The Water Tank as the Battery: Hydraulic Storage Sizing for a Solar Borehole Pump Against the Electrical-Battery Alternative

For a demand of 10.0 m³/day lifted against 40.0 m head, a solar borehole pump needs a computed 2.85 kWh of electricity per day, an array of 0.65 kWp at the annual-mean insolation of 5.5 peak sun hours, or 1.11 kWp at the worst month's 3.2 hours. Storing energy as elevated water beats storing it as electricity on the stated costs at every autonomy examined: three days of autonomy is a 30 m³ tank at 2,700 dollars against 8.5 kWh of battery at 5,129 dollars including a replacement reserve, a ratio of 1.90. **The design's failure season is : sized on the annual mean, the array delivers only 5.82 m³/day in the worst month, a shortfall of 4.18 m³/day, and no affordable tank bridges a season-long deficit — the array must be sized to the worst month, or the shortfall accepted and planned for.** SIMULATED, NOT MEASURED.