Interaction of renewable & conventional energies – large-scale battery systems as a connecting link VGB PowerTech 1/2 l 2017
Authors
Kurzfassung
Zusammenspiel von erneuerbaren und konventionellen Energien – Großbatterie-Systeme als Bindeglied
Durch den großen und auch weiterhin wachsen-den Anteil fluktuierender Erzeugungsanlagen (Wind und Photovoltaik) mit Vorrangeinspei-sung, wird die Einhaltung der Netzstabilität immer anspruchsvoller, da konventionelle Kraftwerke immer weniger eingesetzt werden und somit als Flexibilität im Netz fehlen. Daher werden für die Integration von dezentra-len Erzeugungsanlagen und Lasten virtuelle Kraftwerke zukünftig eine entscheidende Rolle spielen. Durch die Bündelung im virtuellen Kraftwerk ist eine Vermarktung im Strom- und Regelenergiemarkt erst effizient möglich.STEAG sieht das Zusammenspiel von erneuer-baren und konventionellen Energien als wichti-gen Schritt für eine erfolgreiche Energiewende. Daher wird die Vermarktung im Strom- und Regelenergiemarkt, das Bilanzkreismanage-ment und die Reservevorhaltung für konventio-nelle Kraftwerke und dezentrale Erzeugungsan-lagen im STEAG Optimierungs netzwerk „STEAG OneOpt“ zusammengeführt. Hierbei dienen Großbatterie-Systeme als Bindeglied zwischen konventionellen Großanlagen, dezen-tralen Anlagen, erneuerbaren Energien und dem Strommarkt für kurzfristige Flexibilität und können optimal das STEAG-Portfolio er-gänzen.Aus diesem Grund hat STEAG im Oktober 2015 die Investition in sechs Großbatteriesysteme mit einer Gesamtleistung von 90 MW beschlossen.Seit Ende 2016 befinden sich alle Anlagen in der Vermarktung und werden für die Erbringung von Primärregelleistung eingesetzt.Es werden auch noch weitere Einsatzmöglich-keiten von Batteriesystemen gesehen, sowohl in der Erbringung von Systemdienstleistungen im Rahmen der Energiewende als auch zur Kostenoptimierung und zum Risikomanage-ment von Industriestandorten.Weitere Informationen erhalten Sie unter www.steag-grossbatterie-system.com l
Interaction of renewable & conventional energies – large-scale battery systems as a connecting linkChristian Karalis and Michael Mühl
Christian KaralisSTEAG GmbH – Trading & OptimizationMichael MühlSTEAG Energy Services GmbHEssen, Germany
Introduction
Today’s electricity supply in Germany is based on the existence of large central power plants that ensure electricity supply and stability of the supply network. As a consequence of the nuclear phase-out adopted by the government and the pro-gressive energy transition, 55 to 60 per-cent of the German gross electricity de-mand is to be covered by energy from re-newable sources by 2035. The decreasing proportion of energy fed into the grid by conventional power plants and the increas-ing proportion of fluctuating infeed from renewable energy sources require a flexibi-lisation of power supply, especially in low-er-level voltage systems. As photovoltaic systems and wind turbines are unable, due to their volatility and the uncertainty in generation forecasts, to provide the re-quired system services at all times, the de-mand for alternative technologies for the provision of these services is increasing.
Main Part
Battery systems and the “Energiewende”Already today, priority infeed of electricity from renewables causes conventional pow-er plants more and more often to be tempo-rarily squeezed out of the market, when-ever wholesale prices fall below the gener-ating costs. During the resulting shutdown periods the conventional plants therefore cannot contribute to maintaining the sys-tem stability of the European interconnect-ed grid. However, the transmission system operators (TSOs) are obligated to con-stantly take measures to ensure safe opera-tion of the power supply systems. The so-called “system services” include mainte-nance of frequency stability, maintenance of voltage stability, restoration of supply after failures, and operational manage-ment. Battery systems are a fundamental element of the energy transition, in par-ticular as a safeguard for system stability and system security, as they are able to con-tribute to the various system services.
– Maintenance of frequency stability en-sures the balance between generation and consumption. Initially, this task is performed by the instantaneous reserve which is currently provided by the iner-
tia of the rotating masses of the genera-tors in large conventional power plants; this ensures that frequency variations are damped before control power is de-ployed.
– Maintenance of voltage ensures that the stability and the nominal system voltage do not exceed defined limit values. For this purpose, reactive power and short-circuit power are supplied as necessary.
– In the event of a large-scale power fail-ure, the ability to restore supply is a cru-cial property of the electricity system. With the assistance of power plants with black start capability, the responsible system operator must be able to supply its system area with electricity in a con-trolled manner.
– Operational management mainly in-cludes the monitoring of all generators and consumers connected to the electric-ity system as a whole; this task is per-formed by the TSOs, which detect any faults and initiate appropriate counter-measures. This also includes congestion management and feed-in management.
At present, only the supply of control pow-er for frequency stability is put out to ten-der on a dedicated market in an open, transparent and non-discriminatory man-ner. All other system services, such as the provision of reactive power or maintenance of voltage stability are solely requested by the responsible TSO from conventional power plants. To ensure that such system services can likewise be offered by all play-ers participating in the ever more distrib-uted generating environment of the liberal-ised electricity market, it is necessary for new markets to be established on which the individual system services are put out to tender, similarly to the control energy mar-ket. This will enable facilities such as bat-tery systems to be developed for the specific application case and operated profitably.
Primary control powerIf the actual system frequency deviates from the nominal frequency of 50 Hz, pri-mary control power, secondary control power and tertiary control power (minute reserve) are deployed one after the other in order to stabilise the system.Primary control power is activated fully au-tomatically, triggered by the deviation of
VGB PowerTech 1/2 l 2017 Interaction of renewable & conventional energies – large-scale battery systems as a connecting link
the actual frequency from the nominal fre-quency of the system. The frequency devia-tion brings about a positive and a negative power output directly at the generating unit. In all synchronously interconnected control zones of the European integrated grid, primary control power is deployed in accordance with the respective shares of the different control zones in total electric-ity production. In order to balance the re-maining frequency deviation in the grid and restore the nominal frequency, second-ary control power cuts in and replaces pri-mary control power supply after 5 minutes. Thus the primary control capacity is avail-able for new frequency upsets. The higher-level controller of secondary control power supply in each control zone ensures that the planned exchange of electricity with other control zones is restored and the frequency deviation is compensated for. In this context, the frequency deviation is mathematically converted into an adjust-ment setpoint, which is then systematical-ly and jointly met by the generator sets de-ployed for secondary control power sup-ply in the integrated grid control system. In order to ensure that the secondary con-trol range is kept available, secondary con-trol power is replaced by minute reserve power if the frequency deviation per-sists. Minute reserve power is a scheduled product that is manually or automatically requested by the respective connecting TSO and is fully activated within 15 min-utes from the moment the request was is-sued.
Battery systems are able to absorb energy from or feed energy into the grid within a few seconds. Owing to this, they are par-ticularly well suited for providing primary control power. At present, a primary con-trol power volume of ±1,250 MW is put out to tender in weekly auctions via an internet platform (see www.regelleistung.net) for the coupled markets of Germany, Austria, Switzerland, the Netherlands, Belgium and France. The minimum lot size is currently ±1 MW, and a technical availability of 100 % must be ensured for the perfor-mance period from Monday 0:00 hrs to Sunday 23:59 hrs, if necessary by keeping available sufficient back-up capacity.
The provision of primary control reserve is remunerated by payment of a capacity price. After expiry of the deadlines for the submission of bids, the TSOs sort the bids received by capacity price offered and award contracts, starting with the bid with the lowest price, in ascending order until the demand for primary control power to be provided is covered. Unlike in the case of secondary control power and minute re-serve power, the energy actually supplied is not paid for separately.
In order to ensure reliable operation of the supply system, plants that are not subject to a limitation of storage capacity are re-quired to be able to supply the maximum
primary control power for at least 15 min-utes. While conventional plants are able to supply primary control power again when these 15 minutes have expired and a fur-ther system frequency deviation occurs, plants with limited storage capacity first need to adjust their charge condition be-fore they can provide primary control pow-er service again.Simulations of the operation of battery sys-tems during past major disturbances in the European interconnected grid show that the supply of primary control power for at least 30 minutes would have been neces-sary in order to contribute to system stabil-ity. F i g u r e s 1 and 2 show the frequency curves during real faults that occurred in September 2003 in Italy and in November 2006 in the overhead line crossing over the river Ems in Germany; the data were re-corded at the Duisburg-Walsum power plant site. Both situations make clear that the provision of primary control power for a period of 15 minutes would not have been sufficient to compensate for the faults and continue providing primary control power until the normal condition of the system was restored.
The provision of primary control power by battery systems is mainly determined by two parameters. As in the case of conven-tional power plants, the system frequency is the command variable for the provi-sion of primary control power. The second determinant is the charge condition of the battery system, which by means of sched-uled transactions must be kept within a defined working range in order to be capa-ble of both supplying power and absorbing power as required in extreme cases. How-ever, at the time of a major disturbance, scheduled transactions cannot be used, because trading at the electricity exchange would probably not be possible during an incident and, even if trading were possible, the minimum lead time would be 30 min-utes to the next full quarter of an hour.Thus, for a dependable supply which will probably have to be maintained in Germa-ny during an increasing number of hours of the year almost without conventional gen-erating plants, a minimum primary control service of 30 minutes is essential for tech-nical units with limited storage capacity. Should a different requirement be stipu-lated, for instance a minimum service
Interaction of renewable & conventional energies – large-scale battery systems as a connecting link VGB PowerTech 1/2 l 2017
period of just 15 minutes, then instabilities in supply and associated restrictions to sys-tem security are significantly more likely to occur in the event of major incidents.From STEAG’s point of view and against the background of the cost degression expected for battery cells due to the ongoing expan-sion of battery storage capacity, it is even less understandable why a reduction of the service period to 15 minutes should bring an advantage at the expense of system secu-rity. As has been proven with the large-scale battery systems project it is already today economically viable – without drawing on subsidies – to build battery storage systems for primary control service even if the ser-vice period required is 30 minutes.
The large-scale Battery Systems projectSTEAG has gained experience with battery systems for the provision of system servic-es, such as primary control power supply, since 2009. With the LESSY (Lithium-Ion Electricity Storage System) project spon-sored by the German Federal Ministry of Education and Research, one of the first lithium-ion storage units in Germany was approved for grid stabilisation service and has been successfully operated at the Völk-lingen-Fenne power plant site since 2013. Following extensive development work and acquisition of technical know-how, the battery system was prequalified for prima-ry control service in 2014 and incorporated in the power plant pool for commercial op-eration.After the LESSY research project, the expe-rience gained was applied to large-scale battery systems and an economically viable concept for a battery system with 15 MW capacity was developed. Apart from the di-alog with the transmission system opera-tors about grid infrastructure and the nec-essary storage capacity, this also included an analysis of the primary control power market and the development of price sce-narios for the future. Thereafter, a first business case was created and profitability calculations were performed.After a positive assessment of the profita-bility of a large-scale battery system de-tailed specifications for a portfolio of six large-scale battery systems were compiled. Then, the technical equipment was put out to tender and the definitive investment cri-teria were defined. Once the six locations had been defined – Lünen, Herne and Duis-burg-Walsum in the state of North Rhine-Westphalia, and Bexbach, Fenne and Wei-her in the Saarland – the current regulatory framework was clarified with the compe-tent authorities. Upon completion of the decision-making and contract awarding process, implemen-tation of the project started. Since battery systems and the creation of flexibility are instrumental in the implementation of the energy transition in Germany, the financ-ing was deliberately structured without
drawing on any subsidies, in order to dem-onstrate that even in the present market situation large-scale battery systems can be profitably operated in the primary control power market. Based on the planning and project management of STEAG Energy Ser-vices GmbH the installation of the large-scale battery systems has been pushed ahead at all six locations jointly with STEAG Technischer Service GmbH. Com-mercial operation has started at the end of 2016. F i g u r e 4 shows a picture of the large-scale battery system at STEAG’s Lünen power plant site. In all, large-scale battery systems with a total capacity of 90 MW have been installed
at six sites, on a total area of more than 1,500 m2. In order to satisfy the current re-quirements of the TSOs in Germany and provide the required primary control ser-vice for at least 30 minutes, each large-scale battery system has a total storage ca-pacity of more than 20 MWh.The battery cells with highly efficient lithi-um-ion technology are arranged in con-tainers in order to permit a change of loca-tion at a later time. This also helped to minimise the time required for manufac-ture and field erection. At each site, a total of 10 battery containers with a capacity of 1.5 MW each, five transformers and one control container have been installed.
Fig. 3. Overview of the six locations of the large-scale battery systems.
Fig. 4. Picture of the large-scale battery system at the Lünen power plant site.
VGB PowerTech 1/2 l 2017 Interaction of renewable & conventional energies – large-scale battery systems as a connecting link
STEAG is satisfied with the performance of the large-scale battery system since the start of commercial operation.For the future it is planned to investigate further applications of battery systems, in the provision of system services as well as cost optimisation and risk management of industrial locations. They are examining projects and cooperations in Germany and abroad.
Value creationVirtual power plants will play a key role in the integration of distributed generating facilities and loads. Only when they are pooled in a virtual power plant they can be efficiently deployed in the electricity and control energy markets.The interplay of renewable and conven-tional energies is considered to be an im-portant step towards a successful energy transition. Therefore, the marketing in the electricity and control energy markets, bal-ancing group management and provision of reserves for conventional power plants and distributed generating facilities have been combined in the optimisation net-work “STEAG OneOpt”. Thus, large-scale battery storage systems serve as a link be-tween large conventional power plants, distributed facilities, renewables and the electricity market, which provides short-term flexibility and is thus an ideal complement for the company’s generating portfolio.By pooling different technologies in the op-timisation network it is possible to exploit many advantages of the individual tech-nologies even better. For instance, for the required back-up for primary control pow-er capacity, no redundant plants need to be built at the respective sites. If one battery system fails, the needed primary control
power can be kept available or be supplied by another source prequalified for primary control service. In future, continuous ad-justment of the charge condition of the large-scale battery systems will also be pos-sible by drawing on the plants pooled in the optimisation network. Such use of syn-ergies will result in a substantial reduction of the operating costs of the battery sys-tems.
Summary
With its large-scale battery systems project, STEAG is demonstrating that battery sys-tems can already today make a substan-tial contribution to the security and stabil-ity of the electricity supply systems and that they can be profitably operated by par-ticipating in the primary control power markets.As the share of energy from renewable sources continues to increase and, conse-quently, conventional plants are squeezed out of the market, the electricity supply
system of the future will need an additional option to provide flexibility. Especially the high proportion of distributed infeed on the medium voltage and low voltage levels calls for the provision of additional system services on these voltage levels.Owing to their flexible positioning, large-scale battery systems are capable of provid-ing system services on all system levels, and on both the regional and supra-region-al scales. However, in order for the system adequacy under increasing grid restric-tions it is necessary to establish new mar-kets on which the individual ancillary ser-vices which have to be newly define are put out to tender. Only then it will be possible for all players in the market to participate in the provision of system services in a non-discriminatory manner and open to all types of technology. Thus, unbundling re-mains an important aspect for the future of energy supply as well on TSO as DSO level, in order to ensure that the competition for the best solution continues to drive the de-velopment of the energy sector. l
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Measurement systems in conventional and regenerative power and heat generating plants are an essential part of instrumentation and control systems. They provide the information needed to operate the generating plant and, with the exception of local measuring devices, are connected with the automation systems with-out interposition of the operating personnel. This lends special importance to the measurement systems.The safe operation of automation equipment and protective and monitoring devices depends to a crucial degree on the correct and reliable logging of measured values and thus also on the arrangement of the individual components of the measurement system. The arrangement of the various components in process-related areas influences the functioning of the entire measurement system.This VGB-Standard contains a select collection of proven and recommended measuring devices along with practical experience and recommendations. It makes no claim to completeness.VGB-S-170-43 is part of the group VGB-S-170-40 “Field Engineering”. This group is supplemented by VGB-S-170-R-41 “Selection of impulse pipes and sampling lines for water and steam sectors” and VGB-S-170-42 “Sampling Points for Process Measurements in Water and Steam Carrying Systems – Type, Selection and Design”.The VGB-S-170 series comprises the VGB-Standards for I&C systems in generating plants.
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