- This guide is for EPCs and developers, not homeowners — it assumes site work.
- Size against three inputs: total dynamic head, daily water need, and safe borewell yield.
- Total dynamic head = static water level + drawdown + delivery height + friction loss.
- Pick the smallest HP that hits the duty point on the pump curve — don't oversize.
- Plan roughly 0.9-1.2 kWp of panel per HP (verify against the MNRE spec).
- HP slabs (3 / 5 / 7.5 / 10 HP) and caps vary by state — verify with your SNA.
Good solar pump sizing for PM-KUSUM comes down to matching HP to the real head and discharge a site needs. Get it right and the pump lifts enough water on a normal sunny day without ever running the borewell dry. Get it wrong and you either starve the farmer of water or burn out a pump that cost lakhs. This guide is for EPCs and developers who survey sites and build proposals — not for homeowners.
What does sizing mean for a solar pump?
Sizing a solar pump means choosing the pump and panel that deliver the water a farm needs against the lift the site demands. You are picking three things together: the pump HP, the panel kWp, and the pump curve that ties flow to head. The goal is the smallest set that meets the need on a typical clear day.
A solar pump is different from a grid pump in one big way. It runs on a panel, so its power swings with the sun. There is no fixed motor speed all day. That means you size against a sunny-day output and accept that flow drops in cloud and at the start and end of the day. You plan for average daily volume, not peak instant flow.
What are the three inputs you must measure?
Every sizing job rests on three measured inputs: the total dynamic head, the daily water requirement, and the borewell depth and safe yield. Skip any one of these and the sizing is a guess.
1. Total dynamic head (TDH)
Total dynamic head is the full vertical lift the pump fights against, in metres. It is not just how deep the water sits. You add four parts:
- Static water level — the depth to water before pumping starts.
- Drawdown — how much the water level drops once the pump runs.
- Delivery head — the height you must push water above ground to the tank or field.
- Friction losses — the pressure lost in the rising pipe and fittings.
Add all four and you get the head the pump must actually work against. A borewell with a 40 m static level can easily have a 55-60 m total dynamic head once you count drawdown, delivery and friction. Always size on the total, never on the static level.
2. Daily water requirement
The daily water requirement is how many litres the farm needs in a day, set by crop, soil and acreage. Work it out with the farmer for the peak-demand season, not the easy months. The pump must clear that volume during the usable sun hours, so divide the daily litres by realistic sunny hours to get the flow rate you need.
3. Borewell depth and safe yield
Borewell yield is how much water the source can give without running dry. A pump that asks for more than the well can supply will suck air, lose prime and overheat. Check the bore depth, the static level, the drawdown under a test pump, and the recovery rate. The safe yield is a hard ceiling on how much flow you can size for.
How does HP relate to head and discharge?
HP, head and discharge trade off against each other on a single pump. For a given HP, more head means less discharge, and less head means more discharge. You cannot get high flow and high lift from a small motor at the same time. Higher HP buys you more of both, up to the limit of the pump design.
Think of HP as the power budget. A 5 HP pump might give plenty of flow at 30 m head but only a trickle at 70 m. The same head that a 5 HP pump struggles with may be easy for a 7.5 HP pump. That is why you never pick HP from a table alone — you pick it from where your head and flow need lands on the actual pump curve.
How do you read a pump duty point on the head-discharge curve?
The duty point is the single spot on the head-discharge curve where your required head meets your required flow. Every pump model has a curve that plots head on one axis and discharge on the other. The line slopes down: as head rises, flow falls. You find your duty point and check the pump can sit there.
To read it, draw a horizontal line at your total dynamic head and a vertical line at your needed flow. Where they cross is the duty point. If that point sits on or just below the pump's curve, the pump fits. If it lands above the curve, the pump is too weak for the job and you step up a size or change the model.
For a solar pump, the maker usually gives the curve at a rated panel power. Because solar output swings, the real flow rides up and down the curve through the day. You want the duty point to sit comfortably inside the pump's good range at full sun, with margin for the head to creep up as the water table falls.
Submersible or surface pump — which do you pick?
Pick the pump type from the water source and the suction lift. A surface pump sits on the ground and pulls water up, so it suits shallow open wells, ponds and tanks where the suction lift stays under about 10 metres. Past that depth, a surface pump struggles to lift water at all because suction has a hard physical limit.
A submersible pump sits down inside the borewell, under the water. It pushes water up instead of sucking it, so it handles deep borewells that a surface pump can never reach. Most PM-KUSUM jobs use submersible pumps because the source is a borewell tens of metres deep. Use a surface pump only when the source is genuinely shallow and open.
AC or DC pump — what's the tradeoff?
The AC-versus-DC choice mainly trades cost against simplicity. A DC pump wires almost straight to the panel and is simple, but DC motors and spares can be harder to source locally. An AC pump needs a variable frequency drive to turn panel DC into AC, which adds a part, but AC motors are common and easy to service in the field.
For larger HP and deeper bores, AC submersible pumps with a drive are the usual pick on PM-KUSUM sites. We cover the full comparison, including service and warranty notes, in our AC vs DC solar pump guide. Read that before you lock a motor type into a proposal.
How do PM-KUSUM HP slabs work?
PM-KUSUM groups solar pumps into HP slabs, and Component B commonly supports 3, 5, 7.5 and 10 HP pumps, with higher capacities allowed in some states. Each slab has its own benchmark cost and subsidy share, so the slab you propose drives both the hardware and the farmer's out-of-pocket amount.
VERIFY-FLAG: Eligible HP slabs and any HP caps under current PM-KUSUM (e.g. up to 7.5 HP standard, higher allowed in some states) — verify against current MNRE guidelines and your state SNA. These figures are planning estimates only.
The slabs are not the same in every state. A state nodal agency may cap the subsidised HP, set its own benchmark cost, or open a higher slab for special cases. Never quote a slab from memory. Check the live tender and the latest MNRE order for the state you are working in before you size to a slab.
How do you match panel kWp to pump HP?
Match panel kWp to pump HP with a rough planning rule of about 0.9 to 1.2 kWp per HP, then confirm it against the pump spec. So a 5 HP pump points to roughly 4.5 to 6 kWp of panel, and a 7.5 HP pump to roughly 7 to 9 kWp. This is a starting estimate, not a final number.
VERIFY-FLAG: The ~0.9-1.2 kWp per HP rule is a rough planning figure only. Verify the exact panel sizing against the current MNRE technical specification for the specific pump and controller you select.
The real panel size depends on the motor type, the drive, the head, and the MNRE spec for that pump. A deeper, higher-head job often wants the upper end of the range so the pump still moves water in weaker sun. Always cross-check the panel number against the MNRE technical specification for the model before you finalise.
Sizing reference table: HP, head and discharge
The table below is a planning reference, not a sizing decision. It shows roughly which head and discharge each common HP slab tends to serve. Use it to sanity-check a proposal, then confirm the real numbers on the actual pump curve.
Illustrative engineering guide only — actual duty point depends on the specific pump curve; verify HP eligibility against current MNRE specs and your state SNA.
What are the common solar pump sizing mistakes?
Most sizing failures come from a handful of repeat mistakes. Avoid these and most jobs run clean.
- Oversizing — a bigger HP pump can overdraw the bore, run dry and burn out, and it wastes the farmer's money.
- Ignoring drawdown — sizing on the static level alone understates the real head, so the pump moves less water than promised.
- Ignoring the seasonal water-table drop — the level that is fine in monsoon can fall metres by summer, raising the head when water is needed most.
- Picking HP from a table, not the curve — a slab table is a guide; the duty point on the real pump curve is the decision.
- Skipping the source survey — sizing without a measured bore depth, yield and drawdown is a guess that the field will punish.
Oversizing is the costliest of all. A pump that asks for more water than the bore can give will cycle dry, overheat and fail early. The farmer then loses both the water and the warranty. The safe habit is to size to the smallest HP that meets a true duty point, with a sensible margin for the falling water table — and no more.
How do you survey a borewell before sizing?
A proper water-source survey measures the inputs you need before you touch a pump table. Send a field team to the site and record the bore depth, the static water level, the drawdown under a test pump, the recovery rate, and the delivery height to the tank or field. Note the pipe size and length too, since that sets friction loss.
Capture the season as well. Ask the farmer how far the level falls by summer and whether the bore has ever run dry. A survey done in monsoon can flatter the yield. The borewell water-source survey guide walks through the full checklist. With clean survey data, the sizing is almost mechanical; without it, every later step is a gamble.
How SuryaHub helps you survey and size right
Sizing only works when the field data is good and the project stays organised. SuryaHub gives field teams a mobile site-survey module to capture borewell depth, water level, drawdown and discharge on the spot, then runs the whole job through project management from survey to commissioning — so the numbers behind a proposal are real and nothing slips. SuryaHub does not replace the pump curve or the MNRE spec; it makes sure your team works from measured data, not guesses. SuryaHub is pre-revenue; real pilots are Suryantra Energy and RGESPL, and figures here are planning estimates, not guarantees.
Capture survey data in the field
See how SuryaHub records borewell data and runs each pump job to commissioning.
Related guides
Frequently asked questions
How do I size a solar pump for PM-KUSUM?+
To size a PM-KUSUM solar pump, first measure three things: the total dynamic head in metres, the daily water you need in litres, and what the borewell can safely yield. Match those numbers to a pump curve, then pick the smallest HP slab that meets the duty point without overdrawing the well.
What is total dynamic head for a solar pump?+
Total dynamic head is the full lift a solar pump must work against. Total dynamic head adds the static water level, the drawdown when pumping, the delivery height above ground, and the friction loss in the pipe. You size the pump against this total head, never against the static level alone.
How much panel kWp does a PM-KUSUM solar pump need?+
A PM-KUSUM solar pump needs roughly 0.9 to 1.2 kWp of panel per HP as a rough rule, so a 5 HP pump pairs with about 4.5 to 6 kWp. This is only a planning figure. Verify the exact panel size against the current MNRE technical specification for the pump model you choose.
Should I pick a submersible or surface solar pump?+
A solar pump choice depends on the water source. Choose a surface pump for shallow open wells or tanks where suction lift stays under about 10 metres. Choose a submersible pump for borewells, because the pump sits down in the water and can lift from much deeper levels that a surface pump cannot reach.
What HP slabs does PM-KUSUM allow?+
PM-KUSUM commonly supports 3, 5, 7.5 and 10 HP solar pumps under Component B, with higher capacities allowed in some states. PM-KUSUM eligibility and any HP cap change by state and by scheme order, so verify the current slabs against the latest MNRE guidelines and your state nodal agency.
What is the most common solar pump sizing mistake?+
The most common solar pump sizing mistake is oversizing. A larger HP pump can overdraw the borewell, run dry and burn out, and it wastes the farmer's money. The other frequent errors are ignoring drawdown and ignoring the seasonal fall in the water table, both of which raise the real head.
How does SuryaHub help with solar pump sizing?+
SuryaHub gives field teams a site-survey module to capture borewell depth, water level and discharge on the spot, then runs the project from survey to commissioning in one place. SuryaHub does not replace the pump curve or MNRE spec. SuryaHub is pre-revenue; real pilots are Suryantra Energy and RGESPL.
Sources & references
Sizing rules, HP slabs and benchmark figures come from primary government sources. PM-KUSUM HP slabs, benchmark costs and panel specs change by state and by order, so always confirm the current numbers with the latest MNRE technical specification and your state nodal agency before you size a job.
- Ministry of New & Renewable Energy (MNRE) ↗
Technical specifications and benchmark costs for PM-KUSUM solar pumps. Verify current.
- National Portal for PM-KUSUM ↗
Scheme components, eligibility and the live application process. Verify current.
- Rajasthan Renewable Energy Corporation (RRECL) ↗
A state nodal agency that runs PM-KUSUM tenders and HP slabs locally. Verify current.
Written by the SuryaHub team · reviewed against MNRE, PM-KUSUM portal & state SNA sources · updated 19 June 2026.
Method: Sizing logic and HP slabs are taken from the government sources above and re-checked every 30 days. Head, discharge and panel figures are planning estimates — verify each against the live pump curve, the current MNRE spec and your state SNA. SuryaHub is pre-revenue; only Suryantra Energy and RGESPL are real pilots.
Change log: 19 Jun 2026 — first published.