How we calculate

1. Your roof

For a real address we use Google’s Solar API, built from aerial imagery and 3D roof models. It returns each roof face’s direction and pitch, a sun map of the roof, and the spots where panels fit, each with its expected yearly output. We show the imagery date and quality; lower-quality imagery lowers our confidence rating.

You can add or remove panels anywhere; each panel keeps its own yearly output, so shaded or poorly facing spots count for less.

2. What the panels make

• Yearly output per panel comes from the roof data, rescaled to the panel wattage you pick.
• We subtract 14% for inverter, wiring, temperature, dirt and snow losses (you can change this).
• We spread the year across months using day length and typical cloud and snow cover for your latitude, then across hours with a sun curve and day-to-day weather variation.
• Panels lose 0.5% of output a year.

3. What you use

If you enter kWh from your bill, we use it. If you enter a dollar amount, we work backwards through your utility’s rate plan to find the usage that produces that bill. We then shape it by month and by hour using a typical Canadian household profile with morning and evening peaks.

4. Your bill, hour by hour

We simulate all 8,760 hours of a typical year. Each hour, solar first serves the house, then charges a battery if you have one, then goes to the grid. The battery discharges when power is expensive. Every hour is priced on your plan: time-of-use, ultra-low overnight, tiered or flat, plus delivery and regulatory charges, taxes and provincial bill rebates.

Exports follow your province’s rules: net metering credits with their rollover period, net-billing credits at a set rate, or nothing. In Ontario we model two paths for every home: net metering with no rebate, and the provincial rebate with no export.

5. Money

• Price: your province’s average installed cost per watt (midpoint of the range), plus about $1,100 per kWh for batteries. Rebates are only applied if the program is open.
• Savings grow 3% a year with electricity rates and shrink with panel wear.
• We include a $2,500 inverter replacement in year 13.
• Payback is the year your running total turns positive. We also report net present value at a 5% discount rate and the internal rate of return.
• Loan payments use a standard amortisation at an example rate; use the rate on your quote.

6. The verdict

What we don’t know

We can’t see the condition of your roof, your electrical panel, local permit rules or an installer’s real price. Delivery charges for some utilities are approximate. An installer’s on-site assessment confirms everything.

Sources

• Google Maps Platform Solar API
• Ontario Energy Board prices effective November 1, 2026
• Green Building Canada, solar panel costs in Canada (2026)
• Incentives we track, with the date each was checked