A flywheel provides operating reserve on the AC bus, helping to absorb sudden increases or make up for sudden decreases in renewable power output. A flywheel can also maintain power quality and system stability through active and reactive power control, although HOMER does not explicitly model those effects. These effects can be important in medium- and high-renewable penetration systems serving isolated networks or on soft grids (such as near the end of distribution lines). Flywheels typically connect to the AC bus via an AC/AC inverter system that converts the variable-frequency AC power from the flywheel rotor to constant-frequency, grid-quality AC power on the AC bus.
In HOMER, the flywheel adds its "charge/discharge capacity" to the operating reserve as a constant value, and then draws its "parasitic load" constantly from the AC bus. HOMER does not model the state of charge of the flywheel—it is assumed to only add power in time scales shorter than the simulation time step. To model a flywheel as an energy storage device, you can use one of the other storage models, such as the Idealized Storage Model. See the Generic Flywheel 100kW [Idealized Model] for an example.
In the Site Specific Inputs section, you can enter parameters that affect how the flywheel operates in the simulation.
The Parasitic Load is the amount of electricity necessary to operate the flywheel. HOMER models this as a constant electrical load, and considers a system feasible only if it can meet this load at all times during the simulation. The Operating Reserve input is the maximum amount of power the flywheel can absorb or provide. (HOMER assumes that the flywheel's capacity to absorb power is equal to its capacity to provide power.) This is the amount of operating capacity that the flywheel provides to the system.