Statistics so strange you don’t notice them at first

Green Deal assessors have visited ten thousand homes and written down recommendations for saving money on energy bills. Out of this group, 195 householders  were told to install a roof-mounted wind turbine.  This is really, really surprising – not least because these turbines have fared so catastrophically badly on domestic properties. But there are three other concerns as well. One, no-one should ever lightly recommend a roof mounted wind turbine on a domestic property. The turbulence around the roof will usually reduce the output of a turbine to minimal levels. Even in the tiny number of exposed locations where a roof turbine might just work properly, the householder would need to take at least three months of wind speed measurements before risking purchase. The quick inspection by the Green Deal assessor isn’t nearly good enough.

Second, there is virtually no prospect of roof mounted wind turbines meeting the Green Deal’s Golden Rule of cutting energy bills after financing costs. The scheme rules say that therefore they shouldn’t be recommended. The best available roof turbine is the Swift, a 1.5 kW machine costing about £7,000 including an allowance for installation. This might produce 2,500 kilowatt hours a year in the very best location, with a FiT income, including exports, of less than £600. Energy bill savings could add another £150. With Green Deal interest rates of 7% and an annual maintenance charge of perhaps £100, the turbine won’t have covered its cost by the end of a 20 year life. The homeowner would lose money.

Third, if the home really is in an area with very good and steady winds (which must mean the building is on a coast with no trees nearby and clear access to the south west), the right recommendation might be to install a pole mounted small conventional turbine. But, very curiously, none at all of the Green Deal’s first 10,000 households at all were given this advice.

It all seems very strange. The suspicion must be that the assessors for the 195 properties were simply unaware of the sad record of roof mounted turbines in the UK and how wildly inappropriate they would be almost everywhere. This should increase concerns that they the Green Deal assessors are not appropriately trained for the difficult task they are carrying out.