Look out from any beach or cliff along Britain’s coast and gaze out to sea. The chances are that somewhere near the horizon you will see a stand of spinning wind turbines, harvesting the power of our strong coastal winds.
The UK now leads the world in offshore wind energy. The iconic London Array, 175 turbines sitting just outside the Thames estuary, delivers enough power for half a million homes – two thirds of houses in Kent.
Yet this array, officially opened in 2013, is just the beginning. When the Dogger Bank array opens in 2018 it will boast 200 turbines with the capacity to generate 7200 MW – enough to meet one quarter of Britain’s peak energy demand.
But building this large offshore array may not be plain sailing. Today’s offshore wind farms sit close to the shore and transfer electricity directly onto the local grid. Dogger Bank is located more than 100km off Yorkshire’s east coast, beyond the reach of normal cabling systems.
“Traditional cables transmit alternating current (AC), but they are too inefficient above distances of about 80km,” worries Professor Mike Barnes, a researcher in the Department of Electrical and Electronic Engineering. “The obvious alternative is to transmit using direct current (DC), but this presents its own problems. So how can we deliver distant wind energy to consumers?”
Researchers of the SUPERGEN Wind Hub project think that high voltage DC (HVDC) may be the answer. They will develop computer models to show how operators could transmit electricity back to the mainland along many HVDC cables. Although models for HVDC cabling already exist, none are sophisticated enough to account for all the rapid changes in energy flow that can occur.
“But of course operators will also need to convert HVDC into AC when it reaches the mainland,” notes Professor Barnes. He is developing further models to show how operators can use ‘voltage source convertors’ to convert and control the flow of HVDC electricity onto the onshore grid. These convertors can help to prevent fault propagation and stabilise voltages.
His models will investigate how operators could control convertor cells at an individual level and as a unit. “If operators can flick between both levels of control, they may be able to better integrate unreliable wind power onto the National Grid,” explains Professor Barnes. Early results suggest that such multi-level control may be possible.
“Our models should simulate all possible scenarios,” adds Professor Barnes. “For example, if one cable breaks down when the wind is blowing powerfully, will the remaining cables have the capacity to transmit all of the electricity? And will we be able to use them to deliver power where we want?”
He believes that HVDC power lines could also link the UK to other European countries, too, helping to create an international electricity grid that makes energy trading more viable. “When our turbines produce more energy than we need, we can trade it with other countries. And if it’s a calm day in the North Sea, we can buy power from elsewhere, perhaps from somewhere where the wind is blowing,” says Professor Barnes. “Creating a European wide network will cut energy costs for all involved.”