Transcript Capacity credits - EERU | Open University

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Open University
Integrating Renewables Conference
24 January 2006
Wind power on the grid…
What happens when the wind stops blowing?
David Milborrow
[email protected]
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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?
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Electricity systems
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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
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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
Outage time, minutes
14,000
12,000
10,000
8,000
6,000
4,000
2,000
0
Nov 04 Jan 05 Mar
May
Dec
Feb
Apr
June
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Reserves in a power system
Type
Inertia
Frequency
response
Spinning reserve
Standing reserve
Demand-side
management
Amount (UK) % of max demand
Small
~ 900 MW
~1000 MW
~800 MW
Varies
1.5
1.6
1.4
Pumped storage is used as reserve
All can cope with demand increase or decrease
Voltage reductions may be used in emergencies
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Wind characteristics
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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
Wind power output
2,500
2,000
1 farm
(kW)
1,500
West DK
(MW)
1,000
500
0
0
10 20 30 40
Time in hours
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Smoothing of power swings
Time, %
10
1 farm
1
Western
Denmark
0.1
0.01
-100
-50
0
50
Change, % rated capacity
Time interval: 1 hour
100
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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
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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
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Extra back-up capacity
Back-up capacity/wind capacity, %
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Ireland
(Doherty)
8
NREL
Persistence
6
Perfect
4
US (BPA)
Author
Upper
2
0
0
10
20
30
40
Wind capacity/peak demand, %
50
Lower
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Extra costs for backup
Cost of extra balancing, $/MWh
5
NGC
4
Ilex
PacifiCorp
3
BPA/Max
2
/Min
EPRI/Xcel
1
GRE
0
0
2
4
6
8
Wind Energy penetration, %
10
12
MN
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Capacity credits
The “Firm power” issue
+
+
=
?
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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
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Capacity credits - UK
Capacity credit/annual capacity factor
1.6
1.4
1.2
NGC
1
SCAR
0.8
CEGB
0.6
0.4
0.2
0
5
10
15
20
Wind energy contribution, %
25
30
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5 days in the life of west
Denmark (January 2001)
Demand, MW
4,000
Demand
3,500
Demand
-wind
3,000
2,500
2,000
1,500
1,000
500
0
20
40
60
Hours
80
100
120
• Even with 2400 MW of wind, demand variations
still predominate
•Wind reduces net demand at peak times
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Storage
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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
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•
•
•
•
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
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Total extra cost impacts
Onshore wind cost, €/kW
1,400
1,300
10% wind
Extra cost to consumers
1,200
1,100
1,000
900
Lower cost to consumers
800
700
0.4
0.5
0.6
0.7
0.8
Gas price, €/therm
0.9
1
Offshore/onshore split: equal; offshore cost 50% higher
35% capacity factors
Carbon dioxide: €/24/tonne (Oct 2005)
Source: Windpower Monthly, January 2006; method, Power UK 109
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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…………
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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
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Thank you!
The End