Heat plays a crucial role in the energy transition. It is needed to heat our buildings, but also as process heat in industry. What’s more, heat can be stored very cost-effectively.
Ulf Herrmann spoke about this at the latest edition of HC-H2 Brainergy Park Connects. He is a professor of renewable energies and heads the Solar Institute Jülich at Aachen University of Applied Sciences. “Warm, warmer, warmest.” That was the title of his presentation to residents and interested parties at the innovative Brainergy Park business park. The Solar Institute is itself a neighbour, operating the multiTESS facility in the park. And that facility is all about hot air.
Power2X, or Power-to-X, is the name given to energy storage methods that will support the energy system of the future alongside batteries. This is because humans need to store some of the energy generated when the sun shines and the wind blows so that they have enough when production is low. Energy, i.e. power, is converted into X. X can be many things: various gases such as hydrogen and its derivatives, for example.
“Heat pumps also generate electricity demand, which is often not taken into account in municipal heat planning. This is necessary, which is why we are considering this point.”
Prof. Ulf Herrmann, Professor of Renewable Energies and Head of the Solar Institute Jülich at Aachen University of Applied Sciences. Photo: FH Aachen
Or heat, for that matter. Ulf Herrmann from the Solar Institute Jülich spoke about this in the latest issue of Connect. In the future, humans will need various renewable energy sources and correspondingly different storage facilities. There is still a long way to go, as Ulf Herrmann explains with the help of a diagram. It shows the total energy consumption in Germany for 2023, broken down into the sectors electricity, heat for households, transport and heat for industry and commerce. According to this, 60 percent of electricity in Germany will come from renewable sources. The trend has been rising ever since. Across all four sectors, the share of renewable energy in Germany is 20 percent.
Founded in 1992, the Solar Institute is an interdisciplinary team consisting of 50 employees. It works on heat supply solutions and considers heat on a temperature scale from 0 to 1200 °C.
The InnoFlaG project is designed for ice-cold temperatures, i.e. between 0 and 15 °C. “We are looking at an area for which there are still relatively few models, namely near-surface geothermal energy,” explains Ulf Herrmann. Heat pumps for supplying houses are the key technology in this area. They can be fed from structures close to the surface, for example, which do not require deep drilling.
The goal: viewing efficient neighbourhoods as a complete system
Things are a little warmer, in the range of 60 to 90 °C, in the Open District Hub project, which the Solar Institute is working on in collaboration with Fraunhofer IEG. The focus here is again on heat pumps, which are intended to supply more complex systems such as residential neighbourhoods or larger units. “Heat pumps also generate electricity demand that is often not taken into account in municipal heat planning. This is necessary, which is why we are looking at this issue,” explains Ulf Herrmann. The researchers are working on planning and simulation tools that can manage electricity, heat and mobility in neighbourhoods in a resource-efficient and cross-sectoral manner.
The solar collectors used in the project editor can provide higher temperature ranges of up to 420 °C. The curved parabolic trough collectors focus the sunlight onto a point inside, heating a medium located there. Such systems have mostly been used in solar thermal power plants up to now, but now they are also to be able to supply and store heat. A thermal concrete storage tank is used for this purpose. The collected heat is not used immediately, but is stored for a limited period of time, for example until the next morning. This technology is currently being used by a beverage manufacturer in Cyprus. “But it’s also conceivable for Germany,” says Ulf Herrmann. “This would allow us to cover our energy needs even before the sun has risen.”
Decoupling energy supply and demand
An innovative new heating system uses surplus green electricity to heat air to temperatures of up to 1000 °C. This is unusually hot; temperatures of around 750 °C are more common. ‘The whole thing works like a giant hair dryer,’ says Ulf Herrmann, explaining the system in simple terms. The hot air is then transferred to a ceramic body with lots of tiny capillaries and stored there.
The project page describes the purpose of the application as follows: “The stored energy can either be used as base load heat – i.e. around the clock from 50 °C to 1000 °C – or fed into existing combined heat and power plants for demand-based generation of electricity and heat.” This decouples the availability of energy from the fluctuating production of solar and wind power. “After one day, we can retrieve 90 percent of the electricity invested from the stored heat. The efficiency decreases with longer storage periods.”
The Solar Institute Jülich is providing simulation support for a second project in Brainergy Park that is visible from afar. Synhelion Germany GmbH uses a heliostat field, whose reflectors are focused on the reactor of a solar tower, to generate temperatures of over 1200 °C. “Synhelion produces solar fuels to enable sustainable mobility. We produce solar aircraft fuel, diesel and petrol that can directly replace fossil fuels,” the company writes on its website. The Solar Institute Jülich is supporting the project as part of the TwinSF project, in which it is developing a digital twin of the plant. “We want to simulate how the plant can be controlled most efficiently. This requires models that can calculate the future behaviour of the plant in real time and derive optimised operational management,” says the head of the Jülich Solar Institute, describing the project, which aims to further optimise the already completed plant. The partners want to use this to learn how to build larger plants in more productive regions.
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