Divide your yearly electricity use by the yearly output of 1 kW of solar panels in your city. In Lahore, 1 kWp of panels makes about 1,466 kWh a year, so a home using 400 units a month (4,800 a year) needs about 3.3 kW, which is six 585 W panels. This calculator does that sum for eight Pakistani cities, then adds panel count, roof area and an inverter note.
How to use this tool
- Enter your average monthly units (kWh) from your electricity bill. If you only know the bill amount, enter it with your average cost per unit and the tool works out the units. Taxes and fixed charges make this less accurate, so units are better.
- Choose your city and the wattage of the panel you plan to buy.
- Optionally enter a price per watt you were quoted. The tool multiplies it by the system size. We do not show live market prices.
- Read the results: system size in kW, number of panels, roof area, inverter size, estimated monthly generation and the notes on the inverter and net billing. Open Advanced to change the panel area or the roof allowance.
Where do the city numbers come from?
Each city figure is the long-term specific yield (PVOUT) from the Global Solar Atlas, published by the World Bank and modelled by Solargis. It is the energy one kilowatt-peak of crystalline silicon panels produces in a year, after typical losses. The atlas models a fixed, ground-mounted array at the best tilt for that site, with about 3.5% soiling loss and 7.5% for other losses such as cables, inverter and mismatch.
| City | kWh per kWp per year | kWh per kWp per day | Lowest month (kWh per kWp) | Best month (kWh per kWp) |
|---|---|---|---|---|
| Quetta | 1,936 | 5.3 | 141 | 182 |
| Hyderabad | 1,753 | 4.8 | 127 | 165 |
| Karachi | 1,697 | 4.65 | 106 | 167 |
| Multan | 1,608 | 4.41 | 104 | 153 |
| Islamabad | 1,559 | 4.27 | 103 | 157 |
| Peshawar | 1,502 | 4.12 | 100 | 148 |
| Faisalabad | 1,498 | 4.1 | 95 | 149 |
| Lahore | 1,466 | 4.02 | 93 | 147 |
Rooftop systems that sit flatter than the best tilt, face east or west, or get shade from water tanks and walls will produce less. Treat these numbers as an upper planning figure.
What formula does the calculator use?
System size (kW) = (monthly units x 12) / city yield per kWp per year Panels = round up (system size x 1000 / panel watts) Actual size (kW) = panels x panel watts / 1000 Monthly generation = actual size x city yield / 12 Panel area = panels x panel length x panel width
For panel size we use a 585 W monocrystalline module of 2,335 mm by 1,134 mm (about 2.65 m2) from a Jinko Tiger Neo datasheet. Most 550 to 585 W panels sold in Pakistan are a similar size, but check your own panel datasheet. The tool adds a 30% allowance for walkways and gaps between rows. That allowance is our planning assumption, not a standard. You can change the panel area and the allowance under Advanced.
Worked example: Lahore, 400 units a month
- Yearly use: 400 x 12 = 4,800 kWh
- Size: 4,800 / 1,466 = 3.28 kW
- Panels: 3,280 / 585 = 5.6, rounded up to 6 panels (3.51 kW)
- Generation: 3.51 x 1,466 / 12 = about 429 kWh a month on average
- Panel area: 6 x 2.65 = 15.9 m2, about 20.7 m2 (222 sq ft) with the allowance
The same use in Karachi needs only five panels, because each kWp there produces about 1,697 kWh a year. Output also changes by month: in Lahore, 1 kWp makes about 93 kWh in January and about 147 kWh in April, so winter bills will not fall as much as summer bills.
How big should the inverter be?
For an on-grid system, installers usually match the inverter rating to the panel array, often with a little more panel capacity than inverter capacity. If you add batteries for load shedding, size the inverter for the loads you need to run at the same time, such as fans, lights and a refrigerator. Ask your installer for a load list before you buy. The calculator suggests the smallest standard on-grid size at or above your panel kW: 3, 5, 6, 8, 10, 12 or 15 kW.
What changed in net metering in 2026?
On 9 February 2026 NEPRA notified the National Electric Power Regulatory Authority (Prosumer) Regulations, 2026, which replaced the 2015 net metering rules with net billing. As reported by Dawn, exported units for new prosumers are bought at about Rs10 to 11 per unit instead of about Rs26, new agreements run for five years, and the system size cannot exceed your sanctioned load. Dawn also reported that existing prosumers would move to net billing while keeping their other contract terms until expiry. After public criticism, NEPRA published a draft amendment to keep existing net metering agreements on their old rates and terms until they expire. Reports differ on whether that amendment has been finalised. Check the current position with NEPRA and your distribution company before you invest, because the rules are still being reviewed.
Under net billing, the units you use yourself during the day save you the full tariff, while exported units earn much less. That makes it better to size closer to your daytime use rather than oversize for export.
Common mistakes
- Sizing from one summer bill. Use the average of 12 months.
- Ignoring the sanctioned load limit for grid-connected systems.
- Forgetting shade from nearby buildings, tanks or trees.
Tips
- Clean panels regularly in dusty months. The atlas already assumes some soiling, and heavy dust costs more.
- Get at least two written quotes and compare price per watt, not just total price.
Need a calculator like this on your own solar business website? See our website development and custom software services.
Last updated: October 19, 2026
