Moira Cruickshanks
Moira Cruickshanks Geothermal Q&A

Moira Cruickshanks of Imperial College London Engineering Department answers your questions on Geothermal Energy next week in our forum. Here she introduces ways you can use Geothermal Energy.

Post your questions for Moira in the Off-Grid Forum.

Geothermal energy is heat from the Earth. On a large scale, geothermal power plants generate electricity using naturally heated groundwater and steam from deep in the ground to turn turbines.

But we can also use geothermal on a small scale to heat our homes, schools and offices, although it is not yet an off-grid technology. If you want to supplement your grid energy with a renewable off-grid supply, either taking advantage of natural hotspots in the Earth or using the constant temperature of the planet to regulate interior temperatures, you will need to make an initial investment in the technology, and the scale is more for a community than a single home.

It is not quite as easy as plugging a wire into the earth and then lying back and toasting your toes but almost. Go to our Forum to ask questions and get answers on installing Geothermal:


The Government-run Clear Skies project in the UK has 12 million for grants every year. This is spent in both public and private sectors to install renewable energy schemes. For GSHP installation, up to 1200 is available per household in England, Wales and Northern Ireland, and up to 4000 in Scotland.

Direct heating uses heat generated within the Earth which has naturally warmed an area of ground or a thermal spring, like the Roman baths in Bath. In the UK this is most common in the Southwest, the Northeast and the Lake District because underlying rock type and structure in those areas provide the most accessible geothermal energy and localized heating.

But most of us do not live near a hotspot, so we can use a ground source heat pump (GSHP) instead. Pipes containing water or a refrigerant fluid are buried in the ground at up to 100m deep. The fluid is heated by the ground’s constant temperature, which is about 12C and acts as a heat source or sink. In winter this is warmer than the temperature of the building, so heat is transferred from the ground into the building by the heated liquid, using a GSHP to maximize the heat output. This heat can be used to provide both heating and hot water for the building.

GSHP’s do require electricity to run, but they can be used in off-grid applications because moving heat requires less energy than creating it from fuel. It does require a fairly large electrical load, but is still doable with a larger battery bank, and more generation (pv/wind/microhydro/generator/whatever).

In the summer, when the building needs to be cooled, the water in the pipes is heated inside the house and transfers the heat back into the ground, which is now cooler than the air.

GSHPs are the most common method of heating using ground or geothermal energy. Unlike direct heating which relies on the geology of an area, GSHPs can be set up anywhere since they only rely on the ground’s constant temperature. The pump system can be used to heat one house or a small community. Housing associations in both Oxfordshire and Devon have recently started projects to build GSHP-heated homes. A recent development in Shettleston near Glasgow uses ground source heating to heat and supply hot water for 16 houses. Water is heated by ground source heat in a nearby flooded mine and then piped to a fully insulated 10,000 litre tank providing water to the development. The heating and hot water costs are very low, at just 150 on average per house last year.

Ground source heating is used in public spaces as well. The London Zoo Invertebrate House, maintains its constant temperature, essential for animals inside, by using a GSHP system. And the National Trust is considering using them to heat some of the stately homes.

Anyone can set up a GSHP system, wherever you are in the country, provided you have a small area of land and a little start-up capital. Today we have about 400 domestic GSHPs in the UK, a rising figure, and grants and non-existent maintenance costs are making them ever more appealing.

A direct heating scheme was set up in Southampton in 1986 using heated groundwater stored naturally below the surface at up to 75C. Geothermal energy heats groundwater which has been piped so that it warms the air to directly heat Southampton City Hall, main shopping centre and several hotels.

4 Responses

  1. GSHP’s are more popular here in the US for off-grid installations. They do have some significant loads, but not anywhere near as much as electrical resistance heating, and use less energy than burning fuels for heat and hot water. Additional battery storage and wind/pv generation are required. Microhydro would be the best, but those sites are rare. The horizontal slinky coil seems to be the most popular for off-gridders in our extreme cold climate (-40 for a few weeks each winter),

  2. PLEASE be very careful about promoting ground source heat pumps for off-grid use. As far as we know, all GSHP’s currently available on the UK market require full voltage / current to operate and do not support variable speed operation – or part current / part voltage operation. They also have high starting currents – which may cause significant damage and or problems with stand alone off-grid power systems. Potential users must be made aware of these issues – or there will be some very expensive mistakes made. We get enquiries for off-grid applications – but to date we are not aware of any off-grid GSHP installations in the UK.

    Good luck with the online debate.

    Please note that the Shettleston project is a minewater system – not a ground loop system. The National Trust have at least two GSHP systems running – one at Botallack in Cornwall and one on The Wash.


    Robin Curtis
    Technical Manager
    EarthEnergy Limited

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