Solar, so good

Jimmy Saville, super sized flares, choppers and solar water heaters. OK, the upsurge in renewables may be a fairly recent phenomenon, but the solar domestic hot water system has been available in the UK since the 1970s. And according to the Energy Saving Trust, it is still the most cost effective and affordable renewable energy technology on offer. There is now a broad range of equipment to suit many applications, and with the demands of Part L, rising fuel costs and the heightened environmental awareness within society in general, this is clearly a growth industry with huge opportunities for installers.

The government’s Energy Review, published this summer, included a promise to remove planning restrictions on all new solar panel installations. This could prove to be the most significant advance for the renewable energy market so far. Mark Wilkins, brand manager at Valliant boilers says: “Having to apply for planning permission was a bureaucratic stumbling block and a barrier to wider adoption of solar thermal systems for efficient domestic water heating.”

In order to take advantage of these opportunities, however, contractors need training. The Low Carbon Buildings Programme (LCBP) will be launching an accreditation scheme for installers to replace the current list run by the Clear Skies renewable technology grant programme. Installers who are not registered will not attract LCBP funding.

The focus is on ensuring the technology falls into the right hands, so installation standards are of the highest quality. Colin Hilliard, Valliant’s training manager for renewables, explains: “Good domestic central heating installers have most of the basic technical skills required to fit solar domestic hot water systems, but they must still undertake full and detailed training to cover the specific requirements of the technology. And we must, at all costs, keep the cowboys away from this market.”

Sunny outlook

In a standard solar thermal system, aluminium collector panels or evacuated panels are positioned on the roof. Ideally, the panels should be south facing, at an angle of 45°. Roofs which face southeast to southwest can still be used, but the energy harnessed will be lower.

A water/glycol fluid within the pipework is heated and circulated through a heat exchanger in the base of a high efficiency cylinder. The heat is transferred to the domestic hot water supply.

A conventional system uses a twin-coil, indirect hot water tank, which holds 200 litres or more. The lower part is heated by the solar coil, the upper part by the boiler.

Alternatively, a single-coil tank can be used. With this approach, the upper part is heated by an electric immersion heater.

Plates versus tubes

There are two types of solar collectors: flat plate and evacuated tubes. Flat plate systems are cheaper, typically costing £2000-£3000 to install, but are only 30% efficient. Evacuated tube systems cost £3500-£5000 to fit, but occupy a smaller area and have an efficiency of 40%.

Valliant’s Aurotherm evacuated tube solar collectors provide a sound solution where the latter is required. They are delivered pre-assembled with eight or 16 tubes for ease of installation. Collectors can be simply pushed together and up to 16 can be connected in a series to provide a neat and attractive fitting. A range of mounting accessories means they are suitable for pitched or flat roofs.

Most types of system circulate and heat the water directly in the panels, but in areas that are prone to freezing temperatures, either a drain back or a closed loop system is used. An intermediary (anti-freeze) fluid and a heat exchange system indirectly heat the water in the tank.

Vented and unvented systems are available to meet varying needs. Heatrae Sadia recently launched the unvented Megatech and vented Megalife Solar. Megatech offers the homeowner a green option where powerful showers and fast-filling baths are concerned, as the cylinder is fed direct from the cold water mains. There is no loss of performance if more than one tap is used simultaneously.

Where a traditional, vented system is required for new build or refurbishment projects, Megalife Solar is an efficient solution that is also suitable for areas with aggressive water conditions.

Energy benefits

Solar cylinders provide around 60% of a household's yearly hot water requirements. They can provide almost all domestic hot water needs during the summer, but in the winter months, the energy harnessed is much reduced. This means that an additional heating source, such as an immersion heater or a conventional boiler, is required. However, they will not work alongside all types of combination boiler, and those with hot feed washing machines save the most.

As well as making savings, home owners can also reduce their household’s annual carbon dioxide emissions by 400-750 kg.

Government legislation

The LCBP states that a minimum of 30% of the volume of hot water in thermal domestic storage cylinders must be dedicated to solar energy in order for the cylinder to be classified as solar thermal.

Since the beginning of this year, LCBP grants of £400 have been available for households who want to make use of solar thermal systems. However, the DTI allocated a paltry £3.5 million to subsidies for domestic properties wishing to harness renewable technologies in 2006-07, and the funds have already run out. The DTI has now been forced to divert funds from other areas. Such mishaps could be damaging for a fledgling market.

A guide to help ensure conventional SDHWs comply with current UK standards, regulations and best practice is available from www.est.org.uk