| Description: | Group of Generators and Batteries for which a dynamic firm capacity is modeled |
See also Firm Capacity Group Property Reference for a detailed list of properties for this class of object.
Firm Capacity Groups are used to model multi-dimensional firm capacity curves for the purpose of meeting reserve margin targets in LT Plan. Each group consists of a set of Generators or Batteries, typically of a single technology type (such as storage, wind, or solar). Multiple groups are combined together with input points on this curve and assigned to a Region or Zone. Each point represents the total installed capacity of each technology type and the corresponding combined firm capacity that would be attained for the Region or Zone with that combination of capacity values. Each Generator or Battery assigned to one of these Firm Capacity Groups then no longer contributes independently to the target reserve margin, but rather the whole set of groups contributes one total firm capacity value for each capacity optimization period. This value is solved for in the optimization problem which is formulated for the LT Plan and is based upon the user input points (through the Firm Capacity Values and Capacity Points).
When more than one group is used, in the optimization problem the multi-dimensional space is divided up into sections to cover all possible combinations of builds in the set of Firm Capacity Groups. The number of these sections is determined by the product of the Max Tranches values of all groups. For each section, a linear approximation is made based on the nearest input points to the center of this section. This is used to formulate a constraint that defines the linear relationship between the capacity values of the groups and the final firm capacity contribution to the Region or Zone in that section. Binary variables are added (the total number of which for a given capacity expansion period will equal the sum of the Max Tranches of all groups) are used to activate those constraints based on what is actually built in the LT problem. The complexity of the formulation is based on the number of Firm Capacity Groups being used and the Max Tranches value for each. The number of input points used does not affect the size of the formulation, and the more points that are given the more accurate the linear approximation will be.
When only one group is used, a simpler formulation is employed and all input points are modeled directly. In this case, when the problem is convex no binary variables will be added. The Max Tranches input is not used. This setup is similar to using a Generator multi-band Firm Capacity and Firm Capacity and Firm Capacity Unit Count, but the Firm Capacity Groups are more flexible in that multiple Generators and Batteries can be grouped together.
The total firm capacity solved for is reported in the Region Firm Capacity Group Value and Zone Firm Capacity Group Value outputs.