A surveyor’s guide to harnessing geothermal power

geothermal power station

A number of government incentives have been introduced over the years to meet the country’s ‘green’ tagets, including Feed-in-Tariffs in 2010 and Renewable Heat Grants in 2011. Plans are now afoot to harness geothermal power by deliberately flooding disused mines in order to use the heat in community homes and businesses.

We look at how homeowners can use geothermal power to reduce the energy costs of domestic property.

What exactly is geothermal power?

The ground beneath our feet has a significant amount of energy in the form of heat – the closer to the Earth’s core you go, the greater the heat.

Even a few metres below ground level, there is a constant temperature of 11-12ºC and this heat can be harnessed and used either to generate electricity or contribute to a heating system. The average mine reaches temperatures of 14-20ºC and in the deepest mine at 1.4 km deep temperatures would reach around 40ºC.

On a more simple domestic scale, geothermal power would usually be used for heating via a ground source heat pump. By warming the water in a heating system, the boiler becomes more energy efficient as it no longer has to heat the water from cold.

How does a ground source heat pump work?

A geothermal heat pump works by circulating a carrier fluid (usually a water and antifreeze mix) through pipes buried under the ground around the property. As this fluid circulates it absorbs heat from the warm ground. On its return to the property, the heat pump uses electricity to extract the heat from the fluid. This heat is added to the heat gained as a by-product from the pump appliance itself, generated by the pump as it functions. The two heat sources are used cumulatively to help heat the house.

The cooled carrier fluid then continues on its loop. The addition of this loop results in more heat generated than if electricity alone had been used directly for heating.

What are the basic requirements to have a ground source heat pump installed?

Unlike solar power where location is important, geothermal power will, in theory, work anywhere. However, a household considering installation does need a certain amount of land in order to accommodate the piping needed. The rule of thumb in this case is: heating capacity of the heat pump (kW) x 10m.

Where land is more scarce boreholes can be used instead, although the cost for this will be greater. Alternatively, an air source heat pump might be used. With no digging, borehole or slinky (a form of coiled ground piping) requirement, air source heat pumps can provide significant installation cost benefits over ground source systems, although they are generally less efficient.

In general, the wetter the land the better as water conducts heat very well, although the land needs to be firm enough for the trenches and pipes to be laid safely.

There may well be planning restrictions for developments of this type in your area, particularly if you live in a Conservation Area or your building is listed. It is advised that you consult your local planning authority to confirm whether installation requires a formal consent.

How large and noisy would the in-home part of the installation be?

A modern system will only be the size of a fridge, in most cases, and will generate noise at approximately the same level. It is generally recommended that it is located in a garage or outbuilding.

What would the most compatible type of heating be?

Any type of heating can be connected to a ground source heat pump, but some are more effective than others. Radiators generally operate at a water temperature of approximately 70°C and are thus less suitable than underfloor heating, which operates at a comparably low floor temperature of between 25-29°C. The lower the heating temperature required (i.e, the closer to the earth surface temperature of 11-13°C), the more effective the outcome and the greater the saving.

How long have humans been harnessing geothermal energy?

Hot springs have been used for bathing since at least Paleolithic times. The oldest known spa is a stone pool on China’s Lisan mountain built in the Qin dynasty (3rd century BC).In the first century AD, Romans conquered Aquae Sulis (now known as Bath) and used the hot springs there to feed public baths and under-floor heating. As these baths required a fee of entry, they are likely the first commercial use of geothermal power.

The world’s oldest geothermal district heating system at Chaudes-Aigues, in France, has been operating since the 14th century. The earliest industrial exploitation began in 1827 with the use of geyser steam to extract boric acid from volcanic mud in Larderello, Italy.

When was the first use of geothermal technology for a residential development in the UK?

The first use of geothermal power in a UK residential development was in May 2009, when a luxury apartment complex was built in St John’s Wood, London. Planning permission for this development was granted in 2006.

How much of the world’s power is generated via geothermal means?

Over 20 countries around the world generate geothermal energy and the USA is the world’s largest producer. Iceland makes use of its 25+ active volcanoes, many hot springs and geysers to heat buildings and pools, but in the US it isn’t only used for heating property; some cities even use geothermal hot water systems beneath roads and pavements to melt snow and ice.

What advantages does geothermal power have?

Geothermal energy exploits a naturally occurring phenomenon that does not involve the burning or use of any finite materials. It is an entirely green energy, producing none of the pollution associated with fossil fuel burning and produces only a sixth of the carbon dioxide of a natural gas power plant.

Geothermal energy has a significant advantage over its competition in that it does not fluctuate and is an entirely sustainable energy source.

Solar panels rely on the sun shining and their power diminishes in times of cloud cover (all too frequent in this country). Wind turbines rely on the wind blowing and are frequently seen inoperative if the wind is too low or too high. Unlike these, geothermal power relies on the warmth of the earth itself, a factor which never fluctuates beyond one or two degrees and is always a ready source of energy.

Geothermal power is also better value for money than many of its counterparts. Economic studies have shown that the cost for a geothermal installation is significantly cheaper on both per kilowatt-hour and original investment terms. Savings could even be as much as 80% over fossil fuels.

Whilst tidal and other hydropower schemes can have continuous generation of green energy, the ease of maintenance can be significantly harder to operate depending upon the type of scheme.

What are the disadvantages of geothermal power?

Domestic installations can be placed almost anywhere.

However, a larger or commercial geothermal installation would need a site with hot rocks at a depth that can be drilled. The type of rock also matters, as a harder rock will be more difficult, and more expensive, to drill through. In some instances an industrial geothermal site might literally ‘run out of steam’and become inoperable for perhaps even decades.

There is also the possibility that pockets of hazardous gases or minerals might come up from underground. Disposal of these gases or minerals can be difficult and expensive, but there could also potentially be useful by-products. Iron, for example, could be used in the cleaning of contamination from areas containing arsenic.


© www.PropertySurveying.co.uk