City-based Optimization Model for Energy Technologies (COMET)

On this page:

• What is COMET?
• Who should use COMET?
• What are the benefits of using COMET?
• COMET Architecture and Key Components
• How do I get COMET?
• Documentation and User Guidance
• COMET - NYC
• Additional Resources

What is COMET?

City-based Optimization Model for Energy Technologies (COMET) is an advanced open source modeling tool designed to address the complex interplay between energy systems, environmental impacts, and economic considerations at the local level, more specifically cities and/or counties. COMET provides a comprehensive framework for analyzing the entire energy lifecycle—from the introduction of energy sources to their conversion into useful energy forms that meet end-use energy service demands.

COMET is particularly valuable for long-term strategic planning, allowing users to explore the evolution of energy technologies over the next 40 to 50 years. By simulating various scenarios, the model offers insights into how cities can balance their energy systems costs and emissions under different assumptions. This helps municipalities to achieve emissions reduction targets, develop practical and applicable energy policy solutions, and provides a clear picture of potential future energy landscapes.

COMET's scenario analysis capabilities are crucial for assessing trends in air and greenhouse gas (GHG) emissions, exploring the impact of technology adoption, fuel switching, and energy efficiency improvements. Additionally, the model helps identify unintended environmental consequences and potential co-benefits of changes in the energy system, making it a vital tool for holistic policy evaluation.

Who should use COMET?

Local and regional authorities, especially in major cities, are facing many challenges caused by climate change, urbanization, limited natural resources, and aging infrastructure. At the same time, cities are interested in reducing emissions and promoting sustainable urban development while stimulating economic growth. Given a limited number of resources, local planning, energy, or environmental agencies in any city can benefit from systematically evaluating multiple potential strategies for achieving economic and environmental goals related to energy needs.

COMET is designed and built to help urban/regional planning agencies and other stakeholders to:

• Evaluate the long-term economic and environmental benefits of technology and infrastructure deployment strategies.
• Understand the environmental and health implications of energy supply and use in their regions.
• Analyze which energy resources and technologies may contribute to achieving current and future environmental goals.

COMET empowers cities, particularly medium- and large-sized ones, and counties to explore and optimize energy technology solutions to meet their long-term energy demands and emissions reduction targets. By simulating various scenarios, the model provides valuable insights into how energy systems can be balanced, and how costs and emissions might evolve under different conditions. This information is crucial for city officials and stakeholders aiming to make informed policy and program decisions.

What are the benefits of using COMET?

COMET offers a wide array of benefits to city planners, policymakers, and stakeholders by providing a robust platform for evaluating and optimizing energy systems. Here are some of the key advantages:

Comprehensive Scenario Analysis for Long-Term Planning: COMET allows users to explore a variety of future technology scenarios and their impacts on air pollutant and greenhouse gas (GHG) emission levels. By simulating different pathways, cities can identify the most effective strategies for reducing emissions and improving air quality. This long-term perspective helps cities anticipate technological advancements and shifts in energy demand, essential for sustainable urban development and resilience against future challenges.

Cost-Effective Energy Strategies: The model helps users identify cost-effective and environmentally friendly energy strategies for electric generation and meeting the end-use service demands for transport and buildings. By determining the least-cost pathways for energy supply and demand, COMET helps cities optimize their use of resources, ensuring efficient allocation and reducing unnecessary expenditures.

Customization and Flexibility: Users can tailor their scenarios to include specific targets, such as air pollutant reduction, water availability for electricity generation, and advancements in technology. This customization enables decision-makers to address unique local challenges and opportunities.

Enhanced Decision-Making: Energy system technologies, emissions, and environmental and health impacts are interrelated. COMET provides insights into potential trade-offs and synergies. These insights would enable decision-makers to examine their policy options holistically, ensuring that they maximize environmental and health benefits while minimizing negative impacts. 

Stakeholder Engagement: The insights gained from COMET's analysis can be used to engage and inform stakeholders, fostering collaboration and consensus-building around energy and environmental policies.

Adaptability to Local Contexts: COMET's flexible calibration capabilities allow it to incorporate location-specific data, making it adaptable to the unique characteristics of each city. This ensures that the analysis is relevant and actionable for local contexts.

COMET Architecture and Key Components

The generalized version of COMET, called Generative COMET, was developed after deploying a tailored version of COMET in New York City. Generative COMET incorporates innovative features that streamline the calibration process to align with official energy or GHG inventories, based on the level of detail available in city-level data. This modular and adaptable structure enables cities to explore customized strategies for meeting energy demands and achieving GHG reduction targets effectively.

COMET employs a bottom-up energy system optimization approach, integrating detailed technical and economic parameters of various energy technologies. At its core, the model uses the TIMES modeling framework, which is supported by the Energy Technology Systems Analysis Program (ETSAP) of the International Energy Agency (IEA). TIMES is renowned for its ability to analyze complex energy-related issues, including technology transitions, energy security, and climate policy strategies.

Key Components

Reference Energy System (RES): This component serves as the backbone of the model, representing the entire energy system from resource supply to end-use demand. It includes various technologies for resource extraction, conversion, processing, and demand fulfillment, each playing a critical role in transforming energy carriers to meet user needs.

Spatial and Temporal Resolution: COMET models two geographic areas—the city and its electricity grid—allowing for detailed analysis of local energy dynamics. The temporal resolution incorporates milestone years and intra-annual time slices, capturing seasonal and daily fluctuations in energy demand.

Sectoral Scope: The model covers seven sectors—commercial, residential, industrial, transportation, electricity generation, solid waste and wastewater, and energy carrier imports—providing a comprehensive view of the city's energy system.

Data Integration: COMET's flexible calibration capabilities allow it to leverage location-specific datasets, such as building topologies and transportation patterns, to tailor the analysis to each city's characteristics. When detailed local data are unavailable, the model can draw upon regional or national databases, ensuring accurate yet adaptable simulations.

Optimization Goals

As an optimization model, COMET aims to determine the least-cost pathways for meeting energy demands while satisfying environmental constraints, such as emissions reduction targets. It specifies an optimal mix of technologies, identifying cost-effective options to balance energy supply and demand in the long term.
 

How do I get COMET?

COMET runs on Windows. To build, run, and analyze a TIMES model, several software tools have been developed in the past or are currently under development, so that the modeler does not need to provide the input information needed to build a TIMES model directly in GAMS. The model files are ready to be used for VEDA framework. The VEDA framework has extensive documentation. License options are advised for user interface (VEDA) and solver options (GAMS).

Please email us at comet@epa.gov here for your request related to COMET.

Documentation and User Guidance

The COMET model is supported by comprehensive documentation and a user guide, which provide technical guidance for city planners, environmental analysts, policymakers, and others familiar with energy system modeling. These resources cover model structure, functionalities, calibration processes, and potential applications, helping users to directly apply and interpret the model results effectively.

Generative COMET

• Documentation and User Guide
• Model on Data.gov

COMET - NYC

The initial concept of COMET was piloted for New York City due to its immense data sets tailored for buildings and transportation. Built on the TIMES modeling framework, COMET-NYC identifies the least-cost mix of technologies and fuels required to meet projected energy demands from 2010 to 2055 across NYC’s buildings, transportation, and electricity sectors. COMET-NYC is a highly customized model for NYC and distinctly different than Generative COMET.

COMET-NYC uses a scenario-based optimization approach to simulate the deployment of energy technologies under various assumptions, policies, and constraints. The model incorporates local data sources to estimate and calibrate energy consumption and emissions at the borough level. Changes in both greenhouse gases (GHGs) and criteria air pollutants are tracked, supporting city-level climate and air quality policy evaluation.

The model includes detailed modules for the residential, commercial, industrial, and transportation sectors, accounting for current and future technology costs, fuel types, and efficiency parameters. COMET-NYC supports both retrospective analysis (e.g., calibration to 2010, 2015, and 2020) and future scenario exploration, such as electrification strategies.

COMET-NYC is a critical decision-support tool that enables policymakers to evaluate the costs, benefits, and tradeoffs of various technology mixes and policy strategies across NYC’s complex urban energy system. Since 2023, EPA ORD has been collaborating with NYC government on various energy and environment related projects and providing training for staff and researchers. 

• COMET NYC data on Data.gov
• COMET NYC Documentation
• COMET NYC Infographic (.pdf)
• Training

Additional Resources

Highlights

Research Webinar

On August 15, 2023, COMET was featured in an EPA hosted public webinar. Watch the recording: Tools for Helping State and Municipal Decision-Makers Meet Air Quality, Climate, and Energy Objectives: GLIMPSE and COMET

Nature's Science in Shorts Video

A video developed by COMET researchers was selected as one of 50 “science short films” to be featured in Nature’s Science in Shorts video library. The 60-second video highlights research featured in the Nature Energy article, Transportation emissions scenarios for New York City under different carbon intensities of electricity and electric vehicle adoption rates.⁷ 

Watch the video: Electrifying news

Publications and Presentations

1. Wilcox, S., O. Kaplan, AND B. Hobbs. Forecasting the impact of policy and the market on the Big Apple’s gas consumption, infrastructure, and GHG emissions. INFORMS Annual Meeting 2024, Seattle, WA, October 20 - 23, 2024.
2. Kaplan, O. EPA’s City-based Optimization Model for Energy Technologies (COMET) and Applications on Decarbonization Pathways for Cities. EPA - ARC (Atlanta Regional Commission) Meeting, Atlanta, GA, July 31, 2024.
3. Kaplan, O. Application of COMET (City-based Optimization Model for Energy Technologies) to New York City’s Climate Budgeting Efforts. Summer 2024 Semi-Annual IEA's ETSAP Meeting, Bonn, GERMANY, June 24 - 25, 2024.
4. Kaplan, O. EPA’s City-based Optimization Model for Energy Technologies (COMET) and Applications on Decarbonization Pathways for Cities. Briefing to NJ DEP, Trenton, NJ, June 24, 2024.
5. Kaplan, O. City-based Optimization Model for Energy Technologies. U.S. EPA Drivers and Environmental Impacts of Energy Transitions in Underserved Communities Grantee Meeting, Durham, NC, March 13 - 14, 2024.
6. The City of New York Executive Budget Fiscal Year 2025: New York City Climate Budgeting
7. Isik, M., Dodder, R. & Kaplan, P.O. Transportation emissions scenarios for New York City under different carbon intensities of electricity and electric vehicle adoption rates. Nat Energy 6, 92–104 (2021).
8. Isik M, Kaplan PO. Understanding Technology, Fuel, Market and Policy Drivers for New York State’s Power Sector Transformation. Sustainability. 2021; 13(1):265.
9. Kaplan, O. and Isik, M. (2020) “Introducing COMET: City-based Optimization Model for Energy Technologies Application to New York City.” IEA-ETSAP SUMMER 2020 SEMI-ANNUAL MEETING, NA, July 02 - 03, 2020. 
10. Kaplan, O. and Isik, M. (2019) “How Sustainable are New York City’s Buildings and Transportation Policies in the Context of Broader Emissions Reduction Targets?” Brown Bag Webinar (DOE BTO), Boulder, CO, November 05, 2019. 
11. Kaplan, O. and Isik, M. (2019) “Using a bottom-up energy systems model to analyze role of electrification in the end-use sectors in the urban areas.” 2019 USAEE/IAEE North American Conference, Denver, CO, November 04 - 06, 2019. 
12. Isik, M. and Kaplan, O. (2019) “The Performance of NYC’s Transportation Policies in the Context of their 80x50 Targets.” INFORMS Annual Meeting Seattle, Washington, 20-23 October, 2019.
13. Isik, M., J. Pillich, Y. Klein, E. Linky, and Kaplan, O. (2019) “Energy Efficiency Investments in Public Housing:  An Application of the U.S. EPA’s Community Scale Energy Systems Model for New York City.” Presented at Science for Decision-Making in a Warmer World: 10 Years of the NPCC, New York City, NY, March 15, 2019. 
14. Kaplan, O. and Isik, M. (2017) “Overview of EPA Tools for Supporting Local, State and Regional Level Energy and Environment Issues.” South Eastern Environmental Conference, October 29^th -November 1^st, 2017, Orange Beach, Alabama. 
15. Kaplan, O. and Kaldunski, B. (2016) “An Integrated Approach to Water & Energy Infrastructure Decision Making Using the MARKAL Framework: A Case Study of New York City.” 2016 ACEEE Summer Study on Energy Efficiency in Buildings: From Components to Systems, From Buildings to Communities.
16. “New MARKAL Tool Designed to Help Cities Meet Environmental Protection Goals” (2017) EM Magazine, AWMA.