A water-first hybrid renewable energy system with gravity-based storage for remote settlements

This study proposes a water-first hybrid renewable energy system that integrates solar photovoltaic (PV) and wind generation with gravity-based water storage, treating stored water primarily as household infrastructure while enabling opportunistic electrical energy recovery. During periods of surplus renewable production, excess power drives a DC pump that lifts water from a groundwater source into an elevated storage tank; a three-way diverter valve then directs discharge either for direct household use or through a micro-hydropower turbine to bridge renewable shortfalls. A rule-based controller activates pumping only under renewable surplus and enables turbine-assisted discharge only during renewable deficits when sufficient tank volume is available and battery state of charge is constrained. A time-domain simulation (1 s timestep, 24 h horizon) was evaluated for a representative household case (PV peak 2 kW, mean wind 0.5 kW, electrical load ≈18 kWh/day, water demand 1.2 m³/day) using a 30 m³ tank at 60 m effective head and micro-hydropower generation in the 100–500 W range. In the representative case, hybrid operation recovers 2.83 kWh/day of electrical energy from 5.75 kWh/day of pumping input (recovery fraction ≈49%) and reduces unmet household electrical demand from 5.04 kWh/day to 2.21 kWh/day relative to a direct-use baseline. Daily battery discharge remains modest (~0.36 kWh/day). Monte Carlo analysis over 500 trials with randomized renewable generation, electrical load, and water-use timing (design fixed) demonstrates robust performance, with a mean recovered energy of 2.63 kWh/day (95% CI: 2.60–2.66). These results clarify realistic energy scales for micro-scale gravity storage and position the system as a co-designed water infrastructure with secondary, reliability-oriented electrical energy recovery rather than as a primary electrical storage solution. This work provides one of the first quantitative, stochastic evaluations of household-scale gravity storage co-designed with domestic water infrastructure, establishing realistic upper bounds on recoverable energy and reliability impacts.