Abstract
We propose a model for assessing the performance of generation mixes in a mean-variance context. In particular, we focus on the expected price of electricity and the price volatility that result from different generating portfolios that change over time (because of investments and retirements). Our valuation model rests on solving an optimization problem. At any time it minimizes the total costs of electricity generation and delivery. A distinctive feature of our model is that the optimization process is subject to the behavior of stochastic variables (e.g. load, wind generation, fuel prices). Thus we deal with a problem of stochastic optimal control. The model combines optimization techniques, Monte Carlo simulation over the decades-long planning horizon, and market data from futures contracts on commodities. It accounts for uncertain dynamics on both the demand side and the supply side. The aim is to assist decision makers in trying to assess electricity portfolios or supply strategies regarding generation infrastructures. To demonstrate the model by example we consider the case of Great Britain’s generation mix over the next 20 years. In particular, we compare three future energy scenarios and the contracted background, i.e. four time-varying generating portfolios. Major British power producers are covered by the EU Emissions Trading Scheme (ETS), so they operate under binding greenhouse gas (GHG) emission constraints. Further, the UK Government has announced a floor price for carbon in the power sector from 1 April 2013. The generation mix is optimally managed every period by changing input fuel and electricity output as required.
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Notes
- 1.
This is in contrast to related papers that usually perform economic dispatch on an hourly (or shorter) basis with a time horizon extending over one (or a few) year(s). For example, Delarue et al. [12] take hourly load patterns into account (over 7 weeks) and corresponding dispatch issues as ramping constraints. There would be no major problem in using our model for a yearly period on an hourly basis (8,760 steps) apart from the increase in the time required for computation. Unfortunately, our long-term simulation comes at the cost of framing the optimization problem on a longer time span (for example, a week instead of an hour).
- 2.
See Chamorro et al. [11], Appendix C.
- 3.
This does not mean that investors are risk neutral.
- 4.
When there is a floor price for carbon in place (as in the UK), the carbon price (A) can be different from the allowance price on the EU ETS.
- 5.
As shown in National Grid [28], both peak and baseload electricity prices more or less track natural gas prices at National Balancing Point (which does not happen with coal or oil, for instance). This is relevant when we deal with the profit margin included in generation costs; see Chamorro et al. [11], Appendix C.
- 6.
The wholesale electricity market is operated within the British Electricity Trading and Transmission Arrangements (BETTA). It is based on voluntary bilateral agreements between generators, suppliers, traders and customers. In practice BETTA does not set a unique price: the actual price generators are paid or customers have to pay is different if there is underproduction (for generators) or overconsumption (for consumers).
- 7.
UK Department of Energy and Climate Change [35], Table 5.5, support MC Excel spreadsheet.
- 8.
The Climate Change Act of 2008 introduced a legally binding target to reduce GHG emissions by at least 80 % below the 1990 baseline by 2050, with an interim target to reduce emissions by at least 34 % in 2020. It also introduced ‘carbon budgets’, which set the trajectory to ensure these targets are met. These budgets represent legally binding limits on the total amount of GHG that can be emitted in the UK for a given 5-year period. The fourth carbon budget covers the period up to 2027 and should ensure that emissions will be reduced by around 60 % by 2030.
- 9.
Renewables are governed by the 2009 Renewable Energy Directive which sets a target for the UK to achieve 15 % of its total energy consumption from renewable sources by 2020.
- 10.
- 11.
In models where optimal dispatch takes place on an hourly basis the underlying model is able to determine the effective number of operating hours (ENOH). The load factor equals ENOH/8,760. For instance the model in Delarue et al. [12] determines technology specific load factors by optimization. In our case, such a direct calculation cannot be made. Instead, we can calculate the effective electricity output from each technology in a given period and the maximum possible output in that period. Dividing the former by the latter we could get an indirect measure of technology specific load factors similarly by optimization.
- 12.
These prices can be substantially lower than actual prices under market power [22].
- 13.
This overlap is by no means new in the related literature. Even radically different mixes can have nearly identical risk-return characteristics. As Awerbuch and Yang [5] put it: “There are many ways to combine ingredients to produce a given quantity of salad at a given price”.
- 14.
Lynch et al. [24] calculate (hourly) electricity prices from the (hourly) marginal cost of electricity provision and determine the return of each power technology under least-cost dispatch and marginal-cost pricing.
- 15.
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Acknowledgments
Abadie and Chamorro gratefully acknowledge financial support from the Spanish Ministry of Science and Innovation through the research project ECO2011-25064, the Basque Government through the research project GIC12/177-IT-399-13, and Fundación Repsol through the Low Carbon Programme joint initiative.Footnote 15 Usual disclaimer applies.
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Appendix: Estimation
Appendix: Estimation
Load. Sample period: 2002:01–2013:08, i.e. a total of 140 monthly observations for GB. Tables A.1 and A.2 .
Average deseasonalised load over the last 24 sample months: 24.90418 TWh. With transmission losses included: 27.14556 TWh. Load volatility: 0.1801.
Wind load factor. Sample period: 2006:04–2010:12, a total of 52 monthly observations. Tables A.3 and A.4.
Average wind load factor: 0.27. Wind load volatility: 0.9088.
Pumped load factor. Sample period: 1998:01 to 2013:08, i.e. 188 monthly observations.
Hydro load factor. Sample period: 1998:01–2013:08, or 188 monthly observations. Tables A.5 and A.6.
Average hydro load factor: 0.3432. Hydro load volatility: 1.1099.
Pumped load factor. Sample period: 1998:01–2013:08, i.e. 188 monthly observations Tables A.7 and A.8.
Average pumped load factor: −0.0845. Pumped load volatility: 0.4660.
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Chamorro, J.M., Abadie, L.M., de Neufville, R. (2015). Measuring Performance of Long-Term Power Generating Portfolios. In: Ansuategi, A., Delgado, J., Galarraga, I. (eds) Green Energy and Efficiency. Green Energy and Technology. Springer, Cham. https://doi.org/10.1007/978-3-319-03632-8_16
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