Glossary

This section is a glossary of the main concepts used by GEMS. For a detailed specification of each file, see the file structure page.

Input Files

Term	Definition
Library	A file listing all the models representing general unspecified elements of a study. These models are used as "template" for creating their instances, called components
System	A file listing all the "components", the instances of models defined by the library yaml file, representing all the specified elements of the simulated grid. This file also contains all the connections between the components
Dataseries	A table containing all the data through time. It is used by time/scenario dependent components

Concept	Definition
Model	An abstract mathematical configuration representing the general features of a category of grid element. Users can specify any instance of this model for creating each simulated grid's element
Component	An instance using a model as a template. Each component is a specific detailed instance of a model representing a real object. Multiple components can use the same model within a system, each with different parameter values

Concept	Definition
Variable	An abstract mathematical variable of a model, whose value is optimized by the solver. The optimization problem is to find the best set of variables based on the variable's configuration, shared across all model instances.
Parameter	An input data declared in the model, with a value specific to each component (set in the system.yml file). It can be a scalar value, a time-series, or a scenario-series. The optimization problem seeks the best set of variables according to these parameters.
Objective function	The mathematical expression optimized by the solver. Variables are selected to achieve its global minimum based on the input parameters.
Constraint	A mathematical relationship or condition that restricts the values of variables
Binding Constraint	A constraint that links variables or ports across different models or components

Concept	Definition
Port	A communication interface for exchanging expressions, called "fields"
Field	A scalar quantity carried by a port and exchanged between connected components (e.g., a power flow value)
Connection	A link between two components' ports

Concept	Definition
Time	Energy systems modelled and optimized within GEMS are, in most cases, inherently temporal. To make this tractable within a computational framework, GEMS represents time in a discrete rather than continuous manner.
Time dependent	A parameter or variable depending on time. In this case, the parameter is instantiated as a dataseries.
Scenario	Condition of the system environment (e.g., weather patterns, demand levels) over the simulation horizon. Multiple scenarios can be evaluated in a single study to capture variability or uncertainty.
Scenario dependent	A parameter or variable depending on the scenario. In this case, the parameter is instantiated as a dataseries.