Basically, the investigation of energy ratios (Figure 13) involves the 

 same methodology but with only a carefully selected portion of one component 

 (or series of components) of an energetics mode. For example, in Figure 14, 

 yield ratios were calculated for electric power plants, by comparing a coal- 

 fired power plant with that of an oil-fired power plant (Alexander et al . 

 1980b). The output of each hypothetical power plant was held constant at 

 17.83 X 10 coal equivalent calories per year (CE Cal /yr) . The cost to 

 society to mine and transport the fuel, to build and maintain the physical 

 plant, and the operational costs of the plant are shown as the feedback from 

 the main economy. Comparing these feedbacks to the output of each power 

 plant, respectively, shows the yield ratio. The yield ratio of 12.2 for oil 

 and 5.5 for coal illustrates the economy of oil over coal. 



LIMITATIONS OF ENERGETICS MODELS 



Two limitations that frequently affect the use of energetics models are 

 the frequent lack of appropriate data with which to calibrate the simulation, 

 and the difficulty associated with validation of the results of a particular 

 energetics model . 



Collecting the data necessary to estimate the magnitude of each energy 

 flow in the system being studied can be an involved and time-consuming pro- 

 cess. Data are seldom usable as found. Mapped data may not include suffici- 

 ent detail concerning ecological systems, as was mentioned in the methods sec- 

 tion. Data from some governmental agencies are often not always compatible 

 with other government agencies. In some cases, traditional methods used by a 

 particular discipline did not permit easy standardization with data expressed 

 in some other unit of measurement. In cases such as these, baseline research 

 must establish appropriate conversion methodologies. This is being done by 

 more and more users. 



Closely related to the data-availability problems are the problems asso- 

 ciated with validation of the simulation results. If leaders in government 

 and business are to commit their resources to the solutions suggested by ener- 

 getics models, those leaders must know the degree to which the model is a 

 valid predictor of future systems behavior. Unfortunately, the validation of 

 the results of a particular energetics model applied to a particular problem 

 is difficul t. 



In addition, theoretical research is producing verifiable data that can 

 in turn be used by any number of future users. The illustration of energy 

 ratios given in Figure 14 is one such example. In it, the researchers estab- 

 lished the relative energy quality of wood, numerous coal types, fossil fuels, 

 and other energy sources. 



The trend toward a more complex and unified body of knowledge continues. 

 As the body of knowledge surrounding energetics models increases, it will 

 eventually provide a sufficient base allowing for more complex but efficient 

 model simulation. 



302 



