How Solar Production Estimates Work (and How to Validate One)
A production estimate is a promise dressed as a number. Here’s how the good ones are built — and how to pressure-test yours.
Estimated annual production (kWh/year) is the foundation of every savings claim. Reputable installers model it; weaker ones round up and hope.
What goes into a real estimate
- Location-specific sun data (Minnesota irradiance, not a national average)
- Roof orientation and tilt for each plane of panels
- A shading analysis — ideally measured on-site or from imagery, accounting for trees, chimneys and neighbors
- System losses — wiring, inverter efficiency, soiling, snow, temperature
- The actual panel and inverter specs
How to validate one
Ask three questions: What software produced this and what shading data did it use? What loss factor did you assume? Will you put this kWh/year number in the contract? An honest installer answers all three without flinching. A vague “trust us, you’ll save a ton” is the flag.
Reality-check it later
After install, microinverter and hybrid systems report real production per panel through an app, so you can compare actual output to the estimate month over month. Transparency is the point.
Frequently asked.
Why is my estimate lower than a neighbor's?
Orientation, shading, roof tilt and panel choice all differ. Two houses on the same street can have very different production.
Should the estimate be in the contract?
Ideally yes, or at least in the signed proposal. A number you can hold someone to beats a number on a billboard.
Have a question we haven't covered?
Talk to a local iSolar expert — free, no pressure. Call (651) 565-1140.