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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
Nov 04Dec
Jan 05Feb
MarApr
MayJune
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
Outage time, minutes
6 Reserves in a power system
Pumped storage is used as reserveAll can cope with demand increase or decreaseVoltage reductions may be used in emergencies
Type Amount (UK) % of max demand
Inertia Small
Frequency response
~ 900 MW 1.5
Spinning reserve ~1000 MW 1.6
Standing reserve ~800 MW 1.4
Demand-side management
Varies
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
0 10 20 30 400
500
1,000
1,500
2,000
2,500
Time in hours
Wind power output
1 farm(kW)
West DK(MW)
9 Smoothing of power swings
-100 -50 0 50 100
0.01
0.1
1
10
Change, % rated capacity
Time, %
1 farm
WesternDenmark
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
0 10 20 30 40 500
2
4
6
8
10
Wind capacity/peak demand, %
Back-up capacity/wind capacity, %
Ireland(Doherty)
NRELPersistence
Perfect
US (BPA)
AuthorUpper
Lower
13
Extra costs for backup
0 2 4 6 8 10 120
1
2
3
4
5
Wind Energy penetration, %
Cost of extra balancing, $/MWh
NGC
Ilex
PacifiCorp
BPA/Max
/Min
EPRI/Xcel
GRE
MN
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
0 5 10 15 20 25 300.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Wind energy contribution, %
Capacity credit/annual capacity factor
NGC
SCAR
CEGB
17 5 days in the life of west Denmark (January 2001)
0 20 40 60 80 100 120500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
Hours
Demand, MW
Demand
Demand-wind
• 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
Offshore/onshore split: equal; offshore cost 50% higher35% capacity factorsCarbon dioxide: €/24/tonne (Oct 2005)
0.4 0.5 0.6 0.7 0.8 0.9 1700
800
900
1,000
1,100
1,200
1,300
1,400
Gas price, €/therm
Onshore wind cost, €/kW
10% windExtra 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
