# HOMER Pro 3.9

The cycle charging strategy is a dispatch strategy whereby whenever a generator needs to operate to serve the primary load, it operates at full output power. Surplus electrical production goes toward the lower-priority objectives such as, in order of decreasing priority: serving the deferrable load, charging the storage bank, and serving the electrolyzer.

Note: A generator will not produce surplus power just to dump it as excess electricity. There must be some use for its surplus power for HOMER to operate it above the level needed to serve the primary load.

When using the cycle charging strategy, HOMER dispatches the controllable power sources (generators, storage bank, grid) each time step of the simulation in a two-step process. First, HOMER selects the optimal combination of power sources to serve the primary load and the thermal load at the least total cost, while satisfying the operating reserve requirement. To accomplish this, HOMER calculates the fixed and marginal cost of each dispatchable power source:

A generator's fixed cost is equal to its hourly operation and maintenance cost plus its hourly replacement cost plus the cost of its no-load fuel consumption. Its marginal cost is equal to its fuel curve slope times the fuel price. If waste heat can be recovered from the generator and the waste heat is needed to serve the thermal load, the generator's marginal cost is reduced by the value of the thermal energy it produces (which is equal to the marginal cost of thermal energy from the boiler). If a cost is assigned to carbon emissions, the generator's marginal cost is increased accordingly.

The storage bank's fixed cost is zero and its marginal cost is equal to the storage wear cost.

The grid's fixed cost is zero and its marginal cost is equal to the grid power price. If a cost is assigned to carbon emissions, the grid's marginal cost is increased accordingly.

This first step is identical to the load-following strategy.

Next, HOMER ramps up the output of each generator in that optimal combination to its rated capacity, or as close as possible without causing excess electricity.

If a setpoint state of charge is applied to the cycle charging strategy, then when the storage state of charge is below the setpoint and the storage was not discharging in the previous time step, HOMER will avoid discharging the storage in this time step. A generator will likely be called upon to serve the primary load and produce excess electricity to charge the storage bank. So once the system starts charging the storage bank it continues to do so until it reaches the setpoint state of charge.