Welsh National Peltier

Next time you're dismantling a defunct Peltier (thermoelectric) module, examine it closely.

Sandwiched between the two ceramic faces are a series of short pillars with spaces in between them; these are semiconductive material (alternate pillars being N- and P-type). The tops and bottoms of adjacent pillars are connected electrically, so that there is a sort of long, continuous zig-zag path all the way across the module, running up one P- pillar and down the adjacent N-pillar. This arrangement is sufficient to pump heat when a current is passed through the device or, conversely, to generate electricity when one face of the device is warmer than the other (or vice versa, natch).

But you already know that. You probably also know that the temperature of the Earth's rocks increases gradually as you go down. (I mean that the lower rock strata are generally warmer. Obviously, they don't actually become warmer simply because you, personally, are going down.)

Now, come with me, if you will, to Wales, and look around. If you can look at Wales and not think "Peltier!", then you have no soul.

Doubtless you've figured it out already, but here is the plan.

Most of Wales, of course, is riddled with mine shafts. In fact, they only stopped mining because they realized that, if they continued, the entire country would simply flump down a couple of hundred metres and they'd have to start all over again, except this time under water.

If you know your Welsh geology as well as I think you do, you'll be aware that many of these shafts run vertically through dense slate and other imperveable rocks. However, the rocks at the bases of these shafts tend to be porous (which is why they stopped digging downward at that point) - typically sandstones, chalks and the like. Similarly, there are porous sedimentary rocks near the surface.

So, it's all blindingly obvious. The first job is to ensure that the bottom-most layer of porous rock is water-saturated (which it probably is already), and that the water it holds is quite conductive. This can easily be accomplished by using it as a repository for soluble heavy-metal waste, which can be pumped in under pressure.

Once the lower porous layer is rendered adequately conductive, we need to re- open all of those capped-off mine shafts, and start semi-conducting. Based on a large-scale Ordnance Survey map and some careful computations, each mine shaft will be designated either "P" or "N", and will then be filled with molten silicon doped with the appropriate additive.

Fortunately, Wales has a good many sandy beaches which can provide just enough silicon for the project. Naturally, nobody is likely to want to sunbathe on the Welsh coast, so this is an otherwise wasted resource. Local refineries, processing the sand into P- or N-type semiconductor, will provide much-needed employment for the native people.

With the mine-shafts all filled in this way, all that remains is to establish the final conducting layer that links them all together at the top. Once again, a programme of intensive heavy-metal doping (this time of the upper porous rock layers) will be undertaken to accomplish this.

As the conduction-path in the upper rocks is completed, there will be a loud humming noise and a smell of ozone, as a several teraAmps of current start to weave their way up and down, back and forth, beneath what remains of the Welsh countryside. Two enormous terminals (one in Llandudno, one in Cardiff) will then be connected to the National Grid, and Wales will finally have reason to be proud.

[NOTE: If anyone from Wales is having this read to them, no offense was intended.]