Volatile, renewable energy sources are increasingly feeding into the power grid. Can electricity be stored for times of shortage?? There is no one answer, but a bundle of possibilities.
The public power supply has been struggling for several years with the fact that the number of feeders has multiplied and the electricity demand of private end customers is increasingly shifting. While for many decades the peak demand was at midday, when cooking was done up and down the country, changing habits mean that cooking is now more likely to be done in the evening, when electricity from photovoltaic systems, which could well cover the midday peak, is only available to a limited extent.
Those who now do not see temporary load shedding as a timely model for future power supply need to think about how the differences between power supply and demand will be balanced in the future. Most of the time, reference is made to electricity storage, but there are other ways in which the challenges could have been met.
Although the prompt listing of storage fill levels on the web site of the Fraunhofer Institute for Solar Energy Systems (ISE) clearly shows the differences in current electricity storage in the public grids in the DACH region, it concentrates on the (pumped) storage power plants.
Pumped storage power plants
In pumped storage power plants, water is traditionally pumped from a lower reservoir into a higher reservoir at times when electricity is cheap. When the demand for electricity is greater than the supply, the water is passed through turbines and generators are used to produce electricity.
Most pumped storage power plants date back to the days of large-scale power plants, where they could quickly step in when a large-scale power plant failed and bridge the time needed to connect a thermal reserve power plant to the grid.
In addition, the power plants, which are usually equipped with synchronous generators, are also operated in so-called phase-shift mode. A direct link between wind power and pumped storage was recently realized with the wind power plant in the small town of Gaildorf in Wurttemberg.
Another element for balancing the load on the power grid are the reservoirs, mostly located in high mountain areas such as the Swiss and Austrian Alps, whose water enters the lake through natural intakes. In many cases, these reservoirs are located below a glacier, which also stores precipitation during the cold season, which is then collected with the melt in the reservoir. As the alpine glaciers have been retreating for years, the amount of precipitation stored in the glaciers is steadily decreasing.
Whether the operation of such storage power plants will still be worthwhile in the future is a matter of debate. The Swiss power company was unable to find a partner for its power plants that would help bridge the current profitability gap and has therefore sold its industrial business to the French construction group Bouygues.
Battery storage on the grid
In Germany, several dozen battery storage plants are in operation on the grid The majority of these are equipped with lithium-ion batteries; significantly fewer operate with lead-acid batteries or redox flow batteries. Sodium-sulfur cells are used in only two plants. Grid-controlled storage systems are now exempt from electricity tax, unlike private storage in single-family homes.
From the semi-governmental German Energy Agency dena in Berlin there is an extensive study on battery storage in the grid under the title "Optimized use of storage for grid and market applications in the power supply (dena grid flexibility study). An overview of current research projects on battery storage in Germany can be found on the Energy Storage page.
Customer-oriented, decentralized battery storage systems
Most battery storage systems today are located in private households. The German Solar Industry Association (BSW) speaks of several tens of thousands in Germany. They usually have an output of 3.5 kW and a capacity of approx. 8 kWh. The frequently used lithium ion cells pose a problem in case of fire, which many volunteer fire departments have not yet dealt with. Battery storage providers are therefore looking for alternatives. The sonnenBatterie company in Wildpoldsried, Germany, supplies battery storage systems with lithium iron phosphate batteries.
Biogas plants against the dark doldrums
The fear of a so-called blackout, which is repeatedly raised by many concerned citizens in connection with the energy transition and the increased use of renewables such as wind power and photovoltaics, can be alleviated if a power plant whose fuel is also renewable and can be stored is provided for such a case.
Especially in rural areas, where the majority of wind power and photovoltaic plants are located today, biogas plants can usually be integrated very well into the distribution network. In this context, it is clearly helpful if the distribution grids are structured as cellular grids. How well the different renewable energies complement each other can currently be seen in Wildpoldsried.
Power2Gas and Gas2Power
For a long time now, the solution of using surplus electricity to generate gas has been under discussion. This gas can be stored much better than electricity and can also be fed into the existing natural gas network to a certain extent. The economic viability of such plants depends not only on the plant costs but also on the operating conditions. Still clearly beyond an economic realization stands the "Jerk conversion" in electricity than Gas2Power.
In the context of the discussion about smart grids, attention has increasingly turned to so-called sector coupling, not least in connection with the municipal cross-connected companies. In this context, energy supply and demand are considered from the point of view of the economic coverage of the energy demand in the network.
In many cases, for example, it is economical not to store surplus electricity in expensive battery storage facilities, but to use it to heat water, which is traditionally heated with natural gas. The gas not required in the current case can be stored much more cost-effectively than electricity.
The example of sector coupling shows that it makes perfect sense to optimize the energy supply not only from the point of view of individual energy carriers and technologies.