Notes on Determining Depletion Times and Abundance Factors

3 Notes on Determining Depletion Times and Abundance Factors 

A special situation in the determination of depletion times and abundance factors occurs when a resource used in a process is actually a half-product  

Another special situation arises when one resource has its origin in two different processes. For instance, when a process uses the electricity provided by an energy company, it is possible that this electricity is generated partly by burning coal and partly by burning natural gas. In this case, the process should be considered to use two different types of electricity electricity from coal and electricity from natural gas. Both types of electricity then have their own derived depletion time and, based on how much they contribute to the total amount of electricity supplied, their own exergy flow. 

Finally, the concept of depletion times, as it is used in the construction of the sustainability parameter, is also suitable to include the sustainability of production of facilities needed to harvest resources. For instance, solar energy may in principle have a depletion time of billions of years, but the production of photovoltaic cells usually requires some very scarce elements for which the depletion times are much smaller. The sustainability of using solar energy harvested with photovoltaic cells should then be based on these latter depletion times and not on the depletion time of solar energy itself. 

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