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Under-ground heat storage

(Click to enlarge photo)

Storage of heat under-ground is attractive as the heat losses are much less because the ground stays at roughly 7-8 degrees C most of the year and there is no cooling due to the wind, that's the plus side. I thought it might be feasible to use an old oil tank and some oil-drums insulated with straw and water-proofed with plastic sheet as an experiment. The minus side is that it is difficult to stop moisture from getting in and taking away the hard-earned heat. Oh, and the other thing, just about every small animal in creation thinks that nice warm straw underground is a perfect home! If nothing else, this episode taught me that there are no short-cuts with free energy, you have to do the job right!

Having said the above, under-ground storage (or even an insulated building on the surface) is, in my opinion, a completely valid way to achieve energy efficiency. Obviously cost versus returns have to make sense but, given the simple physics of the situation where the cube of the enclosed volume increase with only the square of the surface area (sorry), it becomes inherently cheaper to store hot stuff the larger amount there is in one place. Put another way, the available surface area per cubic metre for heat to leak away through reduces the larger the number of cubic metres being stored. This means that, if you had a big enough store, it would be possible to save heat from the summer and use it in the winter. Similarly, cold could be stored in the winter and used as air-conditioning in the summer. Either or both of these could save us a huge amount of energy and couldn't be much greener. It would also be a ready-made place to dump all the heat from windmills during a gale when energy levels go through the roof! Perhaps our largely non-technical decision-makers here in the UK might like to think about some of the more imaginative solutions rather than the clueless idiocy of make-shift bodges like fracking or nuclear (please see my section on these: Nuclear, fracking and windmills).