There is also a common misconception about energy piles which we would like to clear-up here, before we start this article. The use of energy piles, as described here and as commonly used in this respect, has very little if anything to do with geothermal energy where steam and hot water are used to drive turbines to generate electricity. Geothermal energy requires a source temperature of more than 100 degrees Centigrade to drive a generating turbine. That is not what an energy pile requires or needs.

Besides, very few properties are lucky enough to be located in a part of the globe where a borehole, no more than say 100 feet deep, would experience any significant geothermal temperature rise at all. Energy piles therefore don’t operate at anything like that temperature and are much more useful than geothermal for most of us.

The energy pile is in fact simply a device which uses the thermal capacity of the ground around the pile to act to store heat. It works on a principle similar to a flywheel in that heat pumped from the ground in winter will be replenished during the summer. In fact energy piles can also be used for cooling buildings in summer when they work in reverse, and exactly the same principle works in both cases in hot and cold climates.

Therefore, energy piles are a great idea which could load and unload so-called seasonal thermal storage for huge numbers of properties worldwide. Their usefulness is not limited to the presence of geothermal heat in the nearby rocks. All you need to do is drill one or more piles one hundred to several hundred feet deep beneath or beside the property, and install a closed circuit of pipework.

Energy piles like this, combined with heat pumps (a refrigerator contains a heat pump), and fuel cells using hydrogen to provide the electricity to run the heat pump, would be a very clean method for heating homes and offices.

Such systems are not geographically limited and could be used almost everywhere, except in permafrost zones. They could supply a rapidly increasing proportion of the world’s energy supply if fuel cell technology and sustainable hydrogen production methods can be mastered and developed.

However, unless and until fuel cell technology, and clean hydrogen production to fuel those cells (such as by daily solar recharge of a hydrogen cell), is developed (and available at a low cost), there is still a need for some fossil (carbonaceous) fuel to be used to power the heat pump. Nevertheless, 40% savings in energy use overall can readily be achieved against a fairly low investment in the energy piles, and the necessary heat transfer circuit, from the property to the energy pile or piles.

The cost of the construction of energy piles will vary with the type of ground. Boring into hard rock will cost more than into softer ground.

Concrete piles are usually used in the ground storage system, and they house a closed water pumping circuit made from plastic (usually polyethylene or polypropylene) piping. The piping which is inserted as a loop into the borehole bore, runs from the top to the bottom, before turning and returning to the top.

The pipes are used to circulate a heat transfer fluid, (of water plus anti-freeze in cold climates), which transports the ground temperature to the central control system for the building air conditioning services. These piles can be used either as heat collectors or heat conducting heat dissipater’s.

Steve Evans also writes for the UK Anaerobic Digestion web site.