The project "Aerothermie" investigates the direct conversion of wind energy into heat. The German Aerospace Center (DLR) develops and operates a windthermal pilot plant to demonstrate the functionality of heat generation and storage. The pilot plant generates measurement data that we use to analyse the technical and ecomomic potential of windthermal energy. The project aims to derive targeted optimisation and further development measures.
What inspired us?
Wind is'nt always available when power is demanded. These fluctuations are one of the biggest challenges of wind power generation. Energy storage solves this problem, but is expensive. In July 2017, on the 2nd German-Japanese Workshop on Renewable Energies a possible solution was presented: Heat-storage is less expensive than electricity-storage. Could wind turbines generate this heat directly? This alluring idea, inspired us to develop a windthermal pilot plant. Three DLR institutes collaborated to develop the project idea to develop a functional protoype as quick as possible. In march 2019, we started to convert rotational energy into heat with a thermal platform inside a separte container where a motor emulated the wind turbine. Once we proofed the concept, we connected the thermal platform with a wind turbine. We choosed a PSW model, a northern German manufacturer of small wind turbines, in which a shaft directs the torque downwards, simlifying the integration.
Pilot Plant
The pilot plant consists of a modified wind turbine and the thermal platform. A drive train replaces the electric generator and feeds the mechanical energy into the container. A special brake, a so-called hydrodynamic retarder converts the rotational energy into heat that is stored in a hot water tank. A system of pipies and valves interconnects the components and makes it possible to interconnect the pilot plant to any use case application. In the near future, a mechanical heat pump will be added.
Pilot Plant Components
Wind Turbine
The wind turbine is a commercially available 22 m high wind turbine with a rated power of 15 kilowatts that reaches power peaks of up to 30 kilowatts for short periods at appropriate wind speeds. 2 anemometers precisey determine any measurement deviations on the tower of the turbine. The wind turbine was modified for the project: the electrical generator was removed, and the basis was reinforced and opened up so that a cardan-shaft can connect the wind turbine with the thermal platform.
Hydrodynamic Retarder
The hydrodynamic retarder is a brake that is normally used in trucks. Now we use it to convert wind into heat. The retarder not only generates heat, but also controls the wind turbine. Therfore, it is particularly importat for the pilot plant. The key parameters can be optimised for the wind turbine. This allows us to operate the wind turbine in its optimum-operating-point at any wind speed.
Hot Water Tank
The hot water tank stores the heat and provides heat even when there is no wind. Hot water tanks are very cost-effective compared to other storage technologies such as batteries and are in use for decades. In future, it is conceivable to replace the hot water tank with a latent-heat-storage, which uses a phase transition of the storage medium to achieve higher energy densities at constant temperature levels.
Mechanical Heat Pump
Heat pumps transfer the ambient heat to a higher temperature level. The work required herefore, is usually much less than the amount of heat. It thus has a positive coefficient of performance (COP) and increases the overall efficiency of the pilot plant. In this project, a modulating heat pump will be used, which allows us to operate the wind turbine in its optimum-operating-point at any wind speed, similarly to the retarder.
Next steps
An important development step is placing the thermal components from the container into the nacelle of the wind turbine. This is more user-friendly and minimises costs and mechanical losses. The biggest challenge is the heat transport. We want to base on good heat transmission practices that are used, for example, in concentrated solar power (CSP) plants. The windthermal pilot plant can be easily scaled up. Wind turbines as well as hydrodynamic retarders, modulating heat pumps and heat storage units are already available on the market as off-the-shelf components. Moreover, this technology can be easily integrated into existing use-cases worldwide.
Publications
Research Papers
- Cao KK, Nitto AN, Sperber E, Thess A (2018). Expanding the horizons of power-to-heat: Cost assessment for new space heating concepts with wind powered thermal energy systems. Energy 2018; 164: 925-36. https://doi.org/10.1016/j.energy.2018.08.173.
- Neumeier M, Cöster M, Marques Pais RA, Levedag S (2022). State of the art of Windthermal Turbines: A Systematic Scoping Review of Direct Wind-to-Heat Conversion Technologies. ASME J. Energy Resour. Technol., 144(4): 040802. https://doi.org/10.1115/1.4052616.
Student Works
- Nitto AN (2016). Wind Powered Thermal Energy Systems (WTES). A Techno-Economic Assessment of Different Configurations. Oldenburg University. https://elib.dlr.de/103317/.
- Marques Pais RA (2021). Techno-economic analysis on wind thermal energy converters and renewable heating technologies for process heat in Germany. Oldenburg University. https://elib.dlr.de/143675/.
- Holtorf (2022). Entwicklung einer Hardware-in-the-Loop Simulation für ein windthermisches Energiesystem. Hamburg University of Technology. https://elib.dlr.de/185360/