23. Chemical Storage Materials and Reactions [8].

Materials	Reaction	Material energy density	Reaction temperature (°C)
Ammonia		67 kJ/mol	400-500
Methane/water		n.a	500-1000
Hydroxides		3 GJ/m3	500
Calcium carbonate		4.4 GJ/m3	800-900
Iron carbonate		2.6 GJ/m3	180
Metal hydrides	Metal x H2 ↔metal y H2+(x-y) H2	4 GJ/m3	200-300
Metal oxides (Zn and Fe)	e.g 2 step water splitting using Fe3O4/FeO redox system	n.a	2000-2500
Aluminium ore alumina	n.a	n.a	2100-2300
Methanolation–demethanolation		n.a	200-250
Magnesium oxide		3.3 GJ/m3	250-400

The materials used as energy stored medium should posses some thermal, physical, chemical and economic characteristics highlighted in Table XXIV.

24. Main Characteristics of Energy Storage Materials [8].

Thermal properties	Physical properties	Chemical properties	Economic properties
High change of enthalpy near temperature of use High thermal conductivity in both liquid and solid phases (although not always)	Low density variation High density Small or none undercooling	Stability No phase separation Compatibility with container materials No toxic, no flammable, no pollutant	Cheap and abundant

Ion V. Ion, associate professor, mechanical engineering: “Dunarea de Jos” University of Galati, Faculty of Mechanical Engineering, Thermal Systems and Environmental Engineering Department, 111, Domneasca St., off. G102, Galati, 800201, Romania, tel. +40 740566214, e-mail: ion.ion@ugal.ro

References

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6. http://www.energiestro.com/us/us_technology.htm

7. N. P. Siegel, Thermal energy storage for solar power production, WIREs Energy Environ, 2012, 1, pp. 119–131.

8. A. Gil, M. Medrano, I. Martorell, A. Lázaro, P. Dolado, B. Zalba, L. F. Cabeza, State of the art on high temperature thermal energy storage for power generation. Part 1-Concepts, materials and modellization, Renewable and Sustainable Energy Reviews 14, 2010, pp. 31–55.

9. Abduljalil A.Al-Abidi, Sohif Bin Mat, K. Sopian, M.Y. Sulaiman, C.H. Lim, Th. Abdulrahman, Review of thermal energy storage for air conditioning systems, Renewable and Sustainable Energy Reviews 16, 2012, pp. 5802–5819.

10. V.V. Tyagi, D. Buddhi, PCM thermal storage in buildings: A state of art, Renewable and Sustainable Energy Reviews, 11, 2007, pp. 1146–1166.

11. M. Kenisarin, K. Mahkamov, Solar energy storage using phase change materials, Renewable and Sustainable Energy Reviews, 11, 2007, pp. 1913–1965.

12. Planta Solar Tres/Gemasolar (http://www.psa.es/webesp/areas/ussc/solartres.php)

13. A.H. Abedin and M.A. Rosen, A Critical Review of Thermochemical Energy Storage Systems, The Open Renewable Energy Journal, 2011, 4, pp. 42-46.

Ion V. Ion, associate professor, mechanical engineering: “Dunarea de Jos” University of Galati, Faculty of Mechanical Engineering, Thermal Systems and Environmental Engineering Department, 111, Domneasca St., off. G102, Galati, 800201, Romania, tel. +40 740566214, e-mail: ion.ion@ugal.ro