How the estimate works

Roof Solar Calc sends your system inputs to the official PVWatts v8 model and displays the model’s first-year AC energy estimate.

Inputs used

The model uses latitude, longitude, DC system size, module type, array mounting, tilt, azimuth, and system losses. Weather and solar-resource data come from the dataset selected by the official PVWatts service.

Automatic verification

Before a result appears, the calculator checks that twelve monthly values are present, their total reconciles with annual AC production, capacity factor agrees with annual production and nameplate capacity, and every key value is finite and plausible. If these checks fail, no result is displayed.

What the estimate does not include

PVWatts is a screening model, not a site survey or production guarantee. Trees, nearby buildings, roof obstructions, snow, equipment-specific behavior, outages, degradation, curtailment, and installation quality can change real-world output.

Best use

Use the estimate to compare system configurations and establish an initial production range. Before purchasing a system, obtain a shade analysis, structural review, equipment design, and written production assumptions from a qualified installer.