Community Windpower state: Electricity generated will power approximately 28,000 homes, and by supplying the local distribution network will provide much needed electrical generation in the South West. Over 113,000 tonnes of CO2 would be displaced every year, equivalent to 32,000 cars taken off the road in Cornwall ..turbines typically operate for 75-80% of the time. Current assessments show that an onshore windfarm in the UK typically operates at maximum capacity for approximately 29% of the time, although most carefully selected sites should be able to reach 35-40% of time at maximum capacity. We are not convinced that Community Windpower has a full grasp of the technical issues here, but we interpret their statement as assuming a Load Factor (or Capacity Factor as BWEA call it) of 29%. IT IS IMPORTANT to note that this is not the same thing as producing Maximum Capacity for 29% of the time The usual figure suggested by BWEA is 30% which may or may not be an optimistic average for the windfarms generally, but the load factor achievable at a given site is primarily a function of the local wind climate and topography The Windpower data supplied by the Renewable Energy Foundation for the existing windfarms in Cornwall for the years 2003-2007 has therefore been analysed in the table below Capacity = the total installed capacity for each site Load Factor = (Energy generated per year) / (Capacity x 24 x 365)
Site	Capacity	Total energy (MWh) per year
(click for graphs)	(MW)	2003	2004	2005	2006	2007	Total
Bears Down	9.6	23234	22763	22373	22498	22167
Carland Cross	6.0	14099	13848	13811	13987	12055
Cold Northcott	6.8	13771	14524	13552	14340	13805
Delabole	4.0	8771	8863	9266	9576	9119
Four Burrows	4.5	8898	8573	8383	8394	8578
Goonhilly Downs	5.6	10288	9373	9159	10319	9444
St. Breock	5.0	11780	11778	11189	11010	10174
Totals	41.5	90841	89722	87733	90124	85342	443762
Load factors (%)		25.0	24.7	24.1	24.8	23.5	24.4

This analysis indicates that Load Factor of 25% would be more appropriate. If Community Windpower are trying to show the benefits to the planet from this development, then the onus is on them to provide correct information and in this case demonstrate that their assumed load factor can be achieved in Cornwall Nor are we convinced by their numbers of homes that could be supplied. The table below shows domestic consumption in Cornwall for the year 2007 (source)

Area	Domestic Elecrtical Consumption in 2007 (GWh)	No of Homes	MWh /home
Caradon	208.6	39200	5.3
Carrick	233.8	43800	5.3
Isles of Scilly	8.6	1200	7.2
Kerrier	241.3	44300	5.4
North Cornwall	241.6	42600	5.7
Penwith	165.2	33600	4.9
Restormel	259.4	45600	5.7
Total	1358.5	250300	5.4

Assuming a load factor of 25%, a total installed capacity of 50 MW at Davidstow could produce 109.5 GWh of electricity per year, enough for 20,300 average homes in Cornwall (somewhat less than the developer's figure). However the occupants of these homes would no doubt want to use their electricity even when the wind was not blowing. Therefore a back-up capacity of 50MW would need to be available somewhere else on the National Grid (note that the wind industry disputes this) As for the CO2 saving, The British Wind Energy Association (who appear to be the principal advisor to the Government on matters relating to windpower) have now admitted that the figure they had previously advised as being the saving for CO2 emissions was incorrect as it was at least twice the real amount. The actual figure should be 430 grams CO2 per kilowatt hour On that assumption, the Davidstow site would save 109500 x 0.43 = 47000 tonnes per annum Furthermore no mention is made of the extra carbon produced by the back-up plant running at less than optimum efficiency, so the actual amount saved would be even less