Solar Panel Estimator

How to use the solar panel estimator

1. Enter your Electricity use (kWh) and choose Month (average) or Year under Per.
2. Set the Share of your use to cover (%): 100% aims to produce as much as you use over a year, 50% half of it.
3. Enter the Peak sun hours per day for your location (see below), the Panel power (W) and the System losses (%) (14% by default).
4. Optionally, enter the Area of one panel in m² or sq ft to see the roof area the panels take.
5. Read the System size needed (DC), the number of Panels, the System with whole panels and its Estimated production per year. The steps show each calculation.

All calculations run in your browser; nothing is sent anywhere.

The formula

• Yearly use = monthly use × 12 (or the yearly total you entered).
• Energy to produce per day = yearly use × share to cover ÷ 365.
• System size (kW) = energy per day ÷ (peak sun hours × (1 − losses)).
• Panels = system size × 1,000 ÷ panel watts, rounded up.
• Production per year = panels × watts ÷ 1,000 × peak sun hours × 365 × (1 − losses).

Example: 900 kWh a month is 10,800 kWh a year, or 29.6 kWh a day. With 4 peak sun hours and 14% losses, each kW of panels makes 4 × 0.86 = 3.44 kWh a day, so you need 29.6 ÷ 3.44 = 8.6 kW. With 400 W panels, that is 21.5, rounded up to 22 panels (8.8 kW), producing about 11,049 kWh a year. At 1.95 m² per panel, they cover about 43 m² (462 sq ft) of roof.

Where to find your peak sun hours

A peak sun hour is one hour of sunlight at 1,000 W per m². The number of peak sun hours per day equals the average daily solar energy that reaches the panels, in kWh per m² per day. It depends on your latitude, your local weather and the tilt and orientation of the panels, and it is always an average over the whole year: winter days in Canada give much less, summer days much more.

This tool does not guess it for you: look it up and enter it. Natural Resources Canada publishes photovoltaic potential and solar resource maps for Canadian municipalities, and the NREL PVWatts calculator gives values for any address in North America and beyond. Many Canadian locations fall roughly between 3 and 4.5 peak sun hours for a south-facing tilted array, but check your own. If a map gives you a yearly yield in kWh per installed kW, it already includes typical losses: divide it by 365 to get the sun hours and set the losses to 0.

About the 14% losses

14% is the default loss of NREL’s PVWatts model. It groups soiling, snow, shading, wiring, connections, panel mismatch, light-induced degradation, nameplate rating tolerance and system availability; inverter efficiency is counted separately in PVWatts. Raise it for partial shading, heavy snow cover or an unusual installation.

Limits

This is a rough estimate to see the order of magnitude. It does not check your roof orientation, tilt, shading, structure or local rules, and production varies from year to year. Net metering rules, equipment prices and incentives change by province and utility. Get a site assessment and several quotes from qualified installers before deciding.