Standard Test Conditions

In order to rate solar panels fairly, the Department of Energy, in conjunction with Underwriter's Laboratory, have developed a system for rating panels so that the consumer is getting unbiased and accurate information about panel performance.

All panel power ratings are determined by their performance in laboratories under Standard Test Conditions, in which a light with the strength of 1000 w/m2 flashes on a panel.  The temperature of the room is 25 degrees C (about 75 degrees F).

It also assumes an air mass of 1.5.