STC rating versus a PTC solar electric rating

PTC refers to PVUSA Test Conditions, which were developed to test and compare PV systems as part of the PVUSA (Photovoltaics for Utility Scale Applications) project. PTC are 1,000 Watts per square meter solar irradiance, 20 degrees C air temperature, and wind speed of 1 meter per second at 10 meters above ground level. PV manufacturers use Standard Test Conditions, or STC, to rate their PV products. STC are 1,000 Watts per square meter solar irradiance, 25 degrees C cell temperature, air mass equal to 1.5, and ASTM G173-03 standard spectrum. The PTC rating, which is lower than the STC rating, is generally recognized as a more realistic measure of PV output because the test conditions better reflect "real-world" solar and climatic conditions, compared to the STC rating. All ratings in the list are DC (direct current) watts.

Neither PTC nor STC account for all "real-world" losses. Actual solar systems will produce lower outputs due to soiling, shading, module mismatch, wire losses, inverter and transformer losses, shortfalls in actual nameplate ratings, panel degradation over time, and high-temperature losses for arrays mounted close to or integrated within a roofline. These loss factors can vary by season, geographic location, mounting technique, azimuth, and array tilt.

IMPORTANT !

The advertised system prices that are quoted on this website are based on the our system's DC or STC wattage ratings not their AC wattage rating. Please note that because a solar system's estimated AC power production is site and installation dependent, we do not post our system's estimated AC wattage ratings. To calculate the estimated AC wattage rating of your chosen solar system, multiply the PTC rated output of the solar panels by the number of solar panels multiplied by the CEC weighted efficiency of the inverter, multiplied by the system's design factor which is based on module tilt angle, azimuth angle, shading and geographic location. Other factors that can affect your chosen solar system's AC wattage rating are: Solar module soiling, module mismatch, wire losses, inverter and transformer losses, shortfalls in actual nameplate ratings, solar panel degradation over time, and high-temperature losses for arrays mounted close to or integrated within a roofline.

If you wish to be provided with a solar system's estimated AC power production, please ask your sales representative to provide you with an estimate or you can visit the following web pages and gather your specific solar panel's PTC rating and inverter CEC weighted efficiency and use the following formula to estimate a solar system's AC wattage production:

http://gosolarcalifornia.com/equipment/pv_modules.php

http://gosolarcalifornia.com/equipment/inverters.php

Multiply the PTC rated output of the solar panels by the number of solar panels multiplied by the CEC weighted efficiency of the inverter, multiplied by your system's design factor which is based on module tilt angle, azimuth angle, shading and geographic location.