Panel count is the end of a short calculation, not the start. The starting point is how much electricity your household uses in a year. From that you estimate the system size in kilowatts, and only then divide by the rating of a single panel. Three steps, one example, and a few reasons the answer may not fit your roof.
Step 1: find your yearly use in kWh
Your utility bill, or the online account behind it, shows monthly kWh. Add up twelve months. Typical Canadian households use around 9,000 to 12,000 kWh a year, but the spread is huge. A small apartment can use a third of that, and an electrically heated detached home can use several times as much. If you are planning to add an electric vehicle or a heat pump, include the extra load, since sizing for today’s use can leave you short.
Before sizing, consider cutting waste. Insulation, a heat pump water heater, and efficient appliances lower what you need to generate, and our energy audit guide shows where to begin.
Step 2: estimate yield per kW
A kilowatt of panels in southern Canada often produces roughly 1,100 to 1,400 kWh a year. Where in that range you land depends on location, tilt, orientation and shading. The sunniest parts of the Prairies, including southern Alberta and Saskatchewan, tend to be at the upper end. A shaded or north-leaning roof can fall below it. Treat these figures as typical, and ask installers for a site-specific production estimate with its assumptions listed.
The size formula is simple:
System size (kW) = yearly use (kWh) divided by yield (kWh per kW)
Step 3: convert kW to panels
Divide the size by the rated watts per panel. With 400 to 450 W panels, each kW needs about 2.2 to 2.5 panels.
A worked example
Take a two-storey house in southern Ontario using 10,000 kWh a year. Assume a yield of 1,200 kWh per kW, which is a mid-range planning figure.
- 10,000 divided by 1,200 gives about 8.3 kW to cover the full year on paper.
- With 420 W panels, that is about 20 panels (8,400 W).
- At roughly 1.8 square metres per panel, the array needs about 36 square metres of unshaded roof.
Now see how sensitive the answer is. If the same home had a yield of only 1,050 kWh per kW because of shading, it would need about 9.5 kW, or roughly 23 panels. If the home were in a sunnier spot with 1,350, it would need about 7.4 kW, or 18 panels. The range from 18 to 23 panels is typical, and that is why the production estimate matters more than any rule of thumb.
A quick reference table
| Yearly use | Likely system size | Approx. panels at 420 W |
|---|---|---|
| 6,000 kWh | 4.5 to 5.5 kW | 11 to 13 |
| 10,000 kWh | 7.5 to 9 kW | 18 to 22 |
| 14,000 kWh | 10.5 to 12.5 kW | 25 to 30 |
These assume the same 1,100 to 1,400 kWh per kW range and a system meant to cover most of annual use. They are a starting sketch. Real designs rarely match round numbers because panels are installed in rows and roof planes have to fit them.
Why your roof may decide for you
Roof area is often the binding constraint. Chimneys, vents, dormers, setbacks from the roof edge and shade from trees or neighbours all remove usable space. A complicated roof may fit fewer panels than the formula suggests. In that case you can choose higher-wattage panels to squeeze out more power from the space, which is discussed in the efficiency and wattage guide, or add a ground mount if the property allows it. You can also go through the roof checklist to see what a site visit will look for.
Utility rules can cap the size too. Provinces set limits for net metering or micro-generation, and these thresholds are reported to change. Ontario’s micro-generation threshold, for example, was reported to rise from 10 kW to 12 kW in May 2026, and Saskatchewan has a cap around 100 kW. Check the current limit with your utility.
Should you cover 100 percent?
Not necessarily. Panels produce more in summer than in winter, so a system that offsets your whole year may overproduce in June and underproduce in December. Where export credits are at or near the retail rate and roll over, a full-coverage design can work well. Where credits are lower, a somewhat smaller system that you mostly use as it is produced may deliver better value per dollar. The system size and cost article compares 5, 7 and 10 kW examples.
Seasons change the picture
Production is lumpy through the year. In southern Canada a roof may make several times more energy in June than in December, so a yearly total hides a lot. If your use peaks in winter, perhaps because of electric heating, a system sized to your annual figure will still leave you buying from the grid in the darker months. That is normal, and it is part of why export credits and rollover rules matter so much to the design.
Before you ask for quotes
Gather your twelve months of usage, a note of planned changes such as a heat pump or electric vehicle, and a rough idea of your roof’s orientation. Ask each installer to state the assumed yield, shading loss and panel wattage, so you can compare like with like. If you want to revisit the mechanics, how solar panels work is a good refresher, and the solar basics hub lists related guides.
Quick answers
How many solar panels do I need to power an average house?
For about 10,000 kWh a year, a system of roughly 7 to 9 kW is a common estimate, which is about 16 to 22 panels of 400 to 450 W. Your own figures will differ.
How much roof space do 20 panels take?
A modern residential panel covers roughly 1.7 to 2 square metres, so 20 panels need around 35 to 40 square metres of usable, unshaded roof.
Should I size solar to cover all of my electricity?
Not always. Where export credits are below retail, a somewhat smaller system that you use directly can give better value than a larger one.
Where to verify
Rules and prices change. Confirm current details with the official bodies below.