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City-based Optimization Model for Energy Technologies (COMET)

COMET logo

What is COMET?

City-based Optimization Model for Energy Technologies (COMET) is an energy-environment-economic optimization model. COMET is designed to capture the whole energy system at the city level for a user-defined analyses timeline, from the introduction of the energy sources to conversion into useful energy to meet end-use energy service demands.

COMET allows users to examine the next 40-50 years of energy technology evolution. The model provides long-term prospects for practical and applicable energy policy solutions, especially for cities that aim to achieve emissions reduction targets.  The model results reveal how the energy system can be balanced under a different set of scenario assumptions, and how system costs and resulting emissions change with respect to those scenarios.

The insights gained from this analysis will help city officials and their stakeholders better design policies to reduce emissions. The benefits of scenario analysis using COMET include:

  • Assess the full air and greenhouse gas (GHG) emissions trends for a range of mid- to long-range energy scenarios of interest to partners/clients,
  • Conduct scenario exercises to look at medium- to longer-term alternative scenarios and their impact on achieving air quality goals,
  • Explore how modeling can inform how emissions trends in the transportation sector may evolve due to technology adoption, fuel switching, and energy efficiency,
  • Provide insights on unintended environmental consequences and potential co-benefits of changes in the energy system.

COMET is built to be used within the MARKAL (MARKet ALlocation), an energy-environment-economic optimization framework developed by Energy Technology Systems Analysis Programme (ETSAP) of the International Energy Agency. Its purpose is to help determine the technology investment choice and related fuel consumptions for end-use energy demand sectors, such as buildings and transportation. A version of COMET that uses an updated version of MARKAL called TIMES (The Integrated MARKAL-EFOM System) will be available in the near future.

What is the Purpose of 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 pursuing environmental goals while stimulating economic growth.  Given a limited amount of resources, cities 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 (climate and air quality) 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.

Research Approach

COMET is a technologically detailed linear optimization model of the city-scale energy system. The objective function is to minimize the total energy system cost over the planning horizon. The model equilibrates energy supply and demand for each period.

The first application of COMET is being piloted in New York City (COMET-NYC). A series of case studies are being conducted using COMET-NYC. A generic version of COMET applicable to any city using a starter database is currently in development.

What are the Benefits of Using COMET?

COMET can be used to evaluate the effects of alternative future technology scenarios on air pollutant and GHG emission levels. Users can identify cost-effective and environmentally friendly energy strategies for electric power generation and for meeting the end-use energy service demands for transportation systems and buildings.

Users can customize their future energy scenarios to include reduction targets for carbon dioxide emissions, water availability for electricity generation, and advances in technology. Analyzing these scenarios can provide decision makers with a better understanding of how a changing energy landscape will affect future air quality and aid in meeting mitigation targets and adaptation goals.

Energy system technologies, emissions from energy sources, and environmental and health impacts are all interrelated. A change in one area may impact another, either positively or negatively. COMET allows decision-makers to examine their policy options holistically to ensure they are maximizing the environmental and health benefits.

How can I use COMET?

COMET runs on Windows. Currently, COMET is built to be used on the MARKAL energy optimization framework developed by the Energy Technology Systems Analysis Programme (ETSAP) of the International Energy Agency. The team is in the process of converting COMET to be run within the TIMES framework, which is an updated version of MARKAL. Although there are some open-source solver and modeling options, for immediate access, use of MARKAL/TIMES frameworks is advised.



Where can I get COMET NYC data?

The database that includes New York City specific data for COMET can be made available for interested parties. A generic version of COMET for other cities is under development. For additional information and instructions for accessing COMET-NYC, please contact:

P. Ozge Kaplan, PhD, +1-919-541-5069,

User Guide:

COMET User Guide


COMET Infographic

Other Related Publications/Presentations

  1. 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. 
  2. 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. 
  3. 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. 
  4. 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.
  5. 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. 
  6. 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 29th -November 1st, 2017, Orange Beach, Alabama. 
  7. 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.Exit
  8. “New MARKAL Tool Designed to Help Cities Meet Environmental Protection Goals” (2017) EM Magazine, AWMA.