The first witnesses to be called on behalf of the developer were its Head of Consents, John Ainslie, and planning expert David Stewart.

Mr Ainslie explained how the proposed 18 turbine scheme north of Alnwick would have an operating capacity in the region of 54 to 75 megawatts, with an average output of between 25 and 35 per cent of its maximum.

In comparison, he said the thermal efficiency of a coal-fired power station was in the region of 36 per cent, and less than 50 per cent for gas.

Even a nuclear power station, he added, yielded just over 72 per cent of its full potential.

Wind power, he said, had the strategic advantage of being widespread across the grid in relatively small groupings.

"The point is that a conventional power station has far less than a 100 per cent conversion between the fuel source and the useable energy coming out of the other end," said Mr Ainslie.

"With conventional plants, it's possible to lose one-to-two thousand megawatts at a time if they are off-line, whereas with wind farms there is foreward forecasting so that we can adjust the output to other areas.

"It is very unusual for calm wind conditions to affect the whole UK at any one time.

"There is quite a bit of benefit from the geographical diversity of wind farm development across the UK."

Planning witness David Stewart, who has been involved in wind farm development across Britain, then addressed the potential impact on tourism, one of the biggest concerns of objectors to the scheme.

He said: "There is no material evidence that wind farms have led to the decline in the numbers of visitors in any area I am familiar with.

"The crucial thing that's worth observing is that Cumbria is at least as defensive as Northumberland about tourism, and there is a very long list of wind farm sites which affect every part of that county.

"The fact that new consents have been given in the last few weeks shows that the councils there do not consider wind farms to be the death of tourism in their area."

Mr Stewart added: "All these concerns have appeared time and again at inquiries, but there has been no substantial evidence that there will be any overall decline in visitor numbers."

Parties opposing npower's application will have a chance to cross-examine Mr Stewart on Tuesday morning.

Report: Inquiry Day 1 - Morning