Solar Pump Sizing Guide: How to Choose the Right HP for Your Needs

Solar pump sizing depends on three factors: total dynamic head (borewell depth + delivery height + pipe friction), daily water requirement (litres per day), and peak sun hours (4.5–5.5 in most of India). The formula: HP = (Flow rate × Total head) ÷ (75 × efficiency × 3600). For most Indian farms, 3 HP covers 4–6 acres, 5 HP covers 6–10 acres. Always get a dealer site survey — a ₹500 measurement prevents a ₹50,000 sizing mistake.

Total Dynamic Head is the total vertical distance the pump must push water, plus friction losses. It is the single most important sizing parameter.

TDH = Static water level + Drawdown + Delivery height + Friction loss

• Static water level: Distance from ground to the water surface in your borewell/well when the pump is off. Measure during summer (lowest water table) for worst-case sizing.
• Drawdown: How much the water level drops when the pump runs. Typically 5–30 feet depending on borewell yield.
• Delivery height: Vertical rise from ground level to the highest delivery point (overhead tank or field elevation).
• Friction loss: Resistance in pipes. Add 10–15% of total head for pipe friction, or calculate from pipe diameter and length tables.

Example: Static water level 120 ft + drawdown 20 ft + delivery height 15 ft + friction 15 ft = TDH = 170 feet (52 metres)

Critical: Measure static water level in the driest month (typically May–June). Sizing for monsoon water levels will leave you short during summer peak irrigation season.

Avoid these errors that lead to undersized or oversized systems:

• Measuring water level during monsoon: Water tables are highest during and after monsoon. Size for summer levels — they can be 30–80 feet lower.
• Ignoring drawdown: When the pump runs, the water level drops. A borewell with 100 ft static level may draw down to 130 ft during pumping. Missing this means the pump runs at higher head than planned.
• Oversizing for 'safety margin': A 5 HP pump on a 2-acre farm wastes ₹50,000–₹1,00,000. The pump runs below capacity, and oversized systems cost more under KUSUM too.
• Forgetting pipe friction: Long delivery pipes (100+ metres) add significant head. Use wider pipes (2–3 inch) to reduce friction loss.
• Not accounting for future needs: If you plan to expand acreage in 2–3 years, consider sizing up one HP increment — but only one, not more.

Size up (next HP) when:

• Your TDH is near the upper limit of the current HP range
• You plan to add acreage within 2–3 years
• Your borewell yield is uncertain (lower yield = longer pumping hours needed)
• You are in a region with fewer peak sun hours (Northeast, Kashmir)

Size down (save cost) when:

• You use drip irrigation (30–50% less water needed)
• Your borewell has excellent yield (high flow rate)
• You are in a high-irradiance region (Rajasthan, Gujarat — 5.5+ peak sun hours)
• You have water storage (farm pond) to buffer across days

Online calculators give estimates. For accurate sizing, you need a dealer to visit your site, measure your borewell parameters, and recommend the exact pump model and panel configuration. Solar Vipani connects you with verified dealers who provide free site surveys.

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