Safely through the dark doldrums with short-term storage
If you take a closer look at dark doldrums, you will realise that it is all about a few hours where supply shortages can occur during the course of the day. In Germany, these are hedged several times by power plant reserves outside the electricity market. Nevertheless, it is important that there are already technologies within the electricity market, including short-term storage facilities, which significantly reduce shortages.
The good news: Short-term storage systems do not have to be built specifically for dark doldrums. they are simply built. The current boom in storage expansion, driven primarily by the shift of solar power from the midday peak to the evening, is ensuring that more and more storage systems are being connected to the grid. Storage systems that are now being connected to the grid are fundamentally changing the electricity system - and also have a stabilising effect during the dark doldrums.
Even for longer periods of darkness short-term battery storage systems help to ensure a reliable supply. This may sound counterintuitive at first, so it's worth taking a closer look.
Short-term memory charge and discharge even during the dark doldrums, only then they draw electricity from the grid instead of from a PV system, for example. The storage units are topped up when demand for electricity is low. Even during the dark doldrums Times with low other power consumption from households or industry and thus times of lower residual load.
How do short-term storage units behave in a dark doldrums?
In the electricity market, high prices signal shortages. Prices are particularly high when the Residual peak load and power plants with high marginal costs (especially gas and oil-fired power plants) supply electricity. According to the Merit order principle the most expensive power plant sets the price for the entire German electricity market every quarter of an hour. Short-term storage facilities such as batteries and pumped storage power plants always supply electricity when prices are high. At the same time, they reduce the Residual peak load considerable.
One preconception is that the batteries are empty after a few hours and then remain unused for the rest of the dark doldrums. In reality, however, short-term storage available at any hour. They are charged when the residual peak load and thus the exchange prices are low, such as at night.
Short-term storage systems are thus available again when the residual load, and thus also the electricity exchange prices, are high. They work like a feather, which is slowly stretched when there is time and quickly energised when it is allowed to relax. The game is then repeated daily, often even multiple times. This is shown in the following graphic, which shows the Behaviour of pumped storage power plants in a dark doldrums week in January 2024. Looking ahead to 2030 Large battery storage in Germany will have significantly overtaken the existing pumped storage power plants in terms of output and probably also in terms of storage capacity.
Advantages of short-term storage
Short-term storage caps residual loads
What does this look like in practice? The following Simulation of ECO STOR provide answers. It shows how battery storage systems behave during a dark doldrums. With its system in Bollingstedt, the company operates one of the largest stand-alone battery storage systems in Germany.
It can be seen that the residual peak load decreases with an increasing number of short-term storage facilities, and therefore also fewer power plants, particularly Gas-fired power plants, are necessary in the future.
The study „The value of large-scale battery storage in the German electricity system“ by Frontier Economics (December 2023) showed that large-scale storage can significantly reduce the need for back-up power plants. The researchers arrived at a reduction of nine Gigawatt (GW)!
Change in residual load with different amounts of short-term storage in the system. Source: ECO STOR Short-term storage saves fuel and provides system services
Short-term memory enable a higher expansion of renewable energies. Less wind and, above all, solar power needs to be curtailed. The storage systems also save on grid expansion if they are used as a buffer for fast-charging stations, for example. This makes the Construction of such plants more attractive for operators and reduces the need for other energy sources. Short-term storage therefore contributes Direct and fast to climate protection.
In the summer months, short-term storage systems will shift more and more solar power into the night. The Power stations are coming to a standstill more and more often. Fuels are being saved and the demand for coal and gas is falling. The gas that is saved in summer can then be used in the winter half-year during dark doldrums, for example in gas turbines and gas engines, regardless of whether it is natural gas, Biomethane, biogas or perspectively green Hydrogen is.
In the future, battery storage systems will also provide important system services that are currently still provided by power plant turbines. In combination with grid-forming inverters battery storage systems become the anchor of system stability.
Maxsolar's Reckertshausen solar park has a 4.1 MW battery storage system. Source: Maxsolar GmbH
„Just 60 GW of installed battery storage with a capacity of two to four hours could reduce the need for secured backup power by 15 to 20 GW. The benefit is less in completely bridging dark doldrums lasting several days, but primarily in smoothing out short-term fluctuations and reducing peak loads. This makes the energy system more robust and reduces overall costs.“
Short-term memory: One of several components
However, short-term storage alone will not get us through the dark doldrums in the foreseeable future. They are a Important building block - No more, but also no less. Moreover, they are just one form of flexibility alongside others, such as load shifting for flexible consumers - see the chapter on Demand flexibility. In perspective, there are also Long-term memory. However, these will only make up a small share of the storage market for the time being.
Beyond this, short-term storage will contribute to solving many problems such as Solar power generation peaks. For more information on the many advantages of short-term storage, please read the fact sheet published by the Bundesverband Neue Energiewirtschaft e.V. .
Safely through the dark doldrums: the two-page guide
The fact paper "Dark doldrums" shows on two pages how dark doldrums can be overcome today, tomorrow and the day after tomorrow. Which fuels will we use? Which technologies will be used? How will battery storage help? How will biogas develop over the next few years? We have summarised the most important points on this website for you.