Solar Irrigation Calculator

Estimate the solar energy required to run an agricultural water pump and see how the proposed system can perform throughout the year.

Enter your farm area, pump horsepower, solar panel wattage, sunlight conditions and crop water requirement. The calculator will estimate the required PV capacity, VFD size, number of solar panels, operating hours, water production, irrigation coverage and indicative system cost in PKR.

The calculator starts with the pump horsepower you enter . If you have not yet selected a pump, determine the required water flow and total dynamic head before making a final pump decision.

What does the solar irrigation calculator show?

The calculator helps you match an agricultural pump with the solar equipment needed to operate it.

Depending on your inputs, it estimates:

•  Pump power in kW
•  Solar PV capacity is needed.
•  VFD capacity
•  Number of solar panels
•  Structure and electricity costs
•  Monthly working hours
•  Solar power generation
•  Water movement estimation
•  Estimated irrigation coverage
•  Total cost of the system excluding the pump

This is especially useful when you already have an agricultural pump or the horsepower you are considering and you want to understand the solar equipment needed to run it.

How to use the solar irrigation calculator?

1. Enter your irrigation area.

Enter the total land you want to irrigate in acres. Farm size alone does not determine the required pump horsepower. The pump must be able to deliver the required amount of water within the available irrigation time while controlling the hydraulic conditions of the site.

These conditions may include:

•  Required water flow
•  Water level
•  Delivery height
•  Pipe friction
•  Irrigation pressure

Therefore, crop water demand must be considered in conjunction with pumping conditions.

2. Select your pump type.

Select the option that best represents the pumping system you plan to use. If you already have a pump installed, use its original specifications wherever possible. The type of pump, operating conditions, and water source all influence how the complete irrigation system should be designed.

3. Enter the pump horsepower.

Enter the rated horsepower shown on your pump or the HP of the pump you are considering. The calculator converts horsepower to kilowatts and uses this value to estimate solar PV and VFD requirements. If you do not yet know the exact pump horsepower, first determine the required flow and total dynamic head.

4. Enter the depth of the bore or well.

Enter the depth of the bore in feet. This information is useful for describing the project, but the depth of the bore is not the same as the Total Dynamic Head .

What else can affect pumping heads?

A complete pumping assessment may need to consider:

•  Static water level
•  Dynamic pumping water level
•  Drawdown
•  Vertical delivery height
•  Pipe friction
•  Pipe fittings
•  Required irrigation pressure

These factors help determine the actual duty point of the pump.

5. Enter the Inlet and Outlet sizes.

Select the appropriate pipe or pump connection size. The calculator uses the outlet size as part of its water flow estimate. The actual pump discharge, however, depends on the pump operating against the actual hydraulic head.

For final equipment selection, compare the required flow and head to the manufacturer’s pump performance curves.

6. Select your solar panel wattage.

Choose the wattage of the solar panels you plan to install. Higher wattage panels generally mean that fewer modules are needed to achieve the same total PV capacity. 

For example, the same solar array capacity may require more 450W panels than 550W panels.The calculator rounds the required amount up because partial solar panels cannot be installed.

7. Select the type of solar structure.

Choose either a fixed or movable structure depending on the installation you are considering. This choice affects the estimated structure cost.

Actual structure pricing may depend on:

•  Contents
•  Height
•  Foundation
•  Fabrication
•  Air requirements
•  Installation method
•  Site conditions

Use the displayed cost as a budget reference rather than a final quotation.

8. Enter the distance from the panels to the VFD.

Enter the approximate cable distance between the solar array and the VFD. The calculator uses this distance when estimating cable-related costs.

Final cable selection

The original cable should be selected according to:

•  System voltage
•  Current
•  Cable length
•  Allowable voltage drop
•  Conductor details
•  Electrical protection
•  Installation method

The cable allowance displayed by the calculator should not replace the calculation of electrical cable size.

9. Enter your peak sun hours.

Use a realistic solar resource value for the farm site. You can also adjust the January to December sunlight values to compare seasonal operation. Solar energy availability varies throughout the year, so avoid designing the system only around the month with the most sunlight if irrigation is needed even during periods of low sun.

10. Enter the desired pump runtime.

Enter how many hours per day you want the pump to run. If no runtime is entered, the calculator uses its available sun hours logic. When the runtime is entered, the monthly operation is minimized:

•  Available solar hours
•  Requested pump runtime.

This helps prevent calculations from assuming more solar-powered pumping time than available sunlight.

11. Enter the crop water requirement.

Enter the estimated daily irrigation requirement: m³ per acre per day.

Use a price appropriate for the crop and season you are planning. Crop water needs may change with:

•  Crop type
•  Growth stage
•  Climate
•  Weather
•  Effective rain
•  Irrigation method
•  Irrigation efficiency

Avoid using a common water requirement for each crop.

How does the solar irrigation calculator work?

The calculator starts with the pump horsepower and then estimates the amount of VFD, solar array, and panels needed to support it.

Pump horsepower to kilowatts

The calculator converts horsepower to kilowatts:

• Pump power (kW) = Pump HP × 0.746

For 5 HP pump:

• 5 × 0.746 = 3.73 kW

Therefore the estimated pump power is: 3.73 kW.

How is VFD size calculated?

The calculator applies a 25% margin to the converted pump power:

• VFD requirement = Pump kW × 1.25

For 5 HP pump:

• 3.73 × 1.25 = 4.66 kW

The result is then rounded up to the available VFD size supported by the calculator.

What else matters when choosing a VFD?

The final VFD should also match the motor:

•  Voltage
•  Rated current
•  Step
•  Operating requirements
•  Compatible input conditions

The calculated kW value alone is not sufficient to verify VFD compatibility.

How is solar PV capacity calculated?

The calculator applies a PV size factor of 1.30:

• Solar PV capacity = Pump kW × 1.30

Using the same 5 HP pump:

• 3.73 × 1.30 = 4.849 kW

Estimated Solar PV Requirement: 4.849 kW.

This calculation estimates the solar array from the pre-selected pump horsepower. It does not determine whether that pump is hydraulically suitable for the bore, desired flow, or irrigation system.

How is the number of solar panels calculated?

Once the required PV capacity is known, the calculator divides the array wattage by the selected panel wattage.

The formula is:

• Number of panels = Solar array watts ÷ Panel watts

The result is rounded up to the next full panel.

For example:

• Required PV capacity: 4,849W
• Panel Wattage: 550W

Calculation:

• 4,849 ÷ 550 = 8.82

So you will need:

• 9 × 550W solar panels

Based on the calculator size method.

How is monthly pump runtime estimated?

Monthly operating time depends on available sunlight and the runtime you enter.

The calculator uses the following:

•  Available monthly sunshine hours
•  Requested pump runtime.

This allows you to compare pumping capacity in different months, rather than assuming uniform solar conditions throughout the year.

How much water does a crop need?

Crop water requirement is an important input because it directly affects the estimated area that can be irrigated. Water demand is often expressed in millimeters of water depth per day .

Convert millimeters of water to m³ per acre.

There is a useful change:

• 1 acre plus 1 mm ≈ 4.05 m³

For example, if the crop needs:

• 6 mm per day

The equivalent volume of water is approximately:

• 6 × 4.05 = 24.3 m³/acre/day

This is before adjustments for losses from effective rainfall and irrigation systems.

Why do crop water needs change?

There is no daily watering requirement that applies to every crop. The actual requirements depend on factors such as:

•  Crop type
•  Crop growth stage
•  Temperature
•  Climate
•  Weather
•  Effective rain
•  Irrigation efficiency

Use local agricultural or irrigation information whenever possible when choosing this value.

Bore Depth vs. Total Dynamic Head

Bore depth tells you how deep the bore or well is. It does not tell you the total hydraulic resistance that the pump must overcome during operation.

What is a total dynamic head?

Total dynamic head, or TDH, represents the total head against which the pump operates at the desired flow. Depending on the installation, this may include:

•  Dynamic pumping water level
•  Drawdown
•  Vertical delivery height
•  Pipe friction
•  Related items
•  Desired outlet pressure

Why does TDH matter?

The water flow of a pump depends on the head against which it works. This means that a pump labeled 5 HP does not automatically deliver the same amount of water to every bore or installation.

The required flow rate and total dynamic head together determine the operating duty point. Before purchasing a new pump, compare this duty point to the manufacturer’s pump performance curves.

Understanding your monthly solar irrigation results

Monthly results help you see how changing sunlight conditions can affect pumping and irrigation throughout the year.

Sun hours

This is the value of solar resources used for each month. Adjust the monthly values if you have more appropriate solar data for your farm location.

Pump runtime

It shows the estimated operating period based on available sunlight and entered runtime. Actual operation may vary with weather, VFD behavior, pump conditions and solar array performance.

Solar generation

This estimates the electrical energy available from the solar array under selected sunlight conditions.

The actual race can change due to:

•  Weather
•  Panel temperature
•  Dust
•  Shading
•  Panel direction
•  Panel tilt
•  Electricity losses
•  Equipment performance

Estimated water flow

The calculator uses its available inputs to estimate water movement. Estimate it as an approximate figure. The actual discharge must be confirmed by the performance curves of the selected pump at the actual operating head.

Estimated irrigation coverage

The calculator compares the estimated water delivery to the water requirement of the crop you entered. The reduced crop water requirement will increase the calculated area that can be covered. The crop’s high water requirement will reduce this. This is why it is important to enter into a realistic crop water requirement.

Solar irrigation example: 5 HP agricultural pump

Consider a system with:

Input	Value
Pump size	5 HP
Solar panel wattage	550W
PV size factor	1.30
VFD size factor	1.25

Step 1: Convert pump HP to kW.

• 5 × 0.746 = 3.73 kW

Pump Power: 3.73 kW

Step 2: Calculate the VFD requirement.

• 3.73 × 1.25 = 4.66 kW

Calculation VFD requirement: Next 4.66 kW before selecting the appropriate supported VFD size.

Step 3: Calculate the solar PV requirement.

• 3.73 × 1.30 = 4.849 kW

Estimated solar array requirement: 4.849 kW.

Step 4: Calculate the number of panels.

Use of 550W solar panels:

• 4,849 ÷ 550 = 8.82

Rounded upwards:

• 9 solar panels

This example shows how the calculator determines solar and VFD requirements for a selected 5 HP pump. This does not confirm that a 5 HP pump is the correct hydraulic choice for a particular bore, water requirement or irrigation system.

What affects the efficiency of solar irrigation?

Real-world pumping efficiency depends on more than just the capacity of the solar panel.

Available sunlight

Solar-powered pumping capacity changes with changes in available solar energy.

Cloudy weather and weather conditions can reduce daily working time.

Bore and water level

The actual pumping water level affects how much head the pump must handle. A deep borehole does not mean that water itself is present at the bottom of the borehole.

Pipe length and friction

Long pipes, small diameters, bends and fittings can increase hydraulic losses.

Required irrigation pressure

Drip, sprinkler, and other irrigation systems may require additional operating pressure. This becomes part of the overall pumping requirement.

Solar panel condition

Dust, dirt, shading, and high panel temperatures can reduce available solar energy.

Pump and VFD performance

The performance and operating characteristics of the pump, motor, and VFD affect the actual water delivery.

Solar irrigation and groundwater

Solar pumping can reduce dependence on diesel or grid electricity, but it does not increase the amount of groundwater available. If the system will pump from a bore or well, the water source must be capable of supporting the planned extraction rate.

Why does bore production matter?

A pump may be physically capable of moving a large volume of water, but the bore itself may not be capable of delivering water continuously at that rate. Excessive pumping can cause the water level to drop during operation. Therefore, pump capacity, crop demand, and sustainable water availability must be considered together.

Do solar irrigation systems need batteries?

Not necessarily. Many solar irrigation systems operate pumps primarily during available solar hours. Instead of storing electricity in batteries, the system can sometimes pump water into a storage tank or reservoir for later use.

Water storage vs. battery storage

Storing water can avoid some of the cost and complexity associated with battery storage. Whether this approach is appropriate depends on:

•  Irrigation time
•  Required water volume
•  Storage availability
•  Pumping schedule
•  Form layout
•  Capacity of water sources

If it is necessary to continue pumping when solar energy is not available, another energy or storage solution may be needed.

When is a solar irrigation calculator useful?

Use the calculator when you want:

•  Convert existing agricultural pumps to solar power.
•  Compare different pump horsepower options.
•  Estimate VFD capacity.
•  Estimate solar PV needs.
•  Compare different panel wattages.
•  Compare fixed and movable structures.
•  Estimate the costs of a non-pump system.
•  Compare monthly solar conditions.
•  See how crop water needs affect irrigation coverage.
•  Prepare before requesting installer quotations.

This is most useful when the pump horsepower is known in advance.

What is not included in the solar irrigation calculator?

The calculator focuses on estimating solar and VFD requirements for the entered pump horsepower. It does not provide complete hydraulic, electrical or structural design. The calculation does not independently determine:

•  Sustainable Bor Production
•  Crop evapotranspiration from weather data
•  Effective rain
•  Irrigation method efficiency
•  Dynamic decrease in water level
•  Full dynamic head
•  Detailed pipe friction losses
•  Pump curve matching
•  Precise discharge at the operating head
•  VFD DC-string voltage compatibility
•  Motor starting requirements
•  Motor protection
•  Detailed voltage drop
•  Ultimate electrical protection
•  Structural Engineering
•  Pump purchase price

Equipment and installation prices can also change, so cost figures should be compared to current supplier quotations before purchasing equipment.