We size for somewhere between 2 & 3% loss at rated power, which equates to about 1.something % of annual production.

Contractually, most windfarm electrical systems must have a 2% maximum loss between turbine and grid delivery point.

10% loss seems excessive, and would not comply with either BS7671 or MCS

From your data from 2007 on this site, you are netting about 13,000 kWh a year - If your cable loses 10% at peak power, lets guess 5% on average (depends on your wind distribution and voltage/power curve of the turbine), so over 20 years, the cable will lose around 700 kWh a year x 20 = 14,000 kWh - With a 23p/kWh feed in tarrif, and say 10p for the energy (average of import and export for easy counting), thats £4,620 lost in the cable. Makes it worthwhile to go up a size or 2, especially if you are using a turbine that is running at peak power a lot of the time!

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Bryan Rendall