Not commercially viable

I can see geothermal energy used for heating, but thermodynamic efficiency is, by definition, very low

Two years ago I was involved in exhaustive reviews of the potential for geothermally generated electricity from a deep set of wells in the south of England. The temperature at 2500 metres below grade was 130 degrees and our client thought that was the clincher. By the time we had exhausted every option, from very (very) wet steam to a host of various secondary cycles, from gas to fluids with low boiling points, we, with great reluctance confirmed that it was just not commercially viable. Apart from anything else, the cooling effect on the formation, with the permeability of the rock meant that the power/heat available decayed unacceptably.

We had been pointed towards one low boiling point fluid 'operating' in southern Germany, but despite the glossy brochures, we were unable to get the operators to say much about the actual effectiveness of the system without the use of the supplementary firing in its design. Our conclusion was that if they weren't willing to let us have any positive feedback, others involved with the project that advised it was less than successful might have had a point.

I can see geothermal energy used for heating, but thermodynamic efficiency is, by definition, very low unless you get water coming up at a reasonable temperature. And all the power our system would have generated would have gone into the plant's pumping and cooling systems. I am sorry to be less than enthusiastic, but after all the work we carried out, I find it hard to read an article with so much hype and so little substance.

Lee Horwich

• Read February's Cover Story on Geothermal technology: Deep Heat