Solar Energy [Thermal]

A 'sensible' solar heating system can be expected to provide up to 50% of winter hot water requirements and all of the summer demand.

Solar water heating can be used not just for domestic water heating but also for larger scale applications such as swimming pools.

A solar water heating system for domestic hot water comprises three main components: solar panels; hot water cylinder and a plumbing system.

The principle and operation of these systems are quite simple. Solar panels are fitted to the roof and retain heat from the sun's rays. This heat is then transferred to a fluid and pumped through the plumbing to a hot water cylinder where it is stored for later use.

A range of factors will affect the size and type of system that would be suitable including; the amount of south facing roof space, the existing water heating system and the capital available for the project.

Approximately 2-4 m² of southeast to southwest facing roof space that receives minimal shading during the main part of day will be needed and space to place an additional water cylinder if required.

The amount of solar radiation falling on 1.0 sqm of due south facing surface in say Cheshire would be about 950 kW hrs per annum. However the efficiency of conversion in a solar panel is about 40% giving a 'useful' value of 380kwh/a per 1sqm.

There are two main types of collector:

Flat Plate

Flat Plate where looped copper pipes are bonded to a sheet of dark insulated material. The thin panel is covered with a sheet of glass creating a slim greenhouse.

The suns rays pass through the glass which alters the wavelength reducing their ability to pass back out of the box and heat builds up which is transferred to the water in the copper pipes. The efficiency is increased if the glass is double glazed.

Evacuated Tubes

Evacuated Tubes are more expensive but more efficient. Here each tube is a stand alone unit - individual collector tubes lie in their own glass cylinder which has a high absorbance /low emission coating to increase energy gain and reduce convection loss. The efficiency of the tubes is further improved by creating a vacuum.

Each tube connects to header pipe which collects the contribution from each tube. Evacuated tubes have the advantage that they can be mounted on a vertical surface with each tube rotated so that it is angled optimally to the sun.

A major plus is that it is highly compatible with ground source heat pump technology. The technology involved in both systems is easy to understand and a good plumber probably has all the knowledge required to install it with or without government grant aid. And neither GSHP nor Solar Heating damage the environment or impact on wildlife.

Both systems can share the same storage cylinder and distribution electronics and both are compatible with latest building regulation thinking on insulation and heating e.g. underfloor heating at 40-50° C.

If you have any comments or queries on Solar Heating. Please contact:

George Jardine
Renewables Energy Manager
CMS UK
Spring Farm Business Centre
Moss Lane
Minshull Vernon
Crewe
Cheshire CW1 4RJ
Tel: 01270 522645