Integrating Module - NEMS Documentation
July 2025
Introduction
The National Energy Modeling System (NEMS) is a long-term energy-economy modeling system of U.S. energy markets. The model is used to project production, imports, exports, conversion, consumption, and prices of many energy products, subject to user-defined assumptions. The assumptions encompass macroeconomic and financial factors, world energy markets, resource availability and costs, behavioral and technological choice criteria, technology characteristics, and demographics.
NEMS produces a general equilibrium solution for energy supply and demand in the U.S. energy markets on an annual basis.
EIA's Office of Energy Analysis develops and maintains NEMS to support the Annual Energy Outlook (AEO). EIA analysts perform policy analyses requested by decisionmakers in the White House; the U.S. Congress; offices within the U.S. Department of Energy, including program offices; and other government agencies. Users outside of EIA use NEMS for a variety of purposes.
NEMS was first used for projections presented in the Annual Energy Outlook 1994.
Scope and organization
Publication of this document is supported by Public Law 93-275, Federal Energy Administration Act of 1974, Section 57(B)(1) (as amended by Public Law 94-385, Energy Conservation and Production Act), which sstates, in part:
...that adequate documentation for all statistical and forecast reports prepared...is made available to the public at the time of publication of such reports.
In particular, this report meets EIA’s model documentation standard 2015-1, established under these laws.1
The individual components of NEMS are documented individually. Although the NEMS Integrating Module is a distinct component of NEMS, the Integrating Module is not by itself a model. Rather, it is a framework that connects the subject matter modules, and a component of the overall NEMS model. The Integrating module implements specific aspects of the overall modeling methodology that are not documented elsewhere. The documentation is organized accordingly.
Readers interested in a more comprehensive summary of NEMS should see the latest The National Energy Modeling System: An Overview.2
Chapter 3 describes the NEMS global data structure, which is used for inter-module communication, solution initialization and storage, and certain database operations.
Chapter 4 provides the mathematical specification for the solution algorithm and describes the convergence techniques we use. Chapter 4 also documents other modeling functions of the Integrating Module, including generation of foresight assumptions and carbon dioxide emission policy routines.
Chapter 5 discusses the NEMS job queue and run management, which are used to manage NEMS runs in a distributed environment.
Chapter 6 discusses the NEMS Report Writer, which produces diagnostic tools and the published output from the model.
Chapter 7 discusses the NEMS validator.
Notes and sources
1 See https://www.eia.gov/about/eia_standards.php#standard2015_1.
2 See https://www.eia.gov/outlooks/aeo/nems/documentation/index.php.