Adam Hawkes | Marginal Emissions Rates in Energy System Change

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Presented at the 4th International Conference on Carbon Accounting …

Presented at the 4th International Conference on Carbon Accounting
25th November 2011

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  • This talk is inspired by the fact that many economists hold the view that if one analyses the economics of the marginal system, they might end up with the right answer. But if one were to analyse the economics of the average system, they will definitely get the wrong answer.
  • Radical change, dynamics of this change important
  • Origin of 0.43


    • Dr A.D. Hawkes
    • Principal Consultant in Modelling, AEA
    • Visiting Fellow, Energy Futures Lab, Imperial College London
  • 2. The 2050 target Results from UK MARKAL UK CO 2 Emissions Electricity Emissions Intensity
  • 3. Residential Sector Heating (service demand)
  • 4. CO 2 Reduction Performance
    • Which demand-side technology?
    • Which “baseline” technology will it displace?
    • Where there is an interaction with the electricity system, how much CO 2 will be saved/produced for every kWh saved/used?
    • What about interactions with other parts of the energy system – primary resource choice, sectoral focus of emissions reduction, etc?
  • 5. The standard approach
    • Choose a baseline system
      • E.g. For heating in the UK; the combustion of natural gas in a condensing boiler
    • Figure out how much of each “energy carrier” the alternative system saves/produces (relative to the consumption/production of the baseline).
      • E.g. A CHP system may consume an additional 3000kWh of gas/year, and produce an additional 2500kWh of electricity
    • 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
      • E.g. Change in CO 2 = 0.19*3000 – 0.43*2500 = -1075kg CO 2
  • 6. 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.
  • 7. Baseload
  • 8. Intermittent Generation
  • 9. Dispatchable Generation
  • 10. The observed response of generators in GB
    • ELEXON publishes pre-gate closure dispatch data for every “BM unit” in the GB system
    • 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
    • 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
    • We can create a scatter plot of these
    • We can create a linear fit (through zero)
    • The slope of the linear fit is an estimate of the marginal emissions rate for the system
    • 8 years of data ~ 60,000,000 data points across ~400 generators
    • 140,000 half-hour time periods
  • 11. 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
  • 12. 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
  • 13. Change over time
    • Decommissioning and commissioning of power stations.
    • We know which “BM Units” will be decommissioned out to ~2020. National Grid also projects the types of new generators over the same period.
    • We can replace the old with the new, and repeat the marginal emissions calculation.
    • Resulting in...
    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
  • 14. What does this mean?
    • The actual marginal emissions rate from 2002-2009 was 60% higher than the figure typically used in policy analysis.
  • 15. An alternative view of the build margin
    • Hypothetical Scenario 1
      • G.B. Peak system load increases in small steps – one step for every heat pump added to the system (e.g. 1.4kW each)
      • The supply margin decreases
      • Electricity price becomes more volatile, and generally increases
      • 357,142 (i.e. almost 1GW peak demand) heat pumps are added to the system, with little change in the marginal emissions rate
      • 1 further heat pump is added, triggering investment in a new low emissions power station
      • What is the appropriate marginal emissions rate?
  • 16. An alternative view of the build margin (2)
    • Hypothetical Scenario 2
      • Same as Scenario 1
      • When heat pumps operate, the new power station does not respond to this demand (e.g. power station sits in the baseload)
      • What is the appropriate marginal emissions rate?
  • 17. An alternative view of the build margin (3)
    • Hypothetical Scenario 3
      • Same as Scenario 1
      • When the last heat pump is added, a micro-CHP system is added at the same time
      • No new power station investment occurs
      • What is the appropriate marginal emissions rate for the HP system?
      • What about the CHP system?
  • 18. Framework for analysing the build margin
    • Establish a baseline demand projection
    • Establish a baseline commissioning/decommissioning of power stations
    • Model demand projection with addition of a package of demand side measures
    • Model change in generation fleet
    • Total change in CO 2 over a period, divided by total change in demand
          • => Build-related marginal CO 2 rate
  • 19. Conclusion
    • From 2002-2009, the marginal CO 2 intensity of grid electricity in Great Britain was 0.69 kgCO 2 /kWh.
    • This could reduce to 0.51kgCO2/kWh by 2020-2025.
    • Either of the above numbers are well above the figure typically used in policy analysis in the UK.
    • The dynamics of change in the underlying stock of generators is rather complicated, but very important.