You can only save the electricity used in heating the volume of water in the tank
Quantity of Hot Water
Do not think you will have more hot water than before because you have gone solar – all PAYGS does is to replace the electricity used in heating 1 tank of water per 24 hours
The performance of the solar geyser will fluctuate daily according to weather, cold water temperature, the seasons, solar irradiation depending on your area in the country
Some months you will save more than others, which depends on the performance factors outlined above. On very wet days electricity savings will be less.
Not surprisingly solar works best on clear sunny days, but it still works when there is cloud
System Sizing & Hot Water Consumption
Most homes in South Africa are fitted with electric geysers of 150 litres and some with 200 litres. The electric geyser turns ‘on’ and ‘off’ throughout the day. A 4 person home will typically heat the tank at least twice every 24 hours period.
Going solar requires a system that will meet the demand of hot water used – refer to “What size do you need”.
Orientation and Inclination
The performance of the PAYGS system can be effected if the orientation is not true north.
Roof space and orientation can result in reduced performance (>+/- 10%) if orientation and inclination is not optimal.
Not surprisingly if the solar collector of the solar water heater is shaded by trees or other obstruction the deemed performance will fall. This is not as acute as with solar PV but will affect performance.
Not every home will be suitable for a PAYGS system. This may be as a result of factors outlined above, old plumbing or other factors. The PAYGS appointed installer may decline to install a PAYGS system, even though qualification criteria has been met, if they believe the the savings will not be achieved.