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.