Applications for large storage systems – Project example Stadtwerke Trostberg

In connection with the much-discussed energy revolution, the use of large storage systems in trade, industry and also by energy suppliers is currently on everyone’s lips. They are intended to bridge the gap between the volatile feed-in of renewable energy sources on the one hand and the demand for electricity in the grids on the other. Since the grid cannot store any energy, exactly the same power must be fed into the grids at all times as the consumers consume in total. A wide-ranging coupling of the networks can of course also alleviate this problem, but the public discussion in recent months has shown that the construction of new lines is very difficult after all. Storage systems hardly have this problem of public acceptance, they can be set up at almost any speed and at almost any location and thus stabilise the networks.

However, there must also be someone for every storage facility who has an economic interest in constructing it or investing in it. And that, apart from the few lighthouse projects supported by subsidies, is still a great challenge!

 

A positive example of such a storage project, which can already represent an attractive economic viability due to the good combination of different revenue channels of storage operations, is the latest project of Smart Power GmbH & Co. KG from Feldkirchen near Munich. The investor for this project is Alz Immobilien GmbH & Co KG, which has acquired a commercial building in the network of Stadtwerke Trostberg Energieversorgung GmbH & Co KG and leases it to commercial users. In the course of the negotiations with the municipal utilities, it became apparent that even a “small” energy supplier has to contend with the same problems as a commercial or industrial company. Because also the Trostberger must refer energy from upstream network operators. Physically this is done via two transfer stations, each with 8MVA from the 110kV grid. And similarly as with a trade enterprise beside the energy costs also a achievement price must be paid, in the present case 113 were per kW referred peak power. The Trostberger have also a second problem with your customers common: The upstream network carrier demands that the present reactive power in the net is reduced. One could pass this demand on simply to the customers, but if one does not want to load these overdue, would remain only the investment in own reactive power compensation plants. In this situation, it was certainly an interesting coincidence for the people of Trostberg that Alz Immobilien GmbH had already realized projects with Smart Power GmbH before. So they quickly came up with a proposal for a joint concept that could solve the Trostberger’s problems: In the basement of the aforementioned commercial building, a storage facility with a capacity of 1.2 MW and an energy content of 1.5 MWh will be installed and commissioned in the first quarter of 2018. The storage facility is connected to the Trostberg power grid via a separate transformer station. In this special case, this storage facility will not be used to optimise the performance balance of the building itself, but will rather be operated in peak-shave mode in the Trostberger Stadtwerke network. In order to make this network operation possible, the Trostbergers willingly granted access to the performance data of their network. This enables the storage facility operator to adjust the control strategy to the network data and also to calculate the benefits of storage operation for the energy supplier. The storage operator, of course, does not want to offer storage operation for free: By operating the storage facility on a grid basis, the municipal utilities save network fees because they minimise the maximum power procurement from their upstream network operator. Some of these “avoided network charges” are due to the storage operator, i.e. Alz Immobilien GmbH, in accordance with the “Ordinance on Charges for Access to Electricity Networks (Electricity Network Charges Ordinance – StromNEV), § 18 Charges for Decentralised Feed-In”. These avoided network charges form the first revenue path for the economic operation of the storage facility. No fixed price was agreed for the second service offered by the storage operator to the Trostbergers: The provision of reactive power. An inverter can always generate reactive power for the grid or, to put it another way, compensate for the reactive power in the grid if it is not already 100% utilized with active power. This reactive power compensation is part of the general agreement on the payment of the avoided grid fees and thus makes the model even more attractive for municipal utility operators.

However, all these agreements with the municipal utilities together would not yet justify the investment in a storage facility of this size. A further revenue path is needed here, namely the provision of standard services. This revenue path is also often mentioned for smaller storage facilities if an investment is to be presented as being as attractive as possible. “Ulrich Bürger, technical manager and co-founder at Smart Power, says: “According to Smart Power’s experience, PRL can only be applied in a really meaningful way to relevant quantities, because the effort involved in prequalification and marketing should not be neglected. Furthermore, it is very difficult to predict the development of revenues over the next few years, especially for PRL.”

Nevertheless, in the present example, the provision of standard power is a relevant part of the profitability forecast. Since the timing of network peaks in the Trostberg network can be predicted with a high degree of probability, relevant time windows remain in which the storage facility can be placed on the balancing power market. The size of the storage facility and the powerful 10kV connection of the storage facility to the grid provide the optimum conditions for this. The rest is “only” intelligence, since the various requirements of peak-shave operation have to be optimally mapped in the control strategy with PRL marketing and the necessary “timetable transactions”. “Megabytes instead of megawatts” is what Smart Power likes to call this challenge. Through intelligent control and forecasting, it is possible to use some installed kW and some megawatt hours twice and thus save investment volume, which of course can have an extremely positive effect on the return on investment.

“Saving” is certainly also the keyword for the last special feature to be mentioned for this project. And this does not only refer to money and economy, but also to raw materials, environmental pollution and thus ecology: Because here too something has flowed into the realisation of this project which has been discussed very often but still very rarely realised, namely the second-use use of battery systems from the automotive industry. In this field, Smart Power not only has extensive experience from prototype projects, but also some interesting contracts with major automobile manufacturers. In this project, for example, battery blocks are being used that had spent their first life in a test fleet of Daimler vehicles. With approx. 2.4m x 1.2m x 0.3m and a weight of 550kg, these blocks are not necessarily suitable for small storage systems, but in a suitable rack they can be wonderfully combined into larger units. In comparison to the use in vehicles with extreme alternating loads and extreme temperatures, the use in an industrial environment represents comparatively low requirements for this “second battery life”. Even if they no longer have the full initial capacity, one can assume that the “second life capacity” promised by the car manufacturer can be used over a period of 10 years and more. Another advantage from an ecological point of view is that after this second battery life recycling capacities can be used which do not yet exist, at least the raw materials from these cells will probably start their third life. But back to profitability: Of course, the use of these used battery systems also has an economic aspect, as they are sold by car manufacturers at much lower prices than one would have to pay for new systems. Although additional expenses for mechanical accommodation and voltage adjustment have to be taken into account here, the system technology is still considerably cheaper compared to new procurement, so that one could also speak of a further “virtual revenue path” in terms of overall profitability, which makes the return on the entire project even more attractive.

How does one come to such a project, or rather to a decision as to whether the idea is also an opportunity for economic realization? Professional design tools – that is the answer Smart Power has to this question. The key to profitability is not the often cited PRL marketing, but the PeakShave, i.e. the peak load capping at companies or, as in this case, in the supply network of Trostberger Stadtwerke. In order to assess the economic project chances, the first step is to read in this load profile and to simulate the effects of storage systems with different power and energy dimensions using powerful tools. From the large number of possible storage sizes, the dimensioning with the highest expected return is then generally selected – and hopefully also implemented by the customer.

As far as the realization of the Trostberg project is concerned, the problem here was not so much with the Trostberger Stadtwerk or the investor Alz Immobilien, because both have been convinced of this concept for quite some time. However, the final contractual arrangement with Daimler still had to be concluded, not just a small business partner for Smart Power. But now that the ink has dried and the first battery blocks have been delivered, it can start in spring 2018. Only a few technical products have been granted a second life – but batteries are part of it.

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