Green Renewable Energy

As interest in greener sources of energy increases, more people are looking at environmentally friendly ways of heating their homes. One such option is geothermal heat - with the word geothermal coming from the Greek "earth heat".

The temperature a few metres below the ground surface is a remarkably constant 11°c to 13°c, even during the winter when the air temperature is much lower. This heat is generated by the 50% of all solar energy that is absorbed by the earth. And this geothermal heat can in turn be used to heat your home.

In the UK, geothermal heating systems are installed on a house by house basis, but in other countries geothermal energy is used by power stations to provide the electricity for whole cities. For example, in Iceland, 17% of the country's electricity comes from geothermal sources and in The Philippines that figure rises to 27%. In fact,despite a reputation for dependence on oil, it is the USA that produces most power using geothermal sources. Even in countries with no geothermal power plants, the attraction of geothermal heating is causing a growth in its popularity. 30,000 homes in Canada are heated this way for example.

The heat of the earth is so vast that even if most of the world's energy needs came from geothermal sources it would remove no more than a small fraction.

There are three elements to a domestic geothermal heat system

1. Ground Pipes

To capture this energy, loops of pipes are laid below the ground and a water / antifreeze mix is pumped through them. This water absorbs the heat from the ground.

The pipes can be laid horizontally (six feet below the surface), vertically (up to 150 feet) or submerged in water. In cases where space is an issue, the pipes can even be laid below the foundations.

The size of heat pump and length of pipe will determine the efficiency of the system. Insulation can help cut down your energy requirement but it is important to consult with an accredited installer for the best advice.

2. Heat Pump

The heat pump which drives the water around the ground pipes takes the heat difference in the temperature of the water passing through the tubes and concentrates it to a higher grade of heat using a heat compressor. The principal of heat exchange is exactly that of the refrigerator, only in reverse, with the refrigerant being heated and passing this heat energy on to the condenser which is then transferred throughout the house by the heat distribution system chosen.

For every unit of energy used, three to four units of heat are delivered so the heat pumps are 300% to 400% efficient.

3. Heat distribution system

Typically temperatures of 60 degrees can be attained which makes it an ideal system for use with underfloor heating. Radiators can also be used and in some cases, hot water can be supplied.


Cooling

The system can work in reverse in the summer to cool the house too, removing the heat from the house and discharging it to the earth.


Other Green Systems

In comparison to the heat obtained from a geothermal system, solar energy works best during the summer, the time when it is least needed and wind power is dependant on the weather conditions. Geothermal energy is provided by the earth's heat which varies little even during the depths of winter. The pumps and heat exchangers are made to high standards and are extremely efficient.

Solar or wind power can be used in conjunction with geothermal to power the compressor and pump, allowing you to install a completely renewable system.


Costs And Gains

The costs of these systems vary, but the cost of an 8KW heat pump and the outside pipes is generally around £4,000 - £10,000. The cost of the distribution system - the underfloor heating pipes inside your property - is not included in this so this must also be factored in. Other costs such as improved insulation should also be taken into consideration. However the capital costs of installing a tank for oil or LPG can be eliminated.

The running costs are lower than those associated with oil, electric or LPG but at present mains gas is slightly cheaper.

But as supplies of fossil fuels are not infinite, unlike the heat from the sub earth, these costs can change.

There are also many grants available for the installation of renewable energy systems giving you up to 30% off the cost of installation. For details of currently available grants visit the DTI’s low carbon buildings programme website.