Solar Panel Calculator: How Many Panels You Need
From your monthly electricity units, the number of solar panels you need, the system size in kW, the inverter to buy, the roof area it takes and the panel cost at today's per-watt price.
Pre-filled from Searchable Data: Panel price per watt 29 (14 Sept)
How this is calculated
Divide the monthly units you want to cover by 30 for the daily need. A panel array produces its rated kW times the peak sun hours of the site (4.5 to 5.5 across Pakistan) times a derate of 0.8 for inverter, heat, dust and wiring losses. So:
Array kW = daily kWh / (peak sun hours x 0.8), and panels = array watts / panel watts, rounded up.
The inverter is sized at about 85% of the array (panels rarely produce their full rating at once), rounded up to the sizes sold here. Roof area allows 30 square feet per 585 W panel including spacing; 272.25 square feet make a marla.
Frequently asked questions
- How many solar panels do I need for 500 units?
- About 4.6 kW: 8 panels of 585 W in Lahore (4.5 sun hours) or 7 in Karachi. Pair them with a 5 kW inverter.
- How many panels make a 5 kW system?
- Nine 550 W panels or eight 585 W panels give 5 kW. Older 400 W panels needed 13.
- What size inverter for 10 panels?
- Ten 585 W panels are 5.85 kW; a 5 or 6 kW inverter suits them, since panels seldom deliver their full rating together.
- How much roof space does a 5 kW system need?
- About 250 square feet with walkways, a little under a marla, for eight or nine large panels.
Sources
- Solar panel price per watt in Pakistan, dealer survey, from the Searchable data hub: Searchable
- Global Solar Atlas: photovoltaic power potential for Pakistani cities: World Bank / Solargis
Version 1.0.0 · reviewed 15 Sept 2026. Rates change with the Federal Budget and regulator notifications; we update this tool when they do. Confirm with the primary source before making financial decisions.