Solar Production Estimator
Production note: Production estimates depend on site conditions. Nameplate watts are measured in lab conditions; shade, heat, tilt, snow, soiling, inverter limits, and degradation change real output.
PVWatts is the preferred model. This lightweight version also supports a transparent peak-sun-hour estimate when you do not have an API result.
Inputs
Result
How to use this calculator
Use this estimator to translate a proposed array size into expected energy output and to see which assumptions deserve closer attention.
What the result means
The result estimates AC energy production over a month or year using the production assumptions entered on the page.
What the result does not settle
It does not replace a shade study, production commitment, or site-specific engineering model.
Inputs that change the answer most
- Array size in kW DC
- Local solar resource
- Tilt and azimuth
- System losses, shade, dirt, snow, and temperature
- Inverter clipping and long-term degradation
Readable method
Estimated production = system size × production factor × loss adjustment. Monthly estimates should be confirmed against seasonal weather and shading patterns.
Before you act
Use site-specific data such as NREL PVWatts, installer modeling, shade analysis, and monthly utility usage before relying on a production number.
How this is calculated
Estimate = array kW × peak sun hours/day × 365 × (1 − losses). For bankable production, run PVWatts v8 with the exact location, tilt, azimuth, array type, module type, DC/AC ratio, and losses.
Assumptions and formula
Use these inputs as planning assumptions, not as a final design, tax filing, permit package, or equipment approval.
- array size
- local solar resource
- tilt and azimuth
- shade and weather losses
- temperature, snow, soiling, and degradation
Formula
Estimated production = system size × production factor × loss adjustment, then confirmed by month when seasonal output matters.
Solar Production Estimator Guide
A solar production estimate translates array size into expected energy output. The big variables are local irradiance, orientation, tilt, shade, temperature, inverter clipping, soiling, snow, equipment mismatch, wiring loss, and degradation. Nameplate watts are only the starting point.
What changes annual production?
- Azimuth: south-facing arrays often maximize annual output in the northern hemisphere, but east or west arrays can better match morning or evening loads.
- Tilt: low-slope and steep roofs shift seasonal production.
- Shade: even partial shade can reduce string output unless mitigated with design choices.
- Temperature: hot modules produce less power than their lab rating.
- Clipping: DC capacity above inverter AC rating can be normal, but excessive clipping wastes production.
How to improve the estimate
Use a full year of utility data, site-specific solar resource data, and a shade assessment. If winter reliability matters, compare monthly production rather than relying on an annual total.
Frequently Asked Questions
Why does my system produce less than its nameplate rating?
Nameplate ratings are measured under standard test conditions. Real panels operate with heat, wiring losses, inverter limits, dirt, angle losses, and changing sunlight.
Is west-facing solar bad?
Not necessarily. It may produce less annual energy than ideal south-facing solar, but it can align better with late-day consumption and time-of-use rates.
Sources
Source notes
Use these as starting points when the page affects a purchase, design, tax, utility, or safety decision.