The water below Southampton is heated to 75 degrees centigrade by the earth's core and inside a unique building in the heart of the city this is being used to provide low-cost energy...

NOT many people know what it is or that it's even there, but the red and blue metal building opposite WestQuay shopping centre holds a remarkable secret.

The building is Southampton Geothermal Plant and is completely unique to the city - there isn't another plant in the UK.

It provides energy-efficient heating and chilling for some of the largest organisations in the city as well as numerous homes.

So how did the plant come about? Following the dramatic rise in oil prices in the late 1970s, the Department of Energy set up a research programme looking into the potential for alternative energy sources in the UK, particularly wind, wave and geothermal energy. Geothermal energy is sourced from salt water naturally heated by the Earth's hot interior.

Mike Zorab, supervisor at Southampton Geothermal Plant, said: "A number of locations were identified as possible sites of deep geothermal aquifers which contained water to a temperature sufficient to provide heating for a number of buildings.

"A well was drilled in the centre of Southampton. Water was found at a depth of nearly 1,800 metres and at a temperature of 76C."

However, the size of the resource was deemed too small to develop the planned large-scale heating scheme and the project was abandoned by the Department of Energy.

Southampton City Council refused to let the project fail and, after considerable effort, found Utilicom, a French-owned energy management company, as a partner with whom to develop a scheme.

In 1986, the two partners formed the Southampton Geothermal Heating Company. The scheme, which initially served a core of consumers from the geothermal well, has now grown into an expanding £4m multi-source heating and chilling system.

Mike said: "More than 20 major consumers in the city centre are now served by the district heating scheme.

They include the Civic Centre, four hotels, the Royal South Hants Hospital, Southampton Institute of Higher Education and the Asda store.

"Recent developments include a district chilling system using the latest absorption chilling technology.

"The pipelines which run below the city, lose less than one degree in temperature in the transfer to the Royal South Hants.

"It is a very effective and efficient way of heating.

"We also generate our own electrical power to run six large chiller plants, which use cold water to run the air conditioning system in WestQuay shopping centre.

"The main advantage of the plant is that companies don't need their own boiler plant or own maintenance people.

"We also heat 108 flats in the Polygon area of the city. It costs 25 per cent less than running a back boiler and takes up far less room.

"The installation at the Asda superstore in the city takes up a small cupboard - giving them more room for their shop floor.

"The well will last indefinitely provided that there is only the one well within a ten-mile radius.

"It is surprising that there is only the one geothermal well in the UK, but obviously other areas do not have the foresight of Southampton City Council."

Mike Smith, executive director of Southampton City Council, said: "The city centre geothermal power scheme is a great example of energy efficiency bringing the benefits of lower cost to businesses and householders.

"There is no reason at all why other local authorities should not be developing combined heat and power (CHP) schemes.

"Other public bodies should also be thinking in those terms and I'm pleased that within the city the Southampton University Hospitals Trust, the General Hospital and Ordnance Survey are running CHP schemes.

"With regards to carbon dioxide emissions alone, the city centre scheme is already saving 12,000 tones per annum of carbon equivalent thought the district heating scheme."