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Solar pumping is the one solar application where the equipment is not the starting point. The water duty is. Head, daily volume and the month you cannot afford to be short decide the pump, and the pump decides the array — not the other way round. Systems that start from a panel count are the ones that under-deliver in the season that matters.
This page is for growers, irrigation contractors and rural developers specifying a solar pumping system, and for anyone replacing a diesel pump. It covers the sizing sequence, the three drive configurations, and the failure modes that actually take these systems out.
Start with the water duty, in the worst month
Two numbers define the system: how many cubic metres per day, and the total dynamic head — the static lift plus friction loss plus any pressure needed at the delivery point. Both are easy to get wrong in the direction that hurts. Head is routinely underestimated because friction loss over a long pipe run is left out, and daily volume is routinely taken as an average rather than the peak month.
Solar resource also varies by month. A system sized on the annual average will meet the duty in spring and miss it in the month with the highest demand and the lowest irradiation. Sizing to the worst combination of high duty and low resource is what makes the difference between a system that is trusted and one that is bypassed with a diesel pump in August.
The pump type follows the water source
- Submersible borehole pumps — the default for deep wells. Efficient at high head, and expensive to pull out, which is exactly why dry-run protection is not optional.
- Surface centrifugal pumps — for shallow sources, rivers and canals. Cheaper and easier to service, but limited suction lift.
- Helical rotor (progressive cavity) pumps — for water carrying sand or silt, and for lower flow at higher head. Slower, more tolerant of solids.
Matching the pump curve to the head is where most of the efficiency is won or lost. A pump running well away from its best efficiency point will meet the duty and use noticeably more energy doing it, which means a bigger array for the same water.
Three drive configurations, and what each one buys you
Solar direct — the pump runs whenever the sun is on it, with no battery. Simplest and cheapest, and it suits irrigation with a storage pond or a flexible duty. Water is stored above ground rather than in a battery, which is usually the cheaper place to put it.
Solar with battery buffer — needed where water must move at a fixed rate or outside daylight: livestock troughs, drip systems on a schedule, or a duty that has to complete by a certain hour. The battery decouples pumping from sunshine. Its capacity follows the pumping schedule, night-operation requirement and agreed reserve period.
Grid or generator assisted pumping — where an existing supply can cover solar shortfalls. Confirm source compatibility and the changeover or control arrangement. Any reduction in generator runtime is modelled from the water duty, solar resource and operating records.
The variable frequency drive is not an accessory
A solar array does not deliver steady power. Clouds, low sun at dawn and dusk, and seasonal change all move the available power, and a fixed-speed pump either runs properly or does not run at all. A compatible solar pump drive can adjust motor speed to available power and provide controlled starting. Confirm the pump curve, motor compatibility and drive protection settings for the proposed duty.
Soft start also matters for pump life. Across a season, the difference between starting at full current and starting gently is measurable on a motor that runs every day.
Water storage is usually cheaper than battery storage
If the duty is flexible, compare water storage with electrical storage using the site costs, usable volume, hydraulic losses, evaporation or leakage, and maintenance requirements. Batteries earn their place when the duty is not flexible — when water has to arrive at a specific time, or when the source and the field cannot be connected gravitationally.
The usual design question is therefore not “how much battery” but “how much duty can be made flexible”. Assessing schedule flexibility can reduce the required electrical storage; quantify the change against the actual pumping duty.
What actually kills these systems
Four failure modes account for most of the service calls:
- Dry run — the pump runs with no water and destroys itself. A dry-run sensor or a level probe in the well is cheap; a submersible pump is not.
- Lightning and surge — an array in an open field is the tallest thing around. Surge protection on the DC side and a properly earthed array structure is standard practice, not an upgrade.
- Overheating controllers — a controller in a sealed box in direct sun will derate or trip. Shade and ventilation are design items.
- Sand and debris — in the intake, wearing the pump, or on the modules, reducing output. Both are maintenance items with a schedule.
Specifications at a glance
Configuration reference
Swipe horizontally to view all columns →
| Item | Typical specification | What decides it |
|---|---|---|
| Daily water duty | From a few cubic metres to several hundred | Crop, area, irrigation method and the peak month |
| Total dynamic head | Commonly 20 to 200 m | Static lift, friction loss and the delivery pressure required |
| Pump type | Submersible borehole, surface centrifugal, or helical rotor | Water source, head and whether the water carries solids |
| Drive | Solar direct, solar with battery buffer, or grid-assist hybrid | Whether water must flow outside daylight hours |
| Motor | AC three-phase with variable frequency drive, or DC | Pump type, head and the control strategy |
| Array size | Sized to the pump duty, not to available land | Head, daily volume and the worst solar month |
| Controller | Pump controller with dry-run, over-current and solar-tracking MPPT | Pump protection and how the duty follows the sun |
| Storage | Water storage, battery storage, or both | Whether the duty is flexible or fixed |
| Protection | Lightning arrestor, surge protection, dry-run sensor | Exposure and how expensive the pump is to replace |
| Enclosure | IP54 to IP65 for the controller, shaded and ventilated | Ambient temperature and dust |
| Documentation | Pump curve, duty calculation, wiring diagram and commissioning requirements as applicable | Document scope and availability confirmed with the proposal and order |
| Warranty | Pump and controller 2 years; modules 12 years product, up to 30 years performance | Model and order terms |
Figures are selection references. Confirm the final ratings, dimensions, available certifications and warranty against the current datasheet and written proposal for the selected model or system.
Questions buyers ask about solar pumping
Can it run at night or on cloudy days?
A solar-direct system runs only when the sun is on it, which is why it is normally paired with water storage. If the duty genuinely has to happen at night or in bad weather, that is a battery or grid-assist design, and the sizing changes accordingly.
How do we size it without a pump curve?
We can work from the duty — daily volume and head — and propose a pump with its curve. What we need from you is the static water level, the drawdown, the delivery point and the pipe run. Without the head number any sizing is a guess.
What happens when the well runs low?
That is a dry-run case, and it is handled by a level probe or a dry-run sensor that stops the pump before it is damaged. It should be in the specification from the start rather than added after the first failure.
Is it worth replacing a diesel pump?
Usually, where the duty is daytime and regular. The comparison is fuel plus servicing plus attendance against the capital cost of the array, and it is dominated by how many hours a year the pump runs. Send the running hours and we will put the numbers side by side.
Does it need much maintenance?
Less than a diesel set, but not zero: keep the modules clean, check the controller enclosure and ventilation, and inspect the intake and any level probes. In dusty or agricultural environments, module cleaning is the item that actually shows up in the output.
What to send us
Send the daily volume, the static water level and drawdown, the delivery point and pipe run, and whether the duty is flexible or fixed. We come back with a pump proposal with its curve, the array size and drive configuration, and a written delivery date.
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Send the daily water volume and the head
With the daily volume you need, the total head and the source, the system is sized from the water requirement rather than from a panel count.
Send your requirementsOr reach us directly: +86 136 7367 3267 · sales@gtpsolar.com