This review highlights the need for developing optimization models such as Markov decision processes that can represent uncertainties in renewable energy sources and electricity markets more accurately, constructing multi-objective models that consider not only economic but also environmental impacts, investigating underrepresented solar-PHES systems and PHES sizing problems, addressing nonlinear characteristics of PHES facilities, and optimizing bidding strategies in sequential or coordinated electricity markets.
Open 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.
Open Access
Value of pumped hydro storage in a hybrid energy generation and allocation system
(Elsevier, 2017) Kocaman, A. S.; Modi, V.
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 that 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 that shows significant seasonal and inter-annual variability and uncertainty. With several case studies from India, we examine the role of high hydropower potential in the Himalaya Mountains to support solar energy generation in the form of pumped hydro or conventional hydro system while meeting the demand at various scales. We show that pumped hydro storage can keep the diesel contribution to meet the demand less than 10%, whereas this number can go up to more than 50% for conventional systems where the streamflow potential is limited compared to the demand. We also 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 substitute for energy storage. 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. This means that, most of the current conventional hydropower stations could be converted to pumped hydropower stations without needing to modify the upper reservoir, leading to a significantly reduced diesel contribution and lower system unit cost.