Are dreams of a North Sea HVDC Super Grid unravelling?

Jun 29, 2011 No Comments by

There have been dreams of a North Sea Super Grid for some time. With various areas already released as prime locations for offshore wind farm development, all that power is going to need to come to shore – where the demand is. Radial AC connections (for a long time the standard method of plugging in wind farms) will be burdened by long submarine cables (causing vast issues for large scale power transfer due to capacitance issues). Not only that, but radial connections will require hundreds of kilometres of extra cabling, and will also be a tremendous waste of an opportunity for large scale interconnection between the countries utilising the North Sea as a renewable energy source.

Enter the HVDC Super Grid. The vision is of an interconnected HVDC grid connecting the various wind farms in the North Sea and transferring their power to the various interconnected countries that require it with minimal losses. Furthermore, such a system with controlled power flow at every node would facilitate electricity trading between multiple European countries on a scale not witnessed before. Not only would this drive down prices but it would allow more efficient power transmission, allowing central European countries to make use of the vast hydropower storage reserves in Scandinavia and avoid the need for spinning fossil fuel generation capacity. Yet more benefits include the ability of the power electronics in the HVDC converters to support wind farm reactive power requirements and to electrically isolate them from the AC grids they’re connecting to, making them more resilient to external faults.

It seems like a technical solution with socio-economic benefits too good to be true – and maybe it is.

Wind farm development is already underway and will need to be connected up soon. The amounts of generation being talked about by 2020 (likely to be even higher now that many European countries are shying away from nuclear power [also]) will demand connection capacities in the gigawatts very soon.

So why has no work started on the super grid?

As well as all the clear incentives to get underway, there are many (unfortunately large) hurdles to overcome – not least technologically. HVDC manufacturers are claiming they will have large (over 1 GW) VSC-HVDC converters in the future – but how soon? And at what voltage level? It may be that 800kV is achievable in the future – but it’s not now, and work needs to start now. A constant HVDC system voltage is needed but set it too low and you limit future capacity, set it too high and work can’t start until the manufacturers deliver the developments they’re promising. Then there are DC circuit breakers – currently a nonexistent item but crucial for the success of an interconnected super-grid. No one is going to be happy if the whole grid has to be shut down and isolated on the AC side every time a fisherman trawls through a line. But current technology in this area is lacking – solid state devices have large losses and mechanical ones are too slow (reliant on resonance to force a zero crossing in the current).

Then you have to decide who pays for what? Norwegian customers are not going to be happy if they’re funding a project that benefits Britain far more than themselves. Measuring the socio-economic impact of the grid in order to proportion fair contributions from participating nations is a complex task.

Once it’s built – who will operate it? British regulatory restrictions mean that National Grid can’t directly own or operate the HVDC links – but such archaic restrictions are not in place in other countries. Is it feasible for one single entity to manage the entire network as an HVDC network operator?

Then there is the sheer mammoth scale of the projects and the associated lead times to have equipment built – equipment that is currently not even commercially available. Cables can take up to three years to be produced in the scales required for these projects and we’re only nine years away from the 2020 point by which massive North Sea wind penetration is expected.

The problems could have solutions (provided a lot of R&D work is done on the technological challenges now) but the main show-stopper is that there’s no one here to force the issue through. When the EU was so proactive in signing up to renewable energy promises they overlooked the transmission infrastructure development that would be required and seem somewhat oblivious to it now. The hurdles aren’t insurmountable, but there may not be the drive and motivation to get over them all quickly enough.

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About the author

Published postgraduate researcher working in the areas of HVDC and wide area power system stabilising control. Interested in future grid scenarios and the feasibility of smart grid solutions on the transmission scale.
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