The most expensive solar mistake is guessing the system size. Too small and you are still paying large bills. Too large and you have paid for capacity you cannot use. Here is a reliable method anyone can follow.
Step 1 — Collect 12 months of electricity bills. Find the units consumed (kWh) for each month. Your summer months (May to September) will be significantly higher due to air conditioning. Add all 12 months and divide by 12 to get your average monthly consumption.
Step 2 — Find your daily average. Divide the monthly average by 30. Example: 600 kWh per month divided by 30 equals 20 kWh per day.
Step 3 — Calculate the DC system size. Pakistan's Punjab region receives around 5 to 5.5 peak sun hours (PSH) per day. Using 80 percent system efficiency (for cable losses, inverter efficiency, soiling): System kW = Daily kWh divided by (PSH x 0.80). For 20 kWh per day: 20 divided by (5 x 0.8) = 5 kW DC.
Typical system sizes for Faisalabad households: a 3-bedroom house with 2 ACs and normal appliances uses 500 to 700 kWh per month and needs roughly a 5 to 8 kW system. A 4 to 5 bedroom house with 3 to 4 ACs uses 900 to 1,400 kWh and needs 10 to 15 kW. A factory or workshop — share your bill and load list and we can size it properly.
Should you add a battery? For residential customers in Pakistan where load-shedding is 4 to 10 hours daily, a battery is worth it. A 5 to 10 kWh battery covers evening and overnight loads without grid power. Without a battery, all your solar power must be used instantly — any excess goes to the grid at the low net-metering buy-back rate.
Post your average monthly bill here and I will suggest a suitable system size.
