GLEAM: Greenhouse Gas Life Cycle Emissions Assessment Model

The Greenhouse Gas Life Cycle Emissions Assessment Model (GLEAM), developed by NREL, enables the rapid prediction of life cycle greenhouse gas (GHG) emissions from future electricity generation scenarios.

How the Model Works

GLEAM calculates GHG emissions associated with four life cycle stages for electricity generation and storage facilities:

• Upstream: Emissions from resource extraction, material/component manufacturing through construction of generation facilities, such as combined cycle plants, hydropower reservoirs and turbines, and geothermal turbines and fields
• Ongoing noncombustion: Emissions from obtaining, processing, and transporting fuels (the fuel cycle) and facility operation and maintenance
• Ongoing combustion: Emissions from burning fossil fuels
• Downstream: Emissions from plant decommissioning, waste disposal, and recycling.

GLEAM can model more than a dozen electricity generation technologies, from fossil fuels such as coal and natural gas to renewables such as solar, wind, and hydrogen.

GLEAM includes three modules:

• Core life cycle GHG emissions accounting in carbon dioxide equivalent (CO₂e)
• Disaggregated emissions accounting (breaking down CO₂e emissions into constituent GHGs)
• Emissions accounting for combustion of hydrogen and hydrogen blend fuels, including hydrogen leakage.

The core emissions accounting module is mandatory with every GLEAM run, while the other two are optional depending on user preferences.

The model uses a streamlined approach in the core module to calculate GHG emissions by multiplying annual activity data (installed capacity for upstream emissions, generation for ongoing emissions, and decommissioned capacity for downstream emissions) by technology- and life cycle phase-specific emission factors. These factors were developed as part of NREL's Life Cycle Assessment Harmonization project based on a review of over 3,000 published life cycle assessments.

Disaggregated emissions accounting allows users to estimate emissions of individual GHGs (CO₂, CH₄, and N₂O), while the hydrogen/hydrogen blend module is designed to model electricity generation scenarios that include hydrogen combustion turbines.

GLEAM is configured to accept input data from common capacity expansion models, including NREL's Renewable Energy Deployment System (ReEDS) and Sienna, as well as private sector models such as Encompass. It can also accept data from unit commitment models such as PLEXOS.

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