HOMER Energy Support

Dispatch Strategy and Controllers

Last Updated: Sep 05, 2018 04:23PM MDT
Product: HOMER Pro and HOMER Grid

The dispatch strategy in HOMER Pro and HOMER Grid specify how the HOMER engine operates storage and power sources to serve the load. It turns generators and batteries off and on, and chooses how much power they produce or consume in each timestep to serve the load. HOMER Pro includes several controllers that you can pick, and each includes a distinct dispatch strategy. Load Following (LF), Cycle Charging (CC), Combined Dispatch (CD), Generator Order Dispatch (GO), and MATLAB Link (ML) are the controllers currently available in HOMER Pro. They can be accessed through the Controller button under Projects tab. HOMER Grid uses its own dispatch strategy. Each of these dispatch strategies differ in the rules they apply.

 In HOMER Pro, the two default controllers are Load Following and Cycle Charging. Both of these make economic dispatch decisions; they choose the most economical way to serve the load without looking ahead into the future. Since they are not looking into the future, they differ in the strategy they use for generators. Under load following, the generators produce just enough power to serve the load.  Under cycle charging, generators produce as much power as they can and charge the battery with any excess.  With the cycle charging strategy you can apply a setpoint state of charge, so that the generators keep charging the battery and don't let the battery discharge until it has reached the specified setpoint. Combined Dispatch algorithm intelligently chooses which strategy to use between LF and CC in each time step. The Generator Order dispatch is designed to mimic how small utilities with multiple gensets often operate their systems; you specify the order in which you turn on each set of gensets and HOMER Pro will use the first set that meets the load requirements. If none of these suit your needs, MATLAB Link lets you write your own custom algorithm as a MATLAB program and run it through the HOMER Engine.
In HOMER Grid, the dispatch algorithm is responsible for deciding in each time step on how the electrical load is served by the available electric generation sources. Among the many decisions it takes, it decides if the battery should be charged by the grid, if it makes sense to buy from the grid, and/or if it should run the generator. The dispatch in HOMER Grid has ‘perfect foresight’, meaning that it knows:

•The electric demand for each time step in the future
•The utility rate schedule
•PV production for each time step in the future

HOMER Grid will optimize and find the least cost system by reducing demand charges and engaging in energy arbitrage if viable.

The following knowledgebase article provides further insight into how LF and CC controllers operate: http://usersupport.homerenergy.com/customer/en/portal/articles/2188800-dispatch-strategy
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