Why don't you install a Eoltec Scirocco 6kW. In higher winds it produces 85% of the Bergey Excel-S and in lower wind speeds it produces the same as the Bergey.
This is actual data from high winds of Montana USA. The Eoltec Scirocco is a very advanced Wind Turbine, smaller in size, 5.6 metres compared to the Bergey which is about 7 metres. It uses variable pitch to regulate the rpm. It also produces less noise than the Bergey, because the rpm is lower.
It is a no-brainer to me.
The inverter is a 6kW made by PowerOne which used to be Magnetek.
Your electricity company will very likely not have problem with it because the size is smaller, but you know better now, right.
Visit http://www.eoltec.com for dealers in the UK or visit http://www.solacity.com for more in depth information regarding the Eoltec Scirocco.
We ourselves are a dealer of the Eoltec Scirocco in Canada -
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Wilco
http://www.dommelvalley.ca