Solar System Size Calculator
Not sure how many kilowatts of solar you may need? Use this solar system size calculator to estimate the solar capacity needed based on your monthly electricity consumption and average peak sun hours.
Enter your monthly electricity usage in kWh, then enter the average peak sun hours for your location. The calculator gives an estimated solar system size in kW.
This is a planning estimate. Your final system size can change based on your daytime electricity usage, roof space, shading, panel orientation, inverter configuration, electricity export rules, and other site conditions.
How This Calculator Works
Monthly Electricity Units (kWh)
Enter the number of units you normally use in a month. You can find this figure on your electricity bill.
Average Sun Hours Per Day
Enter the approximate peak sun hours for your location.
Calculated Solar System Size
The calculator estimates the required solar capacity in kW.
How to calculate solar system size
A simple estimate can be calculated using:
Solar System Size (kW) = Monthly Electricity Consumption ÷ (Peak Sun Hours × 30 × 0.8)
For example, if a home uses 600 units per month and receives an average of 4.5 peak sun hours per day:
600 ÷ (4.5 × 30 × 0.8)
600 ÷ 108 = 5.56 kW
So the estimated solar capacity is approximately 5.6 kW.
This does not mean a 5.6 kW system is automatically the final system design. Available panel wattages, inverter capacity, roof space, shading, system losses, and electricity usage patterns also need to be considered.
Why the 0.8 Derate Factor?
The calculator uses an 80% performance factor to account for losses that can occur in a real solar system.
These may include:
- High panel temperature
- Dust and dirt
- Wiring losses
- Inverter losses
- Panel mismatch
- Panel orientation and tilt
- Other system losses
Actual performance can be higher or lower depending on the installation and local conditions.
Average Sun Hours in Pakistan
Solar resource varies across Pakistan. The values below are planning estimates, not fixed sunlight figures for every location.
| City | Approx. peak sun hours used for planning |
|---|---|
| Karachi | 5.3 |
| Lahore | 4.7 |
| Islamabad | 4.8 |
| Multan | 5.1 |
| Quetta | 6.0 |
| Peshawar | 4.6 |
These approximate values are based on long-term solar irradiation data for the listed locations. The World Bank’s Pakistan solar-resource work includes measurement stations in Karachi, Lahore, Islamabad, Multan, Quetta and Peshawar, while Global Solar Atlas provides long-term solar-resource datasets for Pakistan.
For a more precise calculation, use solar-resource data for your specific location rather than relying only on a city average.
How many kW of solar do you need?
Using 4.5 peak sun hours and an 80% performance factor, the following examples show how monthly electricity consumption translates into an estimated solar capacity.
| Monthly electricity use | Estimated solar size |
|---|---|
| 300 kWh | 2.8 kW |
| 500 kWh | 4.6 kW |
| 600 kWh | 5.6 kW |
| 800 kWh | 7.4 kW |
| 1,000 kWh | 9.3 kW |
| 1,500 kWh | 13.9 kW |
These are example calculations, not guaranteed system recommendations.
For example, a household using 1,000 units per month does not necessarily need exactly a 9.3 kW installed system. The final size depends on where the electricity is being used, how much solar generation is available, and how the system will handle surplus electricity.
How many solar panels do you need?
Once you have an estimated system capacity, you can calculate the approximate number of panels.
Number of Panels = System Size (kW) × 1,000 ÷ Panel Wattage
For example, for a 5 kW system using 555-watt panels:
5 × 1,000 ÷ 555 = 9.01
So approximately 9 panels are required.
Nine 555-watt panels provide:
9 × 555 = 4,995 watts
That is effectively a 5 kW panel array.
The actual panel count should also match the inverter’s MPPT voltage and current limits, string configuration, roof layout, and the available panel model.
Does a battery change the solar system size?
A battery does not automatically mean you need more solar panels.
Battery storage changes how electricity is used and stored. A battery can store surplus solar generation for use later, such as during the evening or during a power outage.
The required solar capacity may increase if you want enough generation to cover both your household consumption and battery charging. The amount depends on your electricity usage, backup requirements, battery capacity, and how often the battery needs to be recharged.
If you want to estimate battery capacity, use a solar battery calculator based on your backup loads and required backup time.
Solar system size for a home in Pakistan
There is no single solar system size that fits every Pakistani home.
A household using 300 units per month has very different requirements from one using 1,000 units. Air conditioners, water pumps, refrigerators, fans, washing machines and other large loads can also change electricity consumption significantly.
Your monthly bill is a useful starting point, but it is not the only factor.
Before choosing a system, consider:
- Monthly electricity consumption
- Daytime and nighttime electricity usage
- Available roof area
- Roof direction and tilt
- Shading from nearby buildings or trees
- Panel wattage and model
- Inverter capacity
- Battery requirements
- Electricity export or net billing arrangements
- Future changes in electricity consumption
Is this solar system size calculator accurate?
The calculator provides an estimate for initial planning.
Solar generation varies throughout the year because of weather, temperature, dust, shading, panel orientation and other conditions. Electricity consumption can also change from month to month.
For this reason, the calculator should not be treated as a guaranteed prediction of monthly solar generation or a final engineering design.
For a complete installation, the estimated size should be checked against the proposed panel layout, inverter specifications, roof conditions and expected electricity usage.
Frequently asked questions
How do I calculate the solar system size I need?
Divide your monthly electricity consumption by the product of average peak sun hours, 30 days and an assumed system performance factor.
For example:
600 ÷ (4.5 × 30 × 0.8) = 5.56 kW
This gives an estimated solar capacity of about 5.6 kW.
How many kW of solar do I need for 500 units per month?
Using 4.5 peak sun hours and an 80% performance factor:
500 ÷ (4.5 × 30 × 0.8) = 4.63 kW
So the estimated requirement is approximately 4.6 kW.
The final system size may differ after checking the roof, inverter, panel configuration and electricity usage pattern.
How many solar panels are needed for a 5 kW system?
With 555-watt panels:
5,000 ÷ 555 = 9.01
So approximately 9 panels are required, giving a total panel capacity of 4,995 watts.
Does a battery change the required solar system size?
It can.
If the battery needs to be charged from solar, the solar array may need additional capacity to cover both household consumption and battery charging. The actual requirement depends on the battery size, backup loads and charging pattern.
How accurate is this solar system size calculator?
It is intended for initial planning rather than final system design.
Actual solar output depends on location, weather, temperature, shading, panel orientation, equipment and system losses.
How many solar panels does a home in Pakistan need?
It depends on the home’s electricity consumption and the wattage of the panels.
For example, a 5 kW array using 555-watt panels needs approximately 9 panels. A different panel wattage will produce a different panel count.
What is a peak sun hour?
A peak sun hour is a way of expressing the amount of solar energy available over a day as an equivalent number of hours at a standard solar irradiance level.
It does not mean the sun shines at its maximum intensity for exactly that many hours.
Calculator disclaimer
This calculator provides an estimated solar system size based on the information entered by the user.
Results are for initial planning only. Actual system requirements and solar generation can vary because of location, weather, shading, roof orientation, panel characteristics, inverter configuration, system losses, electricity consumption and other site conditions.
A qualified solar professional should verify the final system design before installation.