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 energy, 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.
The AEO page contains results from many EIA analysis products that rely on NEMs.
The NEMS documentation page has more details about each module. The Assumptions page contains separate reports about the latest assumptions for each module. The Case Descriptions page explains the cases preconfigured in the repository.
We also publish the World Energy Projection System (WEPS), which we use for global analysis and to support the International Energy Outlook.
The NEMS system contains three main parts:
- A central database to store and pass inputs and outputs between the various components
- Energy modules that represent various demand, transformation, and supply projection activities
- An integration, or convergence, module that determines when the system has reached an equilibrium between supply and demand
NEMS is a modular system. The modules represent each of the fuel supply markets, conversion sectors, and end-use consumption sectors of the energy system. The modular design also allows us to use the methodology and level of detail most appropriate for each energy sector. NEMS executes each of the component modules to solve for the prices of energy delivered to end users and the quantities consumed by product, region, and sector. The delivered fuel prices encompass all activities required to produce, import, and transport fuels to end users. The information flows also include such areas as economic activity, domestic production, and international petroleum supply.
NEMS consists of the following modules:
Four supply modules:
- Renewable Fuels Module (RFM)
- Natural Gas Market Module (NGMM)
- Oil and Gas Supply Module (OGSM)
- Coal Market Module (CMM)
Four demand modules:
- Residential Demand Module (RDM)
- Commercial Demand Module (CDM)
- Industrial Demand Module (IDM)
- Transportation Demand Module (TDM)
Two conversion modules:
- Electricity Market Module (EMM)
- Liquid Fuels Market Module (LFMM)
Four other modules:
- Macroeconomic Activity Module (MAM)
- International Energy Module (IEM)
- Emissions Policy Module (EPM)
- Integrating Module
NEMS calls each supply, conversion, and end-use demand module in sequence until the modeling system reaches an equilibrium between supply and demand. The AEO offers a solution for each year through 2050.
This initial version of NEMS is based on the version used for AEO2023, with updated software dependencies, and updates to several series contained in the restart file.
NEMS development is a year-round process led by EIA. A snapshot of the source code corresponding to the regularly scheduled annual release of the AEO is hosted on GitHub at: https://github.com/EIAgov/NEMS.
NEMS is a computationally intensive 64-bit application, which runs on 64-bit Windows. Our servers that run NEMS have large amounts of RAM to accommodate multiple runs and users simultaneously, but a single copy of NEMS may execute on a single-user system with 4 gigabytes (GB) of RAM.
We run the integrated NEMS run in two parts simultaneously (in parallel) to speed run time, so we use two processor cores per integrated run. If a (non-integrated) run is done with modules off (for example, turning off coal, electricity, and renewables), then we need only one processor core per run. With a quad core processor, you can run two integrated parallel runs or four non-integrated runs with little speed loss if sufficient memory is available. To run two integrated runs or four non-integrated runs in parallel, we suggest 16 GB of RAM. You can run NEMS as one process, but it requires about two hours more per cycle.
One run of all components of the NEMS model, or a cycle, takes about four hours on our servers, but most cases are solved by making a series of cycles. A four-cycle NEMS run takes about 14–18 hours. Runs of some individual parts of NEMS, such as the energy demand models, if run separately, can take only a few minutes. All files of a completed run, input and output, take up about 30 GB of storage, but they compress to about 15 GB once the run finishes.
- Intel® Fortran Compiler Classic and Intel® Fortran Compiler
NEMS was installed using a free download of the 23.2.0 release for Intel Fortran Compiler Classic and Intel Fortran Compiler for Windows (2023.2.1). You can find more information on the Intel website.
- Fair-Isaac Corporation's (FICO) Xpress optimizer (license required)
We use the Xpress optimizer to solve the EMM's Electricity Capacity Planning linear program (LP); the LFMM LP; and the Carbon Transport, Utilization, and Storage mixed integer program (MIP). The Carbon Transport, Utilization, and Storage module is incorporated in the EMM, OGSM, and LFMM. To purchase an Xpress license, please refer to FICO's webpage.
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A Fortran-to-SQLite library to use with EMM that holds regional electricity data. SQLite is not required for running NEMS with the default data provided.
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Optimization and Modeling Library (OML) license from Ketron Optimization with XpressMP barrier interface (optional). The EMM in NEMS uses the OML optimizer.
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GAMS. It is used for the Carbon Transport, Utilization, and Storage submodule and for the LFMM. We used GAMS version 43.2 for this release. Our GAMS implementation uses the Xpress solver mentioned above. We purchased the development license (rather than the run-time license), which allows changes to the linear program matrix during execution of a NEMS run.
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Advanced Integrated Multidimensional Modeling Software (AIMMS). AIMMS is used for the CMM, the NGMM, and the Renewable Electricity Storage Submodule within the EMM. We used AIMMS version 4 (release 4.96.4) for this release licensed with the CPLEX solver. The AIMMS Software Development Kit (SDK), which has a programming interface known as the AIMMSLINK library, has been installed at EIA and is also used with the NEMS CMM. The AIMMSLINK library invokes the AIMMS SDK and is linked in for NEMS runs. The AIMMS SDK is no longer supported by AIMMS.
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(Optional) The S&P Global Macroeconomic Model as implemented with the EViews13 software package. We currently use the EViews13 standard edition. The S&P Global macro module is executed as a subprocess to NEMS if the macro feedback switch in NEMS is turned on. You can elect to run NEMS without macro feedback, in which case the run uses static macroeconomic inputs taken as is. When the macro feedback switch is on, NEMS will attempt to call the macro model by executing EViews using the S&P Global model's work files as the input to EViews. These EViews work files are not included in the EIA archive, but you can obtain them from EIA after licensing the S&P Global model. You must also get a copy of EViews to run the S&P Global model. Contact S&P Global for more information.
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Cygwin for certain NEMS utility programs.
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Programming language R. NEMS uses the programming language R (version 2.15.1). Version 2.15.1 is required for NEMS runtime.
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Python 3.11. The NEMS validator (test suite) and the pyfiler utility are written in Python.
- From the NEMS GitHub repository, clone or download NEMS.
- You can find specific libraries to install as part of Cygwin, R, and Python in a separate document with additional installation details.
The NEMS code, as distributed here, is governed by specific licenses.
You can direct questions about the NEMS model to EIA-NEMS-GITHUB@eia.gov.
As part of developing each AEO, EIA schedules working group meetings to gather input from various sectors of the industry. You can find more information on the AEO Working Groups webpage.
Contributions to NEMS are governed by specific rules. You can direct questions about the NEMS model to EIA-NEMS-GITHUB@eia.gov.