Can our electricity grid cope with all the new wind power?
27th April, 2010
Wind energy finally seems to be moving somewhere in the UK, but without some new techniques, our grid is simply not going to cope with this flood of new green power
Earlier this year the Government awarded licences to build 32GW of offshore wind capacity, enough to provide a quarter of our yearly electricity, more than any other country has yet achieved, by 2020. Some analysts claim it can’t be done, and the very attempt will threaten our security of supply. But luckily several European countries are way ahead of us and pioneering a range of approaches could eventually lead to a totally renewable electricity supply.
One of the most ambitious is Spain, where wind capacity has soared in recent years under a system of generous feed-in tariffs. Capacity stands at 19GW today, generating around 14 per cent of the country’s electricity in 2009, and once – on a windy Sunday night last November – briefly delivering 54 per cent of its power. Yet the Spanish government wants to go much further and has set a target of 29GW by 2016.
For a country so determined to grow its wind capacity, it is ironic that Spain has discovered one of the most important factors is the ability to shut wind farms down, or at least reduce their output from time to time. To achieve this, the Spanish grid operator REE (Red Eléctrica de España) has built the world’s first renewable generation control centre, the Centro de Control para el Régimen Especial, or CECRE, housed in an anonymous concrete campus in the shadow of Madrid’s Barajas airport. According to Miguel de la Torre, the REE official who shows me round, CECRE has been crucial to Spain’s success in incorporating so much wind power so far and its future plans.
With great power...
Controlling the power output of wind farms is important for keeping the system within its safety margins when the wind is blowing strongly and demand is low, and all the more so as wind capacity grows. Yet in Britain, the National Grid control room at Wokingham cannot even measure the output of half the country’s wind capacity, still less control it. By contrast technicians at CECRE receive live output data from every wind farm once every 12 seconds, displayed on a wall of huge screens and maps, which helps their colleagues in the main grid control room balance the variable wind output by raising and lowering the production from flexible generators such as gas fired plants.
Wind turbines have priority in the Spanish system, but sometimes output has to be curtailed, and CECRE can send signals back to the wind farms requiring them to trim production within 15 minutes if necessary. That’s important because if they couldn’t control wind output so quickly, REE would have to set production limits a day or more ahead on the basis of less reliable weather forecasts, and allow for a larger margin of error. The control offered by CECRE means they can run the system nearer to its limits, using more wind power overall.
A watery solution?
The ability to turn turbines down is all very well when there’s more wind power than demand, but what about when the wind drops? Spain’s answer is to ramp up production from fast-reacting gas fired power stations, and this could easily end up being the default position for Britain. But Portugal has come up with a more climate-friendly alternative: a massive expansion of hydro electricity.
Portugal already has a lot of wind and hydro, but most of its hydro is ‘conventional’, meaning the reservoirs are rain-fed and the water can only flow downhill once. To make the most of the wind-hydro partnership, the hydro should be ‘pumped storage’, where two reservoirs at different heights are connected by pipes and reversible water turbines. Then when the wind blows at night and demand is low, cheap electricity can be used to pump water uphill, and during the day when demand and prices are high, the water can rush back down to generate power. It takes more energy to pump the water up than is generated on the way down, but that’s the price of storing energy so it can be used when needed, rather than when the wind chooses to blow.
Portugal plans to more than double its wind capacity from 3.5GW to 8GW by 2020. To help balance this it will also increase hydro from 5GW today, of which less than a fifth is pumped storage, to 9.5GW by 2020, when around half will be pumped storage. This will lift the renewable proportion of Portugal’s electricity from 45 per cent today to 60 per cent in 2020, despite a big predicted rise in demand. 'We are very lucky,' admits Josée Medeiros Pinto, deputy director of planning for REN, Portugal’s grid operator, 'if we didn’t have hydro, hitting our renewables targets would be much more difficult and expensive.'
Britain is not quite so lucky. True, we do already have 1.4GW of conventional hydro and almost 3GW of pumped storage, at plants such as Dinorwig in Snowdonia, mostly built decades ago to mop up excess nuclear power during off-peak hours. But the potential to increase capacity is limited. Scottish & Southern recently announced plans to build another 900MW of pumped storage at Loch Lochy and Loch Ness, and it’s estimated Britain could build another 2GW of conventional hydro. But that’s not remotely enough to balance 32GW of wind.
Another way to balance wind is to trade it with your neighbours, which is how Denmark has coped with a huge increase in wind capacity in recent years, although this strategy is starting to creak. Because as well as lots of turbines Denmark also has thousands of combined heat and power (CHP) plants, which are efficient but inflexible. The plants provide district heating and electricity from the same equipment, so if you need the heat you get electricity too, but if the wind is blowing and demand is low, the result is often too much power. The solution so far has been to export excess electricity through interconnectors to Germany and Norway when the wind blows, and import when it doesn’t.
But Denmark will not be able to rely solely on international trade to balance its grid as it pursues ambitious plans to double its wind capacity by 2025 and generate half its annual electricity from wind. That’s because a huge increase in wind farms is also planned in Germany and Norway, so when the wind blows in future, the neighbours won’t be able to absorb the excess power from Denmark. The Danes know they have to find ways to balance the grid within their own borders.
The problem is not trivial. Already wind generation occasionally exceeds total demand in off-peak hours, and with twice the capacity it would often exceed even peak demand (see graph below). Network operator Energinet has launched an industry-wide project to develop an ‘EcoGrid’, where wind power is balanced not only by other forms of electricity supply but also through demand management – shifting consumption to suit supply, rather than the other way around.
|West Denmark currently generates the equivalent 25 per cent of its yearly electricity consumption from wind, and already wind power occasionally exceeds demand during off-peak hours (left hand graph). If capacity and generation double by 2025 as planned, wind generation would exceed even peak demand much more often (right hand graph). Source: Danish Technological Institute|
In an initial report, EcoGrid researchers found that while Denmark’s CHP is part of the problem, it may also offer part of the solution. CHP plants come equipped with hot water storage tanks, and these could be fitted with electrical heaters to soak up excess wind power and save it to be used later as heat. The next step would be to install hundreds of thousands of ground source heat pumps in houses and buildings across the country, which would perform the same role but with greater capacity.
Smartening up the grid
While demand management is clearly vital, it is not much help for the biggest problem of all: when the wind fails to blow for days or even weeks, as during the big freeze in January. Even countries that are way ahead in wind balancing like Spain and Portugal continue to rely on fossil generation to fill this gap. Kjeld Norregaard of the Danish Technology Institute (DTI) freely admits that so far, ‘we have only solved a fraction of the problem’.
In Britain, where power demand ranges between about 20GW and 60GW depending on season and time of day, the National Grid estimates the potential ‘flexible demand’ could amount to 12GW by 2020 (see chart below). But that assumes a fleet of one million electric cars that could be charged on excess electricity, and the company thinks under 8GW is more realistic. Much will depend on smartening the grid, yet the Government’s deadline for the installation of smart meters in every home – a basic building block - is ten years away.
|There could be as much 12GW of flexible demand to help balance the grid by 2020, but National Grid thinks under 8GW is more likely. Source: National Grid|
So how will Britain crack it? Conventional thinking suggests in the short term we will follow the pack. In one planning scenario, ‘Gone Green’, which National Grid describes as ‘plausible but extremely challenging’, 28GW of wind in 2020 is combined with 12GW of new gas fired power and three each of nuclear and coal – perhaps with carbon capture. But an alternative, entirely renewable solution is beginning to take shape far more quickly than anyone could have anticipated.
Beyond the national grid
Two years ago the idea of a continent-wide supergrid seemed science fictional, but today elements are suddenly falling into place. Last December eleven North Sea countries signed a memorandum of understanding to establish a super-efficient high voltage direct current (HVDC) sub-sea grid, largely to trade the output of planned offshore windfarms. Officials from energy ministries, regulators, utilities and the European Commission met in Brussels in February and March and are preparing a detailed action plan to be signed off by the end of the year. In a separate development, ten major power engineering companies - including giants such as Siemens and Areva - launched the Friends of the Supergrid (FOSG) to demonstrate industry confidence that this massive infrastructure project is achievable.
The supergrid would solve the ‘Danish problem’ of reliance on trading power with your immediate neighbours because the distances involved are so much greater and encompass different weather systems. With electricity trunk routes stretching from Ireland to Kazakstan, and Scandinavia to Morocco, the wind would always be blowing somewhere, and there would always be demand for that power somewhere else. ‘I look forward to the day when Scotland turns on the kettle to be powered by North African electricity,’ said John Sturman of Parsons Brinckerhoff, the engineering consultancy at the FOSG launch in London in March. With so many different wind farms – and solar and hydro plants - feeding into the grid, the variations in output would even out to create a far more dependable supply. Renewables would be balanced not by fossil plants, but by each other.
David Strahan is an energy writer and author of The Last Oil Shock
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