Chick, John

Harrison, Gareth

Thomson, Camilla

English

The reduction in Greenhouse Gas (GHG) emissions associated with the generation of electricity from intermittent renewable sources such as wind, wave and tidal power is typically estimated from the average annual emissions associated with the entire power system [1-5]. However, as the UK government continues to encourage development of renewable energy generation, negative headlines are appearing in the media concerning wind farms being paid not to produce as a result of power network constraints and questions are being raised on the future level of backup fossil generation required to handle the variability of renewable energy. This raises doubts over the accuracy of carbon payback calculations and the greenhouse gas intensity of the electricity that is offset by intermittent renewable energy. In order to develop a real picture of the GHG offset associated with renewable energy generation this study examines historic power generation data from the UK grid to identify the effect on the network GHG emissions of the current small penetrations of wind, wave and tidal power output. The resulting marginal GHG offset is then combined with life cycle emissions data for renewable energy converters to calculate the carbon paybacks. The model will build upon the work of Hawkes [6] that examined the marginal CO2 emissions from demand-side interventions to produce an estimate of 0.69 kgCO2/kWh. This is significantly higher than the figures recommended for use in carbon payback calculations by the UK Department for Energy and Climate Change, most recently quoted as 0.50 kgCO2-e/kWh [7]. A recent study of the Pelamis wave energy converter found the global warming potential to be 27 gCO2-e/kWh (assuming a design life of 20 years) [2], which would correspond to a carbon payback of either 9 or 13 months with the above figures.The model developed here will feed into further work to develop more accurate estimates of the true carbon footprint of intermittent renewable energy. This will enable future renewable energy scenarios to be modelled to inform government policy and energy industry plans for renewable generation and network development.1. H. J. Wagner, C. Baack, T. Eickelkamp, A. Epe, J. Lohmann, and S. Troy, "Life cycle assessment of the offshore wind farm alpha ventus," Energy, vol. 36, pp. 2459-2464, 2011.2. C. Thomson, G. Harrison, and J. Chick, "Life Cycle Assessment in the Marine Renewable Energy Sector," presented at LCA XI, Chicago, USA, 2011.3. Varun, I. K. Bhat, and R. Prakash, "LCA of renewable energy for electricity generation systems—A review," Renewable and Sustainable Energy Reviews, vol. 13, pp. 1067-1073, 2009.4. C. A. Douglas, G. P. Harrison, and J. P. Chick, "Life cycle assessment of the Seagen marine current turbine," Proc IMechE Part M: J. Maritime Environment, vol. 222, pp. 1-12, 2008.5. R. P. M. Parker, G. P. Harrison, and J. P. Chick, "Energy and carbon audit of an offshore wave energy converter," Proc. IMechE Part A: J. Power and Energy, vol. 221, pp. 1119-1130, 2007.6. A. D. Hawkes, "Estimating marginal CO2 emissions rates for national electricity systems," Energy Policy, vol. 38, pp. 5977-5987, 2010.7. N. Hill, H. Walker, J. Beevor, and K. James, "2011 Guidelines to Defra/DECC's GHG Conversion Factors for Company Reporting: Methodology Paper for Emission Factors." UK: Department for Environment, Food and Rural Affairs, 2011.<br/

Edinburgh Research Explorer

Do Renewables Reduce GHGs? Marginal Greenhouse Gas Offset for Renewable Energy in the UK Images from Harvey McDaniel and www.pelamiswave.com.  Camilla R Thomson, GP Harrison and JP Chick Institute for Energy Systems, School of Engineering, University of Edinburgh, UK 26th September 2012 Introduction • Identify the Greenhouse Gas (GHG) offset of intermittent renewable energy sources by examining the real marginal effects of wind power. • Found marginal offset to be 0.75 kg CO2e/kWh, significantly higher than the values typically used in carbon payback calculations. Introduction • Identify the Greenhouse Gas (GHG) offset of intermittent renewable energy sources by examining the real marginal effects of wind power. • Found marginal offset to be 0.75 kg CO2e/kWh, significantly higher than the values typically used in carbon payback calculations. Carbon Payback • LCA is used to calculate the Greenhouse Gas intensity of renewables, but carbon paybacks and carbon savings need to be estimated to assess whether they will achieve carbon reductions  • Carbon payback is typically calculated from mean network emissions, in accordance with UK government recommendations. • Intermittent renewables may also have hidden carbon impacts associated with reserve capacity and reduced efficiency of other generators. Images from www.guardian.co.uk and cleantechnica.com 25th June 201201020304050Generation (GW)WindPumped StorageOtherHydroGasCoalOilFranceHollandIrelandNuclearGeneration in the UK • Marginal emissions rate – the greenhouse gas emissions associated with a marginal change in wind output. Data from Elexon, 2012, National Grid Data: Generation by Fuel Type, ELEXON Limited 13th December 201101020304050Generation (GW)WindPumped StorageOtherHydroGasCoalOilFranceHollandIrelandNuclearGeneration in the UK • Marginal emissions rate – the greenhouse gas emissions associated with a marginal change in wind output. Data from Elexon, 2012, National Grid Data: Generation by Fuel Type, ELEXON Limited Previous Work • Data from Hawkes A. (2010) Estimating marginal CO2 emissions rates for national electricity systems. Energy Policy, 38, pp 5977–5987 • Linear result inevitable due to constants being applied for the greenhouse gas intensities of generation Hawkes A.D. (2010): Estimating marginal CO2 emissions rates for national electricity systems. Energy Policy, 38(10), pp. 5977-5987. Method Method Method Method • When the change in total load is zero ALL changes in GHG are due to the change in wind generation. Results Results • Marginal offset of wind -0.747 kg CO2e/kWh ± 0.027 • Marginal emissions rate of system 0.763 kg CO2e/kWh ± 0.001 Results • Wind causes a reduction in greenhouse gas emissions so the gradient is negative.  Quarterly Trends 01234567Q4 2008Q1 2009Q2 2009Q3 2009Q4 2009Q1 2010Q2 2010Q3 2010Q4 2010Q1 2011Q2 2011Q3 2011Q4 2011Q1 2012Q2 2012Max Wind Production (GW)-1.2-1.0-0.8-0.6-0.4-0.20.0Marginal Offset of Wind (tCO2e/MWh)Max Wind CO2 Trend of CO2Monthly Trends Max Wind0123456781 2 3 4 5 6 7 8 9 10 11 12MonthMax Wind Production (GW)-1.5-1.0-0.50.00.51.0Marginal Offset of Wind (tCO2e/MWh)2009201020112012Carbon Paybacks • Current DECC grid-average emissions are 0.457 kg CO2e/kWh [3] • Wind carbon payback [4-6]: – DECC: 5 to 8 months – Marginal: 3 to 5 months • Wave carbon payback [7]: – DECC: 33 months – Marginal: 20 months • Tidal stream carbon payback [8]: – DECC: 20 months – Marginal: 13 months [Numbers in square brackets refer to references] Images from www.pelamiswave.com and www.marineturbines.com Payback of UK Wind • Currently there is 6.9 GW of installed wind in the UK [9]. • Published LCAs provide an estimate for the embodied GHG per MW of rated output of 0.5 - 2 Mt CO2e/MW [4-6]. • Worst case life cycle emissions of current installed capacity are 14 Gt CO2e.  • If the marginal offset of wind is 0.747 t CO2e/MWh, 17 Gt CO2e has been offset since November 2008, a carbon saving of at least 3 Gt CO2e. Conclusions • The marginal offset of wind has been calculated to be 0.747 kg CO2e/kWh, significantly higher than the average grid emissions.  • This suggests wind is offsetting some coal generation, in addition to gas and hydro. • If wind is taken as typical of large-scale intermittent renewables, this finding can significantly reduce estimated carbon paybacks. • The entire wind capacity currently installed in the UK is estimated to have already paid back its embodied carbon. • Much of the installed capacity in the UK is less than 4 years old, with a design life of around 20 years. • However, this model needs to be developed to include the carbon impacts of reserve capacity and efficiency penalties. References 1. Elexon, 2012, National Grid Data: Generation by Fuel Type, ELEXON Limited 2. Hawkes A.D. (2010): Estimating marginal CO2 emissions rates for national electricity systems. Energy Policy, 38(10), pp. 5977-5987. 3. AEA (2012): 2012 Guidelines to Defra/DECC's GHG Conversion Factors for Company Reporting. Defra and DECC, UK. 4. Ardente F., Beccali M., Cellura M. , Lo Brano V. (2008): Energy performances and life cycle assessment of an Italian wind farm. Renewable and Sustainable Energy Reviews, 12(1), pp. 200-217. 5. Crawford R.H. (2009): Life cycle energy and greenhouse emissions analysis of wind turbines and the effect of size on energy yield. Renewable and Sustainable Energy Reviews, 13(9), pp. 2653-2660. 6. Tremeac B. , Meunier F. (2009): Life cycle analysis of 4.5 MW and 250 W wind turbines. Renewable and Sustainable Energy Reviews, 13(8), pp. 2104-2110. 7. Thomson C., Harrison G. , Chick J. (2011): Life Cycle Assessment in the Marine Renewable Energy Sector. LCA XI, Chicago, USA, 5th October 2011. 8. Douglas C.A., Harrison G.P. , Chick J.P. (2008): Life cycle assessment of the Seagen marine current turbine. Proc IMechE Part M: J. Maritime Environment, 222(M1), pp. 1-12. 9. RenewableUK, (2012). UK Wind Energy Database. Retrieved 20th August 2012, from http://www.bwea.com/ukwed/index.asp. Thank You! 01234567Q4 2008Q1 2009Q2 2009Q3 2009Q4 2009Q1 2010Q2 2010Q3 2010Q4 2010Q1 2011Q2 2011Q3 2011Q4 2011Q1 2012Q2 2012Max Wind Production (GW)-1.2-1.0-0.8-0.6-0.4-0.20.0Marginal Offset of Wind (tCO2e/MWh)Max Wind CO2 Trend of CO2

Energy performances and life cycle assessment of an Italian wind farm. Renewable and Sustainable Energy Reviews,

Guidelines to Defra/DECC's GHG Conversion Factors for Company Reporting. Defra and DECC,

Life cycle assessment of the Seagen marine current turbine.

Life cycle energy and greenhouse emissions analysis of wind turbines and the effect of size on energy yield. Renewable and Sustainable Energy Reviews,

National Grid Data: Generation by Fuel Type,

UK Wind Energy Database. Retrieved 20th August 2012, from http://www.bwea.com/ukwed/index.asp. Thank You!

Marginal Greenhouse Gas Offset for Renewable Energy in the UK

Marginal Greenhouse Gas Offset for Renewable Energy in the UK

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