Solar pumps are now widely used by homeowners, farmers, and small business owners. However, the size of a solar pump varies with the quantity of water needed by its buyer. The depth of the borewell, the height of water delivery, and the availability of sunlight also determine the solar pump size. It is essential to calculate the required size of the solar pump before buying one. If the pump is smaller than required, the purpose of buying it will not be fulfilled. On the other hand, buying a much larger pump can be a waste of money.
Importance of Calculating the Exact Required Size of a Solar Pump
A solar pump is designed to draw energy from solar panels. Its size determines the number of solar panels to be installed for supplying adequate energy. The perfect size of the solar pump offers the following advantages –
- Sufficient water supply
- More energy efficiency
- Lower operating cost
- Lesser installation charges
- Better longevity of the pump
- Lower maintenance costs in the future
What Are the Steps to Be Taken to Estimate a Solar Pump Size?
Expert engineers can guide customers in calculating the size of a solar pump, based on several factors, among which Total Dynamic Head (TDH) is the most important.
Get an estimate of your daily water requirements
We can get a rough estimate of the daily usage of water for different purposes, which are listed below –
- Household use: 500 – 1500 liters
- Irrigation of a kitchen: 2000 – 5000 liters
- Livestock: 5000 – 10,000 liters
- Small farm: 20,000 – 60,000 liters
- Irrigation of 1 acre of land: 25,000 – 35,000 liters
- Medium farm: 80,000 – 1,80,000 liters
- Static Water Level is the distance from ground level to the water surface inside a borewell when the solar pump is switched off.
- Drawdown is the amount of water when the level drops after the pump starts working.
- Delivery Height is the vertical distance from the pump to the destination where the water is pumped, like an elevated tank or the irrigation point.
- Friction Loss is the resistance caused by the length, diameter, and bends of the pipe. Expert engineers suggest adding 10% – 20% extra head to the total lift to account for friction losses.
- Flow means liters of water delivered per hour
- Head means the Total Dynamic Head (TDH)
- Efficiency means the solar pump efficiency
However, these numbers may vary according to the type of crops, irrigation method, and climatic conditions.
Measure the Total Dynamic Head (TDH)
Total Dynamic Head (TDH) is the total of the vertical and frictional resistance that should be overcome by the solar pump to lift water.
So, the formula for calculating TDH = Static Water Level + Drawdown + Delivery Height + Friction Loss
For example, if the Static water level is 100 ft, the Drawdown is 20 ft, the tank height is 15 ft, and pipe friction is 15 ft; then TDH = 100 + 20 + 15 + 15 = 150 ft.
Evaluation of the Required Flow Rate
Flow rate is the amount of water delivered by the solar pump in an hour. It is calculated by the formula:
Flow Rate = Daily water requirement / Peak hours of sunlight
For example, if the user needs 50,000 liters per day and that location receives 5 peak hours of sunlight, the Flow Rate is 50,000/5 = 10,000 liters/hr. It means the solar pump needs to supply 10,000 liters of water in an hour during the peak hours of sunlight.
Calculation of the Required Solar Pump Size
The size of a solar pump is usually expressed in Horsepower (HP). The formula for calculating the solar pump size is –
HP = (Flow x Head) / (75 x Efficiency x 3600),
Where
Solar pumps of 0.5 HP to 1 HP deliver up to 40 liters of water per minute. These pumps of TDH range 50 – 100 ft are suitable for use in shallow wells, to supply water for small gardens and livestock.
Solar pumps of 1.5 HP to 3 HP can deliver up to 100 liters of water per minute. These pumps of TDH range 100 – 200 ft are best for deep borewells, drip irrigation, and to fill large storage tanks.
Solar pumps of 5 HP to 10 HP are capable of delivering up to more than 200 liters of water per minute. These pumps of TDH range 200 – 300 ft are needed to meet large-scale agricultural needs and industrial applications.
All these are general estimates only, which can give an idea to the buyers while selecting solar pumps for their requirements. However, they need to consider the actual pump capacities and field conditions.
Consider the Size of Solar Panels
The wattage capacity of the installed solar panels should be around 1.5 times the wattage of the solar pump’s motor. Hence, the solar pump can function on cloudy days or during a system fault. For example, a 1 HP solar pump of 750 W needs the solar panel array of 975 W – 1125 W, comprising three 330 W panels. A 2 HP solar pump should be paired with solar panels of capacity 1.8 – 2.4 kW, a 3 HP pump needs solar panels of 2.7 – 3.6 kW capacity, and a 5 HP pump has the requirement of solar panels of 4.5 – 6 kW capacity.
Conclusion
Selecting the right solar pump involves more than just choosing the pump size. Factors such as Total Dynamic Head (TDH), daily water requirements, borewell depth, and pump efficiency all play an important role in achieving reliable performance. Measuring water levels during summer and planning for future irrigation needs can help in making a better long-term investment. Choosing a dependable brand like Unnati Pumps ensures access to efficient and durable solar pumping solutions designed for consistent water supply, lower maintenance, and improved energy savings. A properly selected solar pump system can enhance irrigation efficiency while supporting sustainable and cost-effective farming.