A combination of process analysis and input/output analysis was used to compute the energy balance parameters for each supply system. Process analysis involves a detailed balance of energy flows into and out of a system. It is the most accurate and most involved method and can be applied to situations where a great deal of process-specific information exists. Input/ output (I/O) analysis uses an analogy to economic input/output analysis to determine the energy ’’costs” of any energy supply. It involves an identification of the interactions between sectors of the economy required to produce energy and a translation of the flow of goods and services among sectors into energy equivalents. Each of the systems chosen for evaluation is described as a collection of system elements. Each element represents a particular piece of hardware, processing step, energy conversion step, or transportation mode. The energy balance of each system element is described in Fig. 4.41. The primary input is in the form of fuel (e.g., coal into a coal-processing plant) or energy (e.g., heat from a solar collector into a boiler). The ancillary operating inputs are those energy forms required to keep the process operating. The gross output is the energy or processed fuel that results from the system element. A portion of this gross output may be used to meet internal energy requirements. The balance is the net output that goes on to become the primary input of the next system element. The losses are the difference between the outputs and the inputs. Up to this point, a straightforward energy balance can be carried out since all quantities of materials and their energy contents can be directly computed. This is the extent of the process analysis used in this assessment. The indirect energy requirements of the system are embodied in the capital energy inputs, i.e., the materials, fuels, and electricity required to build the system element, and in the energy required to supply the electricity, fuels, and materials for operating inputs. A simplified analysis was used to compute direct energy requirements during this phase of the analysis. Fig. 4.41 Schematic of Energy Balance
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