Energy, exergy and environmental impacts analyses of Pumped Hydro Storage (PHS) and Hydrogen (H2) energy storage processes

The objective of the present research is to compare the energy and exergy efficiency, together with the environmental effects of energy storage methods, taking into account the options with the highest potential for widespread implementation in the Brazilian power grid, which are PHS (Pumped Hydro Storage) and H2 (Hydrogen). For both storage technologies, energy pathways were envisioned, starting with electricity production from renewable sources (mostly intermittent ones), delivering more power than required during low-demand periods, and using the excess power, respectively, to pump water from the bottom to the top of hydroeletric powerplant lakes or to create gaseous H2 through water electrolysis. One and the other processes proceed with the energy recovery (re-electrification) stage, either utilizing traditional hydroelectricity technology or by combustion of H2 using latest gas turbines, when necessary, for ultimate consumption. The resources and emissions associated with both energetic pathways were investigated using the LCA (Life Cycle Assessment) approach, together with the latest established exergy-environmental methodologies and available data. It was considered that the identical quantity of stored power is re-electrified in the Pumped Hydro Storage situation. For an accurate comparison, it was also hypothesized that the same amount of energy a PHS could pump is electrically available for the Hydrogen storage case. With regard to energy and exergy efficiency, exergy costs of non-renewable, renewable, and total resources, in addition to the emissions cost of CO2 of both researched energy storage alternatives, numerical and comparative data were produced and presented. A sizable advantage for PHS is seen in the energy and exergy efficiency findings (more than 23 percentual points). The environmental exergy calculations for this scenario's findings show that PHS has benefits over H2 in that it uses only 84 % of the Hydrogen alternative's total resource exergy costs and emits 23 % less CO2.