Nameplate Capacity

Nameplate capacity is the maximum rated power output of a solar system or individual panel under ideal Standard Test Conditions (STC). It is the “official” size of your system, expressed in kilowatts (kW) or watts (W), and is the number used in system specifications, contracts, and incentive applications.

For example, a system with 20 panels rated at 400W each has a nameplate capacity of 8 kW (8,000 watts). However, real-world production is almost always lower than nameplate capacity because actual conditions rarely match the ideal laboratory settings used for STC ratings (25°C cell temperature, 1,000 W/m² irradiance). Factors like high temperatures, shading, soiling, wiring losses, and inverter clipping all reduce actual output below the nameplate rating. A system’s real-world output is typically 75–85% of its nameplate capacity. This difference is accounted for by the derate factor. When reviewing solar proposals, understand that the nameplate capacity represents the best-case peak output, not the constant output you should expect.