http://icarb.org/2013/05/06/5th-international-conference-minutes-and-presentations/

1. Estimating the CO2 impact of electricity
demand and onsite generation choices
interactions with commissioning of large power stations
Dr Adam Hawkes
Centre for Energy Policy and Technology (ICEPT)

2. 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 plant
commissioning and decommissioning
• Marginal emissions rates and the future generation mix

3. Recap – how marginal emissions have been viewed
Source: Hawkes (2010) Estimating Marginal CO2 Emissions Rates for National Electricity Systems. Energy
Policy. Volume 38, Issue 10, October 2010, Pages 5977–5987
One day in the GB electricity system

4. GB Historical Marginal Emissions 2002 to 2009
• ½ hourly data from approx 200
large generators
• Emissions rate from each
generator
• Therefore – can estimate ½ hourly
CO2 rate change for the system as a
whole
• Linear regression of CO2 rate
against system load change gives
the marginal emissions rate
Source: Hawkes (2010) Estimating Marginal CO2 Emissions Rates for National Electricity Systems. Energy
Policy. Volume 38, Issue 10, October 2010, Pages 5977–5987

5. Introducing plant commissioing and decommissioning
• We know which plant are going to
be decommissioned to approx 2020,
and can make educated guess
about the rest
• Also have data on power system
trajectory to 2050 from MARKAL
and similar
• Therefore can estimate future
operational marginal emissions
rates
Emissions rate
in 2016
(kgCO2/kWh)
Emissions
rate in 2020-
2025
(kgCO2/kWh)
Lower
Estimate
0.54 0.42
Central
Estimate
0.60 0.51
Upper
Estimate
0.66 0.58

6. Summary of previous work….and the next challenge
•The current operational marginal CO2 emissions rate has been estimated
(1st
order phenomena)
•This includes the influence of commissioning and decommissioning of
large power stations on operational marginal CO2 emissions (1st
order
phenomena, for future years)
•BUT, does not include the fact that demand-side choices lead to the
commissioning (or not) of large power stations
•This 2nd
order impact could be much larger than the 1st
order analysis so
far

7. How can we attribute commissioning activity to
demand-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 at
peak times
• Each addition of generating capacity or demand reduction on the demand-
side leads to reduced requirement for generating capacity on the supply
side
• “Capacity credit”
• Each addition of demand lead to increased requirement for generating
capacity
• Negative capacity credit, or
• “Capacity debit”?
• These can be seen to interact with commissioning and decommissioning
of power stations

8. Heat pump capacity credit (or debit)

9. A simple dynamic model of supply-demand capacity interaction
Existing stock of
demand-side
technology and
retirement profile
+
Replacement
technology (i.e.
demand-side
choices)
=
Demand (and peak
capacity
requirement in
electricity system)
Demand Side
Existing stock of
centralised
generators and
retirement profile
+ Replacement
power stations = Available supply
capacity
Supply Side
+
Capacity margin
=
For each time period (e.g. year) ….

10. Hypothetical example: a simple technology substitution
The electrification of heating in the UK, and decarbonisation of
electricity
•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 electricity
demand the next 1GWe plant will be commissioned in 2016
• Alternative: Increasing peak demand due to electrification of heat leads to
increased generation capacity requirement, and subsequently a nuclear plant
of 1.5GWe is commissioned in 2015.

11. A baseline (counterfactual) and a scenario
Baseline Alternative Scenario
Impact of demand-side intervention
Addition of 500MWe of low carbon baseload capacity, and addition of the
original 1GWe of low carbon baseload capacity 1 year earlier

12. Baseload versus mid-merit
Source: Hawkes (2010) Estimating Marginal CO2 Emissions Rates for National Electricity Systems. Energy
Policy. Volume 38, Issue 10, October 2010, Pages 5977–5987

13. 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

14. 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

15. Conclusions
1.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 capacity
credit)
1.The operational marginal emissions rate is a function of the specific
emissions rates of dispatchable generation in the system. Recently
0.69kgCO2/kWh.
2.The long-term marginal emissions rate, which is a function of the specific
emissions rate of the next generators to be commissioned, and (to a lesser
extent) whether or not these new generators are more baseloaded than
those they replace.
3.For a decarbonizing power system, long-run marginal emissions for
electrification actions are likely to be negative.

16. Next steps
• Application to the GB energy system…

17. Power sector projection
Source: CCC (2010) The Fourth Carbon Budget – reducing emissions through the 2020s

18. Residential heating projection
Source: Hawkes (2011) Pathways to 2050 – Key Results: MARKAL Model Review and
Scenarios for DECC’s 4th Carbon Budget Evidence Base. A report by AEA for DECC.