Solar Thermal Energy

Solar Thermal Energy

Solar thermal energy can be captured by solar panels. There are two main types of solar panels which use completely different technologies to make use of the energy from the sun. Solar water heating collectors are panels that absorb the energy from the sun and transfer it to heat water. Photovoltaic (or solar electric) panels transform solar radiation directly into electricity.

Heating water using solar thermal energy

Solar water heating systems use panels connected to a domestic hot water system to reduce or eliminate the need for the boiler to run in warmer or sunnier weather. In most cases, solar panels cannot be used with combi boilers, as they require a special hot water tank with a second heat exchanger loop for the solar circuit. Until the introduction of feed-in tariffs (internal link) for PV they were the most popular form of small-scale renewable energy in the UK with many thousand successful installations. Solar water heating systems typically provide around 40% of a household's hot water requirements over the year. There are two main types of solar water heating collector: flat plate and evacuated tubes.

Flat plate collectors
Solar water heating panels in their simplest form are made from a sheet of metal painted black which absorbs the suns energy. Water is fed through the panel in pipes attached to the metal sheet and it picks up the heat in the metal. For the UK climate, the pipework contains non-toxic anti-freeze. The pipes are often made of copper for better conduction. The metal sheet is embedded in an insulated box and covered with glass or clear plastic on the front. The system is usually installed on the roof. Some, more expensive systems, integrate the collector plates into a unit that can be fitted flush with the roof, as a form of solar tile, and these may be acceptable on listed properties or in conservation areas where traditional solar systems are deemed unsuitable.   

Evacuated tubes
The evacuated tube system is a series of glass heat tubes grouped together. The tubes are highly insulated, due to a vacuum inside the glass. Evacuated tubes generally have a slightly higher output than flat plate systems, offsetting a higher purchase price.  

The cost of installing a solar hot water system ranges from approximately £500 - £1,500 for a DIY system, to £2,000 - £5,000 for a commercially installed system. These prices, however, are dependent on the size of the system. A typical installation in the UK has a panel of 3m2 to 4m2 with a storage tank of 150- 200L (2m2 for evacuated tubes). However, the optimum size will depend on actual hot water use. This can be calculated using software to simulate system performance throughout the year. Householders can benefit from financial support under a Renewable Heat Premium Payment, which will be replaced by the Renewable Heat Incentive in 2014. 

For more information about solar water heating and a list of suppliers, please visit the Solar Trade Association's website.

Generating electricity using photovoltaics (solar electric)

Photovoltaic (PV) or solar electric offers us all the ability to generate electricity in a clean, quiet and renewable way. The variety of applications for solar electric are numerous. Photovoltaic (PV) cells were initially used in simple or off-grid applications such as calculators and watches and for boats or caravans, but over the past decade have become widely installed on buildings to generate electricity for export to the National Grid. The daylight needed is free, but the cost of equipment can take many years before receiving any payback. In recent years, the introduction of Feed-in Tariffs has made PV a much safer investment, and has led to the installation of many building-integrated systems in the UK.

Passive solar
The use of passive solar design is possibly the simplest form of solar energy. Many buildings today are designed to utilise the energy of the sun as efficiently as possible. The location and orientation of the building are all key factors in optimising passive solar design. Passive solar design can be best applied in new buildings, where the orientation of the building, the size and position of the glazed areas, the density of buildings within an area, and materials used for the remainder of the structure are designed to maximise free solar gains. Use of overhangs, seasonal planting or brise-soleils can reduce the risk of overheating in summer, while allowing maximum solar gain in cooler months. Designing a property to maximise free solar gain need not add to the price of construction. 

Studies on houses in Milton Keynes have shown that low-cost passive solar design features together with draughtproofing and insulating measures reduced heating bills by 40%. Savings paid back the costs in two years. More sophisticated designs, including those to the Passivhaus standard, which also requires high insulation levels and often uses mechanical ventilation with heat recovery (MVHR) instead of a conventional heating system, may take a little longer, but provide a degree of resilience against future energy costs.

Other active solar
In addition to solar panels, there are a number of more specialist active solar systems. Some provide a contribution towards space heating, for example by pre-heating air for a warm-air central heating system, or contain specially designed collectors in a solar wall. Solar can also be used to some extent to provide cooling in summer, through the use of 'Solar Thermal Absorption Cooling', either as a lower energy alternative to air-conditioning or for small scale industrial processes.