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MATCHING SUPPLIES OF ELECTRICITY TO VARIABLE DEMANDS FOR ELECTRICITY

MATCHING SUPPLIES OF ELECTRICITY TO VARIABLE DEMANDS FOR ELECTRICITY, DESERTEC UK, August 12, 
It is sometimes suggested that renewable sources of electricity cannot provide more than about 20% of our electricity supplies because they are intermittent or variable. But all sources of electricity are intermittent because they need to be taken out of service for scheduled maintenance and because, like any kind of equipment, they are liable to unscheduled breakdowns. With all sources of power, load factors are normally well short of 100%.

The variability of sources such as wind power is much less of an issue than is sometimes suggested, as described in Managing Variability (PDF, 402 KB, a report by independent consultant David Milborrow commissioned by Greenpeace, WWF, RSPB, Friends of the Earth, July 2009).

Not only are all sources of electricity intermittent, and many of them are variable, but the demand for electricity is variable too—and there can be quite large changes from one minute to the next. The often-quoted example is how there can be a sharp peak in demand for electricity when there is a commercial break in a popular TV programme and many people go and put the kettle on to make a cup of tea.

There is a range of techniques available for matching supplies with constantly varying demands. When electricity supply systems are properly engineered, they should be able to accommodate sources of electricity that are 100% renewable.

Any or all of the following techniques may be used:

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  Large-scale ‘HVDC’ transmission grids. In an area like Europe, there are several potential benefits from building a ‘supergrid’ of highly-efficient HVDC transmission lines to link existing HVAC transmission grids (see electricity transmission grids). One of the most important benefits is that this kind of large-scale grid can make it much easier to match variable supplies with variable demands. For example, the wind may stop blowing in any one spot but it almost never stops blowing everywhere across a wide area like Europe. If there is a peak in demand in any one area, it can almost always be met from spare capacity in one or more other areas. Large-scale storage facilities, such as pumped-storage systems in Norway and the Alps, may be widely shared. Submarine HVDC transmission lines that have been laid between Norway and Denmark and between Norway and the Netherlands enable both pairs of countries to benefit in this way.
• Complementary sources of power. In load-balancing via the grid, it is helpful if different kinds of generators have complementary characteristics. For example, there is a good fit between solar power—which is strongest in the summer—and wind power—which is strongest in the winter (see, for example, Seasonal optimal mix of wind and solar power in a future, highly renewable Europe, Dominik Heide and others, Renewable Energy 35, 2483-2489, 2010).
• Power on demand. One of the most useful attributes in any source of electricity is the ability to respond quickly to peaks in demand. Sources of electricity such as coal-fired power stations or nuclear power cannot respond quickly in that way and are really only suitable for ‘base load’. Non-renewable sources that provide power on demand are gas-fired power stations and stand-by generators (See Emergency power systems to be worth £1.5bn by 2020, The Telegraph, 2011-11-09). Renewable sources of power that can provide power on demand include:……  http://www.desertec-uk.org.uk/elec_eng/supply_demand.html

August 8, 2012 - Posted by Christina Macpherson | 2 WORLD, renewable