Excess electricity is surplus electrical energy that must be dumped (or curtailed) because it cannot be used to serve a load or charge batteries. Excess electricity occurs when surplus power is produced (either by a renewable source or by the generator when its minimum output exceeds the load) and the batteries are unable to absorb it all.
Note: It is possible to have a capacity shortage on one bus and excess electricity on the other in the same time step if there is an undersized converter or a converter without the "Parallel with AC generator?" option selected.
A resistive heater (often called an electric boiler) can convert excess electricity into thermal energy that can meet the thermal load. In HOMER, this component is called the Thermal Load Controller, available under the Components tab. In a real system, if it cannot be put to use, excess electricity might have to be dissipated. This is often called a secondary load, which is usually a simple resistive heater or a bank of light bulbs. In some cases, excess energy can be curtailed rather than dissipated.
HOMER tabulates the excess electricity experienced by the system in each time step. You can see the time series and the annual total in the Simulation Results window, which appears when you double-click a system in the Optimization Results table on the Results page.