Floating Photovoltaic Systems Coupled with Pumped Hydroplants under Day-Ahead Electricity Market Conditions: Parametric Analysis

Abstract

The intermittent nature of the solar resource together with the fluctuating energy demand of the day-ahead electricity market requires the use of efficient long-term energy storage systems. The pumped hydroelectric storage (PHS) power plant has demonstrated its technical and commercial viability as a large-scale energy storage technology. The objective of this paper is to analyse the parameters that influence the mode of operation in conjunction with a floating photovoltaic (FPV) power plant under day-ahead electricity market conditions. This work proposes the analysis of two parameters: the size of the FPV power plant and the total process efficiency of the PHS power plant. Five FPV plant sizes are analysed: 50% (S1), 100% (S2), 150% (S3), 350% (S4) and 450% (S5) of the PHS plant. The values of the total process efficiency parameter analysed are as follows: 0.77 for old PHS plants, and 0.85 for more modern plants. The number of daily operating hours of the PHS plant is 4 h. These 4 h of operation correspond to the highest prices on the electricity market. The framework of the study is the Iberian electricity market and the Alto Rabagão dam (Portugal). Different operating scenarios are considered to identify the optimal size of the FPV power plant. Based on the measured data on climatic conditions, an algorithm is designed to estimate the energy production for different sizes of FPV plants. If the total process efficiency is 0.85, the joint operation of both plants with FPV plant sizes S2 and S3 yields a slightly higher economic benefit than the independent mode of operation. If the total process efficiency is 0.77, there is always a higher economic benefit in the independent operation mode, irrespective of the size of the FPV plant. However, the uncertainty of the solar resource estimation can lead to a higher economic benefit in the joint operation mode. Increasing the number of operating hours of the PHS plant above 4 h per day decreases the economic benefit of the joint operation mode, regardless of the total process efficiency parameter and the size of the FPV plant. As the number of operating hours increases, the economic benefit decreases. The results obtained reveal that the coupling of floating photovoltaic systems with pumped hydroelectric storage power plants is a cost-effective and reliable alternative to provide sustainable energy supply security under electricity market conditions. In summary, the purpose of this work is to facilitate decision making on the mode of operation of both power plants under electricity market conditions. The case studies allow to find the optimal answer to the following practical questions: What size does the FPV power plant have to be in order for both plants to be better adapted to the electricity market? What is the appropriate mode of operation of both plants? What is the economic benefit of changing the turbine pump of the PHS power plant? Finally, how does the installation of the FPV power plant affect the water volume of the upper reservoir of the PHS plant? Knowledge of these questions will facilitate the design of FPV power plants and the joint operation of both plants.