Climate-neutral heating with lime – DLR develops pilot plant

The primary advantage of lime storage reservoirs is that they experience almost no heat loss, as lime can chemically store energy for months. This type of thermochemical energy storage is very well suited to seasonal storage that enables energy generated from renewable sources to be stored in summer and used in winter.

Energy transition in the heating sector

"Energy storage systems allow us to react as energy requirements fluctuate according to the time of day or season. DLR is working intensively on various storage media and technologies that will prove indispensable for the energy transition in the medium and long term," says Karsten Lemmer, DLR Executive Board Member for Innovation, Transfer and Research Infrastructure. "Germany has set itself the goal of generating 80 percent of its energy from renewable sources by 2050. But in order to ensure network and system security, that supply has to be efficient and flexible. Energy storage is key to balancing supply and demand."

In Germany, heating and hot water account for more than 80 percent of the energy requirement of an average household. At present, this demand is mainly met using fossil fuels. There have traditionally been few options for effectively heating a house using energy renewable energy in winter, when the demand for heat is particularly high. However, it is possible to generate large amounts of renewable energy through methods such as photovoltaic systems or concentrated solar energy at other times of year, especially in summer. Thermochemical energy storage can be used to store this energy long term and regulate the supply of this energy across seasons.

Heating with lime and water

The DLR Institute of Engineering Thermodynamics has been researching lime storage technology intensively for several years. "We have been able to achieve heating capacity of eight kilowatts in the laboratory," says Matthias Schmidt, DLR researcher and project lead for the development of the pilot plant. "This can be used to heat a small, detached house. The heat generated is used almost entirely within the building, which means it is possible to reach an efficiency of up to 90 percent."

One major advantage of lime storage systems is that their storage capacity can be easily adjusted to meet respective needs. The more lime a plant contains, the more energy it can store. Approximately six cubic metres of quicklime is enough to provide self-sufficient heating to a modern detached house for a month in winter.

"Lime storage tanks use the chemical reaction of quicklime and water to generate heat. First, lime powder is heated in an oven to over 450 degrees Celsius. This allows the water bound in the lime to escape, forming quicklime. In a mixing chamber, the quicklime then chemically reacts with water to form slaked lime. This creates temperatures of over 100 degrees Celsius. Depending on requirements, the heating output can be regulated based on the amount of lime and water," explains Schmidt. "If the slaked lime is burned again, it can store energy again. This process can be repeated indefinitely."

Pilot plant heats the world’s first adaptive high-rise building

In collaboration with the University of Stuttgart, DLR researchers are integrating the pilot system into the world's first adaptive high-rise building. The building’s façade and surface components adapt to the sunlight, saving material resources and reducing emissions.

The operation of the pilot plant in this research building will help the DLR researchers draw conclusions that will feed into the everyday use of lime storage. "Among other things, we are looking at how the system has to regulate itself in order to respond optimally to a brief change in the weather," says Schmidt.

Cost-effective and environmentally safe