View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Energy 83 (2015) 15e28 Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy Assessing the economics of large Energy Storage Plants with an optimisation methodology * Giorgio Locatelli a, , Emanuele Palerma b, Mauro Mancini c a University of Lincoln, School of Engineering, Brayford Pool, Lincoln, LN6 7TS, UK b Politecnico di Milano, Department of Energy, Via Lambruschini 4, 20156 Milano, Italy c Politecnico di Milano, Department of Management, Economics and Industrial Engineering, Via Lambruschini 4B, 20156 Milano, Italy article info abstract Article history: Power plants, such as wind farms, that harvest renewable energy are increasing their share of the energy Received 12 August 2014 portfolio in several countries, including the United Kingdom. Their inability to match demand power Received in revised form profiles is stimulating an increasing need for large ESP (Energy Storage Plants), capable of balancing their 9 January 2015 instability and shifting power produced during low demand to peak periods. This paper presents and Accepted 16 January 2015 applies an innovative methodology to assess the economics of ESP utilising UK electricity price data, Available online 9 March 2015 resulting in three key findings. Firstly the paper provides a methodology to assess the trade-off “reserve capacity vs. profitability” and the possibility of establishing the “optimum size capacity”. The optimal Keywords: Energy storage reserve size capacity maximizing the NPV (Net Present Value) is smaller than the optimum size capacity Energy system minimizing the subsidies. This is not an optimal result since it complicates the incentive scheme to align Wind farms investors and policy makers' interests. Secondly, without subsidies, none of the existing ESP technologies Economics are economically sustainable. However, subsidies are a relatively small percentage of the average price of CAES (Compressed Air Energy Storage) electricity in UK. Thirdly, the possibility of operating ESP as both as a reserve and do price arbitrage was PHS (Pumped Hydroelectric Storage) identified as a mean of decreasing subsidies for the ESP technologies. © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction demand requirements [2]. Examples of sources producing dis- patchable electricity are thermal power plants powered by natural During the last decade the electricity production from renew- gas and coal, nuclear power plants and hydro-electricity using able sources has increased all over the world. In Europe, where dams; non-dispatchable electricity comes from sources such as further development of large hydroelectric plants is limited by the wind farms and solar photovoltaic plants. A high penetration of shortage of new locations, solar, biomass and particularly wind RETs (producing non-dispatchable and highly variable electricity) farms will play a key role in increasing the share of renewable negatively affects power system reliability and efficiency requiring energy in the next decades [1]. The increasing penetration of var- mitigations such as [1]: iable RET (Renewable Energy Technologies) in power provision is becoming a key issue for the management of the electrical grid. A 1. availability of large ESP (Energy Storage Plants), mainly CAES high percentage of RET (particularly RET generating non- (Compressed Air Energy Storage) and PHS (Pumped Hydro- dispatchable electricity) requires flexible power systems that can electric Storage); quickly react to variability in supply and demand. Having a lev- 2. availability of power plants (e.g. natural gas fired plants) pro- elised cost of electricity greater than fossil fuel power plants, RET ducing readily dispatchable electricity; requires further expense in ancillary service as the electricity pro- 3. more grid interconnections: isolated systems have more diffi- duced is not dispatchable. Generally the electricity is defined as culty managing the instability of wind generation than inter- dispatchable if it is possible to plan and regulate it in order to fulfil connected areas. For isolated locations thermal plants (mostly Diesel engines and gas turbines) are commonly used to support the production of electricity. For instance for the Fair Isle (a * Corresponding author. Tel.: þ44 (0) 1522 83 79 46. small Scottish island) two thirds of the community's power is E-mail addresses: [email protected] (G. Locatelli), emanuelepalerma@ supplied by wind turbines, and a third by diesel generators [3]. gmail.com (E. Palerma), [email protected] (M. Mancini). http://dx.doi.org/10.1016/j.energy.2015.01.050 0360-5442/© 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 16 G. Locatelli et al. / Energy 83 (2015) 15e28 ESP (Energy Storage Plants) can play a key role in power sys- 2.1.2. Power availability tems, bridging the gap between variable sources of energy and The impact on the adequacy of power is determined by long- electricity demand [4]. Renewable energy sources producing non- term wind variability and by the low capacity factor (20e40%) of dispatchable electricity are expected to increase in the UK (United wind farms [17]. Because of this variability, wind turbines do not Kingdom) because the government issued a “National Renewable increase system-generating capacity by themselves. This is done by Plan” [5] targeting approximately one third, of all electricity con- increasing the capacity of the dispatchable power generator or sumption by 2020 to come from renewable sources. storing electricity. Where there is a strong penetration by wind In this paper we introduce and apply a methodology to inves- farms, the electricity system will need a higher installed capacity to tigate the technical and economic feasibility of building an ESP supply the power required and to ensure the reliability of the according to two scenarios: system even in case of long periods of still weather. 1. ESP operating only on price arbitrage 2.1.3. Grid 2. ESP operating on price arbitrage and operating reserve. A high penetration of wind farms may affect the grid for the following reasons: The method is applied from both the investors' and policy makers' point of view. The research focuses on the UK because of 1) The fluctuations of wind farm output can affect transmission the availability of appropriate public information. Nevertheless, the efficiency. method and the results are widely applicable. 2) Improvements to the grid may be necessary to smooth short- term variability and uncertainty. 2. Literature review 3) An improvement of the grid is necessary to switch from a centralized generation to a distributed generation. 2.1. Effect of wind on the power system and its cost An ESP can operate as a transmission congestion relief, reducing According to a study by the Royal Academy of Engineering [6] in considerably the impact of wind power integration on the grid. the UK, the levelised cost of generating electricity from wind farms is higher that of fossil fuel, moreover there are standby generation 2.2. Energy Storage Plants costs that can increase the wind farms generation cost by another 30%e50%. Standby costs exist since electricity output varies as the 2.2.1. ESP technologies cube of the wind speed [7]. This causes variability in electricity There are many types of ESP, some of them are already production. In addition, there is uncertainty as to when wind en- commercially available, others are still in the Research & Devel- ergy is available. Variability and uncertainty affect different areas of opment phase. ESP can be clustered according to: the power system and the relevance of their impact varies with the time scales considered [8]. The cost of coping with this variability Storage Properties: storage scale, ESP efficiency, charge/discharge and uncertainty is ultimately paid by the consumers. time. With regard to variability, very short-term variations (minute Operation Properties: facility response time, partial load feature time scale) are partially smoothed by the inertia of wind turbines lifetime and reliability. rotor and are levelled out when a large area of production is Storage Costs: consisting of energy costs, power costs, and O&M considered [9]. In suitable regions (usually not in the UK) short- (Operation & Maintenance) costs. term variations arise mostly from the change of weather patterns and can be moderately smoothed by interconnecting various wind As seen in Section 2.1 the deployment of wind farms requires farms installed in locations with different weather patterns [10,11]. additional operating reserves and additional long-term power Long-term variations are considered as variations of output with system flexibility. This section focuses on large ESP suitable for time intervals greater than four hours. operating both as an operational reserve and as a load following/ With regard to uncertainty, it is not possible to exactly define shifting facility and considers ESP technologies both commercially the wind intensity in a specific location at a given time. The residual available and in the pre-commercial phase [18]. Table 1 highlights error between real data and model results depends on the lead- time considered and on geographical