We first note that whilst solar energy is renewable ad infinitum, it is not infinite in its rate of energy supply. Thus, the total insolation on the surface of the globe is approximately 10,000 times the total present energy use and we define a local “solar ratio” as the ratio of the total insolation on a given area to the energy use in that area. Since the oceans cover approximately two-thirds of the surface of the globe, the solar ratio for the land areas is approximately 3,000. Table 3 shows the solar ratios for several specific areas. The figures for the highly industrialized areas such as the UK+ are startling: solar converters of 1% net efficiency could not supply the energy needs even if the entire country were covered with converters! It is also important to note that, unlike entropy, the solar ratio is constantly decreasing as consumption rises and the supply remains the same. How much of the solar radiation in any area can we exploit? This depends upon the conversion efficiency with some examples given in Table 4. Thus, the dream of vast areas of bio-converters — even of much improved species — is limited to a few areas of the world where population density (i.e., energy consumption per unit land area) is low and the land is cheap. Putting collectors or PV panels on roofs is an approach for overcoming, in part, the solar ratio limitation. Thus, Israel has some three million sq m of collectors on tThe solar ratio for West Germany is almost identical to that for the UK.
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