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Ground force

Renewable energy is becoming more competitive with traditional energy sources such as oil and gas. Geothermal energy through a ground source heat pump can be an economical long-term solution to providing hot water and heating in your home. Andy Moore explores the use of a ground source heat pump to provide a cost-effective and environmentally friendly solution in Scotland.

Dubbed the 'sleeping giant' of renewable energies, geothermal energy offers an opportunity for Scotland to reduce its reliance on non-renewable sources. Geothermal International’s Managing Director in Scotland, Dee Ward, said: "The potential for harnessing geothermal energy in Scotland is massive."

Ground-sourced heat pumps provide one means of accessing this renewable energy resource that has been exploited for decades in the US, Scandinavia, Germany and France. But why is the technology still low key in the UK?

Earth energy

Ground sourced energy offers considerable potential to achieve renewable energy targets for Scotland, making the country a cleaner and greener place. Burning fossil fuels produces greenhouse gases which contribute to global warming. Ground source heat pumps, on the other hand do not directly produce CO2 and require only a relatively low amount of electricity to operate. But how does it work?

Whilst above the ground the temperature fluctuates throughout the year, just a metre below the ground surface the temperature remains almost constant at around 10°C.  With depth the temperature increases gradually.  A ground source heat pump system is used to collect this heat and to convert it to a warmer temperature to provide heating and hot water.  The loop can be installed in a shallow trench or, particularly where space is at a premium or disturbance of the ground is undesirable, can be installed as a vertical loop in a borehole.  Similarly, deeper lochs and ponds can provide constant temperature environments which can be tapped as an energy source.

A series of pipes are laid below the surface of the ground or submersed in a pond or loch in a loop.  The pipes contain a fluid which is pumped around the loop, collecting the heat and transferring it to an indoor heat pump.  Stewart Warwick, Director of Ice Energy Scotland explained that the heat pump works in a similar way to a fridge:  “Just like a fridge, the heat pump has an evaporator to take the heat from the ground, a compressor to move the fluid around the heat pump and compress it until it reaches the desired temperature, and a condenser to transfer the heat to the hot water system.  But unlike a fridge, the refrigerants used in our ground source heat pumps don’t contain any harmful CFCs which harm the ozone layer.” 

In addition, before the cooled fluid is returned to the ground within the loop, this can be utilised for comfort cooling of the building environment, removing the need for and cost of unsightly rooftop plant.

According to the Department for Trade and Industry (DTI), there are currently over 250 ground-source heat pumps installed in the UK every year. More importantly, the DTI estimates there are over 1,550 large industrial sites in the UK where geothermal systems could be installed. Scotland is no exception to the potential for capitalising on geothermal energy.

Saving money

Typically, electric power is used only to operate the heat pump.  It has been estimated that the ground-source heat pump can deliver three to four times more energy as heat than the electricity it consumes.

Not only is the technology more environmentally friendly than using fossil fuels, but it can save money on heating costs as well. Stewart Warwick said: “Savings of 30-60% on energy bills can be achieved depending on the current fuel type.  For a typical four bedroom home, installation costs can vary from £7,000 to £10,000.” 

There are grants available from Scottish Community and Householders Renewables Initiative (SCHRI) for domestic properties to pay for 30% of the project cost up to a maximum of £4,000. This means that if an average installation costs £8,500, the grant and the energy savings rapidly pay for the system. Ice Energy Scotland suggest pay-back periods ranging from to six to eight years depending on the property age, energy usage and grant received.

Ground source heat pumps can be used for a range of developments, from small crofts to hospitals and schools, with energy requirements ranging from a few kilowatts to over 10 megawatts of power. Although new-build houses or houses undergoing major refurbishment are the most cost effective, VAT is only charged at the reduced rate of 5% on retrofits. This may, however, entail additional work to the plumbing for the system to work efficiently.  Developments with underfloor heating are most effective to harness geothermal energy because the system runs at lower temperatures but it is also possible to use the technology with conventional radiators.

Future potential

A key benefit of harnessing geothermal energy is that systems can be installed in almost any location across Scotland. This approach may be particularly suited to the provision of energy in remote or environmentally sensitive regions in Scotland. Although the construction period may be disruptive, once the installation is complete there is often little or nothing to see.

Mr Ward added: "Unlike wind or wave power, which is more subject to the whims of Mother Nature, geothermal energy is able to work every day regardless of the weather conditions. Furthermore, the system does not pose some of the visual problems encountered with wind and wave energy. Geothermal is hotting up in Scotland."

Grants in Scotland:

Grants in England, Wales and Northern Ireland:

Department of Trade and Industry:

Groundsource Heat pumps:

Geothermal heat pump consortium:

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