Solar Water Heating (Domestic Renewable Heat Incentive)
Solar water heating panels work by utilising the ‘greenhouse effect’ – directing light onto either a flat panel or tubes residing in a vacuum. A vacuum is an excellent insulator as you’ll recognise from use of vacuum flasks.
This helps to keep heat loss to a minimum. What counts is the amount of light falling onto them, rather than ambient temperature. In fact, solar panels have been successfully used in the Antarctic for some time now. Care must of course be taken to ensure they are not shaded and work best when facing south, though any roof facing within 90°s of south will be suitable.
The UK receives plenty of light throughout the year, enough that a panel area of 1m² is generally sufficient to provide hot water for each adult in the property. The minimum panel area would normally be in the region of 2.5m².
One of the most common configurations is to have 2 coils in the hot water tank, one for the solar heating, one for a conventional back up such as gas or electricity. This is both more convenient and efficient.
Over the course of a year, the panels should provide some 60% of the property’s water heating needs, Summer naturally being the most effective with close to all needs being met, though even during the Winter, around 20% of water heating needs should be met, chiefly by raising significantly, the temperature of the water before it is necessary to heat it further by conventional gas or electric methods.