1 Open University Integrating Renewables Conference 24 January 2006 Wind power on the grid… What happens when the wind stops blowing? David Milborrow

2 Scope MUST examine electricity networks  Problems with intermittent generation sources, e.g. nuclear, gas, cross-channel link, etc Behaviour of wind plant Assimilating wind into networks  Issues and costs  Storage  Capacity credit Denmark and Germany: Lessons to learn?

3 Electricity systems

4 Why integrated systems? Smoothing of Demands and Generation sources Peak/average ratios  House: 15  UK: 1.5 Lower plant margins needed -  House: at least 2*peak  Large electricity system: ~1.2* peak All leads to LEAST COSTS

5 Firm power is a concept ONLY 1.UK-France link  5 trips, Jan-Jun 2005, "cause unknown" °24 Jan, 03:37, 13:51, 9 May, 06:56, etc  Outage times cover maintenance+faults  Source: UCTE 2. Typical utility (ERCOT) forced outages: ~2%, + ~7% planned outages

6 Reserves in a power system Pumped storage is used as reserve All can cope with demand increase or decrease Voltage reductions may be used in emergencies

7 Wind characteristics

8 Smoothing makes a difference Wind turbines smooth wind variations Wind farms smooth them more Wind farms over the country smooth them even more! We now have data from Denmark that illustrates this

9 Smoothing of power swings Time interval: 1 hour

10 Running electricity systems Managing electricity systems is all about managing risks All estimates of uncertainty come with a range of probabilities, and Uncertainty margins do not add arithmetically – a “sum of squares” law applies So the extra impacts of wind are small

11 Costing the effects of wind Scheduling error with wind enables extra reserve capacity needs to be estimated Establish cost of extra reserve, based on  Reduced efficiency of part-loaded plant  Cost of plant, or,  Market rates System operators do not care what the reserve is – as long as it can increase or reduce output when asked

12 Extra back-up capacity

13 Extra costs for backup

14 Capacity credits The “Firm power” issue ++= ?

15 Capacity credits depend on:- Amount of wind on system Wind speeds Wind turbine types Winds at time of peak demand Utility operating procedures When “normalised” for differences in wind speed, good agreement between most estimates for northern Europe

16 Capacity credits - UK

17 5 days in the life of west Denmark (January 2001) Even with 2400 MW of wind, demand variations still predominate Wind reduces net demand at peak times

18 Storage

19 Storage "Renewables need storage" ?  Rather misleading! Only the intermittent sources "Storage can transform the economics of the intermittent renewables" ? Only if they are very low cost! Most studies conclude that economics must be studied separately; may be useful to system, or as reserve

20 Storage - problems With dedicated storage: How do you size the store?  Can you be sure it will not "overflow"  Or run out during calms Very difficult to get best value from a store UNLESS USED FOR BENEFIT OF SYSTEM Even then Value>cost? is the acid test  US DoE and UK SYSTEM cost targets ~ £500/kW  more if paid for ancillary services Economics of isolated systems are site-specific, so dedicated storage may be worthwhile

21 Total extra cost impacts Extra cost to consumers Lower cost to consumers Source: Windpower Monthly, January 2006; method, Power UK 109

22 Lessons from Denmark and Germany West Denmark (20% wind) “Irrelevant”, say critics……  but links with Sweden, Germany and Norway are finite, so “effective” penetration about 10%  and S.O. could manage with 100% wind – without the links, or storage Germany (~6% wind) but wind speeds lower than UK; so  higher balancing costs,  low capacity credit…………

23 Wind integration – conclusions Thermal power sources (and consumers) will determine bulk of reserve costs for many years to come Capacity credits? – Yes, roughly=average power; declines as wind % increases Problem areas?  May be preferable, once wind input exceeds ~10%, to curtail wind output on a few occasions …..but wind will NEVER impose “jolts” on the system comparable with loss of a circuit of cross-channel link, or a 1320 MW nuke

24 Thank you! The End