Energy System Graph-Based Representation

This section of the documentation provides an overview of how Locations and Assets are internally represented in Macro, to help modelers create new sectors and assets effectively.

Sector Networks

As mentioned in the Getting Started section, Macro is structured around two main components:

1. Locations: Represent geographical areas with some demand or supply for several commodities.
2. Assets: Represent means of producing, storing, transporting, and consuming one or more commodities. Each asset can be sited at a specific location.

While this high-level view is useful, modeling new sectors and assets often requires a deeper understanding of how Locations and Assets are internally structured. In Macro, the energy system is modeled as a collection of interconnected sector networks. Each sector network includes nodes and edges:

• Nodes: represent the demand or supply for a specific commodity or sector.
• Edges: represent the flow of commodities between nodes.

More importantly, sector networks are connected through elements called transformations. A transformation is a special type of vertex in the full network that connects two or more commodity networks. It represents a physical conversion process, such as an electrolyzer, natural gas power plant, or biorefinery.

So, in the full network, the definitions of Locations and Assets are expanded as follows:

1. Locations: Collection of nodes, each indicating demand or supply for one or more commodities.
2. Assets: Collection of transformation vertices representing conversion processes, storage, and edges connecting nodes across different commodity networks.

Therefore, the high-level figure above can be expanded into the following detailed representation:

This figure illustrates the internal structure of the energy system. Each location is expanded to show sector-specific nodes and edges. Yellow nodes represent demand in the electricity sector, light blue nodes represent natural gas nodes (modeled exogenously in this example), and the grey node represents a CO₂ sink.

The next section outlines the core components of Macro and how they work together to model an energy system.

Macro Internal Components

As seen in the previous section, an energy system in Macro is composed of the following components:

• Vertices: Represent balance equations.

  There are three types of vertices in Macro:

  • Nodes: Represent demand (outflow) or supply (inflow) of a commodity.

  • Transformations: Represent conversion processes. These are special vertices that convert one or more commodity types into one or more other types. Each transformation is defined by a set of stoichiometric equations specifying conversion ratios.

  • Storage: Represent storage systems that hold commodities for future use. The flow of commodities into and out of storage is governed by storage balance equations.

• Edges: Represent the flow of commodities into or out of a vertex.

  Capacity sizing decisions, CAPEX/OPEX, and both planning and operational constraints are associated with edges.

By combining these components, Macro enables the fast and flexible assembly of new technologies and sectors.

In the following sections, we’ll describe how to create new sectors and assets, as well as how to debug and test the resulting system.