Solar Panel Calculator
Estimate the solar system size, number of panels, inverter, roof space and batteries for your home.
Runs in your browser — your data never leaves your device.
About the Solar Panel Calculator
Thinking of going solar? Enter the units on your electricity bill to estimate the system size you need, how many panels, the inverter size and roof space — and, if you want backup at night, the battery bank.
Most of Pakistan gets about 5 to 6 peak sun hours a day on average, so the default is 5.5. Get a site survey and quotation from a trusted installer before buying; this is a planning estimate.
How to use the Solar Panel Calculator
- Enter your monthly units (from your bill — use a summer month for a safe size) or your daily kWh.
- Check the sun hours and choose a panel size.
- Optionally add the units you use at night to size batteries.
- Click Estimate system.
Formula
System size (kW) = daily kWh ÷ (peak sun hours × 0.80). The 0.80 allows for heat, dust, wiring and inverter losses.
Panels = system watts ÷ panel watts, rounded up. Roof space ≈ panel area + 15% for spacing.
Battery kWh = night kWh ÷ (usable share × 0.9 inverter efficiency); lithium ≈ 90% usable, lead-acid ≈ 50%.
Examples
- 450 units a month (15 kWh a day) with 5.5 sun hours → 3.41 kW → 6 panels of 585 W (3.51 kW), about 463 units a month, roof space about 18 m² (192 sq ft).
- Adding 5 kWh of night use with lithium batteries → about 6.2 kWh (130 Ah at 48 V).
Frequently asked questions
How accurate is this?
It is a planning estimate using standard formulas. Real results depend on the equipment, installation and conditions, so confirm with a qualified installer before buying.
Should I use summer or winter units?
Summer bills (with fans and AC) give a larger system; winter output is lower because days are shorter. Many people size for an average month and accept some grid use in peak summer.
What about net metering?
With an on-grid or hybrid system and net metering, extra daytime units can be exported. Rules and rates are set by NEPRA and your DISCO — check the current policy.