Biological solar energy
Biological solar energy
Oil, gas, and coal provide us with most of the energy needed to power our technologies, heat our homes, and produce the wide range of chemicals and materials that support everyday life. Ultimately the quantities of fossil fuels available to us today will dwindle, and then what? Even before that we are faced with the problem of increasing levels of carbon dioxide in the atmosphere and the consequences of global warming (Climate Change, 2001). To address these issues it is appropriate to remind ourselves that fossil fuel reserves are derived from the process of photosynthesis. Plants, algae, and certain types of bacteria have learnt how to capture sunlight efficiently and convert it into organic molecules, the building blocks of all living organisms. It is estimated that photosynthesis produces more than 100 billion tons of dry biomass annually, which would be equivalent to a hundred times the weight of the total human population on our planet at the present time, and equal to about 100 TJ of stored energy. In this chapter we emphasize the enormity of the energy/carbon dioxide problem that we face within the coming decades and discuss the contributions that could be made by biofuels and developing new technologies based on the successful principles of photosynthesis. We will particularly emphasize the possibility of exploiting the vast amounts of solar energy available to extract hydrogen directly from water. The success of this energy generating and storage system stems from the fact that the raw materials and power needed to synthesise biomass are available in almost unlimited amounts: sunlight, water and carbon dioxide. At the heart of the reaction is the splitting of water by sunlight into oxygen and hydrogen. The oxygen (a ‘waste product’ of the synthesis) is released into the atmosphere where it is available for us to breathe and to use for burning our fuels. The ‘hydrogen’ is not normally released into the atmosphere as H2, but instead is combined with carbon dioxide to make organic molecules of various types.
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