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2.4.2 System Control

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The System Control menu in the Project tab allows you to modify how HOMER simulates your systems.

Dispatch Strategy

A dispatch strategy is a set or rules that govern the operation of the generator(s) and the battery bank. HOMER can model two dispatch strategies, cycle charging and load following. Which is optimal depends on many factors, including the sizes of the generators and battery bank, the price of fuel, the O&M cost of the generators, the amount of renewable power in the system, and the character of the renewable resources. If you choose to model both, HOMER will simulate each system using both dispatch strategies and you will be able to see which is optimal.

Under the load following strategy, whenever a generator is needed it produces only enough power to meet the demand. Load following tends to be optimal in systems with a lot of renewable power, when the renewable power output sometimes exceeds the load.

Under the cycle charging strategy, whenever a generator has to operate, it operates at full capacity with surplus power going to charge the battery bank. Cycle charging tends to be optimal in systems with little or no renewable power.

If you can apply a setpoint state of charge to the cycle charging strategy, the generator(s) will not stop charging the battery bank until it reaches the specified state of charge. The sensitivity button to the right allows you to do a sensitivity analysis on this setpoint.

Note that the dispatch strategy is abbreviated "Dispatch" in the sensitivity and optimization results tables. The rows contain "CC" for cycle charging or "LF" for load following.

Select the option "Allow diesel-off operation" if the system can maintain stability without the generator running. This option only has an effect if there is a generator in the system which can sometimes be turned off. Some systems require a generator to maintain bus voltage and frequency. If the system includes a "grid-forming" component other than the generator, you can deselect this option, and HOMER will turn the generator off if the load can be supplied with other sources.

The check box "Multiple generators can operate simultaneously" only affects the operation of systems that include two or more generators on the same bus. If you check this box, HOMER will allow multiple generators on the same bus to operate at once whenever necessary. Otherwise, multiple generators on the same bus must take turns operating.

Note: To the right of each numerical input is a sensitivity button (shots_sensitivity-button) that allows you to do a sensitivity analysis on that variable. For more information, see Why Would I Do a Sensitivity Analysis?

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