How Many Solar Panels Do You Need? A Practical Sizing Method for Canadian Homes and Cabins
"How many panels do I need?" has no single answer, but it does have a method. The method depends on whether you are connected to the grid, because the two cases are sized against different goals: a yearly total for a grid-tied system, and the worst month for an off-grid one.
Both methods start from the same place. If you have not yet worked out how much electricity you use, do that first with our guide to calculating your daily energy use.
Method A: grid-tied home, sized to the year
- Find your yearly use. Add up 12 months of kWh from your electricity bills.
- Find the photovoltaic (PV) potential for your location. Natural Resources Canada publishes PV potential maps that give the expected annual kWh per kW of panels for a south-facing array tilted at the latitude angle. NRCan states that its lifetime average annual values for most systems should be within about 10%, and its modelling assumes a performance ratio of 0.75, which already allows for typical system losses.
- Divide. Yearly use divided by PV potential gives the array size in kW.
- Convert to panels. Divide the array size by the wattage of one panel and round up.
Here is a worked example. Every number is illustrative; use your own bills and your own location's PV potential.
| Step | Example value | Result |
|---|---|---|
| Yearly electricity use | 9,000 kWh | |
| PV potential for the location (example only) | 1,200 kWh per kW per year | |
| Array size needed | 9,000 ÷ 1,200 | 7.5 kW |
| With 460 W panels | 7,500 ÷ 460 = 16.3 | 17 panels |
| With 500 W panels | 7,500 ÷ 500 | 15 panels |
You do not have to offset 100% of your use. Roof space, budget, shading and the system size limits set by your utility or province may all point to a smaller array.
Method B: off-grid cabin, sized to the worst month
Off-grid systems cannot average the year. They have to work in the weakest month you will be there. The usual approach is:
Array size (kW) = daily energy needed (kWh) ÷ (peak sun hours × system efficiency)
Peak sun hours are the number of hours per day with the equivalent of full-strength sunlight (1,000 W per square metre). They are much lower in December than in July. Use solar-resource data for the month you care about, such as the Natural Resources Canada solar irradiance dataset, which gives daily averages on tilted surfaces for locations across Canada.
| Step | Example value | Result |
|---|---|---|
| Daily use | 2 kWh | |
| Add a 25% margin | 2 × 1.25 | 2.5 kWh |
| Winter peak sun hours (example only) | 2.0 | |
| System efficiency (example) | 0.75 | |
| Array size needed | 2.5 ÷ (2.0 × 0.75) | 1.67 kW |
| With 460 W panels | 1,670 ÷ 460 = 3.6 | 4 panels |
Even then, a run of cloudy days will leave the array short. That is what the battery bank and, for many owners, a backup generator are for. Winter is the reason; our guide on solar in Canadian winters explains why.
Check that the pieces fit
- Physical space: panel dimensions are on the datasheet. Measure your roof or ground area before deciding on panel count.
- Inverter or charge controller limits: there are maximum input voltage and current limits, and the number of panels in each string has to respect them.
- Shading: even a small shadow from a chimney or tree can reduce output more than you would expect.
- Utility rules: grid-connected systems may be limited in size by your utility or province.
Common mistakes
- Sizing an off-grid system from summer sun hours.
- Forgetting to include a margin for losses and future loads.
- Buying panels before choosing the inverter, charge controller and battery they must work with.
- Treating a rule of thumb from a forum as a design.
Panels in our catalogue
Panel sizes in our solar panels collection range from small rigid panels, such as the RVPOZWER 100W rigid panel, to home-scale options such as the LONGi full black panel (460W–500W) and the LONGi Hi-MO X10 HPBC 2.0 (495W–500W). Once you know your target array size, divide by the wattage of the variant you choose.
These calculations are for planning only and use illustrative numbers. A qualified designer or installer should confirm final system size for your site.