The man behind plans to build a controversial wind farm between Burnham-On-Sea and Brent Knoll has this week hit back at protestors in a heated row over power generation calculations.

Speaking to, Dale Vince, Managing Director of Ecotricity, disputed claims made by the KNOll to Wind Farm group that the turbines (shown above in a photomontage) would produce less electricity than his company had predicted.

Dale Vince, Managing Director of EcotricityIt comes after the protestors publicly questioned on their Web site the claims made by Ecotricity that the five turbines would generate enough electricity to meet the needs of more than 8,000 local houses.

In his first detailed interview covering the power generation calculations, Mr Vince, pictured, told “Knoll primarily use Load Factor to challenge the figures for annual yield that Ecotricity have calculated. Load Factor is a broad brush statistic, it is a not the way to calculate the annual yield of any specific site. It can be useful for comparing regions, countries even wind farms – but it has no use whatsoever in the calculation of yield, assuming you wish to have any degree of accuracy at all.”

“The load factor figures that Knoll use nonetheless require further comment. They have chosen a very short period of time – just two years, while the UK has 15 years wind experience to draw upon. The DTI recently published load factor figures from the UK, we believe that this is the source used by Knoll, but they have incorrectly quoted the load factor figure – not the first time that they have misquoted the DTI. The DTI report clearly states that the UK aggregate load factor is 28%. Knoll claim that 24% or 26% are the right figures (years 03 and 04 only) and for that reason our 28% is a reason to question our figures. The facts are that 28% is the UK long term figure and Knoll are incorrect to claim any other and incorrect to use that as a basis to challenge our own figures.”

“It also needs to understood that the DTI figure is an average of the good and less good sites (which can vary greatly) and also an average of old and new technology. There’s no scientific rationale in expecting the load factor from a good site using the latest and best technology, to be not more than the long term UK average of all sites and all machines. Performance of wind turbines has grown significantly in the last few years alone. Some of our own projects achieve in excess of 30% load factor.”

“The whole approach of using load factors from the UK to judge the likely output from Brent Knoll is fundamentally flawed and unscientific, even if Knoll had used the correct UK figure.”

“The Knoll group claim to have provided details of their calculation, but actually all they provide is the statement to the effect that they have ‘taken data from a nearby met station and used it in conjunction with the turbines power curve’. The problems with this approach are – Met stations do not have wind data at the hub height of wind turbines, therefore you need to calculate the wind shear to arrive at a wind speed at the hub height wind speed. Knoll appear to have either overlooked the need to calculate shear, or they have overlooked the need to provide the information on how they calculated it and what value they came up with. This is an item of significant impact on energy yield calculations. Knoll claim to have had experts review their figures, one has to wonder what field these experts work in, it would seem not to be wind energy as they would have seen these fundamental flaws themselves.”

“Secondly, Knoll do not say what period the data from the Met is for, without that knowledge it is hard to verify further that they have done their sums correctly.”

“Knoll make further fundamental errors when it comes to the number of houses Brent Knoll will power, following their own ‘calculations’ which claim a lower figure for output they go on to then challenge how many houses can be powered in any event – on some different grounds.”

“Firstly they claim that we have used the wrong figure for typical annual average household consumption of electricity. They cite two other examples, one from a group in Bristol the other from the BWEA. The figure we use is the one used by the electricity industry regulator OFGEM and its consumer champion arm EnergyWatch. This same figure has been endorsed by the ASA, which the Knoll group would have known as they have read the adjudication concerned, but they have failed to mention this.”

“The bigger error however, on this issue, is to believe (or to say at least) that the issue here is the instantaneous power requirements of a house that count. The figures we have provided are for the supply of average houses per year over the whole year. We believe it is clear and that it is a relevant, to describe the annual output of wind parks in terms of the equivalent number of homes it could power each year. The average person is not familiar with the units of energy generation – MWh or GWh – to have relevance to the public we need to express it in relevant terms – numbers of houses equivalent is right for that.”

“Knoll ‘calculations’ are simplistic and unscientific, they are bound to lead to significantly different numbers than a professional approach would produce.”

“Their experts, who reviewed the work, cannot be experts in wind energy (and they remain unnamed so we cannot verify their qualifications) as they would not have made such large and fundamental errors.”

“Some special interest group from America cannot know more about UK load factors than the DTI does.”

“The basis for our calculations is set out in our planning application and ES, both of which are in the public domain already.”


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