Solar thermal technologies use the sun’s radiation to heat water. There are a variety of different panels or plates available that can heat water to certain temperatures. For instance, a flat plate panel is used for low level heating which may be used to heat a swimming pool. Medium level installations heats water for domestic uses and a high level solar thermal technology uses extremely high temperatures (several thousand degrees!) to ultimately generate steam to be driven around in a turbine to generate electricity.

This article will go into more detail on medium level solar thermal heating as this is the technology range that you are most likely to see.

How does it work?

There are two types of domestic solar thermal panel: evacuated tube and flat plate collectors.

Evacuated TubeThis type of solar thermal panel is more likely to produce a higher temperature than a flat plat collector panel. Depending on the time of day and season, temperatures could reach well over 170^oC.  It is called an evacuated tube because all the air has been sucked out/evacuated, from inside the glass tube. This is to reduce convection within the glass, and therefore reduces heat loss. There will be (as with the flat plate collector) a controller that links with the pump for the system that regulates the amount of water flowing past the panel. This ensures a limit as to how much heat is transferred to heat the water in your boilers (as you don’t want a scalding bath!)

Flat Plate Collector

In basic form, the flat plate collector is made up of 3 layers. The (uppermost) glazing layer, absorbing plate (middle) and then an insulation layer (underneath). The absorber plate houses the tubing which is usually made out of copper. The tubing allows the fluid to flow throughout the panel.Temperatures reach anywhere between 40 and 50^oC+. The idea behind solar thermal panels (especially flat plate) is to take a chunk out of the cost of heating your boiler. For example, your boiler should be set to around 60^oC. If the flat plate collector is producing a temperature of 45^oC, then your boiler will have to make up a further 15^oC to reach the desired temperature. This 15^oC will be produced by you electricity or gas bill, and the 45^oC will be produced for free by the solar thermal panel!

Suitability

The suitability of having a panel installed very much replies on the same issues as with PV panels.

• Strength of roof
• Area needed (although this is less than the area required for PV panels)
• Unhindered access to the sun. At least access between 10am and 4pm and facing south

The ability of your panel to generate heat is limited by the time of day. However, just like a PV panel, solar thermal panels will still generate energy on overcast days or winter months. This may be a lower temperature than that generated during the summer, but it is still saving you money on heating your water.

What do you expect to generate?

According to the Energy Saving Trust (EST), typical savings per year are only moderate. This will depend on the existing fuel you are substituting it for. Bear in mind that solar thermal panels are really there to offset your heating bills, as they will not be cost effective in providing all of your heating.

All savings (Table 1) are approximate and are based on the hot water heating requirements of a 3 bed semi detached home with a 3.5m squared panel [1].

Cost and Payback

From the calculations by the EST, the initial cost of an installation is between £3,000 and £5,000.

Solar thermal technologies are not covered by the new feed-in-tariff. They used to be covered by the Low Carbon Buildings Programme, which offered a £400 or 30% of the cost, depending on which was lower. Solar thermal is now going to become part of the Renewables Heat Incentive, which is set to be in place by April 2011. According to the preliminary consultations and papers of the RHI, solar thermal will get a lower incentive than other thermal technologies. However, it could be possible that the RHI would give you around £400 a year for 20 years! It may be wise to wait until next year for the RHI to be finalised (?).

How to go about getting solar thermal panels installed

Planning permission for Solar Thermal panels are the same as for PV panels. No planning permission is required, unless you site your panels in view of conservational areas, the panels are free standing and exceed more than 4m high and/or larger than 9m² and finally, if the panels protrude out from your roof more than 20cm. In Scotland, Wales and Northern Ireland, it is a little more complicated. If you live in these areas, firstly look up information regarding planning over the internet, and secondly, consult your local planning authority.

There are many installers around for this genre of technology. A good suggestion is to get quotes from several installers (around 5). An installer, installing a micro renewable technology must be accredited with an MCS, Mircogeneration Certification Scheme.

Maintenance

Little maintenance is required apart from occasional cleaning. Service checks are often included as part of the quote from the installer and are typically performed every 4 to 5 years of the installations lifespan. An installations lifespan may last up to 40 years.

[1] The Energy Saving Trust. June 2010. Available [Online]