2. Tutorial - Structure of energy system models

While nodes handle the flow of energy in the different grids, they lack the capability to create, consume, and convert energy between grids. Similar to nodes, there is a lot of different ways that units can be made to function, depending on the parameters given in the input data. The most important properties of units are briefly explained below.

• Generation and consumption of energy: The quintessential property of units is the capability to generate energy to a node, or consume it.

• While units can be defined to generate limitless free energy out of thin air, more often the generated energy is defined to increase the consumption of defined fuels (which usually have a cost attributed to them), or have limited generation capabilities based on data (solar, wind, hydro).

• Consumption of energy is treated as “negative generation” when it comes to units, and unless some form of energy conversion is defined for the unit in question, the consumed energy is transferred out of the model boundaries.

• While nodes could be used to emulate some of the functionality of the units, units provide parameters capable of defining the way energy generation and consumption work in much more detail.

• Conversion of energy between grids: While energy can diffuse and be transferred between nodes within each grid, units are currently the only way of transferring (referred to as conversion for units) energy between nodes in different grids.

• This functionality essentially means that a unit can be connected to multiple nodes, and the energy generation and consumption variables in each node are linked to each other according to desired conversion rules and constraints.