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MARGINAL EMISSIONS RATES IN ENERGY SYSTEM CHANGE <ul><li>Dr A.D. Hawkes </li></ul><ul><li>Principal Consultant in Modelling, AEA </li></ul><ul><li>Visiting Fellow, Energy Futures Lab, Imperial College London </li></ul>

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The 2050 target Results from UK MARKAL UK CO 2 Emissions Electricity Emissions Intensity

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Residential Sector Heating (service demand)

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CO 2 Reduction Performance <ul><li>Which demand-side technology? </li></ul><ul><li>Which “baseline” technology will it displace? </li></ul><ul><li>Where there is an interaction with the electricity system, how much CO 2 will be saved/produced for every kWh saved/used? </li></ul><ul><li>What about interactions with other parts of the energy system – primary resource choice, sectoral focus of emissions reduction, etc? </li></ul>

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The standard approach <ul><li>Choose a baseline system </li></ul><ul><ul><li>E.g. For heating in the UK; the combustion of natural gas in a condensing boiler </li></ul></ul><ul><li>Figure out how much of each “energy carrier” the alternative system saves/produces (relative to the consumption/production of the baseline). </li></ul><ul><ul><li>E.g. A CHP system may consume an additional 3000kWh of gas/year, and produce an additional 2500kWh of electricity </li></ul></ul><ul><li>Multiply change in consumption for each energy carrier by the respective standard emissions rates; ~0.19kgCO 2 /kWh for gas, and 0.43kgCO 2 /kWh for electricity in the UK </li></ul><ul><ul><li>E.g. Change in CO 2 = 0.19*3000 – 0.43*2500 = -1075kg CO 2 </li></ul></ul>

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An alternative method - marginal CO 2 rates The CO 2 actually saved due to a change in electricity demand is related to which power stations actually respond to that change.

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Baseload

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Intermittent Generation

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Dispatchable Generation

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The observed response of generators in GB <ul><li>ELEXON publishes pre-gate closure dispatch data for every “BM unit” in the GB system </li></ul><ul><li>We know which generators these are, and can estimate their efficiency, so we can calculate the CO 2 production rate change associated with a change in output </li></ul><ul><li>We can do this for every generator, so we can find the aggregate change in CO 2 produced in any ½ hour period, along with the change in aggregate system load </li></ul><ul><li>We can create a scatter plot of these </li></ul><ul><li>We can create a linear fit (through zero) </li></ul><ul><li>The slope of the linear fit is an estimate of the marginal emissions rate for the system </li></ul><ul><li>8 years of data ~ 60,000,000 data points across ~400 generators </li></ul><ul><li>140,000 half-hour time periods </li></ul>

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GB Electricity Marginal Emissions 2002 to 2009 inclusive Source: Hawkes, A.D. (2010) Estimating Marginal Emissions Rates in National Electricity Systems. Energy Policy 38(10) 5977-5987. doi:10.1016/j.enpol.2010.05.053 Change in System Load (GWh/h) Change in System CO 2 Rate (ktCO 2 /h) Linear Fit: y = 0.69 x

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Stats of the MEF Change in System Load (GWh/h) GB System Load (GW) Change in System Load (GWh/h) Change in System CO 2 Rate (ktCO 2 /h) Marginal Emissions Factor (kgCO 2 /kWh) Number of Observations Probability of System Load y = 0.69 x

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Change over time <ul><li>Decommissioning and commissioning of power stations. </li></ul><ul><li>We know which “BM Units” will be decommissioned out to ~2020. National Grid also projects the types of new generators over the same period. </li></ul><ul><li>We can replace the old with the new, and repeat the marginal emissions calculation. </li></ul><ul><li>Resulting in... </li></ul>Time Period Marginal Emissions Rate (kgCO2/kWh) 2002-2009 0.69 kgCO 2 /kWh 2016 0.6 kgCO2/kWh 2020-2025 0.51 kgCO 2 /kWh

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What does this mean? <ul><li>The actual marginal emissions rate from 2002-2009 was 60% higher than the figure typically used in policy analysis. </li></ul>

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An alternative view of the build margin <ul><li>Hypothetical Scenario 1 </li></ul><ul><ul><li>G.B. Peak system load increases in small steps – one step for every heat pump added to the system (e.g. 1.4kW each) </li></ul></ul><ul><ul><li>The supply margin decreases </li></ul></ul><ul><ul><li>Electricity price becomes more volatile, and generally increases </li></ul></ul><ul><ul><li>357,142 (i.e. almost 1GW peak demand) heat pumps are added to the system, with little change in the marginal emissions rate </li></ul></ul><ul><ul><li>1 further heat pump is added, triggering investment in a new low emissions power station </li></ul></ul><ul><ul><li>What is the appropriate marginal emissions rate? </li></ul></ul>

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An alternative view of the build margin (2) <ul><li>Hypothetical Scenario 2 </li></ul><ul><ul><li>Same as Scenario 1 </li></ul></ul><ul><ul><li>When heat pumps operate, the new power station does not respond to this demand (e.g. power station sits in the baseload) </li></ul></ul><ul><ul><li>What is the appropriate marginal emissions rate? </li></ul></ul>

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An alternative view of the build margin (3) <ul><li>Hypothetical Scenario 3 </li></ul><ul><ul><li>Same as Scenario 1 </li></ul></ul><ul><ul><li>When the last heat pump is added, a micro-CHP system is added at the same time </li></ul></ul><ul><ul><li>No new power station investment occurs </li></ul></ul><ul><ul><li>What is the appropriate marginal emissions rate for the HP system? </li></ul></ul><ul><ul><li>What about the CHP system? </li></ul></ul>

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Framework for analysing the build margin <ul><li>Establish a baseline demand projection </li></ul><ul><li>Establish a baseline commissioning/decommissioning of power stations </li></ul><ul><li>Model demand projection with addition of a package of demand side measures </li></ul><ul><li>Model change in generation fleet </li></ul><ul><li>Total change in CO 2 over a period, divided by total change in demand </li></ul><ul><ul><ul><ul><li>=> Build-related marginal CO 2 rate </li></ul></ul></ul></ul>

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Conclusion <ul><li>From 2002-2009, the marginal CO 2 intensity of grid electricity in Great Britain was 0.69 kgCO 2 /kWh. </li></ul><ul><li>This could reduce to 0.51kgCO2/kWh by 2020-2025. </li></ul><ul><li>Either of the above numbers are well above the figure typically used in policy analysis in the UK. </li></ul><ul><li>The dynamics of change in the underlying stock of generators is rather complicated, but very important. </li></ul>