How to Size a Solar System in Pakistan
Calculate solar kW, panel count, inverter capacity and realistic generation from your own electricity use.
Start with daily energy use in kWh, divide it by realistic peak-sun-hours and total system efficiency, then round the array to available panel sizes. Check inverter limits, daytime load, roof area, shade and any battery requirement separately.
What to remember
- ✓ Size energy from several recent bills, not one unusually low month.
- ✓ Panel kW, inverter kW and battery kWh solve different problems.
- ✓ A site survey and qualified electrical design are still required before installation.
Convert bills into daily energy
Collect at least three to twelve months of units so seasonal air-conditioning, heating or business loads are visible. Divide the selected monthly units by the number of billing days to obtain average daily kWh.
Decide whether the system should offset the full annual average, only the daytime load or a smaller budget-limited target. Oversizing without understanding export rules and daytime consumption can weaken the financial result.
Estimate array capacity
A planning formula is required array kW = daily kWh ÷ (peak-sun-hours × system efficiency). System efficiency accounts for temperature, inverter conversion, wiring, dust, mismatch and other losses.
For example, 20 daily kWh divided by 5 peak-sun-hours and 0.80 efficiency gives about 5 kW. This is a planning size, not a production guarantee; location, orientation, shade and weather change generation.
- Use conservative peak-sun-hours for the city and season.
- Allow realistic losses instead of panel nameplate output.
- Round using the wattage and count of actual modules.
Check panels, inverter and roof
Panel count equals required array watts divided by one panel's wattage, rounded to a practical string layout. The chosen inverter must accept the strings' voltage and current within its MPPT limits under hot and cold conditions.
Roof area is not the only constraint. Setbacks, walkways, water tanks, shade, wind loading, structure and maintenance access reduce usable space. A physical layout prevents unrealistic panel counts.
Treat batteries as a separate design
Grid-tied energy offset does not automatically provide outage backup. Battery sizing begins with essential backup watts and required hours, then accounts for voltage, usable depth of discharge and conversion losses.
Ask installers for expected monthly generation, loss assumptions, warranties, protection equipment, earthing and an itemised quotation. Compare these with your own estimate before selecting a proposal.
Limitations and responsible use
Solar production and savings depend on the site, weather, tariff, export arrangement, equipment and installation. Obtain a site survey and qualified design before purchasing equipment.
Sources and further verification
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