Solar Water Pumping That Stores Water, Not Electricity: A Battery-Free Design for Drinking Water and Small-Plot Irrigation

A battery-free solar water pumping design: a photovoltaic array drives a pump directly, water is stored in an elevated tank, and distribution is by gravity. Sized for 3,000 litres per day (drinking water for 20 people plus irrigation for a 400 square metre plot) through 40 metres of head at 4.2 peak sun hours in the worst month. SIMULATED, NOT MEASURED; nothing was built or hardware-tested. Lifting the water takes 817.5 Wh of electricity per day; a 250 W/m2 pump start threshold loses 3.3 hours and 10.0 percent of the worst-month day. An array of 312.4 Wp is required (340 Wp installed) and delivers 3.265 cubic metres per day in the worst month. A 6.67 cubic metre tank gives two days of autonomy at 0.687 to 0.895 bar. Over 20 years the system costs $5,756.54 in present value ($0.263 per cubic metre) against $6,806.93 ($0.311 per cubic metre) for a lithium battery-buffered equivalent, saving $1,050.39. The paper states where the elevated tank loses (flat land, no tower budget, very high head) and the fallback design in each case.