The Smart Energy 25 is a 25 kWh, 100 kW carbon fiber flywheel. It is an AC device, but HOMER will connect it to the DC bus because it cannot model AC electrical storage. To model this flywheel in HOMER, you should add a converter, but make it free, 100% efficient, and larger than the aggregate capacity of the largest number of flywheels that you are considering. If your system also includes PV, we recommend modeling the PV as an AC device with the inverter costs and losses included with the PV module.
In a hybrid power application, energy storage provides a buffer so that diesel generators can be turned off and remain off during short lulls in the wind or passing clouds. To maximize this benefit HOMER may use the full range of the energy storage device's state of charge before turning on another generator and recharging the device close to 100% state of charge.