What is the performance output of the PAYGS Systems?


Performance of PAYGS Compared to Electricity Used to Heat Water


The amount of electricity used in heating a tank of water from cold at 16 °C to the typical thermostat setting of 60 °C is shown in the beige bars for each tank size. The deemed performance of the electricity saved by the PAYGS systems at 20MJ m2 per day (the South African average) is shown in the green bars. The efficiency in replacing electricity is 100%+/- depending on the day

Knowledge and Information


Solar water heaters are tested at the South African Bureau of Standards (SABS) for performance

A ‘Q’ test is performed under SANS 6211 which measures the deemed output of the systems on a typical South African day at 20MJ m2 per day.

The performance of the solar system in kWh can then be compared with electricity used to heat the water in the tank of the same size.

The electricity used to heat water is calculated using the specific heat of water formula which is volume (the size of the tank) x temperature differential (the difference between the cold water entering the tank and the geyser thermostat setting) and ÷ by a constant of 860 = kWh’s used to heat the water.


Tank Volume Litres Cold Water in at °C Geyser Hot at 60°C Difference in °C kWh (average) Hot Potable at 40°C
150 16 60 44 7,67 275
200 16 60 44 10,23 367
250 16 60 44 12,79 458
300 16 60 44 15,35 550

Additional testing using monitoring and verification instrumentation is also used to compare consumption before and after installation