Question 1

How much solar power do I need to run an off-grid water pump?

Accepted Answer

The solar power needed depends on your daily water demand, pumping depth (total dynamic head), and local sun hours. As a general rule, a typical off-grid water pump system requires 200W to 2000W of solar panels. For shallow wells under 50 feet pumping 100 gallons per day with 5 peak sun hours, approximately 300-400W of solar panels is sufficient. Deeper wells or higher volumes require proportionally more solar capacity.

Question 2

What size battery bank do I need for a solar water pump?

Accepted Answer

Battery size for a solar water pump depends on daily energy consumption and desired days of autonomy. Most off-grid water pump systems use 1-3 days of autonomy. Calculate by multiplying the pump's daily watt-hours by the number of autonomy days, then dividing by battery voltage and depth of discharge (typically 50% for lead-acid or 80% for lithium). A system pumping 500 Wh per day with 2 days autonomy on a 24V lithium system would need approximately 52Ah of battery capacity.

Question 3

How do I calculate total dynamic head for a water pump?

Accepted Answer

Total Dynamic Head (TDH) is calculated by adding the vertical lift (distance from water source to discharge point), friction losses in pipes, and any pressure requirements at the discharge point. Friction loss depends on pipe length, diameter, flow rate, and pipe material. For a quick estimate, add 10-20% to the vertical lift to account for friction in typical residential pipe sizes. TDH is measured in feet or meters and directly determines the pump horsepower needed.

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