This International Standard specifies a method of evaluating the annual energy performance of solar water heaters using a combination of test results for component performance and a mathematical model to determine an annual load cycle task performance under specified weather and load conditions. The procedure is applicable to solar water heaters with integral backup or preheating into a conventional storage or instantaneous water heater and to integral collector storage water heaters. System operating requirements specified in this International Standard are for the purpose of determining an annual performance rating for domestic water heaters. There are no product design or operation requirements in this International Standard.