Renewable HVDC 'Supergrid' Concept Has Staying PowerOct 25, 2013 - bulletin.pbworld.com
Editor's Note: Bulletin asked Dr. Norman MacLeod, Technical Director, High Voltage Direct Current (HVDC) Power Networks, to reflect on the push to develop an HVDC “supergrid” across Europe, and Parsons Brinckerhoff's role in
Modern electricity transmission grids use alternating current (AC) to transport energy from large, centralized generating plants – powered principally by coal, oil, gas, and nuclear energy – to the major load centers. However, as concerns have grown about the environmental impact of carbon dioxide emissions from fossil fuels and about the safety of nuclear installations, there has been a strong reciprocal escalation of political pressure to increase the amount of renewable energy used to power our world.
Europe has abundant sources of renewable energy: off-shore wind farms in the North Sea and the Baltic Sea; hydropower plants in Scandinavia and the Alps; and solar stations around the Mediterranean Sea. However, these energy sources are mostly remote from the main load centers in continental Europe.
Existing AC grids were never designed to transport significant power from these remote regions and are not adequate to the task. Thus, the concept of a pan-European high voltage direct current (HVDC) overlay grid has evolved to link these renewable energy sources to the load centers.
By its nature, renewable power sources provide intermittent sources of energy. For example, solar power is only directly available for about half of each day. However, as the sun sets in one place, it rises somewhere else, so in a broad sense solar power really is available 100 percent of the time, provided you can store and share its energy. Therefore, by interconnecting the networks that transmit renewable energy into a so-called “supergrid,” the impact of this intermittency may be “smoothed out.”
There are issues to overcome, of course. Even among the geographically close-knit countries of Western Europe, national and regional power grids operate at different voltages. To avoid the need to synchronize the present systems of Ireland, the United Kingdom, Scandinavia, and North Africa with the main European grid, DC current is an obvious choice for such a supergrid. Transporting electrical energy by DC is also now more efficient and more controllable than by AC.
The issues involved in the building of a supergrid are the subject of considerable activity in Europe, and engineers from Parsons Brinckerhoff are heavily involved in many of these activities.
The European Network of Transmission System Operators for Electricity (ENTSO-E) represents 41 European transmission system operators (TSOs), covering 34 countries, and has initiated a working group – of which Parsons Brinckerhoff is a member – to develop a network code for HVDC schemes. The group considers regulatory and operational aspects of the code at a high level but is not involved in planning an actual supergrid.
In reality, the supergrid will evolve “organically” in the 21st century from multiple independent schemes becoming interconnected, in much the same manner as the AC grid evolved in the 20th Century.
For example, the recently completed, award-winning 500-MW East-West Interconnector between Ireland and the UK can be seen as one such link in the future supergrid. This scheme uses new voltage source converter (VSC) technology, which creates a very compact site. On this project, presently the largest VSC scheme in the world, Parsons Brinckerhoff acted as the owner’s engineer on behalf of EirGrid, the Irish TSO, providing expert professional services on HVDC converter stations as well as submarine and underground cables, all supplied by ABB Inc., linking the two countries.
However, to build a supergrid you need more than two HVDC terminals connected together, and Parsons Brinckerhoff is working with the three UK TSOs (Scottish & Southern, Scottish Power, and National Grid) to develop a three-terminal system along the eastern coast of the UK. Acting as HVDC technical advisor, we are consulting on the issues involved in the development of an ambitious 2000-MW VSC HVDC link, the primary purpose of which is to direct wind power generation from the north of Scotland to load centers in the south of Scotland and the north of England. Extending the concepts of a three-terminal system to a multi-terminal system creates a supergrid.
In the North Sea, there is at present one 400-MW wind farm connected to Germany via an HVDC link built by ABB, with seven more schemes totaling 5,530 MW under construction by Siemens, Alstom, and ABB. In the UK sector of the North Sea, there is the capacity to develop up to 35,000 MW of off-shore wind power, most of it connected to shore via radial HVDC links.
Parsons Brinckerhoff engineers are working with many of the developers of these schemes, such as Inchcape (eastern Scotland), East Anglia, and Hornsea (eastern England). This work proposes solutions for the on-shore converter stations, the submarine cable links, and the off-shore converter stations located on large marine platforms. Some of these schemes will be of the 1000- to 2000-MW range, pushing the boundaries of HVDC and marine technologies. These schemes are typically 100 kilometers (62 miles) from the coast of the UK and Germany and there is logic in interconnecting such schemes to provide the developers with access to two electricity markets. When there is no wind blowing, the HVDC links can act as conventional interconnectors, exchanging energy between countries. Such HVDC schemes in the North Sea for the connection of wind farms can be considered to be the genesis of the future supergrid.
In addition to our consultancy role with TSOs and wind farm project developers, Parsons Brinckerhoff engineers are also heavily involved with thought leadership among international industry groups, such as CIGRE (International Council on Large Electric Systems) and the Friends of the Supergrid, of which we were a founding member. Within CIGRE, we are represented on many technical working groups on HVDC, cables, sub-stations, protection systems, etc. In the Friends of the Supergrid, we are represented at the main board level and also on the regulatory/economic and technological working groups.
There are still many technical challenges to be overcome to finance, build, operate, and regulate a supergrid; and Parsons Brinckerhoff is here in the thick of it, helping to define the evolution of what will surely become the major infrastructure project in Europe in the 21st century.