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Wind Balancing

The debate over how much back-up capacity is needed to balance wind variations continues. Everyone agrees you need some, but some say you need 100% and that, as a result, wind power won’t save many or, even any, emissions, net. See for example: http://environmentalresearchweb.org/blog/2011/11/does-wind-power-reduce-carbon.html

There is, in this debate, usually a confusion between, firstly, short term balancing (which is done all the time, even without variable wind on the grid) to deal with occasional unexpected plant or grid trip-outs and the daily demand variations, using frequency adjustments and by winding-up power from ‘spinning reserve’ plants; and, secondly, longer term possibly larger and longer loss of power issues, when you may need to crank up extra plant to meet gaps, calling on the built-in extra plant margin that grids have for this purpose.

For the moment, most grids can cope with the amount of wind linked in relatively easily, as many reports have indicated. The latest, ‘Strategies and Decision Support Systems for Integrating Variable Energy Resources in Control Centers for Reliable Grid Operations’, produced by Alstrom for the US Dept of Energy, offers first- hand perspectives on how variable energy sources, including wind, actually impact grid operations. It finds that the ability to forecast variable energy output is vital to integrating variable energy. It also describes several decision support tools that are currently used by grid operators. http://energy.gov/articles/new-report-integrating-variable-wind-energy-grid

But some extra fast start-up back-up, and maybe extra marginal gas plant, may be needed as the share of variable renewables grows. Key roles can also be played by other grid-balancing strategies, e.g. smart-grid interactive demand management and importing power from other countries via HVDC supergrids.

Alstrom’s US report does note that upgrading grid transmission links is a key long-term requirement - not least to deal with the perhaps more relevant problem of how to deal with excess power from wind and other variable renewables.

All that said, you will still find substantial contrarian assertions (e.g. from the US energy collective.com and the North American Platform against Wind Power: www.na-paw.org) that the variability of wind is an unresolvable issue. Similar lines of attack have been adopted by some UK centre-right think tanks, most recently by CIVITAS.

Much is made of the large and rapid swings from full power to low power that can occur, despite the fact that grids already deal with large demand swings daily. True, the existing swings are usually predictable, which is why the US Alstrom report looks to improved wind forecasting. But, while there’s no one solution, given smart grids/DSM and storage plus supergrid imports, it should be possible to balance even large variations- though it may be harder in the US, where cross national grid links are weaker and there’s less gas/CCGT, although of course shale gas may change that.

Back in the UK, we have a good well integrated grid system and last year a Poyry report for the Committee of Climate Change spelt out how it, and some upgrades and extensions, could help us balance some ‘stretching but feasible’ scenarios with high levels of renewables (reaching up to 94% in the Max scenario).

They found that ‘the electricity system was able to accommodate these high levels of renewable generation whilst complying with the specified constraints on emissions and security of supply. However, this was at the cost of shedding low variable cost generation and construction of new peaking capacity; predominantly in the two 2050 scenarios and Max scenario’.

Shedding power (or ‘curtailing’ excess output) is wasteful, but building new low cost gas-fired capacity is relatively cheap, and they say, not urgent ‘Construction of peaking plant is not required until after 2030 in either the VeryHigh or the High scenario’.

Overall they say ‘Sufficient technical resource appears to be available to deliver very high levels of renewable penetration’, but if offshore wind then dominates, diversity is reduced making grid balancing harder. So they are keen on a wider range of renewables being used.

So how robust is their projected future renewables-based system? They report that their scenarios were also tested against ‘more extreme weather conditions, as defined as increased frequency of low wind periods (‘lulls’) and greater variability of wind output.’

They say ‘In our (very) high renewable scenarios, we found that there is relatively little difference between the level of security of supply…in an average weather year and from the level in one of our extreme weather years’. But ‘CO2 emissions increase in the year with more lulls because fossil fuel plants run at higher load factors to compensate for lower wind output. In contrast, there is a (slightly) higher average annual load factor for wind in the more variable wind year. This leads to lower emissions, particularly in 2030.’

For the moment there should be no major problems, but we will need to act later; ‘The closure of unabated gas plants will reduce generation flexibility by 2050’: while in 2030, the electricity system is able to accommodate high levels of renewable penetration ‘in 2050, around 40TWh of low variable cost generation is shed in the High and Very High scenarios, with a need for new peaking capacity of 6GW and 10GW respectively’.

The situation is even worse in the Max scenario when ‘shedding increases to 120TWh a year, and 21GW of new peaking capacity is required to meet the desired level of security of supply. This is despite an assumed increase in demand-side flexibility and an expansion of interconnection capacity between 2030 and 2050 (and between 2050 and the Max scenario).’

So in addition to grid extensions and demand side management, after 2030 you also more peaking plant., although they add ‘a more diverse renewables mix helps the system to accommodate high renewables. Increasing the deployment of solar and tidal range (and reducing offshore wind deployment) in the High scenario leads to a big fall in the amount of shedding and required new capacity build in 2050.’

They say that, although it in basically inflexible, nuclear might also play a role: ‘despite the increase in shedding, construction of nuclear capacity is still cost-effective given the assumed set of fuel and carbon prices and generation costs’, but they add, ‘alternatively, interconnectors could be used to provide GB with access to a more diverse renewables mix in Europe’.

We do seem to have plenty of options. And Pyorys analysis does seem to be an answer to all those contrarians who say renwables can’t do it , though some still say ramp-up rates will be high, and hard for existing peaking plant to cope with. The debate continues

Pyory report ‘Analysing technical constraints on renewable generation to 2050’, to the CCC, March 2011

Posted by Dave Elliott on February 4, 2012 10:48 PM | Permalink