For each system element the quantities of materials, fuels, and electricity required to build and operate the system were compiled with the aid of published data on energy requirements 170-173 expressed either in joules per ton of materials or joules per dollar of material cost. The physical material quantity or material cost is converted into an energy requirement equivalent. Energy Balance Parameters. A number of energy balance parameters were calculated, including gross efficiency, operating efficiency, operating ratio, lifetime efficiency, lifetime ratio, and payback period. Gross efficiency measures the amount of energy delivered per unit of input energy. Operating efficiency is a more complete measure of how effectively the basic energy resource is being utilized, i.e., how efficiently a given technology extracts useful energy from a primary energy form. The operating ratio eliminates the energy content of the primary resource from the calculation. This parameter is a measure of how much useful energy can be extracted from a primary resource. It considers the primary resource as fundamentally unusable in its basic state and measures the amount of energy that must be expended to convert it into usable form. The lifetime efficiency and lifetime ratio are analogous to the operating efficiency and operating ratio. They include the capital energy investment in the balance process, which represents the energy required to construct the system. Payback period is the time required for the system to produce enough useful energy to match the energy investment in building and operating it. All of these parameters must be considered because the efficiency and payback calculations tend to be better for the coal and nuclear systems than for the solar energy systems, whereas the operating ratio and lifetime ratio calculations tend to be better for the solar-based systems than for the coal and nuclear systems. Annual and lifetime net outputs are computed in terms of electrical units. All inputs are computed in thermal units but do not consider the thermal energy content of the fuels or materials involved, only the energy expended on such activities as mining, processing, and transportation. These are the usual conventions for doing a net energy analysis. Thus, this approach represents a short-term view of the use of a nonrenewable resource base; for example, in computing payback, the interest is in determining at what rate an energy system returns electrical energy, given the investments (inputs) required. It does not consider the issue of depletion of a nonrenewable resource base, which must be addressed as a lost opportunity issue for alternative uses of the resource. Furthermore, if the thermal content of a nonrenewable resource were considered, the payback period for systems based on nonrenewable resources would be infinite, by the second law of thermodynamics . Results. Table 4.38 summarizes the baseline calculations. The coal and nuclear* systems are two to five times more efficient than the solar systems but operate on nonrenewable resources. The calculation of efficiency *0f the nuclear systems, only the LWR was studied in detail. The LMFBR, although it has higher capital energy costs, should at least break even due to lower fuel energy costs. LMFBR fuel is produced by chemical separation, which is less energy intensive than the diffusion process needed to enrich fuel for the LWR.
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