Power consumption is subject to daytime fluctuations. Load peaks occur mainly in the morning, when heavy machinery in industrial plants is started up and millions of people are starting their days. Next comes lunch time when cafeterias and restaurants experience their rush hour and then, in the early evening, when televisions and ovens are switched on almost simultaneously by millions of people. The diagram below illustrates this by showing the energy consumption on one day in Germany as an example.
Load curve progressions can be predicted very reliably thanks to many years of data collection by power plant management. Base load requirements can easily be planned long-term, the medium load covers foreseeable peak loads in the morning, at mid-day and in the evening. Unforeseen peak loads, however, meaning very high and sudden load increases or unexpected high power consumption must be covered by peak load power plants, for example pumped-storage plants, which can make high outputs available within seconds.
But there is yet another solution: stationary battery storage. Stationary batteries can respond even faster than pumped-storage plants and are therefore becoming increasingly popular for Frequency Containment Reserve (FCR). FCR can more or less be considered the most challenging discipline in the electricity balancing market. The main task of FCR power plants is to maintain supply frequency at 50 Hertz with as little deviations as possible. According to data from grid operators, more than 380 MW of battery storage power was made available on the German PC market in late 2019 and the trend is rising: In 2019 alone, more than 100 MW of additional battery storage supply was pre-qualified for participation in the FCR market. This means that stationary storage plants can now provide up to 66 percent of primary control power required in Germany.
Second life as an eco-friendly and efficient solution
The Mobility House contributes more than six percent of the battery storage output installed in Germany to the FCR market – around 30 MW of battery storage is installed at the two sites in Lünen and Elverlingsen alone. The special thing about The Mobility House’s stationary storage systems is that they consist exclusively of batteries that were previously installed in electric cars – so-called second-life storage systems – or are currently in storage as spare parts and waiting to be installed in electric cars. At the end of its lifecycle in a vehicle, the battery still retains a residual capacity of around 70 to 80 percent of its original output performance, which is more than enough for a “second life” as part of the power grid.
This approach not only improves material efficiency and reduces the CO2 footprint and lifetime costs of the batteries as well as electric mobility in general, it also creates a steady revenue stream for owners. In 2019, the approximately 2550 electric car batteries in The Mobility House projects generated an average turnover of more than 800 euros. According to estimates, an economically viable stationary operation will be possible for at least another ten years, before a finally depleted battery will have to be recycled.
Stationary storage plants create stability
The importance of quick responses to short-term fluctuations in the grid became apparent once again in June 2019, when several large-scale power outages were narrowly avoided in Germany. The situation in the power grid became critical on June 6th, 12th and 25th, because demand for electricity exceeded generation. As a result, supply frequency dropped drastically across the entire European grid. If mains frequency falls below the 49.8 Hertz mark, consumers are forcibly disconnected from the grid. In other words, local power outages occur. This was prevented in June.
The incident, however, triggered discussions about the FCR supply: The Association of the European Transmission System Operators (ENTSO-E) is currently considering a general supply increase. The German Energy Storage Association (German abbreviation: BVES) welcomes the move, as supply frequency deviations in the power supply system have increased exponentially in recent years. Their data shows that the number of deviations of more than 75 MHz has doubled. 19 deviations of more than 100 MHz have been recorded in January 2020 alone. These severe and increasingly common frequency deviations in the power grid are more and more endangering grid stability and supply security, as at the same time the amount of control energy held in reserve is reaching its limits.
The BVES recommends bolstering the grid with stationary storage plants as an immediate measure to mitigate the situation, as batteries can respond to supply frequency changes in seconds. According to a statement from the BVES, “they are ideal for ensuring frequency stability and can safely mitigate risky incidents.”
In light of the current situation, the BVES welcomes the ENTSO-E plan to increase supply frequency stability across Europe from 3000 MW to 5400 MW in the short term by introducing quick PC reserves from stationary storage plants. This would provide enough capacity to react quickly to dangerous fluctuations.
Batteries in short-term trade enable rapid expansion of renewable energies
Stationary storage plants will not just be beneficial to the grid in terms of PC supply. The Mobility House markets the capacity and output of its storage plants, that are not tied to FCR, in short-term energy trading. Due to the price fluctuations on the European Energy Exchange (EEX), these surplus capacities generate high additional revenues. The procedure is much like trading in shares: Power reserves from the stationary storage plants are offered for sale when prices are high, e.g. when the wind is not blowing and the sun is not shining. The batteries are then recharged when electricity is cheap. They therefore make an important contribution towards preventing extreme fluctuations in the output that must be provided by conventional power plants, and towards dealing with forecast deviations, e.g. due to sunlight deviating from the forecast. The CO2 footprint is also greatly reduced, as these fluctuations no longer must be mitigated by CO2-intensive peak load power plants operating in uneconomical efficiency ranges. The following chart once again shows an example of the price development on one day on the EEX Intraday Auction Market.
According to a current study, renewable energies will be able to cover 100 percent of all global energy requirements by 2050. And at a lower cost than today. Efficiency will be particularly high in industry sectors with a high degree of electrification, such as transport and heating, resulting in four to five times more electricity generation than in 2015. The energy costs for a completely sustainable energy system will therefore fall from 54 euros per MWh in 2015 to 53 euros per MWh in 2050, as outlined by the Energy Watch Group and LUT University in their study “Global energy system with 100 percent renewable energies”. Battery storage devices play an important role in the scientists' calculations.