Solar Thermal Guide

Energy from the Sun can be harnessed in two ways:

By converting light through photo- voltaic (PV) cells into electricity .
By concentrating light into useful heat – thermal heat.

Thermal heat typically can be used domestically for producing hot water, or less dramatically for heating the air through the windows. In a number of designs the heat is sufficient for cooking when there is sunlight- ‘Sun Ovens’ Commercially it is capable of powering boilers, which in turn can make electricity.

Production
There are three methods now used:

Lens concentration, where light is concentrated by a lens to create a very hot point to heat a fluid.
Evacuated tubes where light strikes an array of vacuum tubes ,heating fluids in each to a high temperature. This is now a well tested method.
Trough or parabolic arrays, where light is concentrated by the shape of the trough onto a tube at the focus point, heating fluids to a high temperature.

Domestic and small scale commercial applications
Currently the most widely used is the evacuated tube method. An array of tubes is located to catch the sun. The heated fluid is connected to an extra coil within the hot water cylinder and replaces heat produced from Grid electricity.

Positioning
The array is typically attached to the building-on a pitched or flat roof, or wall. It needs to be at least 12.5degrees from the horizontal and can be vertical.
Arrays to hang on Flat balconies soon!

Cost
Because the installation is usually attached to the building, the total cost is confined to the array and new cylinder plus connections. It is a candidate for DIY for those with electrical and plumbing ability.

Output
Details are provided elsewhere, but as a general rule in the UK about 25% of hot water bills can be saved.