Guide to Solar-Powered Borehole Irrigation

A borehole may provide abundant water, but when the pump runs on expensive grid electricity or diesel, irrigation costs rise quickly. A proper guide to solar-powered borehole irrigation begins with one fundamental fact: the panels are not sized according to the number of hectares, but according to the pump's actual hydraulic and electrical requirements.

Solar-powered irrigation can drastically reduce operating costs and provide energy autonomy for agricultural plots where a grid connection is expensive or inadequate. However, it is not a “install panels and it works” solution. Proper design requires borehole data, pump curves, daily water requirements and a realistic estimate of solar irradiation throughout the irrigation season.

How solar-powered borehole irrigation works

In an off-grid system, photovoltaic modules generate direct current. A dedicated solar pump inverter or a suitably designed inverter converts and regulates the energy to drive the submersible or surface pump. The inverter varies the motor speed according to the available solar power, enabling smooth starting and more efficient operation.

As solar irradiation increases, the water flow rate generally increases as well. This is not a problem when a storage tank is available or when irrigation can be adapted to production hours. In practice, water serves as the project's most economical “battery”: it is pumped during the day and stored for use when needed.

There are three main architectures. The first is a fully off-grid photovoltaic system that operates only with sunlight. The second is hybrid, with the option of support from the grid or a generator during periods of low irradiation. The third combines photovoltaics, batteries and an inverter when pumping is required at strictly defined times or when other loads must be supplied in parallel. The choice depends on the crop, seasonality and the project's tolerance for interruptions.

The study starts with the pump, not the panels

The most common mistake is selecting the photovoltaic array based solely on the pump's nominal power. A 7.5 kW pump does not automatically require 7.5 kWp of panels. The actual requirement varies with the pumping depth, water level, elevation to the tank, network pressure and pipework losses.

The technical study must determine the flow rate required by the crop, usually in cubic metres per hour or per day, as well as the total dynamic head. This includes the borehole's dynamic water level, the elevation difference, the desired pressure and friction losses through pipes, filters, valves and drip emitters.

Critical information required before any quotation

At least the following data is required to size a system correctly:

• pump motor power, voltage and type
• borehole depth and dynamic water level during pumping
• desired water flow and daily operating hours
• pipework diameter, length and material
• tank elevation or required irrigation pressure
• available area and orientation for the photovoltaic modules

If this information is missing, the quotation may be no more than an estimate. In agricultural pumping, even a small error in total head or flow rate can result in a pump that does not meet the crop's needs or in excessive equipment costs.

How many photovoltaic panels does a borehole need?

The answer is “it depends,” but there is a clear methodology. First, the daily energy required for pumping is calculated. For example, a pump that actually draws 5 kW and needs to operate for six hours per day consumes approximately 30 kWh, before accounting for inverter and cable losses and variations in operation.

The photovoltaic capacity is then selected to deliver the required production under irrigation-season conditions, not only on an ideal summer day. The installed panel capacity is often greater than the pump's electrical power. This enables an earlier start in the morning, better performance during hot weather or light cloud cover, and more stable operation during transition hours.

Oversizing is not always wasteful. In a pumping system, the correct ratio between the photovoltaic array and inverter can substantially increase the cubic metres of water pumped per day. Conversely, excessive capacity without a technical study raises the initial cost without a corresponding benefit.

Batteries or a water storage tank?

For most boreholes, a storage tank is more economical than a large bank of LiFePO4 batteries. Water storage has a lower cost per useful unit of storage, simpler maintenance and a long service life. The pump operates when sunlight is available, and the water is supplied later by gravity or by a lower-power booster pump set.

Batteries make sense when there is insufficient space for a tank, when irrigation must take place after sunset, or when the same system supplies a home, warehouse, cold room or other critical loads. In these cases, careful calculation of cycles, discharge power and autonomy is required. A battery that can support lighting and small loads is not necessarily suitable for starting and operating a pump for several hours.

Inverter selection and essential protections

The inverter is the installation's control centre. For new or replaceable pumps, a specialised pump inverter with MPPT can deliver excellent results because it adapts motor operation to the available solar production. For more complex off-grid or hybrid projects, a combination of premium inverters, controllers and storage is required, with proper communication between the subsystems.

Protection is equally critical. Running without water, overcurrent, overvoltage, overheating and dry running can cause serious pump damage. Level sensors in the borehole and tank, surge protection, earthing, correct DC and AC fuses, and suitable cables are part of the investment, not optional details.

Cost and payback: what to calculate realistically

The cost of a photovoltaic pumping system is not determined by the panels alone. It includes the inverter, mounting structures, protection boards, cabling, possible borehole work or pump replacement, the tank, hydraulic materials and installation. A project with difficult access or a long distance between the photovoltaic array and the borehole has different requirements from an installation next to an agricultural storage building.

Payback is usually more attractive when diesel is replaced, when a new electricity connection is avoided or when irrigation consumption is high every summer. In installations with an existing grid connection, the value lies in reducing electricity bills and protecting against future increases in energy costs. The correct comparison is not only “how much does the system cost?” but “how much will each cubic metre of water I pump cost over the coming years?”

What distinguishes a reliable installation

A good installation does not simply promise free pumping. It delivers measurable water flow, safe operation and access to technical support when needed during the irrigation season. The choice of certified equipment, a properly designed mounting structure, allowance for shading and correct inverter configuration have a direct impact on daily performance.

Hellenic Energy approaches pumping projects with a free technical study, examining actual consumption and the borehole's characteristics before recommending equipment. This reduces the risk of incorrect sizing and creates a system capable of supporting production for years.

Water is critical for the crop, and the energy used to pump it should not remain an uncontrolled operating cost. With actual borehole data and a proper technical study, solar-powered irrigation can turn sunshine into stable, predictable irrigation.