A group of reservoirs may be obligated to meet the power demands of preferred customers before this energy is used for other purposes. For example, if a group of reservoirs is owned by another entity, the energy demand of their customers must be met before the energy is coordinated with the other reservoirs in an economic objective, and in this sense, their customers are preferred. In such a situation, some (and perhaps all) of these reservoirs are also treated as allocated energy that can be flexibly used in coordination with the remaining reservoirs.

The methods in this category model the energy needs of the preferred customers. The preferred customers are identified by membership in a Preferred Customer subbasin. This is a predefined type of subbasin.

Preferred customers are not used in the economic valuation.

In simulation, the Preferred Customer Energy slot holds the amount of energy that should be sent to the preferred customers. This energy is subtracted from the allocated energy when evaluating the economic value of hydropower.

In optimization the Preferred Customer Energy is a variable. The optimization adds a constraint that limits the energy consumed by preferred customers to the energy limits of the reservoirs in the Preferred Customer subbasin by automatically adding the following constraint when the preferred customer method is selected.

The first sum is over the subbasin reservoirs that are optimized while the second sum is over the subbasin reservoirs that are not optimized, but instead are part of allocated energy. In the first case, the maximum energy value is accessible through the configuration menu of the energy slot on each reservoir. In the second case, the Allocated Maximum slot on the thermal object holds a value for each time step.

Typically, when preferred customer energy is used, the modeler will add a prioritized constraint to the optimization requiring that the preferred customer energy be met. The Energy demand must be specified on a slot on a data object.

As in simulation, the Preferred Customer Energy is subtracted from Allocated Energy in the economic evaluation.