Solar energy storage

Triplet-sensitised photocycloaddition of norbornadiene (N) leads to formation of the energy-rich quadricyclane (Q) by an intramolecular reaction  

This reaction has the potential to be used in systems for the collection and storage of solar energy. 

Although quadricyclane is highly strained, it is kinetically very stable on account of the large activation energy for the Q — N reaction. Use of suitable catalysts allows the stored solar energy to be released as heat. 

The availability of solar energy is subject to diurnal-, seasonal-, and weather-related variations. Therefore, if solar energy is to meet continuous energy demands, it must be stored. On small installations, such storage can be provided by high-density batteries. (NGK Insulators Ltd. of Japan, for example, manufactures sodium-sulfur batteries that can store 7 mWh.) On midsized installations, pumped hydrostorage can be considered. 

In even larger installations, one solution is the storage of heat in high-temperature (400°C or higher) oil or in molten salt. Hot oil storage is more common, but in other cases such as the 64 mW solar power plant called Solar One, in Boulder City, Nevada, excess solar energy is planned to be stored in molten salt. These plants store the molten salt at high temperature and when electricity 

Post-Oil Energy Technology After the Age of Fossil Fuels 

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The facile, photoinduced valence isomerization of ethyl 1//-azepine-l-carboxylate to ethyl 2-azabicyclo[3.2.0]hepta-3,6-diene-2-carboxylatehas been studied as a potential solar energy storage system.101102 Unfortunately, the system proved to be inefficient due to build up of polymeric material during the thermally induced, exothermic retro-reaction. 

Gopal, R., B.R. Hollebone, C.H. Langford and R.A. Shigeishi, 1982. The rates of solar energy storage and retrieval in a zeolite water system, Solar Energy, 28, 421-424. 

Photoelectrolysis of Aqueous Solutions to Hydrogen—An Approach to Solar Energy Storage... 

Koukouvinos A, Lygerou V, Koumoutsos N (1982) Design of a system for solar energy storage via water electrolysis Int J Hydrogen Energy 7 645-650... 

Fig. 32. Flow type solar energy storage system Fig. 33. Polymer battery. AX (n-Bu,N)CI01, utilizing immobilized sensitizer (30) and catalyst LiC104 etc.

Conductive polymers are useful semiconductors or coating materials to construct solar cells. A new photodiode is proposed to be made from a film of a polymer metal complex. Immobilized catalysts on polymers are used for solar energy storage systems. 

Flowing streams of pebbles also have been used in the chemical industry for removing heal from gases. Pebbles and stones arc also used in some solar energy storage systems. See Fig. 11 See also Solar Energy. 

There are very many options available for solar energy storage but this chapter is concerned solely with the use of solar energy to decompose water into hydrogen and oxygen, the former of which will be used as a fuel (see equation 1). 

As discussed above, and considering Figure 3, it is clear that only systems which involve the use of two or four photons to decompose one water molecule need to be considered as practical candidates for efficient solar energy storage. However, the complexity of designing a four-photon system means that most attention has been given to the two-photon system. 

Nevertheless, the requirement for UV light and the generally stoichiometric nature of the reactions renders them unsuitable for solar energy storage. Cyclic systems based on Fen/I" and Ce111/lv are discussed in detail below. 

A pilot plant jointly funded by the EU, the Paul Scherrer Institute (PSI), and the Swiss Federal Institute of Technology of Zurich (ETHZ) has successfully demonstrated this process in a 300 kW pilot plant at the Weizmann Institute of Science (WIS) in Rehovot, near Tel Aviv, Israel. The plant has produced 45 kg of zinc per hour. This method of solar energy storage is not yet commercially available. 

A. Szent-Gyorgyi, in SubmolecularBiology and Cancer, p. 1, Excerpta Medica, New York (1978). Ideas on photons and solar energy storage in biomass. 

In connection with solar energy storage investigations, Mukai and co-workers reported on the use of cationic sensitizers 33-37 in the photocycloreversion reaction of strained molecules [79,80] (Eq. 16). Acetonitrile solutions of the... 

Fig. 2.5 Ancient Egyptian papyrus demonstrating the combination of solar radiation and skin ointment for the treatment of skin disease (reproduced from the front page of the invitation to the 4 International Conference and Workshop on Solar Energy Storage and Applied Photochemistry, January 1997 by permission of M.S.A. Abdel-Mottaleb, Ain Shams University, Cairo, Egypt).

Photochemical electron transfer reactions have been examined in micellar systems as probes for the diffusion and location of quenchers, and as environments for solar energy storage 2 3>90 95 96>. The relative rates of quenching will depend on the location of the donor and acceptor (Scheme XXXII). For example, the rate of quenching of a hydrophobic donor located inside the micelle by Cu2+ is much faster in anionic micelles compared to cationic micelles. Similarly a hydrophobic excited state is quenched faster by a hydrophobic donor or acceptor than by a hydrophilic one in micellar systems. 

Norik AJ (1993) Second Internal Conference on solar energy storage and appl photochemistry (Cairo), Proc (in press)... 

Intramolecular addition is observed in the pyrimidine-6-azapyrimidine dinucleoside analogue (153) to give the cis,syn-adduct (154), and surprisingly 2-phenylbenzoxazole (155) is reported to undergo dimerization to the 1,3-diazetidine (156) on irradiation in cyclohexane. This adduct is stable in the solid state at room temperature but reverts to monomer in solution the possible use of this reversible transformation in solar energy storage has been discussed. 

Preparation of vesicles and monolayers has been described. It is claimed that such structures are relevant to solar energy storage devices but experimental support is still lacking. 

Polymers can be used to locate reagents at particular sites and to provide unique surface environments. The possible applications of functionalized polymers in solar energy storage systems have been reviewed in detail. Metalloporphyrins or bipyjRu " " can be attached to various water-soluble polymers via covalent or electrostatic linkages. The ability of the dye to photoreduce dissolved in the aqueous phase, depends strongly upon... 

EXAMPLE 5 6 Solar Energy Storage in Trombe Walls... 

Cu2l2(PPh3)2(dpk)], and (Cu4l4(dpk)3] (dpk di-2-pyridyl ketone) in the solar energy storage reaction, norbornadiene/ quadricyclane. ... 

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