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Windthermal Energy Research

Motivation

The energy transition, i.e. the transformation towards renewable energies, is one of the major challenges of our time. The security of energy supply must be maintained without increasing energy prices. Renewable heat generation and sector coupling make our energy supply more flexible. Power-to-heat, i.e. the conversion of excess wind generation into heat, is a possible game changer. But why not generate heat directly from wind? Windthermal energy, i.e. the direct conversion of mechanical wind energy into heat, saves one conversion step and is potentially cheaper and more efficient than indirect heat generation (wind-to-power-to-heat).

 

Windthermal Energy: Potential and Opportunities

Technical Potential

  • Efficiency: Windthermal energy saves one conversion step and thus potentially has a higher system efficiency than power-to-heat from excess wind generation.
  • Off-the-shelf components: The technology can be developed quickly by integrating existing off-the-shelf components.
  • Simple construction: Windthermal turbines require fewer components than electric wind turbines. This potentially reduces weight, investment, maintenance and operating costs, and reduces the risk of errors.

Economic Potenzial

  • Target market: Windthermal energy can meet up to 25% of the world's energy needs, if it reaches an output temperature of 200°C.
  • Cheap energy generation: Windthermal energy is potentially cheaper than power-to-heat from excess wind generation.
  • Cheap energy storage: Thermal storage is significantly cheaper than electrical storage.

Further Potential

  • Existing infrastructure: Windthermal energy are easy to integrate into existing district heating networks.
  • Environmental costs: Windthermal energy potentially harms the environment less than other technologies.

 

Application Scenarios

Wind thermal plants can be operated in the same way as electric wind turbines, as large wind farms or small wind turbines. Small-scale plants can provide space heating up to 100°C. Potentially, large-scale plants are also conceivable that can generate process heat up to 600°C [1,2].Windthermal application scenariosPossible areas of application are:

  • Space heating
  • District heating
  • Seawater desalination
  • Greenhouses
  • Paper industry
  • Food industry
  • Textile industry
  • Heat to Power
  • Wastewater treatment
  • Other applications (especially in rural areas)

 

 

Previous Windthermal Energy Research

The idea of generating heat directly from wind is not new. The first prototype dates back to the 1970s. US researchers developed, commissioned a wind turbine directly coupled with a mechanical heat pump [3,4,5,6]. Starting the new millenium, a similar project was implemented in Taiwan [7,8,9]. So far, other windthermal concepts are still on laboratory scale, with a motor emulating the wind turbine.

 

How does it work? - Windthermal Conversion Technologies

Theoretically, there are three different ways to convert mechanical wind energy into heat [10].

1. Compression-based Windthermal Conversion

Compression-based windthermal converters are operated with pumps or compressors (e.g. a piston compressor). The drive train stimulates the cylinder to move up and down. This movement compresses a fluid that heats up due to the compression.

 Compression-based windthermal conversion

2. Friction-based Windthermal Conversion

Friction-based wind heat converters use the principle of a Joule apparatus, which James Joule once used to proved the equivalence of mechanical work and heat: A liquid is stirred and thus heated. In its simplest form, the wind-thermal turbine drives an impeller in a water tank [11]. Alternative brakes such as hydrodynamic retarders can be used, that allow a more accurate and sensitive wind turbine control [12].

Friction-based windthermal conversion

3. Induction-based Windthermal Conversion

Induction-based wind heat converters work with the eddy current of an alternating magnetic field. The wind thermal turbine rotates a conductor between two permament magnet. This generates an alternating magnetic field and the resulting eddy current that is dissipated as heat. Additional heat is generated by magnetic hysteresis [13].

Induction-based windthermal conversion Bibliography

  1. Garvey SD, Pimm AJ, Buck JA, Woolhead S, Liew KW, Kantharaj B, Garvey JE, Brewster BD. Analysis of a wind turbine power transmission system with intrinsic energy storage capability. Wind Eng. 2015, 39 (2), S.149–174. https://doi.org/10.1260/0309-524X.39.2.149.
  2. Okazaki T, Shirai Y, Nakamura T. Concept study of wind power utilizing direct thermal energy conversion and thermal energy storage. Renewable Energy 2018. 83, .332–338. https://doi.org/10.1016/j.renene.2015.04.027.
  3. Braymer J, Pinotti M, Dybbs A. A wind powered heat pump. In: Yuan SW, editor. Energy, Resour. Environ., New York: Pergamon Press; 1982, S. 528–35. https://doi.org/10.1016/b978-0-08-029396-7.50070-7.
  4. Gunkel WW, Furry RB, Lacey DR, Neyeloff S, Porter TG. Development of a wind-powered water heating system for dairy application. Work. Wind Energy Appl. Agric., 1979, S. 124–57.
  5. Gunkel WW, Kromann GB, Nattuvetty VR. Performance analysis of a wind-assisted heat pump for a dairy. Trans ASAE 1985;28. https://doi.org/10.13031/2013.32237.
  6. Klueter HH, Liljedahl LA. Feasibility of wind-powered mechanically-driven heat pump for a dairy. Trans ASAE 1981; 25: 0745–51. https://doi.org/10.13031/2013.33606.
  7. Jwo C-S, Chien Z-J, Chen Y-L, Chien C-C. Development of a wind directly forced heat pump and its efficiency analysis. Int J Photoenergy 2013; 2013. https://doi.org/10.1155/2013/862547.
  8. Ting C-C, Lee J-N, Shen C-H. Development of a wind forced chiller and its efficiency analysis. Appl Energy 2008; 85:1190–7. https://doi.org/10.1016/j.apenergy.2008.03.014.
  9. Ting CC, Lai CW, Huang CB. Developing the dual system of wind chiller integrated with wind generator. Appl Energy 2011;88:741–7. https://doi.org/10.1016/j.apenergy.2010.09.002.
  10. Neumeier M, Cöster M, Marques Pais RA, Levedag S. State of the art of Windthermal Turbines: A Systematic Scoping Review of Direct Wind-to-Heat Conversion Technologies. ASME J. Energy Resour. Technol. 2021; 144(4): 040802. https://doi.org/10.1115/1.4052616.
  11. Chakirov R, Vagapov Y. Direct conversion of wind energy into heat using joule machine. IPCBEE (International Proc. Chem. Biol. Environ. Eng., vol. 19, 2011, S. 12–7.
  12. Cao KK, Nitto AN, Sperber E, Thess A. 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.
  13. Chen L, Pei Y, Chai F, Cheng S. Investigation of a novel mechanical to thermal energy converter based on the inverse problem of electric machines. Energies 2016;9:518. https://doi.org/10.3390/en90705188.