Solar–hydrogen energy cycle

Solar–hydrogen energy cycle is an energy cycle where a solar powered electrolyzer is used to convert water to hydrogen and oxygen. Hydrogen and oxygen produced thus are stored to be used by a fuel cell to produce electricity when no sunlight is available.[1]

## Contents

* 1 Working
* 2 Features
* 3 Use of hydrogen iodide
* 4 Advantages
* 5 See also
* 6 References

## Working

Photovoltaic panels convert sunlight to electricity. In this cycle, the excess electricity produced after consumption by devices connected to the system, is used to power an electrolyzer. The electrolyzer converts water into hydrogen and oxygen, which is stored. This hydrogen is used up by a fuel cell to produce electricity, which can power the devices when sunlight is unavailable.[1]

## Features

The Solar–Hydrogen energy cycle can be incorporated using organic thin film solar cells[2] and microcrystalline silicon thin film solar cells[3] This cycle can also be incorporated using photoelectrochemical solar cells. These solar have been incorporated since 1972[4] for hydrogen production[5] and is capable of directly converting sunlight into chemical energy.[4]

## Use of hydrogen iodide

An aqueous solution of hydrogen iodide has been proposed as an alternative to water as a fuel that can be used in this cycle. Splitting of hydrogen iodide is easier than splitting water as its Gibbs energy change for decomposition is lesser. Hence silicon photoelectrodes can decompose hydrogen iodide into hydrogen and iodine without any external bias.[4]

## Advantages

* This cycle is pollution free as the only effluent from this cycle is pure water.[1]

## See also

* Energy storage
* Photoelectrolysis of water
* Photocatalytic water splitting
* Power to gas

## References

1. ↑ 1.0 1.1 1.2 "Schatz Solar Hydrogen Project". schatzlab.org. http://www.schatzlab.org/projects/real_world/schatz_solar.html. Retrieved 2011-06-18.
2. ↑ Nakato, Y.; Jia, G.; Ishida, M.; Morisawa, K.; Fujitani, M.; Hinogami, R.; Yae, S. (10 June 1998). "Efficient Solar-to-Chemical Conversion by One Chip of n-Type Silicon with Surface Asymmetry". Electrochem. Solid-State Lett. (Osaka , Japan: Electrochemical Society) 1 (2): 71–73. doi:10.1149/1.1390640. http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=ESLEF6000001000002000071000001&idtype=cvips&gifs=yes&ref=no. Retrieved 2011-07-20.
3. ↑ Yae, Shinji; Kobayashi, Tsutomu; Abe, Makoto; Nasu, Noriaki; Fukumuro, Naoki; Ogawa, Shunsuke; Yoshida, Norimitsu; Nonomura, Shuichi et al. (15 February 2007). "Solar to chemical conversion using metal nanoparticle modified microcrystalline silicon thin film photoelectrode". Solar Energy Materials and Solar Cells (Japan: ScienceDirect) 91 (4): 224–229. doi:10.1016/j.solmat.2006.08.010.
4. ↑ 4.0 4.1 4.2 "Water splitting to produce solar hydrogen using silicon thin film". spie.org. http://spie.org/x8413.xml?ArticleID=x8413. Retrieved 2011-08-30.
5. ↑ Fujishima, Akira; Honda, Kenichi (7 July 1972). "Electrochemical Photolysis of Water at a Semiconductor Electrode". Nature (Japan: Nature Publishing Group) 238 (1): 37–38. doi:10.1038/238037a0. PMID 12635268.

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