Objective Function
The objective function is the single expression the optimizer maximizes (or minimizes). Every constraint in the model keeps the solution physically feasible; the objective function decides which feasible solution is best. Understanding it is the key to understanding why the model dispatches the way it does.
Energy Balance
Before examining individual assets, it is important to understand how Catalyst couples them together. Unlike models that use a single global power-balance constraint, Catalyst enforces balance implicitly through the bus topology: every connection between two assets is an equality, and the network of equalities collectively ensures that power is never created or destroyed at any point in time.
Grid Asset
The grid asset represents the physical interface between the project and the external network. It enforces power flow limits and, in its tariff variant, monetizes the cost of energy flowing through the connection.
Renewable Asset
The renewable asset — called producer in the model — represents a generation source with an exogenous power profile: typically a wind turbine array, a PV plant, or a run-of-river hydro unit. The optimizer does not control how much power the resource generates; weather determines that. The optimizer decides how much of the available generation to deliver and how much to curtail.
Storage Asset
The storage asset is the most complex component in Catalyst. It models an electrochemical battery with:
Consumer Asset
The consumer asset represents an electrical load that must be supplied with power — for example, an industrial consumer, a building, an EV charging hub, or a hydrogen electrolyzer. The optimizer decides how to route energy to the consumer and, when configured, whether to accept any unmet demand.
Day-Ahead Market
The Day-Ahead market is the primary spot market for electricity. Positions are cleared in an auction held the day before delivery. Catalyst models DA as a price-taking participant: it takes the exogenous DA price $\lambda^_t$ as given and optimizes the volume it sells or buys at each hour.
Intraday Market
The Intraday market allows participants to adjust their positions closer to real-time, after the DA auction has closed. In Germany, the continuous ID market operates up to 30 minutes before delivery. Catalyst models ID using the same mathematical structure as the DA module, with one key difference: how the price input is interpreted.
FCR Market
FCR — Frequency Containment Reserve — is a primary frequency reserve product. Its purpose is to stabilize grid frequency within seconds of a disturbance. A battery commits a symmetric power band (MW) for a block period; the grid operator pays a capacity price for this commitment. If frequency deviates from 50 Hz, the battery automatically activates proportionally, earning additional energy revenue.
aFRR Market
aFRR — Automatic Frequency Restoration Reserve — is a secondary frequency reserve product. Where FCR responds within 30 seconds to contain frequency deviations, aFRR restores frequency to exactly 50 Hz over a longer window of several minutes. The two products complement each other: FCR stabilizes quickly; aFRR corrects precisely.
EEG Market
The EEG module represents the German Renewable Energy Act (Erneuerbare-Energien-Gesetz) feed-in framework. It models the market premium mechanism, under which renewable generators receive the spot market price plus a premium to guarantee a minimum level of remuneration. Two variants are available: a simple model for standalone generators and an advanced model for co-located renewable and storage systems.
Notation & Symbols
This page is a consolidated reference for all mathematical notation used in the Catalyst model documentation. Every symbol listed here appears in at least one of the mathematical-model pages; cross-references are provided for context.