This article examines the potential of environmenttemperature variability as a source of usable energy for free. For example, on the Moon, the diurnal temperature swing reaches 300 K (approximately 100 K to 400 K), enabling a heat engine to operate with a Carnot efficiency of about 75%. On Earth, the most favorable conditions occur in the Taklamakan Desert, where a diurnal variation of 35 K (from roughly 255 K to 290 K) corresponds to a Carnot efficiency of 12.1%. The analysis employs the classical Carnot efficiency for systems with two heat reservoirs of constant temperature and introduces the concept of exergy efficiency for configurations in which only one reservoir maintains a constant temperature. Opportunities for practical implementation are discussed for selected locations on Earth and within the Solar System. Both substance working fluids and radiation working media are considered. For context, the study also compares these results with the exergy efficiency of natural solid fuels, which can exceed 100%.
References
[1]
Petela, R. (2021) Thermodynamic Analysis of Processes. http://www.eolss.net/sample-chapters/c08/E6-107-20.pdf
[2]
Szargut, J. and Petela, R. (1965) Energija [Exergy]. WNT. (In Polish)
[3]
Petela, R. (2010) Engineering Thermodynamics of Thermal Radiation, for Solar Power Utilization. McGraw Hill.
[4]
Morofsky, E. (2007) History of Thermal Energy Storage. In: Paksoy, H.？., Ed., Thermal Energy Storage for Sustainable Energy Consumption, Springer, 3-22. https://doi.org/10.1007/978-1-4020-5290-3_1
[5]
Bejan, A. (2016) Advanced Engineering Thermodynamics. Wiley. https://doi.org/10.1002/9781119245964
[6]
Priya, S. and Inman, D.J. (2009) Energy Harvesting Technologies. Springer. https://doi.org/10.1007/978-0-387-76464-1
[7]
Brusa, E., Carrera, A. and Delprete, C. (2023) A Review of Piezoelectric Energy Harvesting: Materials, Design, and Readout Circuits. Actuators, 12, Article 457. https://doi.org/10.3390/act12120457
[8]
Bejan, A., Tsatsaronis, G. and Moran, M. (1996) Thermal Design and Optimization. Wiley. https://www.wiley.com/en-us/Thermal+Design+and+Optimization-p-9780471584674
[9]
？engel, Y.A. and Boles, M. (2015) Thermodynamics: An Engineering Approach. McGraw Hill.
[10]
Szargut, J., Morris, D.R. and Steward, F.R. (1988) Exergy Analysis of Thermal, Chemical, and Metallurgical Processes. Taylor & Francis Inc.
[11]
Senft, J.R. (1998) Theoretical Limits on the Performance of Stirling Engines. InternationalJournalofEnergyResearch, 22, 991-1000. https://doi.org/10.1002/(sici)1099-114x(199809)22:11<991::aid-er427>3.0.co;2-u
[12]
Romanelli, A. (2020) Stirling Engine Operating at Low Temperature Difference. AmericanJournalofPhysics, 88, 319-324. https://doi.org/10.1119/10.0000832
[13]
Senft, J.R. (1996) An Introduction to Low Temperature Differential Stirling Engines. Moriya Press.
[14]
Cabeza, L.F. (2015) Advances in Thermal Energy Storage Systems. Woodhead.
[15]
Sharma, A., Tyagi, V.V., Chen, C.R. and Buddhi, D. (2009) Review on Thermal Energy Storage with Phase Change Materials and Applications. RenewableandSustainableEnergyReviews, 13, 318-345. https://doi.org/10.1016/j.rser.2007.10.005
[16]
Rowe, D.M. (2005) Thermoelectrics Handbook: Macro to Nano. CRC Press.
Petersen, K.E. (1982) Silicon as a Mechanical Material. ProceedingsoftheIEEE, 70, 420-457. https://doi.org/10.1109/proc.1982.12331
[20]
Vasavada, A.R., Paige, D.A. and Wood, S.E. (1999) Near-Surface Temperatures on Mercury and the Moon and the Stability of Polar Ice Deposits. Icarus, 141, 179-193. https://doi.org/10.1006/icar.1999.6175
[21]
Siegler, M.A. and Smrekar, S.E. (2014) Lunar Heat Flow: Regional Prospective of the Apollo Landing Sites. Journal of Geophysical Research: Planets, 119, 47-63. https://doi.org/10.1002/2013je004453
[22]
Zhu, L., Raman, A.P. and Fan, S. (2015) Radiative Cooling of Solar Absorbers Using a Visibly Transparent Photonic Crystal Thermal Blackbody. Proceedings of the National Academy of Sciences of the United States of America, 112, 12282-12287. https://doi.org/10.1073/pnas.1509453112
[23]
Encyclopaedia Britannica (2025) Moon. https://www.britannica.com/place/Moon
[24]
Rumble, J. (2024) CRC Handbook of Chemistry and Physics. 105th Edition, CRC Press.
[25]
Dincer, I. and Rosen, M.A. (2011) Thermal Energy Storage: Systems and Applications. 2nd Edition, Wiley.
[26]
Zondag, H.A., et al. (2013) Chemical and Sorption Heat Storage. Renewable and Sustainable Energy Reviews, 22, 1-13.
[27]
Scapino, L., Zondag, H.A., Van Bael, J., Diriken, J. and Rindt, C.C.M. (2017) Thermochemical Energy Storage: A State of the Art Review. Renewable and Sustainable Energy Reviews, 76, 770-803.
[28]
Pierrehumbert, R.T. (2010) Principles of Planetary Climate. Cambridge University Press. https://doi.org/10.1017/cbo9780511780783
[29]
NASA (2024) Planetary Fact Sheet—Metric. https://nssdc.gsfc.nasa.gov/planetary/factsheet/
[30]
Barry, R.G. and Chorley, R.J. (2010) Atmosphere, Weather and Climate. 9th Edition, Routledge.
[31]
World Meteorological Organization (2024) Global Weather & Climate Extremes Archive. https://wmo.asu.edu
[32]
Petela, R. and Milner, G. (1997) Significance of the Fluid Working on the Power Cycle. FLOWERS’97, Florence, July 30-Augst 1 1997, 1053-1060.
[33]
Petela, R. (2024) Thermodynamic Analysis of the Concentration Process of Solar Radiation. InternationalJournalofEnergyandPowerEngineering, 13, 97-107. https://doi.org/10.11648/j.ijepe.20241305.12
[34]
Szargut, J. and Styrylska, T. (1964) Angen？herte Bestimmung der Exergie von Brennstoffen. BrennstoffW？rmeKraft, 16, 589-596.
[35]
Dulong, P. (1826) Recherches sur la mesure des températures. Annales de Chimie et de Physique, 2, 225-264.
[36]
Petela, R. (1966) Influence of the Geological Age of Natural Solid Fuels on Their Exergy. Koks Smola Gaz, No. 5, 168-173.
