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Sizing a Solar Water Heating system

Before sizing a system make sure you have taken measures to reduce hot water consumption as far as possible e.g. low-flow shower heads.

When going solar, the last thing you want to do is to under-size a system leading to situation that it does not deliver according to one’s expectations.

The table below provides a guideline based on potable hot water consumption.

A soft science approach is to start at the temperature that one washes or showers at being 40 ºC.

A good 10-minute long, shower at 10 litres per minute amounts to 100 litres per person at 40 ºC .

Two people will therefore use 200 litres. In order to get 200 litres of 40 ºC hot water, a solar water heater of 150 litres will provide this but it needs a Q performance of at least 17.5 to 20.5 at 20MJ /m2 per day.

Check with your supplier both the size and the power output of the system at 20 MJ.
Too small or not powerful enough and you will always be using the electrical back up, and will be disappointed by the electrical savings.