Vattenfall Nearshore Wind Farms to Keep Danish Grid Stable

Vattenfall's two new offshore wind farms, Vesterhav Syd and Vesterhav Nord, will be the first in Denmark to be directly involved in stabilising the electricity grid and thus the power supply, the Swedish developer said.

Vesterhav Syd and Vesterhav Nord will comprise a total of 41 Siemens Gamesa 8.4MW turbines, bringing the overall capacity of the wind farms to around 350MW.

Project construction is scheduled to begin next year, with the full commissioning expected in 2020.

In addition to increasing Danish electricity generation from wind turbines by more than 10 percent, the two nearshore wind farms will be able to actively deliver some of the voltage stability the network needs to maintain the reliable power grid in the West Jutland region, Vattenfall said.

The two new wind farms are close enough to the coast and at a short enough 'electrical distance' for the turbines to be connected directly to a 150kV transformer, thus actively supporting the grid.

"A wind turbine is now just as large as a small combined heat and power plant of almost 10 MW, so we can really deliver some strength to the grid, which would otherwise come from power plants. But there aren't many of those in the area where Vesterhav Syd and Nord are being built," said Kenneth Skaug, Senior Engineer in the System Design department at Vattenfall.

Connection of offshore wind farms, principle illustration. Source: Energinet

Until now it has been necessary to have large power plants running to ensure the stability of the grid, but with the new agreement between Vattenfall and Energinet, which operates the large Danish high-voltage grids, the wind turbines can easily adjust the amount of energy to match demand – and at a millisecond's notice, unlike the large, heavy power plants that preferably operate with a constant output and take time to adjust, according to Vattenfall.

According to Chief Engineer Poul Mortensen from Energinet, the agreement on voltage regulation is ground-breaking as it is the first in Denmark to involve two wind farms as an integral part of the primary operation and support to ensure a stable and reliable electricity system.

"Thanks to the two wind farms, the electricity system will have voltage support that is fully in line with the performance that traditional power plants can deliver and, even more importantly, the connection is placed exactly where there is a need for voltage support in current and future electricity systems based on renewable energy," said Mortensen.

Skaug has helped develop the idea and agreement between Vattenfall and Energinet and sees even more potential in the use of wind turbines.

"Part of the West Coast grid needs this support in the local area. The wind turbines have now gone from destabilising the grid, as in the old days, to acting as a stabilising factor. At one point, Denmark operated for 41 days without having the large power plants in operation. This wouldn't have been thought possible 10 years ago. In addition to the two offshore wind farms, Vattenfall's onshore wind turbines are now also under consideration,'' Skaug said.