If the U.S. is serious about offshore wind, regulators should think seriously about how the energy gets back to shore.
“There’s a strong case to be made for taking the transmission portion [of projects] and treating it as a separate entity,” said Neil Kirby, HVDC business development manager at GE Energy Connections.
If every project developer takes responsibility for their own grid interconnection, then some may end up choosing a technology that is less than optimal for their projects, thereby increasing costs.
Offshore wind farms can use either alternating current (AC) or high-voltage direct current (HVDC) links to export current to shore. Selecting the right technology for a given location can make a measurable difference to capital costs and production losses.
In a nutshell, HVDC has higher capital costs but is much better than AC for transporting large amounts of energy over long distances.
A single wind farm might almost always find it cheaper to go for an AC link. But if several projects share an HVDC connection, they could incur fewer transmission losses and deliver energy at lower cost.
The critical point at which it makes sense to invest in HVDC rather than AC is when the export volume reaches roughly a gigawatt, Kirby said.
And that’s the problem: If the interconnection is the developer’s responsibility, then they are unlikely ever to install an HVDC line unless they win a gigawatt’s worth of projects in the same area, which is an unlikely prospect.
Across Europe, which had more than 12 gigawatts of capacity installed at the end of 2016, this problem has led to a proliferation of AC interconnections even in places where HVDC would be preferable.
In the U.K., for example, “They have been stretching the capabilities of the cable and the compensation needed,” Kirby said.
GE, which is keen to push HVDC for renewable energy transmission elsewhere, last month installed its first-ever HVDC converter platform for offshore wind.
The DolWin3 offshore converter station in the southwestern German North Sea, approximately 80 kilometers from land, was awarded by the transmission system operator TenneT and will connect two wind farms.
“The technology represents a crucial turning point for offshore wind...and how we are able to move that energy efficiently,” said Patrick Plas, general manager of HVDC and grid solutions at GE Energy Connections, in a press note.
Plans to set the U.S. offshore wind industry up with an East Coast HVDC network got off to a good start in 2010, when Google said it would invest $5 billion in a 350-mile transmission system called the Atlantic Wind Connection, with up to 6 gigawatts of capacity.
The focus of the project was New Jersey, which at the time had just signed an Offshore Wind Economic Development Act with the intention of supporting over a gigawatt of capacity.
New Jersey’s offshore wind ambitions failed to take off, however, and the Atlantic Wind Connection website stopped giving updates on the project in 2013.
Given the sluggish pace of progress for the U.S. offshore wind industry, it remains to be seen whether the Atlantic Wind Connection, or another plan like it, will materialize.
Deepwater Wind, developer of America’s sole operating commercial offshore wind farm, had to build its own interconnection link to get power from the Block Island project in Rhode Island.
At 30 megawatts and 3 miles away from the shore, the Block Island project is relatively small. It made sense for the transmission system to be based on AC.
And with analysts predicting that U.S. offshore wind installations won't reach HVDC-worthy levels until at least the middle of the next decade, it looks as though most upcoming projects will find it cheaper to stick with AC if developers have to build their own grid links.
For the sake of a more efficient, cost-effective industry, it would be better if another party took on the decision-making process for them, Kirby argued.
Separating wind farm projects from interconnection infrastructure “would be a big step forward,” he said, since a move to adopt HVDC technology “is never going to happen based on pure economics.”