standard cubic feet is used. An order of magnitude estimate of this upper limit based on solar powered production costs and energy content of gaseous hydrogen (342 BTU/standard cubic feet) yields a cost of $4.28/kWh. [Brandhorst, 1992] If future energy sources ever come close to the hydrogen cost limit, they will cease to be used unless other factors make them more appropriate than hydrogen for a particular application. The lower end of the energy cost range can be approximated by current energy sources. For example, the current cost of electricity using coal is approximately $0.07/kWh, which is roughly two orders of magnitude below this upper limit. Having established the upper and lower bounds for energy costs, the following paragraphs will present an overview of current and projected energy costs (where available) and a brief discussion of the factors which may influence the cost of energy in the future. A considerable amount of work has been done in past solar power projects to try to estimate future energy costs. Table 2.3 gives quantitative projected costs for the delivered cost of fossil fuels in a future scenario considered as “the most probable case” in a report prepared by Argonne National Laboratory. [ANL/EES-TM-120,1980] These results show the cost of coal, oil, and gas rising two to four times in the next 40 years. Recent trends for photovoltaic energy production show the opposite with costs decreasing from $60.00 in 1970, to $1.00 in 1980, and to the current cost of $0.30/kWh. [Sci. Am, 1990, ppl47] Other current cost estimates for renewable energy sources are wind at $0.07-0.12/kWh and hydroelectric at $0.05-0.10/kWh. Because of their limited contribution to supplying future energy demand, cost projections for these sources are not discussed here. Predicting the cost of future energy must consider production cost as well as market conditions. This section will discuss, in some detail, the factors which contribute to production cost. There is also a brief mention of supply and demand relationships which will be developed further in Chapter 3. The major factors that influence production cost are mining, transportation, type of conversion process, and environmental constraints (including nuclear safety considerations). As easily accessible resources are depleted, the cost of mining other available sources (e.g. oil from shale or tar) will increase. The technologies for transportation and energy conversion are well established and costs should remain fairly stable. However, since mining, transportation, and energy conversion all require a power source, as energy costs increase it will also become more expensive to produce. Table 2.3 Delivered Fossil Fuel Prices, 1978$/kWh Figure 2.7 shows the sequence of operations between the discovery of an energy source and conversion. [Scientific american, Inc. 1971] The type of conversion can be any of those discussed in the previous section and allows comparison between the various energy sources. In the figure, “preliminary conversion” refers to production of intermediate products (such as various grades of fuel from crude oil) which are usually more easily stored or transported for final use. The energy forms indicated are Latent (L) for nuclear and fossil fuel sources. Potential (P) and Kinetic (K) for water sources, including tidal and hydroelectric, Radiant (R) for solar energy, and both Latent and Thermal (T) for geothermal energy. The presence or absence of a dot in each of the “operation” boxes illustrates the impact of some of the characteristics described in Table 2.1 (storability) and Table 2.2 (location). The number of steps to a particular operation, such as “store” or “transport”, provides information about how easily adaptable a particular energy source is to a given application. As mentioned earlier, because of their different characteristics, energy sources may not be readily interchangeable. Each of the operational sequences represented in this figure requires supporting
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