Design and analysis of a floating photovoltaic based energy system with underground energy storage options for remote communities

Abstract

Remote communities are highly dependent on transported food and fuel and require resilient energy systems. This study proposes a solar energy-based resilient system with energy storage options which is uniquely designed to generate electricity, heat, cooling, hydrogen and hence ammonia. Floating photovoltaic plant integrated with an anion exchange membrane electrolyser, pressure swing adsorption air separator with ammonia reactor and a heat pump. The underground energy storage options are pumped-hydro storage, high-grade heat storage, medium-grade heat storage and cold storage. The proposed system intends to exploit the infrastructure of abandoned mines with underground storage, as well as unutilized water surfaces with floating photovoltaic plant. Among the direct useful outputs of the system, agricultural activities and food production can be supported with a greenhouse heater, a food drying system and an ammonia fertilizer. The proposed system is then analyzed through the first and second laws of thermodynamics by using mass, energy, entropy and exergy balance equations. A time-dependent analysis with simulation is carried out to analyze each hour in terms of energy and exergy balances by considering commercially available component data as well as actual meteorological data. The proposed system with a 120 MWp floating PV plant and energy storage options, is determined to be sufficient to meet all of 51 GWhe/year non-thermal electrical, 23.8 GWhth/year heating, and 7.7 GWhth/year cooling loads for a community with 5320 people by exploiting unutilized natural bodies and abandoned mines. The pumped-hydro storage system has 67.24 % round trip energy efficiency, while the hydrogen-based energy storage option possesses 46.50 % round trip energy efficiency in a typical meteorological year under average conditions. The overall energy and exergy efficiencies of the overall system are found to be 15.9 % and 17.1 % on average.