Start with your bills
Collect your last 12 electricity bills and note the units (kWh) for each month. Summer months with AC usage are the highest. Your system should be sized around how much you use, especially in the daytime when the sun is out.
A rough rule of thumb
In much of Pakistan, a well-placed 1 kW of panels produces very roughly 3.5 to 5 units a day on average, depending on the season, dust, shade and direction. So divide your average daily units by about 4 to get a starting size, then let a mistri adjust it after seeing your roof. Treat this only as a first estimate.
Things that change the size
- Big daytime loads: inverter ACs, water motor, washing machine and iron.
- Night backup: if you want to run things at night, you need batteries sized for that.
- Roof space and shade: water tanks, trees and nearby buildings reduce output.
- Panel direction and tilt: south-facing with a suitable tilt usually works best in Pakistan.
- Your metering rules: when exporting pays less, it is better to match your own use.
Common mistakes
- Choosing only by price per watt and ignoring the inverter and structure quality.
- Skipping proper earthing and DC protection to save money.
- Buying a system too small for summer AC use, or far too big for actual needs.
- Not getting a written list of brands, models and warranties.