PM-KUSUM solar pump sizing calculator

The wrong pump size sinks a PM-KUSUM job. Too small and the farmer cannot irrigate; too big and you bust the benchmark cost and your margin. This guide shows the simple sizing method, gives you a worksheet, and walks one full example — so your survey turns into a defensible HP slab every time.

What this solar pump sizing calculator does

This solar pump sizing calculator is a method and worksheet, not a live software tool — it shows how to turn a borewell's head and a farmer's water need into the right HP, kWp and daily discharge. You read off your two site numbers, follow the steps, and land on an eligible PM-KUSUM Component B pump slab.

Treat every figure on this page as an illustrative estimate. The eligible HP slabs, the array sizes and the water-output benchmarks are set by the MNRE technical specification and repeated in each state tender. They move when MNRE revises the spec, so confirm them against the current spec and the live tender before you commit a number to a bid.

The five inputs you need

Sizing a solar pump starts with five inputs you collect at the borewell, not at your desk. Get these right and the maths is easy.

1. Total dynamic head (metres)

The total dynamic head is the full lift the pump fights. Add the static water depth, the drawdown when the pump runs, the height to the delivery point above ground, and the friction loss in the pipe. This is the most important input — small errors here swing the HP slab.

2. Daily water need (litres per day)

The daily water need comes from the crop and the area. Multiply the irrigated area by the crop's daily water rate, or use the tank and channel demand the farmer describes. Size for the peak-demand month, not the average.

3. Peak sun-hours (hours per day)

Peak sun-hours is the number of effective full-sun hours the site gets in the design month. Much of India sees roughly four to six peak sun-hours, but it dips in monsoon and winter — use the worst month the crop must be watered in.

4. Pump set efficiency (percent)

Pump set efficiency is the combined motor-and-pump efficiency at the design point, read from the pump curve. A realistic figure is often in the 30–45% range for the whole system; never assume 100%.

5. The design month

The design month ties the other inputs together. It fixes the sun-hours and the peak water need at the same point in the year, so you do not mix a winter sun figure with a summer water demand.

The sizing method, step by step

The method has three calculations: hydraulic energy, then array size, then the HP slab. Each one feeds the next.

Step 1 — Hydraulic energy

First find the daily hydraulic energy — the real work of lifting the water. A handy form is: hydraulic energy in watt-hours ≈ 2.725 × head (m) × volume (kilolitres). The 2.725 factor folds in gravity and unit conversion. So lifting 50 kL through 40 m needs about 5,450 Wh of useful work.

Step 2 — Array size (kWp)

Next convert that work into a panel array. Divide the hydraulic energy by the sun-hours and the pump set efficiency: array (kWp) = hydraulic energy ÷ (sun-hours × efficiency × 1000). The efficiency term covers the losses between sunlight and lifted water, so a low efficiency means a bigger array.

Step 3 — Map to an eligible HP slab

Finally, round the array up to the nearest eligible PM-KUSUM slab — commonly 3, 5, 7.5 or 10 HP — and read the matching panel rating from the MNRE spec. Never quote a slab below the calculated need, and confirm the slab and its array against the live tender, because the spec sets the exact panel watts for each HP.

The input/output worksheet

Use this worksheet on every survey. The first four rows are inputs you collect; the last three are outputs you compute. Where you read each input is in the third column.

Worksheet structure: SuryaHub method. Formulas and HP slabs are illustrative estimates — verify against the current MNRE technical specification.

A worked example

Here is the method run end to end for a real-feeling site. The numbers are illustrative — your site will differ.

Site: a 2-hectare plot, water table at 30 m, drawdown of about 6 m, delivery 4 m above ground, and roughly 5 m of pipe-friction loss. The crop needs about 50,000 litres a day in the peak month. The design month gives 5 peak sun-hours, and the chosen pump set runs at about 35% efficiency.

• Total dynamic head = 30 + 6 + 4 + 5 = 45 m.
• Hydraulic energy = 2.725 × 45 × 50 (kL) ≈ 6,131 Wh/day.
• Array = 6,131 ÷ (5 × 0.35 × 1000) ≈ 3.5 kWp.
• HP slab = round up → a 5 HP set (≈4.8 kWp per the spec) gives headroom for off-design days.

Notice the calculated array (3.5 kWp) sits between the 3 HP and 5 HP slabs. Quoting 3 HP would leave no margin for a deeper drawdown or a cloudy week, so the safer, defensible choice is 5 HP. Always confirm the exact panel rating for that slab against the live tender.

HP, kWp and discharge reference table

This reference table maps each common HP slab to a typical panel rating, a head band and an illustrative daily discharge. It is a sanity check, not a substitute for the calculation.

Figures are illustrative estimates only. Discharge depends heavily on head — verify each slab's array and output against the current MNRE specification and live tender.

Common solar pump sizing mistakes

Most sizing errors come from the head and the demand month, not the maths. Watch these.

• Ignoring drawdown — the water level drops while the pump runs, so the real head is deeper than the resting level.
• Forgetting friction loss — long or narrow pipe adds head you must include, or discharge falls short.
• Using average sun-hours — size for the worst irrigation month, not the annual average.
• Assuming high efficiency — a whole pump set is far below 100%; use the real curve.
• Quoting below the calculated slab — never round down to save cost; the farmer ends up under-watered.

Matching the MNRE specification

Your sizing must match the MNRE technical specification, because the tender's panel rating, motor type and controller are fixed by it. The spec pairs each HP slab with a minimum panel wattage and a universal solar pump controller, and it sets the water-output benchmark a pump must hit on test.

If your calculation lands between two slabs, you choose the higher slab — but you cannot oversize past what the spec and benchmark cost allow. Read the MNRE technical specification guide and the AC vs DC pump comparison before you finalise, and confirm the current panel and controller numbers against the live tender.

How SuryaHub helps you size and quote faster

SuryaHub turns the survey into a quote without re-keying. Your field crew captures the head, water need and borewell data in the mobile field app, your sizing method runs on it, and the result flows into the quotation engine and the bid cost sheet — so the HP slab, array and price all line up. SuryaHub is pre-revenue; the only real pilots are Suryantra Energy and RGESPL, and every sizing figure here is a scheme-level estimate, not a guarantee.

Related guides

Frequently asked questions

Sources & references

The sizing slabs, panel ratings and water-output benchmarks come from primary government sources. Confirm the current figures with the MNRE specification and the live state tender before you quote.

• Ministry of New & Renewable Energy (MNRE) ↗

  PM-KUSUM scheme guidelines and the solar pump technical specification with water-output benchmarks.

• PM-KUSUM National Portal ↗

  Component B pump sizes, the State pump-cost data and the universal controller rules.

• SECI ↗

  Model tender documents and pump technical schedules used by many state nodal agencies.