HOMER User Tip: Modeling Critical and Priority Loads
HOMER Pro’s two distinct electric loads can be used for many different purposes (residential vs. commercial or air conditioning vs. lighting) with different efficiency options and load growth assumptions. But one of the more interesting and little-known applications of this feature is using it to distinguish the priority of the loads and, in systems with an advanced Grid component, specifying critical loads.
In situations where there is not enough power or energy to meet the entire load, HOMER Pro reduces the power to Electric Load #2 first and treats Electric Load #1 as the priority load. Sensitivity analyses on the size of these loads and on the Maximum Capacity Shortage allows you to analyze the amount of non-critical load that will be unmet.
In models with a Grid component using Real Time Rates or Scheduled Rates, you can choose to turn off Electric Load #2 when there is a grid outage. Simply check the box "Turn of Electric Load #2 when grid is off", found under the Reliability tab of the Grid component.This will disable Electric Load #2 and HOMER will only serve Electric Load #1 when the grid component has an outage. Note: this feature requires the Advanced Grid Module.