Estimating the CO2 impact of electricitydemand and onsite generation choicesinteractions with commissioning of large power stationsDr Adam HawkesCentre for Energy Policy and Technology (ICEPT)
Contents of this talk• Recap – historical marginal emissions rates 2002 – 2009• Recap – introducing plant commissioning and decommissioning• Demand-side perspectives on accounting for emissions• Which generators respond to demand-side changes?• Capacity credit (and capacity debit?)• A simple model of demand-supply interaction in terms of plantcommissioning and decommissioning• Marginal emissions rates and the future generation mix
Recap – how marginal emissions have been viewedSource: Hawkes (2010) Estimating Marginal CO2 Emissions Rates for National Electricity Systems. EnergyPolicy. Volume 38, Issue 10, October 2010, Pages 5977–5987One day in the GB electricity system
GB Historical Marginal Emissions 2002 to 2009• ½ hourly data from approx 200large generators• Emissions rate from eachgenerator• Therefore – can estimate ½ hourlyCO2 rate change for the system as awhole• Linear regression of CO2 rateagainst system load change givesthe marginal emissions rateSource: Hawkes (2010) Estimating Marginal CO2 Emissions Rates for National Electricity Systems. EnergyPolicy. Volume 38, Issue 10, October 2010, Pages 5977–5987
Introducing plant commissioing and decommissioning• We know which plant are going tobe decommissioned to approx 2020,and can make educated guessabout the rest• Also have data on power systemtrajectory to 2050 from MARKALand similar• Therefore can estimate futureoperational marginal emissionsratesEmissions ratein 2016(kgCO2/kWh)Emissionsrate in 2020-2025(kgCO2/kWh)LowerEstimate0.54 0.42CentralEstimate0.60 0.51UpperEstimate0.66 0.58
Summary of previous work….and the next challenge•The current operational marginal CO2 emissions rate has been estimated(1storder phenomena)•This includes the influence of commissioning and decommissioning oflarge power stations on operational marginal CO2 emissions (1storderphenomena, for future years)•BUT, does not include the fact that demand-side choices lead to thecommissioning (or not) of large power stations•This 2ndorder impact could be much larger than the 1storder analysis sofar
How can we attribute commissioning activity todemand-side actions?• There is already a measure of a generators contribution to firm capacity,and this concept can be equally applied to demand increase/decrease atpeak times• Each addition of generating capacity or demand reduction on the demand-side leads to reduced requirement for generating capacity on the supplyside• “Capacity credit”• Each addition of demand lead to increased requirement for generatingcapacity• Negative capacity credit, or• “Capacity debit”?• These can be seen to interact with commissioning and decommissioningof power stations
A simple dynamic model of supply-demand capacity interactionExisting stock ofdemand-sidetechnology andretirement profile+Replacementtechnology (i.e.demand-sidechoices)=Demand (and peakcapacityrequirement inelectricity system)Demand SideExisting stock ofcentralisedgenerators andretirement profile+ Replacementpower stations = Available supplycapacitySupply Side+Capacity margin=For each time period (e.g. year) ….
Hypothetical example: a simple technology substitutionThe electrification of heating in the UK, and decarbonisation ofelectricity•Demand side• Baseline: Condensing gas boilers remain dominant• Alternative: Electric heat pumps rapidly gain large market share•Supply side• Baseline: New build is nuclear, and under an unchanging future electricitydemand the next 1GWe plant will be commissioned in 2016• Alternative: Increasing peak demand due to electrification of heat leads toincreased generation capacity requirement, and subsequently a nuclear plantof 1.5GWe is commissioned in 2015.
A baseline (counterfactual) and a scenarioBaseline Alternative ScenarioImpact of demand-side interventionAddition of 500MWe of low carbon baseload capacity, and addition of theoriginal 1GWe of low carbon baseload capacity 1 year earlier
Baseload versus mid-meritSource: Hawkes (2010) Estimating Marginal CO2 Emissions Rates for National Electricity Systems. EnergyPolicy. Volume 38, Issue 10, October 2010, Pages 5977–5987
Marginal Emissions Rate•After making a number of assumptions…•System load change = 2.61TWh per year•System CO2 rate change = -0.51MtCO2 per year•Marginal emissions rate = -0.51/2.61 =-0.2 kgCO2/kWh
Marginal Emissions Rate (2)•If the commissioned plant is a coal-fired power station•System load change = 2.61TWh per year•System CO2 rate change = 2.59 MtCO2 per year•Marginal emissions rate = 2.59/2.61 =0.99 kgCO2/kWh
Conclusions1.The marginal emissions rate can be viewed in 2 ways• The marginal rate during system operation. Useful for;» measures that don’t influence peak demand, and» measures installed now• The long-term marginal rate due to plant commissioning. Useful for;» measures which change peak demand (i.e. have +ve or –ve capacitycredit)1.The operational marginal emissions rate is a function of the specificemissions rates of dispatchable generation in the system. Recently0.69kgCO2/kWh.2.The long-term marginal emissions rate, which is a function of the specificemissions rate of the next generators to be commissioned, and (to a lesserextent) whether or not these new generators are more baseloaded thanthose they replace.3.For a decarbonizing power system, long-run marginal emissions forelectrification actions are likely to be negative.
Next steps• Application to the GB energy system…
Power sector projectionSource: CCC (2010) The Fourth Carbon Budget – reducing emissions through the 2020s
Residential heating projectionSource: Hawkes (2011) Pathways to 2050 – Key Results: MARKAL Model Review andScenarios for DECC’s 4th Carbon Budget Evidence Base. A report by AEA for DECC.