Renewable energy and the National Electricity Market: Issues & Challenges© CEEM, 23 November 2005
Integrating renewable energy in the NEM: Technical issues
2Integrating renewable energy in the NEM: technical issues © CEEM 2005
OutlineWind energy as intermittent generationIntermittent generation- definition & issuesTrends in wind farm installations in AustraliaNetwork-related issues:– Connection & security issues
Power variability issues– Forecasting, ancillary services & power system security
3Integrating renewable energy in the NEM: technical issues © CEEM 2005
Energy service delivery in the stationary energy sector
Primaryenergyformse.g:
coal, gas, nuclear,
renewable
energy losses & external impacts
generation transmission distribution
The electricity supply industryend-use
equipment delivering
energy serviceseg: light,
heat,motivepower
transmission distributiontreatment
The natural gas supply industry
Energy service companies focus on end-use options, eg:efficiency, CHP, solar
Equipment providers
4Integrating renewable energy in the NEM: technical issues © CEEM 2005
Key issues for the electricity industryPart of the stationary energy sector:– In competition with other energy vectors to deliver
end-use energy servicesSignificant externalities:– Environmental (eg climate change)– Social (eg “essential good”)
Characteristics of electrical energy:– A high quality, secondary energy form:
Expensive to make but easy to use
– Flows at the speed of light from generators through the network to end-use equipment:
Can be difficult to maintain continuous energy flow
5Integrating renewable energy in the NEM: technical issues © CEEM 2005
Specific properties of electrical energy:– No cost-effective storage of AC electricity– Instantaneous transmission & distribution– Energy flows according to network laws:
From all generators to all consumers
Implications:– Supply & demand balance physically at all times:
A flow industry that benefits from active demand-side participation
– Electrical continuum - power station to end-useCannot assign energy from a particular power station to a particular consumer:
– ‘pool’ rather than ‘bilateral’ physical trade
– Wholesale & retail trading activities not easily separated
6Integrating renewable energy in the NEM: technical issues © CEEM 2005
An electricity trading framework
transmissionnetwork
distributionnetwork
Interchange to other
wholesale market regions
WholesaleMarket region
distributionnetwork
distributionnetwork Retail
Market 3RetailMarket 1
Retail Market 2large consumer
• Wholesale & retail market designs should be compatible• Both should include network models
Primary energy markets
• Small consumers, embedded generators & storage should be supported by energy service advisers
risks to end-useenergy service
delivery
most consumers
large generators
embedded generators
7Integrating renewable energy in the NEM: technical issues © CEEM 2005
Australian wind resource(Estimate of background wind (m/s) – AGO)
8Integrating renewable energy in the NEM: technical issues © CEEM 2005
Comparing AusWEA prediction (www.auswea.com.au)& readily acceptable (RA) wind capacity for Australia (www.ceem.unsw.edu.au)
8900500500(?)500220031002100RA MW
2240160280127029621713Total MW
1370402157201922000ApprovedMW
870120675501041713Inst MW
AusWATasSAVicNSWQld
9Integrating renewable energy in the NEM: technical issues © CEEM 2005
Wind penetration in SA & Eleswhere
10Integrating renewable energy in the NEM: technical issues © CEEM 2005
Physical context for wind - power system integration (photo courtesy AusWEA)
Shared,distributed,time-varying,non-storablewind energyflux
Independentlyowned wind farms
Sharedelectricitynetwork
&Powerstationsof other
types
End-useequipmentproviding
energyservices
11Integrating renewable energy in the NEM: technical issues © CEEM 2005
Key issues for wind energy integrationPhysical complexity:– Shared, non-storable, time-varying wind energy flux– Shared, non-storable, time-varying electrical energy flow
Commercial complexity:– Electricity industry infused with short- to long-term risks that are
difficult to commercialise (correctly allocate to industry participants)
Institutional complexity:– Shared issues in wind farm approvals, grid connection &
management of power system security
High wind energy penetration tests design adequacy of electricity industry restructuring
12Integrating renewable energy in the NEM: technical issues © CEEM 2005
Illustration of complexity: managing supply-demand balance in the electricity industry
Frequency is a measure of supply-demand balance:– always varying due to fluctuations in the power flows
associated with particular devices– Wind energy is only one of many fluctuating power flows
Thermalpower stations
Wind farms
Hydrogenerators
Industrial
Commercial
Residential
Generator input power Load electrical powerplus network losses
+ _
13Integrating renewable energy in the NEM: technical issues © CEEM 2005
Demand forecast errorsSouth Australia,2004 Q4 (NECA, 04Q4 Stats, 2005)
14Integrating renewable energy in the NEM: technical issues © CEEM 2005
Timeline for electricity trading in NEM(requires locational detail & active demand-side participation)
Financial instrument (derivative) trading &
spot market projections
ancillary service“actuation markets”
for period tforward-looking ancillary service
(AS) “acquisition markets” & security assessment
ancillary service“actuation markets”
for period t+1
Spot marketfor period t
Spot marketfor period t+1
time
spotperiod t
spotperiod t+1
uncertainty increases looking forward
Physical issues(centralised)
Commercial issues(decentralised)
15Integrating renewable energy in the NEM: technical issues © CEEM 2005
Dispatch, Pre-dispatch, PASA, SOO & ANTS(source: NEMMCO)
0 day 1 day 2 week 1 month 1 year 1 year 2
Medium Term PASA (2 yr, daily peak)
Pre-dispatch, re-bid & final dispatch schedule
Short Term PASA (7 days, 30 min res, 2hr update)
SOO & ANTS (10 yr)
• ST & MT Projected Assessment of System Adequacy support reserve assessment & participant operating decisions. ST PASA projects region demand & reserve for 7 days @ 30 min resolution, updated every 2 hours. MT PASA projects region daily peak demand & reserve for 2 yrs, updated weekly.
• Statement of Opportunities (SOO) & Annual National Transmission Statement (ANTS) are intended to inform generation, demand & network investment decisions (10 year horizon, issued annually)
16Integrating renewable energy in the NEM: technical issues © CEEM 2005
Managing variability in supply or demand
Commitment of slow-start plant1-2 days
Commitment of fast-start plant10-300 min
Central dispatch & spot pricing process5-10 min
Ancillary services< 5 min
Voltage & frequency perturbations moderated by system inertia & passive damping
<4 sec
Issue Time period
17Integrating renewable energy in the NEM: technical issues © CEEM 2005
Predicted 1% probability change in output for 1000 MW wind in SA (www.esipc.sa.gov.au)
18Integrating renewable energy in the NEM: technical issues © CEEM 2005
Simulated 6-day dispatch of gen’n in SA with 1000 MW of wind (www.esipc.sa.gov.au)
19Integrating renewable energy in the NEM: technical issues © CEEM 2005
NEMMCO concerns about wind energy (NEMMCO, 2003)
Frequency control in normal operation:– Frequency regulating service costs ~5 $/MWH
Security control - largest single contingency– Will wind farms ride-through disturbances?– Adequacy of wind farm dynamic models
Interconnection flow fluctuations:– Exceeding flow limit may cause high spot price
Forecast errors due to wind resource uncertainty:– Five minute dispatch forecast (spot price)– Pre-dispatch & longer term (PASA & SOO) forecasts
20Integrating renewable energy in the NEM: technical issues © CEEM 2005
Western Power’s proposed wind penalty charge (c/kWh) (Western Power, 2002)
21Integrating renewable energy in the NEM: technical issues © CEEM 2005
Wind energy as intermittent generation
Renewable energy fluxes are time-varying:– Solar, wind, hydro (tidal), biomass, geothermal, wave
Wind & solar are non-storable:– Can be described as intermittent
22Integrating renewable energy in the NEM: technical issues © CEEM 2005
Intermittent generation (NER)National Electricity Rules (NER) definition of intermittent generation:– “A generating unit whose output is not readily
predictable, including, without limitation, solar generators, wave turbine generators, wind turbine generators and hydro generators without any material storage capability”
Issues identified by NEMMCO:– Forecasting & reserves; frequency control ancillary
services (FCAS); voltage control; management of network flows; modelling & security assessment
23Integrating renewable energy in the NEM: technical issues © CEEM 2005
Network issues for wind farms #1Networks are shared, centrally planned resources:– Must limit network disturbances caused by wind farms– Wind farms must survive disturbances from the network
Renewable resources are often distributed differently from fossil fuel resources:– Weak network conditions likely to be more common in
Australia & New Zealand than Europe or North AmericaNetwork must be built to carry peak flows:– Want good estimates of aggregation & seasonal effects
Benefits of staged development of wind resources:– Network savings; reduced voltage & frequency impacts
24Integrating renewable energy in the NEM: technical issues © CEEM 2005
Network issues for wind farms #2Wind turbine starting & stopping transients:– Severity can be alleviated by soft-start &
high wind-speed power-managementSome wind turbine designs:– May cause voltage distortions:
Harmonics &/or transients
– May have poor power factor, eg:Uncompensated induction generator
– May not ride-through system disturbancesTemporary voltage or frequency excursions
25Integrating renewable energy in the NEM: technical issues © CEEM 2005
Wind turbine type comparison(Slootweg & Kling, 2003, http://local.iee.org/ireland/Senior/Wind%20Event.htm)
26Integrating renewable energy in the NEM: technical issues © CEEM 2005
Size of wind turbines used by Western Power (www.wpc.com.au)
27Integrating renewable energy in the NEM: technical issues © CEEM 2005
Wind turbine starting transients for Esperance 2 MW wind farm 9 x 225 kW turbines with squirrel cage IGMagnetisation inrush current may cause a voltage dip - starts should be spaced out
(Rosser, 1995)
28Integrating renewable energy in the NEM: technical issues © CEEM 2005
Network connection issues & examplesApproximate ability of a transmission line to accept a wind farm:– 66kV ≤ 30MVA– 132kV ≤ 100MVA– 330kV ≤ 200MVA– Constraints may be determined by several factors:
Thermal, voltage, fault clearance, quality of supplyThermal ratings depend on line temperature & wind speed
Relevant wind farm rating is its maximum output, not the sum of turbine rated powers:– Coincident output of the connected wind turbines
29Integrating renewable energy in the NEM: technical issues © CEEM 2005
ConclusionsIntermittent generation:– Brings new challenges for electricity industry
restructuring (technical, market design, regulation)– Separate category only appropriate for small
penetrationsWind energy:– The first significant form of “intermittent generation”– Network connection issues:
Often distributed differently to traditional resources
– Forecasting & system security issuesRegional, rather than project specific