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Solar Thermal

The Technology

Solar Thermal Hot Water (STHW) uses heat from the sun to heat your hot water and runs alongside your existing water heater. The most common forms in domestic use are flat panels and evacuated tubes. Larger systems can be used for commercial purposes such as heating swimming pools.

How it works

A solar thermal system consists of a collector panel which absorbs the energy from the sun and transfers it to a working fluid (usually water). This is pumped around a loop which transfers the heat collected to a hot water or buffer tank. There is a control system which determines when to pump the fluid around, depending on the level of heat being provided by the sun at the time. Flat panels consist of a flat ‘radiator’ covered with glass and insulated. Their efficiency depends on their construction, for example some now use double glazed glass. They can be integrated into the roof itself, which can be more aesthetically pleasing and in the case of a new/replacement roof, will reduce the amount of roofing material required. Evacuated tube collectors consist of a series of vacuum tubes which collect the heat onto a fin and tube arrangement. They are more efficient and therefore less area is required. They also heat the water to a higher temperature and remain effective on cloudy days.

 

Collector types

There are two types of solar collector panels commonly in use, flat panels and evacuated tubes.

Flat plate collectors

Thermal_Collector_Flat1

Flat plate collectors can be mounted either ‘in-roof’ and form part of the weather covering , or can be mounted ‘on-roof’ using brackets that are flashed in to prevent water ingress.

A flat-plate collector consists of an absorber, a transparent cover, a frame, and insulation. Usually an iron-poor solar safety glass is used as a transparent cover, as it allows transmission of the short-wave light spectrum. The transparent cover prevents heat escaping and also prevents loss through the wind factor. Together with the frame, the cover protects the absorber from adverse weather conditions. The insulation on the back of the absorber and on the side-walls lessens the heat loss through conduction. Insulation is usually of polyurethane foam or mineral wool.

 
 

Evacuated-tube collectors

In this type of collector, the thermal energy is absorbed by a copper strip located within a glass tube. The glass tube is under vacuum so heat collection is maximised while losses are kept to a minimum. The heat transfer fluid flows through the absorber within each tube directly.  The solar collector is usually made up of 20 or 30 tubes connected together via a manifold.  A heat pipe collector incorporates a special fluid which begins to vaporize even at low temperatures. The steam rises in the individual heat pipes and warms up the carrier fluid in the main pipe by means of a heat exchanger. The condensed liquid then flows back into the base of the heat pipe.

The pipes must be angled at a specific degree above horizontal so that the process of vaporizing and condensing functions.  Evacuated tubes offer the advantage that they work efficiently with high absorber temperatures and with low radiation.
Thermal_Swimming Pool

 

Domestic hot water

Solar hot water heating systems perform well in the South West due to the relatively higher levels of solar radiation. The solar fluid is through the panels to collect heat and then pumped through a separate coil with your hot water cylinder to transfer the heat energy to you hot water. A solar controller will monitor the temperature within the solar panel and the hot water cylinder; from this it will calculate whether to run the pump and how fast, thus transferring free energy from your roof to your cylinder and stores it for use later in the day. Solar heating can provide almost all of your hot water requirements during the summer months and is therefore very cost effective.
Thermal_Collector_Flat1

 

Swimming pool

Using a dedicated solar thermal system is a highly efficient way of heating swimming pools, and can be much cheaper and far more energy efficient than using conventional fuel sources. A swimming pool solar thermal system works in much the same way as those used in domestic properties, and allows for solar energy absorbed by the collectors to be transferred to the pool water using a heat exchanger. What’s more, the use of swimming pools tends to be concentrated during the summer months, which is also when solar thermal systems receive the most radiation. If you only need to heat an outdoor pool during the warmer months, a solar system may be able to completely replace your existing heat source, saving you money and reducing your carbon footprint. A dedicated solar thermal system for a swimming pools will need to be larger than domestic systems, as there will be significantly more water to heat.
Thermal_Swimming Pool

 

Requirements

The optimum installation will have a pitch of 30 degrees on a south facing roof. However most roofs facing between east and west will offer a usable contribution to your domestic hot water requirements. Solar collector panels can also be mounted on a frame on the ground or on a flat roof. The area required will depend on the amount of heat required and the type of collector used.

It is likely that for a system to be most effective an upgrade to the hot water tank will be required. A larger hot water tank will be able to store more of the solar energy that is collected and will increase efficiency.

If the building is listed or in a protected area, planning permission may be required.

Funding

Solar Thermal Hot Water heating qualifies under the RHI Scheme. Other limited funding may be available for small or large projects, whether domestic or commercial depending on various factors of eligibility.

If you are thinking of investing in renewable energy systems for your home or business, you can find out more about eligibility at: http://www.energysavingtrust.org.uk/