ELECTRICITY TRANSMISSION GRIDs
In many parts of the world, electricity is transmitted from power stations to
consumers via an electricity transmission grid.
Until recently, the wisdom of this arrangement was never challenged. But a
recent report by Greenpeace UK ("Decentralising
power: an energy revolution for the 21st century") implies rather strongly that we can do
without an electricity transmission grid.
Greenpeace are right to stress the advantages of combined heat and power (CHP) and
microgeneration but they are quite wrong to imply that we can do without an
electricity distribution grid. Here are some of the benefits of transmission grids, especially large-scale HVDC grids described below:
- Reducing wastage. Without a grid, electricity supply systems waste energy and
this is particularly true with renewable forms of energy. If for example, the wind is blowing strongly in Scotland, producing more electricity than the local people can use, that surplus energy is simply wasted unless it can be moved to places where it is needed. If there were affordable systems for bulk storage of electricity, that would make a difference but it would not remove the need to move electricity from areas of surplus to areas of need.
- Security of supply. A related point is that large-scale transmission grids help to ensure the security of electricity supplies in any one area. This is because any local shortage of electricity or local peak in demand can almost always be met from one or more other areas where there is spare capacity.
- Sharing of large-scale storage facilities. Large-scale storage facilities, such as pumped-storage systems in Norway and the Alps, may be widely shared.
- Smoothing out variations in supply and demand. Another advantage of transmission grids is that, if they cover a large area like Europe or EUMENA, they reduce
the variability of energy sources such as wind. The wind may stop blowing in any
one spot but it is very rare for it to stop blowing everywhere across an area the size of a continent. Without a large-scale grid, it may be necessary to maintain conventional power stations on 'spinning reserve' to supply electricity at short notice if the wind drops, and this spinning reserve is wasteful. In a similar way, large-scale grids can help to smooth out variations in demand.
- Accessing sources of renewable energy. Without a transmission grid, it would not be possible to take advantage of
the large amounts of energy that may be obtained from large-scale but remote sources of renewable electricity such as wave farms,
offshore wind farms, tidal lagoons, and tidal stream generators—and concentrating solar power!
- Opening up new sources of energy. A related point is that a large-scale transmission grid can open up entirely new sources of energy that might not otherwise be considered. For example, there is potential to import geothermal energy into the UK from Iceland via a submarine HVDC transmission line.
- Reducing the need for ‘plant margin’. A transmission grid helps to reduce the amount of 'plant margin'—the difference between actual generating capacity in any area and the theoretical minimum generating capacity—that is required. This is because a large-scale grid smooths out much of the variability in electricity supply and demand and because spare generating capacity that is needed to meet contingencies can be shared across a relatively wide area, thus reducing the amount that is allocated to any one area.
- A large-scale supergrid is needed for the proper working of a single market for electricity across a wide area. The UK government and the European Commission wish to create a single European market for electricity (as we have in the UK), unbundling power generation from power transmission and promoting competition between different suppliers and sources of electricity. A large-scale HVDC supergrid is needed for the proper working of that single market. In that connection, Andris Piebalgs, EU Commissioner for Energy, has written: "The single electricity market could not exist without electricity interconnections, and the lack of a European electricity market, as for gas, weighs heavily on the internal market as a whole.
This is why it is essential to optimize the use of interconnections, and to invest in the 'missing links'" (from the Foreword to Report on electricity interconnection management and use, EU Commission de régulation de l'énergie, June 2008).
- Getting the best available price for electricity. Transmission grids that cross time zones may increase the value of electricity by moving it, at any one time, from areas where it is cheap to areas where it will fetch a good price. More generally, large-scale grids allow customers to obtain electricity from wherever it is cheapest at any one time, and that may vary throughout each day.
- Stabilisation of frequencies and voltages. An HVDC supergrid (see below) can help to stabilize frequencies and voltages in the
HVAC grids to which it connects.
- Export potential. The UK (and Scotland in particular) has great potential for wind power, wave power, and power from tidal lagoons and tidal streams. If these are developed as they should be, stronger grid connections to the continent will be needed to facilitate exports of renewable electricity from these sources (see Study backs undersea cable to export Scotland's wind and wave power). Likewise for Ireland, bearing in mind that it has a much smaller population than the UK (see Ireland launches ocean energy initiative).
The high-tension power lines that most people are familiar with use
alternating current (AC) for reasons that were worked out by Nikola Tesla—a
fascinating story in its own right. High voltages are needed to ensure that
electricity can be transmitted over long distances without losing too much of
the energy in the form of heat. AC has the advantage that voltages can be raised
or lowered easily using transformers. Nikola Tesla invented an electric motor
that would run on AC electricity to save having to convert it to direct current
But over very long distances, AC transmission lines become increasingly
inefficient (because of the effects of 'capacitance' and 'impedance' in the
system). So, although voltage conversions are not so easy with DC electricity,
long distance transmission lines use DC electricity. Also, DC is normally the preferred option for submarine cables.
Although long-distance transmission of electricity over HVAC transmission lines is not efficient, it appears to be possible, up to certain limits, to make efficient long-distance 'transfers' of electricity via HVAC transmission grids, provided that there are electricity generators and electricity consumers at points along the route. This is explained on a page about the cascading principle.
With modern HVDC
transmission lines, transmission losses are very low.note And they are also cheaper to build than HVAC lines because only two cables
are needed instead of three.
HVAC and HVDC transmission lines are often carried overland via pylons
because this saves the cost of insulating the cables. But, for extra cost, they
can be insulated and laid under the ground or under water as envisaged in proposals from the wind energy company Aitricity for a pan-European HVDC supergrid constructed using submarine power cables. With "HVDC Light" technology from ABB, and for distances greater than about 500 km, submarine or underground cables are only about 10% to 20% more expensive than overhead lines.
note Transmission losses in HVDC transmission lines are normally about 3% per 1000 km but losses can be reduced by adding capacity (at more cost) or vice versa. In addition to the actual transmission losses there are losses at each end in converting from AC to DC and converting from DC to AC. Taking both ends together, conversion losses for an HVDC transmission line are normally about 1.5% to 2%. So, over a distance of 2000 km (which is about the distance between North Africa and the UK), total losses would be about 6% (for transmission) + 2% (for conversions) = 8% overall.
Large-scale HVDC transmission grids
Given the advantages of transmission grids detailed above, and
given the advantages of HVDC transmission lines for long-distance transport of
electricity, there are several proposals to build large-scale HVDC
- A Europe-wide supergrid has been proposed by Airtricity as a means of
reducing the effects of intermittency in wind power across Europe and to
facilitate the trading of electricity. In this proposal, it is envisaged that all the
cables would be laid under the sea (see the web page About the supergrid, a press release (in MS Word) and the European Offshore
Supergrid® Proposal (PDF, 4.8 MB)). Dr. Eddie O'Connor, CEO of Airtricity, describes the supergrid concept in an interview with Stephen Lacey of Renewable Energy Access (MP3, 13.9 MB, the interview starts at 7:55 into the recording). He has also written about it in "The European offshore supergrid: a vision for creating a more powerful Europe".
- Dr Eddie O'Connor, who pioneered the supergrid concept as CEO of Airtricity, is continuing to promote the concept as CEO of Mainstream Renewable Power.
- An agreement has been reached amongst 10 countries bordering the North Sea to develop a supergrid in that area (see EU countries launch North Sea electricity grid, EurActiv.com, 2010-12-06).
- Friends of the Supergrid is a group of companies working on the supergrid idea.
- Medigrid is a consortium of companies aiming to build transmission links across and around the Mediterranean sea.
- The North Sea Countries Offshore Grid Initiative is also working to develop the supergrid.
- The European Commission has proposed a Europe-wide supergrid of submarine power cables similar to what has been proposed by Airtricity (see above). The article contains a quote from a spokeswoman for the British government: “We have been calling for the EU to do more on energy security. The idea of a supergrid could support the Government’s aim of developing offshore wind power and other renewables and implementing more interconnection between European electricity markets.”
- The investment company Imera has announced a Euro 4.4 billion plan to start building a pan-European electricity grid composed of submarine cables.
- Study shows £4.7 billion needed for power grid (Reuters, 2009-03-04).
- As a part of the Desertec concept, the Trans-Mediterranean Renewable
Energy Cooperation (TREC) propose an HVDC grid spanning the whole of
Europe, the Middle East and North Africa (EUMENA) to take advantage of the
enormous quantities of energy falling as sunlight on deserts, and wind
energy in those regions too (see also Desertec-UK).
- The Desertec concept, including large-scale HVDC transmission, is the basis for the "Mediterranean Solar Plan" of the Union for the Mediterranean.
- Dr Gregor Czisch has proposed a EUMENA-wide supergrid.
- The European Climate Forum has proposed a EUMENA-wide SuperSmart Grid, combining a low-loss HVDC 'supergrid' with 'smart' electronics to promote responsiveness and efficiency in its operation. This proposal is based on and extends the Desertec proposals.
- The Renewables Grid Initiative is promoting a large-scale for Europe, with HVDC technologies and smart electronics.
- Greenpeace Belgium and 3E propose A north sea grid electricity grid [r]evolution (PDF, 2.8 MB, September 2008).
- An EASAC project aims to answer the question: "How could existing and new technologies help the progress in building the new European large electrical energy transport system and enable a well-functioning electricity market?"
- American Electric Power has proposed Transmission: the next interstate system, a new vision for transmission in the U.S. (see also Interstate transmission superhighways: paving the way to a low-carbon future, RenewableEnergyWorld.com, 2008-07-30).
- The US Energy Secretary, Professor Steven Chu, has said that the nation's grid must be modernized and the smart grid must be developed (see EEI Expo: secretary Chu describes life in a carbon-constrained world, RenewableEnergyWorld.com, 2009-07-07).
- The Global Energy Network Institute (GENI) proposes a World Wide Web of electricity transmission lines to link consumers and renewable energy resources around the world.
- A similar concept is described by TerraWatts.com.
- A report in Engineer Live describes a proposal for a world-wide grid of HVDC
transmission lines. There is an interesting discussion of the case for such a grid in "World web of electricity charged up", an article in Carbon Free.
- e-Parliament calls for "Clean Energy Supergrids"
These grids would not replace existing HVAC grids: they would be designed to
integrate with them and complement them.
In line with the European supergrid concept, the report "Energy, Politics, and Poverty" from the University of Oxford (PDF, 763 KB, June 2007) calls for "completion of the physical European grid for ... electricity" and a unified market for energy in Europe.
EU energy commissioner Andris Piebalgs has endorsed this concept (see EU's Piebalgs says grid infrastructure needed quickly for offshore wind energy, 2008-03-31).
Quite apart from the strategic proposals mentioned in the previous section, the process of creating a large scale HVDC grid in EUMENA is beginning to happen in an incremental manner, in much the same way that the Internet developed piece-by-piece. Here are some examples of current proposals and developments, most of which involve submarine power cables:
- ABB in £388m deal to bring Irish wind power to UK (New Energy Focus, 2009-03-30). See also Swedish firm ABB to link Irish grid to UK (Construction Digital, 2009-03-30).
- Imera to boost Ireland's energy supply (The Calco Power Presidium, 2007-12-07).
- Algeria eyes solar energy exports to Europe (Zawya.com, 2008-05-13). See also Un câble électrique reliera l’Algérie à l’Allemagne (El Watan, 2007-11-14).
- Siemens connects Majorca to power grid on the Spanish mainland (2007-10-11)
- The NorNed HVDC submarine connection between Norway and the Netherlands is due to be completed in 2007. See also the NorNed HVDC link.
- The development of an HVDC submarine and underground link between Germany and a new 400 MW wind farm 100 km out in the North Sea using ABB's "HVDC Light" technology (2007-09-18; see also ABB technology gives offshore wind farms new capabilities, 2008-05-04 and ABB to connect German offshore wind farms to power grid, 2008-03-28).
- The development of HVDC transmission links in the Middle East (2007-06-02. See also 2007-09-11).
- The development of the 'BritNed' HVDC submarine link between the UK and the Netherlands (2007-06-02, 2007-06-01, and 2007-05-22).
- A new HVDC transmission link in Denmark (2007-05-18, 2007-05-14).
- A proposed HVDC submarine cable to export geothermal electricity from Iceland to the UK and Germany (2007-05-13).
- A project to lay HVDC submarine cables between the UK and Ireland (2007-03-07).
- The UK Crown Estates is examining the possibility of laying an HVDC submarine transmission line down the east coast of the UK (2007-02-03; see also Undersea cable plan linking isles to England, 2007-05-18).
- The Estlink HVDC submarine cable between Estonia and Finland (2006-12-12).
There are some figures for the cost of proposed HVDC transmission lines, and comparisons with other costs, on the page about CSP costs.
Cost-benefit analyses of large-scale transmission grids show that they are very good value for money (see Interstate transmission superhighways: paving the way to a low-carbon future, RenewableEnergyWorld.com, 2008-07-30).
- EU : European initiative for $40 billion gigantic off-shore renewable energy super-grid project (Instalbiz, 2010-01-06).
- Sun, wind and wave-powered: Europe unites to build renewable energy 'supergrid' (The Observer, 2010-01-03).
- Brussels green lights billions in energy investment (Business Green, 2009-05-08). "More than €2.3bn of [new EU energy] funding has been earmarked for the development of a new European super-grid and improved gas infrastructure designed to better support renewable energy technologies and limit Europe's exposure to fluctuating gas prices."
- From AC to DC: going green with supergrids (New Scientist, 2009-03-14). This is an article by David Strahan, a member of Desertec-UK.
- Green Power Express in the USA from ITC
- Stepping up the voltage (PDF, 2.9 MB, Energy Engineering, issue 21, March 2009, pp 54-56). Describes UHVDC transmission technologies.
- Study shows £4.7 billion needed for power grid (Reuters, 2009-03-04).
- Power supergrid plan to protect Europe from Russian threat to choke off energy (Times Online, 2008-11-13; see also a schematic plan of the proposed supergrid)
- SuperSmart Grid, a European Climate Forum project.
- Google and GE in energy deal (BBC News, 2008-09-18). The article reports Google's view that the benefits of renewable electricity cannot be fully realised without updating US power transmission lines into a "smart grid" that lets people track and control what types of power they use and when. "This 21st century electricity system must combine advanced energy technology—a major GE focus—and cutting edge information technology—a major Google focus."
- Interstate transmission superhighways: paving the way to a low-carbon future (RenewableEnergyWorld.com, 2008-07-30). Discusses electricity transmission in the US and includes references to studies showing the substantial economic benefits of transmission grids.
- Demonstrating the technical feasibility of a system of electricity generation 100% renewable(bulletin-electronique.com, 2007-10-18). Kassel University study.
- EU's Piebalgs says grid infrastructure needed quickly for offshore wind energy (Forbes.com, 2008-03-31).
- The HVDC 'supergrid' concept should not be confused with the concept of a 'smart grid' designed to manage power transmission intelligently. No doubt, every supergrid should also be a smart grid.
- Peter Meisen, Director of GENI, is interviewed by Marc Strassman here:
- Wind-fuelled 'supergrid' offers clean power to Europe (The Independent, 2007-12-07)
- Analysis: A 'super grid' for Europe? (United Press International, 2007-11-02)
- Creating a 21st century grid (Renewable Energy Access, 2007-11-09)
- An interesting radio programme about The National Grid (and the potential benefits of a larger-scale European grid and single market for electricity) was broadcast on BBC Radio 4 (You and Yours) on 2007-09-24. Click on the link to hear it (using Real Player). See also the BBC's web page about it.
- Where the wind blows (The Economist, 2007-07-26)
- There is more information in a useful article by Gunnar Asplund called Sustainable energy systems with HVDC transmission (PDF, 170 KB).
- GreenNet (Europe)
- HVDC review paper by Roberto Rudervall (ABB), J. P. Charpentier (World Bank US) and Raghuveer Sharma (ABB).
Last updated: 2012-10-10