As the sun finally breaks through the cloud five miles off the Kent coast, one of the 440ft wind turbines standing stoically in the shallow waters is lit up as transfer vessel EMS Vulcan drifts closer.

The boat is one of four owned by Excel Marine, a Herne Bay company that is transporting crew from the shore to the £160 million extension work being carried out at Kentish Flats wind farm.

Vattenfall, the Swedish energy company, is more than halfway through the construction of 15 new turbines, adding to the 30 that have rotated off the coast of Whitstable and Herne Bay for the last 10 years.

The project, due to be fully operational in November, will allow the wind farm to power another 35,000 homes a year, almost doubling the 40,000 homes it already caters for on average, thanks to advancing technology and efficiency.

Its construction is not just good news for Vattenfall, which is employing another 11 skilled technicians to join the 54 already working out of the Ramsgate operations base. Contractors have also benefited, like Excel Marine, which employs 15 people.

Its six-month contract to supply three boats during the construction work – one based at Ramsgate harbour and two at Whitstable – is expected to make up about 35% of the firm’s turnover this year.

“This contract is good because it’s local for us and we don’t have to pay for all the guys’ fuel or accomodation to stay in another part of the UK,” said managing director Griff Sargent. “That’s the advantage of working from your home port.”

Mr Sargent’s business might not exist if it was not for the wind farm. He originally had a single fishing boat that was run “more as a hobby” than a business, but things took off when he and his colleagues began running crews to the original Kentish Flats project 10 years ago.

The business became a limited company and upgraded its ship, then bought several more to meet demand. Today, it carries crews to wind farms and diving operations around the UK and Europe.

He said: “This contract is a nice one for us to have, but we have had longer ones. We have had construction jobs last for three years before.

“I know Vattenfall were keen to get as much of the local workforce involved as possible, but once these are up and running, it will probably have less local impact.”

A couple of miles down the Old Thanet Way in Whitstable, Gale Barnes runs her property-letting business from her home.

Her company Whitstable Holiday Homes has been taking bookings for Vattenfall engineers and technicians since 2010, with five of her 40 properties rented to workers on the construction project. Yet the timing of the bookings, during the more popular summer season, limits their impact.

She said: “These bookings have been nice for me because they are a good block booking, but they are not the mainstay of my business.

“Whitstable sustains itself on general tourism. My main market is London and north Kent, with more people beginning to travel down from the north as well.”

Speak to staff at Vattenfall and the story is positive.

Project director Matthew Green counted 20 boats in Ramsgate harbour that Vattenfall is contracting to transport staff to the Kentish Flats extension.

“This makes a really big difference to the economy of the harbour area,” he said.

“This makes a really big difference to the economy of the harbour area...” - Matthew Green, Vattenfall

“It’s the underlying stimulus the area needs. It has gone from something static to something dynamic.

“I wouldn’t like to guess how many people have been employed, but we have been spending money locally.

“There’s also an impact on local hotels. Having 20 people staying in hotels in Ramsgate or Whitstable is not insignificant.”

Yet when construction finishes next month, Vattenfall will employ 65 people to maintain the wind farm for the next 20 years, a fraction of the numbers it is employing now.

The company believes its £160 million investment is the largest in Kent this year but says the work is likely to be the last off the county’s coast for a long time.

Vattenfall’s energies will next be focused offshore on the ‘East Anglia zone’, with onshore wind subsidies due to be cut by the government.

Gunnar Groebler, head of business area wind at Vattenfall, who sits on the firm’s board, said: “There is nothing in Kent we would be close to any decision on.”

It is hard not to be impressed by the wind turbines when you lean back and look up at the giant structures from a CTV, or crew transfer vehicle.

“When the water is flat and they turn slowly, I think they look majestic,” said Gunnar Groebler, head of business area wind at Vattenfall.

Mr Groebler, who sits on the company’s board, is on his first visit to the extension work, having set off on a boat from Ramsgate harbour about an hour earlier.

We are still depended on support schemes but to have this as a sustainable business going forward we need to get the cost level down..." - Gunnar Groebler, Vattenfall

“This is an extension of an existing wind farm so we can reduce the cost level neatly here,” he said.

“Reducing cost is key going forward. We are still depended on support schemes but to have this as a sustainable business going forward we need to get the cost level down. We can’t depend on subsidies forever.

“We won’t get public support for this unless we can deliver cheap energy.”

Many of the boats leave from Thanet so the operation can continue around the clock, unhindered by tidal changes at Whitstable or Herne Bay.

At the time of our journey, five turbines of the 15 have been installed since the work began in May, with the project due to end ahead of time next month.

Although the water is relatively shallow at about 20ft, project director Matthew Green describes the complicated engineering efforts which go into installing the turbines and cabling which carries the electricity to shore.

The foundations are driven about 100ft into the seabed, with each windmill weighing about 600 tonnes.

Mr Green said: “It is quite difficult to install anything offshore when you take into account sea states, wind, corrosion and sea beds we don’t know much about.”