How large a solar water heating system do I need?


Sizing a solar domestic hot water system for residential use is not that difficult. The CSA standards rate systems for 150, 225 and 300 litres (33, 50, 66, Imperial gallons) per day. These ratings roughly correspond to the daily hot water consumption of 2-3, 3-4, and 5-6 adults.

Another correlation is the number of square metres of solar collector per adult using hot water. Typically this number is 1 - 1.5 square meters per adult. This is based upon achieving a solar contribution of approximately 50% towards the hot water load. Larger solar fractions can be achieved by adding solar collectors, however the the returns diminish quickly as you try to achieve an annual performance above 50%.

A significant issue with trying to achieve a percentage greater than 50% is the fact (assuming the hot water load is esentially constant over the year) making the solar system larger will over-size it for the Summer, causing it to overheat and potentially damage the heat transfer fluid or the solar equipment itself.