all windfarms and in fact any other way of generating electricity will always feed back into the grid so nothing benefits the local population as such. It's no secret, there simply isn't any other way of doing it. You can look at national grid's maps with are publically available on the net to see where stuff connects if you want.
My home solar panels feed into the grid by phase-matching to the mains power through a device called an inverter. This takes the low voltage DC (14-28V) from the solar panel and makes it into 230V AC.
Electricity can't be stored on a commercial scale. This is why my home system feeds back electricity. The electricity I generate won't get very far (someone in my street would use it) and most of the time it will be used entirely by stuff in my home.
Wind power is exactly the same. A wind farm of about 90MW will just feed electricity into the grid at some point for use by the general population. This PDF
shows you how it all connects together.
This is what the national grid is all about and why it was invented. They predict demand and make sure there is enough electricity going into the grid from power stations, wind farms and abroad etc to keep the lights on.
Before 1924 electricity was locally generated, this meant that there were different standards all over the country and local power stations could no sell excess electricity to other places. You couldn't guarantee that the hair straightners you bought in Liverpool would work in Newcastle at the time. Birkenhead once had its own generating station in Bentwick Street.
Now electricity is supplied either through a link with Lister Drive, Liverpool (through the Bhead road tunnel) or from Capenhurst in Ellesmere Port. Prenton substation steps the electricity down for local use.
As for viability of windfarms, I'm not really qualified to comment on the economics of them; it's far more than just electricity and payback period, but the jobs that they bring to the local area where they are installed. This was why the likes of Traws nuclear powerstation was built with so little resistance, local people wanted it for the employment and local work it would bring.