Reading a Solar Production Estimate Before You Sign

What does a solar production estimate actually say?

The headline number is usually annual kWh. Behind it sit a handful of inputs: system size in kilowatts of panels, roof tilt and direction, shading, local weather data and a loss factor for wiring, inverter and dirt. The estimate is a model, not a promise, and weather in any single year will differ from the average the model uses.

Ask which software produced it and whether the file can be shared. Industry tools exist for this, and a reputable installer will show you the inputs, not just the result.

How do you turn kWh into something comparable?

Divide the annual kWh by the system size in kW. The result is often called specific yield, in kWh per kW per year. Suppose one quote offers 7.0 kW with 8,400 kWh, and another offers 6.0 kW with 7,500 kWh. The first gives 1,200 kWh per kW and the second 1,250. Those figures are made up for the example, but the method is real: the second system extracts more from each kW even though it is smaller.

Yield differs by location. Sunshine, covered in solar peak sun hours in Canada, varies from city to city, and clear cold winters can help panel efficiency while short days limit output. If the specific yield in a quote is far above or below what other local quotes show, ask why.

Keep an eye on the denominator too. Some quotes quote kW of panels (DC) and others quote kW of inverter output (AC). A 7 kW array on a 6 kW inverter is a normal, deliberate design, but dividing the kWh by the wrong figure will make one system look better or worse than it is. Write both numbers down for every quote before you divide.

Why do two quotes for the same roof differ?

Common causes are different tilt or direction assumptions, different treatment of shading, and different loss factors. A quote that assumes no shading on a roof with a tall tree is likely optimistic. One that applies a heavy loss factor to protect itself may look low.

• Roof direction and tilt: check against the best solar panel direction in Canada.
• Shading: ask whether it was measured on site or estimated from a photo.
• Snow: see solar panels in winter for how winter is modelled.
• Degradation: whether the estimate includes the slow yearly decline covered in solar panel lifespan and degradation.
• Inverter and wiring losses: the quote should state a total system loss.

How can you sanity check an estimate yourself?

Start with your own electricity use from the last twelve months of bills. Compare it with the estimate: a system modelled to produce twice what you use needs a clear reason, such as a planned electric vehicle or a heat pump. Then check the specific yield against other quotes and any local data your utility or provincial energy ministry publishes.

A useful dry run: multiply system size by a plausible kWh-per-kW range for your region, from two or three sources, and see whether the installer’s figure sits inside it. If it falls well outside, ask for the inputs. Our guide to sizing a system covers the other side of the equation, which is how much you actually need.

What should you ask before you rely on the number?

• What software and weather dataset were used?
• What tilt, azimuth and shading did you assume?
• What is the total loss factor, and how is it split?
• Will you guarantee the estimate, or monitor against it? See what to track when monitoring a solar system.

Compare in the full context of how to compare solar panel quotes. The production estimate is only one line; warranty, equipment and installation quality matter just as much.

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