Solar Thermal, hot water

Solar water heating systems have been in use for many years and although the basic principal remains the same, solar collectors have improved and become cheaper with the result that a system now, if properly installed can be a very good capital investment.

Solar thermal collectors fall into two main types, flat plate or vacuum tubes the latter being generally considered to be more suitable for the UK climate as they do not need direct sun and will work in overcast conditions.

There are several applications, the most used being to compliment an existing boiler to supply hot water requirements. Most boilers are suitable and can be gas, oil, solid fuel and all electric systems.

Vat has been reduced on solar installations and grants are available for both domestic and other applications.

Environmental reasons suggest that we all must make use of alternative means of generating energy to protect our planet and to leave something behind for future generations.

Installations are usually straight forward, a new hot water cylinder would be installed to combine with existing boiler.

Grants are available under The Low Carbon Buildings Programme, subject to certain criteria and availability.

How does a system work

Panels or tubes are mounted usually on a southerly roof or can in some cases be mounted on "A" frames on the ground. A replacement specialist hot water cylinder is installed with a solar heat exchanger coil, a transfer fluid is pumped via a pressurised circuit from the collectors thus heating the hot water cylinder. A solid state differential controller is usually included with various valves and safety features.

Here is a typical active solar heating system. An electronic controller constantly compares the temperature of the solar collectors with the temperature of the water in the cylinder.

Whenever the collectors are hotter than the cylinder, the controller switches on the circulating pump. A mixture of antifreeze and water is then circulated through the collectors and the cylinder's heat exchanger, heating the cylinder in just the same way as a central heating boiler.

Installation is straightforward and usually involves changing the existing hot water cylinder to a twin coil cylinder and connecting this to the solar tubes. The work involved is mainly external and is usually completed within 2 days.

This system can work in tandem with virtually any other heating system and requires very little maintenance - a check every three or four years.

We recommend the Thermomax system for most homes. This world-leading UK-made system uses vacuum tube technology giving total insulation against cold winds and temperature. It works solely on daylight - works in cloudy conditions - and therefore gives good year-round performance. A 20 tube system, covering an area of 2 square metres is suitable for a 3-bedroom house. This should provide 90% of the hot water from April to November and pre-heat water throughout the winter months.

Systems Design - Domestic Hot Water

A special storage cylinder with two heat exchange coils is used. The top coil is connected to the conventional boiler. The lower coil is heated by a solar collector.

Energy from a solar collector is transferred to a secondary storage cylinder. This cylinder now becomes a pre-heater to the main storage cylinder until its temperature reaches a desired level. At this point, a divertor valve stops the pre-heating function and the solar heated water is supplied direct to the hot water taps.