What a production estimate actually means
A solar production estimate is the predicted annual energy output of your system in kilowatt-hours (kWh) for year one. A typical 8 kW system in the U.S. produces between 9,000 and 13,000 kWh per year, depending on location, roof orientation, tilt, and shading.
The benchmark: kWh per kW per year
The cleanest way to sanity-check production is kWh per kW (sometimes called specific yield). Take the annual production estimate and divide by the system size in kW. Here are realistic ranges:
| Region | Realistic kWh/kW/yr |
|---|---|
| Arizona, Nevada, New Mexico | 1,500 – 1,700 |
| California, Texas, Florida | 1,400 – 1,600 |
| Mid-Atlantic, Midwest | 1,200 – 1,400 |
| Northeast, Pacific Northwest | 1,050 – 1,250 |
| Alaska | 900 – 1,100 |
If your proposal claims 1,600 kWh/kW in Boston or 1,400 kWh/kW in Seattle, the estimate is inflated. Period.
How to validate with PVWatts
NREL's PVWatts calculator is the industry-standard tool. It's free, takes 60 seconds, and uses real weather data for your zip code. Plug in your address, system size in kW, panel tilt (typically your roof pitch), and azimuth (south = 180°). Compare the output to your proposal. If the proposal is more than 10% higher than PVWatts, ask the installer to explain.
What shading does to output
Shading is the biggest variable in real-world production. Even partial shade on a few panels can reduce a string inverter system by 20–30%. Microinverters and DC optimizers help, but they don't eliminate the loss. A proper proposal includes shading analysis software output (Aurora, HelioScope, or Solar Pathfinder) showing TSRF — Total Solar Resource Fraction — for each panel. TSRF should ideally be 90%+ for the system as a whole. Read more about equipment differences in our inverter comparison.
Year-over-year degradation
Solar panels lose a small amount of output every year. Standard panels degrade about 0.5–0.7% annually. Premium panels (REC Alpha, Maxeon, Qcells G11+) degrade 0.25–0.4%. Over 25 years, that's the difference between 87% and 94% of original output. A good proposal models degradation in its 25-year savings projection. See best panels guide for details.
What to do if you under-produce
Most installers offer a production guarantee on the year-1 estimate, typically with a 5–10% tolerance band. If you produce less than guaranteed, the installer pays you the difference at the avoided utility rate. Read your contract carefully — some "guarantees" exclude weather variability or have so many exclusions they're meaningless.
We sanity-check production for you
Upload your solar proposal and the analyzer compares the estimate against PVWatts for your address — and flags any inflated kWh projections.
Check My Production Estimate →Frequently asked questions
How close should real production be to the estimate?
Within ±10% of the estimate over a full calendar year. Year-to-year variation of ±5% is normal due to weather.
Why is my system underperforming in winter?
Solar production is heavily seasonal. Most systems produce 60–70% of annual energy between April and September. Winter underperformance is normal — what matters is the annual total.
Does panel orientation matter?
Yes. South-facing is best in the Northern Hemisphere. East- or west-facing roofs lose 10–15% versus south. North-facing panels lose 25–35% and usually aren't worth installing.
How is production affected by snow?
Snow blocks production while it's on the panels but typically slides off within a few days. Annual production is reduced by 1–4% in snowy regions.