Renew On Line (UK) 57

Extracts from NATTA's journal
Renew, issue 157 Sept-Oct 2005

5. Intermittency? No problem! 

Research at the Environmental Change Institute at Oxford University shows that intermittent renewables, combined with small scale domestic combined heat and power (dCHP) could provide the bulk of Britain’s electricity on a reliable basis.  In a very timely report in the Guardian (May 12th) Oliver Tickell quoted ECI’s Graham Sinden’s  conclusion that “By mixing between sites and mixing technologies, you can markedly reduce the variability of electricity supplied by renewables. And if you plan the right mix, renewable and intermittent technologies can even be made to match real-time electricity demand patterns. This reduces the need for backup, and makes renewables a serious alternative to conventional power sources.”

Tickell notes that Sinden initially looked at just three generation technologies: wind, solar and dCHP. ‘He ran computer models of power output based on weather records going back up to 35 years, and found that electricity production could be optimised by creating a mixture of 65% wind, 25% dCHP, and 10% solar cells. The high proportion of wind is because the wind blows hardest in the winter, and in the evening- when demand is highest. The dCHP also produces more at peak times, when demand for hot water and heating is also strongest. Solar makes a smaller contribution, and produces nothing at night. But it is still important to have it in the mix as it kicks in when wind and dCHP production is lowest.’  It could also have an increasing role in powering air conditioning in the summer.

Sinden argues that it is also essential to disperse the generators widely in geographical terms, so that some power is always being generated somewhere.  For example, in an article in the Oxford Times (April 2005), Tickell reports that Sinden found that there has not been a single moment in the last 40 years when the wind has not been blowing somewhere in the UK. ‘You may have calm, still weather in southern England, but the wind will still be blowing across the Highlands. The key to creating a reliable electricity supply from wind is to have the turbines in lots of different places, even in less windy parts of the country. That way, the need for spinning reserve and other backup is reduced.’

In his Guardian piece, Tickell noted that the dispersed approach goes against current practice, which is to put wind turbines where the wind is strongest. He added ‘Sinden’s approach is remarkably effective in reducing the need for standby capacity. If offshore wind power alone were to provide an average 3,500MW of electricity- 10% of electricity demand in England and Wales- it would need to be backed up by an extra standby generating capacity of 3,135MW- 90% of average production. But using Sinden’s proposed mix of technologies, only 400MW of new standby capacity would be needed- just 11%.’  This conclusion was relayed in evidence he presented to the House of Lords Science and Technology Committee in 2003.

Tickell then notes that in his latest work, commissioned by the Carbon Trust, Sinden has been looking at roles for wave and tidal power:‘Wave power output is concentrated into autumn and winter, when demand is greatest: 75% of wave power is produced between October and March. Tidal power output is predictable, but variable: at any site it drops to zero four times a day on the turn of the tide; and output is three or four times greater on the spring tide than on the neap tide.’

 He quotes Sinden’s view that: “a marine-based renewable system works best when it includes both tide and wave. The combination has lower variability, is better at meeting demand patterns, &  makes better use of expensive transmission infrastructure.”

Tickell spells out Sinden’s rationale for integrating in wave and tidal power in more detail in his Oxford Times piece: although wave is similar to wind in that it delivers more power in winter, it is more evenly spread out through the day, and wave power output is actually only weakly correlated with wind power output, so adding an element of wave will help to smooth the overall production curve. Moreover, although tidal power varies on a daily and lunar-monthly cycle, it is very predictable.

Sinden says ‘You can smooth out some of the daily variations by having a number of tidal stations at different points along the coast where high tide will come at different times. But the lunar cycle will have to be smoothed with electricity from other sources. The good thing is that because it is so highly predictable, conventional capacity can be scheduled well in advance, and with great certainty.’

In his Guardian piece Tickell concludes ‘Putting these figures together with estimates of Britain's available renewable resources, wind (onshore and offshore) could realistically provide some 35% of the UK’s electricity, marine and dCHP each 10-15%, and solar cells 5-10%. In other words, more than half the UK’s electricity could ultimately derive from intermittent renewables.’  He adds that, although Sindens work, which is supported by SuperGen Consortium and the Department of Applied Economics, Cambridge, illustrates that the government’s emphasis on wind, to date, is well placed, in the future ‘it must distribute wind farms more widely, and it must be more aggressive in deploying other renewables and dCHP, currently scheduled to be in 80,000 homes by 2010. The alternative is that Britain will have to pay huge and entirely avoidable costs, both economic and environmental, in providing standby power capacity.’

There have been similar renewables integration studies in the past. What Sinden has added in particular is a role for micro-CHP, plus up to date data on wind availability- and we now have several decades of experience with actual wind technology. The only problem is that at present,we have no organisational mechanism for scheduling domestic micro-CHP. It is all ‘below the 3MW market’. The technology is there, but getting from today’s BETTA market to a future multi-level structure could take a while.

For more see:  www.eci.ox.ac.uk/lowercf/intermittency/renewables.html

SDC gives wind a clean bill of heath

Wind power on land ‘is one of the cheapest forms of renewable energy and increasing supply to 20% by 2020 would present only a very modest increase in cost for consumers that compares well with other energy sources. Indeed, as fossil fuel prices increase and wind turbines become cheaper to build, wind power may even become one of the cheapest forms of electricity generation over the next 15 years’. 

So says the the Government  backed Sustainable Development Commission, following a comprehensive study of wind energy in Britain.  The 176-page report concludes that “wind power, along with other renewables, offers the only truly sustainable domestically sourced option for electric generation over the long term”. 

Jonathon Porritt, the commissions chair, added that  it aimed “to provide an antidote to what we see as systematic misrepresentation of the arguments for and against wind power”.  The report concludes that wind energy is quiet, economic and popular with people living near the turbines.  It dismisses  claims that wind power is unreliable and requires expensive back-up power stations, and claims that  even with a 20% wind contribution, the use of balancing capacity would only reduce the carbon emissions avoided by around 1%.  Indeed it claims that, although there are diminishing carbon saving gains and increasing costs beyond about a 20% contribution,‘technological advances mean there are no limits to the amount of wind capacity that can be added to an electricity system’.

The report is at:  www.sd-commission.org.uk/

TPA on variable wind

The UK Energy Research Centre says that wind intermittency will be the first research project to come from its Technology & Policy Assessment  group, which will ‘gather and analyse information from different domains on wind intermittency in the UK to help  inform policy makers & the wider public debate’.

* The intermittency issue is discussed further in the Features section of Renew 157, and it  will be  the topic of  an EERU Conference  'Integrating Renewables into the energy system'  at the Open University on Jan 24^th: see  under 'Conferences'  at http://eeru.open.ac.uk