| S = | units | What is the supply of the resource? | |
| U = | units per year | What is the usage rate (demand) of the resource? | |
| r = | % per year | How fast is demand growing? |
Static reserve (how long the resource lasts with steady demand): years
Exponential reserve (how long the resource lasts with changing demand):
This page demonstrates the concepts of static and exponential reserve from Section 23.2 of the textbook For All Practical Purposes (FAPP). By specifying a non-renewable resource's supply (S) and demand (U), and the rate r at which demand is changing (increasing or decreasing), you can estimate how long the resource will last.
The "bars" shown represent the entire supply of the resource; they are subdivided into chunks which show how they are consumed over time. In the case of static reserve (steady consumption), all chunks (except perhaps the last) are the same size, and represent the same amount of time. For exponential reserve, each chunk represents similar (but not identical) total demand, over varying numbers of years.
Static reserve is computed as SR = S / U, while exponential reserve is ER = ln(1+SR⋅r) / ln(1+r).
For example, consider this question (paraphrased from FAPP 8th edition, #23.11, page 758): If the world supply of oil is 2900 billion barrels, and daily consumption is 84.7 million barrels, growing at 1.9%, what are the static and exponential reserves? To answer this, enter S = 2900000, U = 84.7*365, and r = 1.9.
(March 29, 2016) First release - incomplete. Only tested with Chrome and Firefox (so far).
The contents of this page are © 2016 Darryl Nester. It is available to anyone who wishes to use it (like most things on the Internet). Please send me an email if you have found it to be useful, or if you have suggestions.