With the UK’s first onshore wind farms now over 20 years old, a new trend is emerging to replace the existing turbines with more powerful models.
Constituent parts of five new 100m tall, 2MW wind turbines will soon be on their way to the St Breock Downs overlooking Wadebridge in North Cornwall. They are due to arrive on a fleet of road transporters via Bristol docks for erection on the site in January next year. Once connected into the grid - estimated to happen in February - the local community will have an upgraded renewable energy source.
This is one of the UK’s first wind farm repowering projects. Wadebridge was previously supplied with electricity from 11 smaller wind turbines erected on the same site in 1993 to form one of the UK’s first commercial wind farms.
Since 2012, developer and operator Renewable Energy Generation (REG) has had planning permission to replace the 1990s wind power technology to double the site’s output from 4.95MW to 10MW.
According to the company, supply of the new V80 wind turbines from the Danish manufacturer Vestas is so far the only part of the project’s supply chain resting outside of the UK. REG’s wind power division is the project client, which has appointed north Wales-based Jones Bros Civil Engineering to carry out the necessary civils work and oversee the decommissioning and turbine erection procedures through a £2M design and build contract.
Smith Brothers from Huddersfield is the project’s electrical contractor, while SKM - now Jacobs - carried out the decommissioning design. Contracts for the transportation and erection of the new turbines have yet to be awarded for the £12M project.
“A big advantage for the St Breock project comes from the site’s existing high voltage power infrastructure having sufficient capacity to cater for the expansion”
Neil Beresford, Jones Bros
St Breock has developed into a positive news story in the local area, says REG Windpower community relations manager Claudia Richard.
“We received 95 letters of support for the project and only seven objections,” she says. “There tends to be a lot more positive feeling towards wind farms once they are in place.”
Local approval will probably not be damaged by a community benefit fund set up as part of the St Breock project to which REG Windpower is donating £50,000 a year index linked for the duration of the wind farm’s operating life.
“The fund will be administered by Wadebridge Energy Network, an independent not for profit cooperative consisting of panels of local councillors. Wadebridge parishes will decide how the money is to be spent on local projects,” Richard says.
The power will go to the local area first, coordinated by Western Power Distribution. Wadebridge will get what it needs and the surplus will be distributed across the wider area.
Minimal upgrade work
This will be via an existing substation and overhead power lines. “A big advantage for the St Breock project comes from the site’s existing high voltage power infrastructure having sufficient capacity to cater for the expansion,” explains Jones Bros south west regional manager Neil Beresford. “The viability of repowering stacks up better if minimal electrical work is needed for the upgrade.”
The construction element of the scheme is fairly straightforward, Beresford says. Jones Bros has built a new 4km access road to the site, together with the turbines’ 15.5m diameter circular reinforced concrete bases.
The contractor has also reinstated a network of access tracks and built hard standings for the lifting operation at each new turbine location, which are spaced out in an irregular pattern, typically 200m apart.
“There is potential for a lot more of this sort of work as the first generation of wind power sites reach the point where they are ripe for repowering”
Neil Beresford, Jones Bros
Each of the bases has been cast in situ in two sections straight onto bedrock. The bulk of the bases was cast first, with a circular array of bolts cast almost to the full depth of the structure. A second smaller pedestal cast on top forms the “can” for seating and bolting the turbine tower.
Working in remote and often environmentally sensitive areas is usually the main challenge of wind power projects, Beresford says. The 4km access road has been built on green field, connecting the site to the A39.
“Previously access was from Wadebridge via smaller side roads, which are far less suitable for bringing in construction vehicles and large transporters laden with heavy equipment,” says Beresford.
“Meeting the programme in variable weather presented a considerable challenge. The ground was fairly good, although with some wetter areas that caused problems after rain,” he adds.
“Conversely, during dry periods keeping the dust down was not easy. It was difficult to get a water supply and we had to keep delivery wagons and site vehicles’ speeds down.
The client had an environmental team permanently on site, who were happy with all that we were doing.”
Jones Bros has developed considerable expertise in wind farm infrastructure, Beresford says, and the firm is now building a reputation for decommissioning sites that are coming to the end of their natural life.
More work potential
“There is potential for a lot more of this sort of work as the first generation of wind power sites reach the point where they are ripe for repowering,” he explains. “A key role for us is in overseeing the decommissioning and lifting procedures - ensuring the lift contractor has all of the correct equipment and method statements in place.”
Decommissioning of the previous smaller turbines was carried out between January and March this year. A single 250t all-terrain crane was used for the job; each of the turbines’ three, 18m blades, hub, nacelle and two tower sections were taken down in turn, tethered with lanyards.
“Erection of the new turbines will make use of two cranes. A minimum of a 500t all-terrain crane will do the main part of the work, with a smaller slave crane to help support each turbine piece in a tandem lift,” says Jones Bros site agent James Lockwood.
Ironically, wind farm erection work relies on periods of little wind. With perfect conditions, each whole turbine can be erected in about 24 hours, Lockwood says. In reality, each will typically take three days.
The first of the V80 turbines is due to be delivered to site early in January with the rest arriving in turn. Three tower sections will rise to the hub height of 60m, followed by the 42m blades.
“A star lift is often possible, with blades and hub connected on the ground and lifted as one piece,” says Lockwood. “We have undulating ground at St Breock, so the hubs will be lifted in with one blade attached, then followed by the other two blades. Getting it all done in four weeks will be good going.”