Anl. Rev. Ener. 1979. 4:353-401 Copyright 1979 by Annual Reviews Inc. rghts rerd PHOTOCHEMICAL CONVERSION AND STORAGE OF SOLAR ENERGYl James R. Bolton +11069 Photochemistry Unit, Department of Chemistry, University of Wester Ontario, London, Ontario, Canada, NA David 0 Hal Department of Plant Sciences, University of London, King's College, Ha Moon Lane, London SE24 United Kingdom INTRODUCTION In this era of depleting fossil fuel resources, the use of solar' energy as a renewable alterative has been gaining very serious attention by many goverments and industries. Solar energy is an immense resource-the surface of the earth receives about 3 X 1024 J per year. Since the estimated proven reserves of oil, natural gas, coal, and uranium are only about 2.5 X 1(2 J (8X 1011 tonnes coal equivalent) (1), we see that in less than one week the eanh receives from the sun an amount of energy equal to the total reserves of nonrenewable energy. Put in another way, if the earth were covered to an extent of only 0.1% of its surface with collectors converting solar energy at only 10% efciency, then all of the current world annual needs for energy (3 X 1020 J/year) would be met! However, solar energy has two major drawbacks-it is intermittent and difuse. The frst requires some form of a storage system so that the energy can be made available when it is needed and the second requires large of collectors. Both of these factors place Severe but not insurmountable economic constraints on solar energy systems. Most of the current and proposed applications of solar energy involve the conversion and collection of sunlight as heat to be used directly in space and ·Publiction No. 20 of the Photohemistry Unit, University of Wester Ontario. 33 0362-1626/79/1010-0353$01.0 Annu. Rev. Energy. 1979.4:353-401. Downloaded from www.annualreviews.org by University of Alberta on 09/26/12. For personal use only.