The Case against Windfarms
The Case Against Windfarms is an authoritive, referenced document written by Dr John Etherington ( © Dr JR Etherington).
6. Homes supplied by a wind 'farm'
What 'they' say : -
"4700 is the average UK household electricity consumption in kW hours." (British Wind Energy Association 2005)
Most wind ‘farm’ planning applications or advertising fliers cite the number of homes supplied and the electricity industry has always done this - it is not a new tack on the part of wind developers. However the method of calculation is not well understood and for an unpredictably intermittent source such as wind, causes much controversy
For it to be correct, given these terms of reference, it must be based on the actual electricity supply from the wind ‘farm’ – i.e. (installed capacity x load factor)
The "domestic" consumption is based on a DTI estimate in the Annual Abstract of Statistics which subdivides UK total consumption into three parts: -
For 2003 (A.A.S. 141 Table 22.8): -
Industrial 115 TWh
Domestic 116 TWh
Other 108 TWh
The number of UK homes in 2003 was 24.5 million (HMSO, 2005 Social Trends).
Thus the annual average domestic consumption is (116 TWh)/(24.5 million) which is 4,735 kWh per home and dividing by (24 x 365 h) is equivalent to 0.54 kW continuous consumption per home.
This is the source of the BWEA figure 4,700 kWh per home http://www.bwea.com/edu/calcs.html and it rounds-down to a memorable 0.5 kW continuous consumption per home allowing easy mental arithmetic.
How does this work for wind and other intermittent sources? If a home subscribes to a 'green' tariff with a wind power company, the company guarantees to supply the electricity grid with the same amount of wind electricity as the customer's annual consumption. On average this will be 4770 kWh supplied to the customer from the grid.
There is no implication that it is the 'same' electricity in the sense that it would be if the wind turbine were cabled to the home.
If a wind developer or campaigning group claims that a wind ‘farm’ supplies the entire need of an area, this may or may not be correct in terms of total amount of electricity. It is only correct if the whole consumption of a town or county has been accounted for - in other words almost three times the 'domestic consumption'.
The claim may also be made that the supply is “up to” X,000 homes – a maximum value. In this case the calculation will have been based on installed capacity and will be three to four times the average number of homes supplied.
Some campaigners get very excited about this 'homes' matter and point out (quite truthfully) that wind power cannot 'support' ANY homes as it has to feed indirectly via the network to iron out intermittence. Hayden (2004) consequently describes claims such as “this windmill farm will provide enough power for 25,000 homes” as “misleading garbage.”
However there is an advantage to fighting them on their own ground: -
A 1.0 MW wind turbine at 30% load factor will support 600 homes
A 1,000 MW 'proper' power station at 80% load factor will support 1,600,000 homes
No real contest is there? - given that it would require 2667 1.0 MW wind turbines to make as much electricity and that they would occupy over 500 km 2, not to mention the constant fluctuation of supply, with all its disadvantages.