Solar Panel Calculator — How Many Panels Do I Need?
Enter the units on your electricity bill (or your daily kWh) to see what size solar system covers it and how many panels that means.
Updated
Results are estimates for planning. Actual figures depend on local conditions, prices and quotes — verify before making decisions.
About this calculator
Defaults: 5.5 peak sun hours, 80% system efficiency and 585 W panels. Change them to match your city and quote.
Formula
Daily energy = Monthly units ÷ 30
System kW = Daily energy ÷ (Peak sun hours × Efficiency)
Panels = System W ÷ Panel W (rounded up)
Peak sun hours convert a day's sunlight into the equivalent hours of full-strength sun. Efficiency accounts for heat, dust, wiring and inverter losses.
Examples
300 units/month
You need about 2.27 kW of solar — 4 × 585 W panels (2.34 kW)
500 units/month
You need about 3.79 kW of solar — 7 × 585 W panels (4.1 kW)
1,000 units/month
You need about 7.58 kW of solar — 13 × 585 W panels (7.61 kW)
Important information
- Generation is lower in December–January and on smoggy or dusty days, and higher in spring and summer.
- Panels lose output in high heat; good ventilation behind panels helps.
- Grid-tied (on-grid) systems need net-metering/net-billing approval from your DISCO; rules have changed recently, so check current NEPRA policy.
Frequently asked questions
How many solar panels do I need for 500 units?
With 5.5 sun hours and 80% efficiency, 500 units a month needs about 3.8 kW — seven 585 W panels.
How much roof space do I need?
Roughly 25–30 sq ft per modern panel, plus walking space. A 10 kW system needs around 500–600 sq ft.
What are peak sun hours?
The number of hours per day the sun would need to shine at 1,000 W/m² to deliver the day's total sunlight. Much of Pakistan averages 5–6.
On-grid, off-grid or hybrid?
On-grid is cheapest but stops in load-shedding unless you add batteries. Hybrid systems with batteries keep running during outages.
How big an inverter do I need?
Usually close to the panel capacity, and large enough for your peak load. The solar load calculator can help.
Learn more
- How Many Solar Panels Do I Need? (Pakistan) — Size a home solar system from your electricity bill, understand peak sun hours and efficiency, and estimate payback.
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