This repository contains the MATLAB code and input data used to estimate plant-level emissions and costs for post-combustion carbon capture and storage (CCS) retrofits at U.S. coal and natural gas combined cycle (NGCC) power plants.

Requirements

• MATLAB (R2019a or later; no additional toolboxes required)
• NREL Cambium 2023 dataset (see below)

Repository Structure

McGrid_Dryad/
├── Code/
│   └── CCS_emissions_code.m       # Main emissions and cost model
├── Input_Data/
│   ├── power_plant_geologic_storage_control_technology_parameters.csv
│   └── neighboring_GEA_regions/   # 18 CSV files defining neighboring grid regions
└── Output/                        # Output CSVs are written here after running

Downloading the Cambium 2023 Dataset

The model requires hourly electricity generation data from the NREL Cambium 2023 dataset, which must be downloaded separately and is not included in this repository due to its size (864 files).

1. Navigate to the NREL Scenario Viewer: https://scenarioviewer.nlr.gov/
2. Download the Cambium 2023 hourly data for the following scenarios:
   • HighRECost
   • LowRECost
   • MidCase
3. Place the downloaded files in the following directory structure within Input_Data/:

Input_Data/
└── Cambium_2023/
    ├── HighRECost/
    │   └── Cambium23_HighRECost_hourly_<region>_<year>.csv
    ├── LowRECost/
    │   └── Cambium23_LowRECost_hourly_<region>_<year>.csv
    └── MidCase/
        └── Cambium23_MidCase_hourly_<region>_<year>.csv

How to Run

1. Open MATLAB and set the working directory to McGrid_Dryad/Code/.
2. Open and run CCS_emissions_code.m.

Output CSV files will be written to the Output/ folder at the root of the repository.

Model Description

The model loops over all combinations of the following scenarios and produces plant-level emission and cost estimates for each:

Key Modeling Steps

1. Plant selection: NGCC and coal plants are identified from the power plant database for each of the 18 GEA grid regions. Plants are retired based on assumed lifetimes (52 years for coal, 40 years for NGCC). If no eligible plants exist in a region, neighboring regions are used.
2. Demand allocation: Each plant is assigned a share of regional electricity demand based on its historical generation capacity fraction, scaled to total annual demand from the Cambium hourly data.
3. Emissions calculation: Plant-level emissions (kg) are computed for NOx, SO2, CO2, CH4, N2O, CO2-equivalent, PM2.5, and NH3. For CCS plants under the Full CCS scenario:
   • An energy penalty of 11% (NGCC) or 16% (coal) is applied to account for increased fuel use.
   • CO2 emissions are reduced by the capture efficiency (99%, 95%, or 90%).
   • NH3 emissions from the amine scrubbing solvent are added using emission factors from the literature.
   • Methane leakage from increased natural gas consumption is included for NGCC plants.
   • CO2-equivalent is calculated using GWP values of 30 for CH4 and 273 for N2O.
4. Cost calculation (NOTE: Not used in the publication): Private CCS costs (2024 USD) are estimated for capture, transport, storage, SCR (selective catalytic reduction), and FGD (flue gas desulfurization), discounted at 5% per year. The 45Q tax credit ($85/tonne CO2) is also computed.

Output Files

For each scenario combination, five CSV files are written to Output/:

• emission_results_ngcc_nonccs_combined_...csv — Non-CCS NGCC plants, all regions combined
• emission_results_ngcc_ccs_combined_...csv — CCS-eligible NGCC plants, all regions combined
• emission_results_coal_nonccs_combined_...csv — Non-CCS coal plants, all regions combined
• emission_results_coal_ccs_combined_...csv — CCS-eligible coal plants, all regions combined
• emission_results_all_combined_...csv — All plant types combined

Each file contains the full plant database columns plus the following computed columns:

Missing Data in Power Plant Database

The file power_plant_geologic_storage_control_technology_parameters.csv contains empty cells in three groups. Empty cells have been left blank (rather than filled with a placeholder value) to avoid introducing errors in the MATLAB model, which reads this file numerically. The empty cells and their causes are described below:

PM2.5 emission rate (column 22) - 6 plants
Six plants do not have a PM2.5 emission rate value. This data was not reported for these plants in the eGRID source database and is therefore not available (N/A). These plants are still included in the model; their PM2.5 output emissions are recorded as zero.

Fuel_Specifics (column 23) - 22 plants
Twenty-two plants do not have a value in the Fuel_Specifics column. This field is a descriptive label sourced from eGRID and was not reported for these plants. This column is not used in the emissions model.

GEA region code and geographic attributes (columns 25-43) - 14 plants
Fourteen plants are missing values across all geographic columns (GEA_region_code through y coordinate). These plants could not be spatially matched to a GEA grid region during the GIS spatial join, most likely because they are located in U.S. territories or areas outside the coverage of the GEA region shapefile. Because the model filters plants by GEA region code (column 25), these 14 plants are effectively excluded from all model calculations.

Power Plant Database Column Descriptions

The file power_plant_geologic_storage_control_technology_parameters.csv contains one row per plant (777 plants total). Emission rates are sourced from the U.S. EPA Emissions & Generation Resource Integrated Database (eGRID). Geologic storage distance and cost data are derived from the U.S. DOE National Energy Technology Laboratory (NETL) storage resource databases. All columns are described below.

Neighboring GEA Regions Files

The neighboring_GEA_regions/ folder contains 18 CSV files, one per GEA region. Each file is named neighbors_<REGION>.csv and contains a single column of GEA region codes (integers, no header) listing the regions that are geographically adjacent to the named region. These files are used by the model when a region contains no eligible plants: the model looks to neighboring regions to find suitable coal or NGCC plants as substitutes.

Example: neighbors_CAISO.csv contains the codes for NorthernGrid_South (9), NorthernGrid_West (10), and WestConnect_South (18), which border the CAISO region.

GEA Region Codes