A sensitivity variable is an input variable for which multiple values have been specified. HOMER performs a separate optimization procedure for each possible combination of sensitivity variable values. The total number of sensitivity cases is the product of the number of variable values specified for each sensitivity variable. With several sensitivity variables, each with several values, the number of sensitivity cases can be very large, and result in a long computation time.
In some cases you may not be interested in all combinations of sensitivity variable values. Some sensitivity variables tend to vary together, and so it makes sense to vary them together for the sensitivity analysis. In this case, a linked sensitivity may be appropriate. Linked sensitivities can greatly reduce the number of optimizations HOMER runs.
When you link two sensitivity variables, HOMER optimizes the system with each pair of values. You must specify the same quantity of values for all variables in a sensitivity link. Capital cost and replacement cost are good candidates for a sensitivity link. If the capital cost is higher than expected, it is likely that the replacement cost will be higher too.
You can specify a sensitivity link from the sensitivity variable editor. Click on the sensitivity button to open the sensitivity variable editor. Enter values for the sensitivity variable. Then click ok. Now, if you open the editor for any other sensitivity variable, you can set a link using the drop-down menu labeled "Link with:" shown in the image below.
Once you select the variable with which to link, HOMER will create a "link group" for these sensitivity variables. HOMER will display a warning until the member variables of the link group all have the same number of entries. You can add another variable by opening its sensitivity variable editor and using the drop-down menu to select the desired link group. You can have many link groups, and you can have any number of variables linked together in each group.
In the example above, HOMER will optimize with pairs from each row in the table: (0.5, 0.5), (0.75, 0.75), (1.0, 1.0), and so on. In this example, HOMER will run 5 optimizations for the 5 sensitivity cases. Without the sensitivity link here, HOMER would run 25 optimizations instead of 5: (0.5, 0.5), (0.5, 0.75), (0.5, 1.0), and so on.
For more information, see Why Would I Do a Sensitivity Analysis?