NREL: REopt Targets Emissions for Tomorrow’s Cleaner, Healthier Built Environment

The REopt® web tool is a techno-economic decision support platform used by researchers to optimize energy systems for buildings, campuses, communities, microgrids, and more. Users enter site-specific data to determine the optimal size and combination of energy systems to maximize cost savings while meeting resilience or energy performance goals.

With the current administration’s ambitious new goals to reduce economy-wide greenhouse gas (GHG) emissions to 50% below 2005 levels by 2030, there is no time to waste in optimizing our energy systems for tomorrow’s built environment. In response, REopt has greatly expanded emissions accounting functionality to support industry and government in making smart energy investments—while also helping tackle the climate crisis. Users can now model climate and health-related emissions and their costs to consider the impacts of potential future carbon emissions costs, quantify environmental justice considerations related to emissions, or set renewable energy or emissions reduction targets for their site.

Clear Eyes on Clear Skies: Sharpening the Focus on Emissions for Environmental and Energy Justice
REopt already allows users to quantify the hourly impact distributed energy systems have on “year one” carbon dioxide (CO2) emissions (by offsetting grid-purchased electricity or on-site fuel burn). With the newest version of REopt, planners, engineers, and energy and facility managers can also model and optimize:

Health-related emissions from grid-purchased electricity and on-site fuel burn—a key consideration for energy justice and local health impacts of our electricity systems
Total life cycle emissions, which factor in future changes in grid emissions intensity—a more dynamic metric offering insights as to how a new distributed energy system will perform in our wider energy ecosystem in the decades to come
Optional total life cycle emissions costs to estimate potential social, climate, and public health cost savings related to the project’s CO2, NOx, SO2, and PM2.5 emissions impacts
Least-cost pathways to achieve a renewable energy or emissions reduction target at a particular site and quantify the associated investment and savings
Flexible renewable energy and emissions accounting methodologies, with options to include or exclude exported clean electricity as an emissions offset and/or in renewable energy calculations—allowing users to tailor their analysis to varying GHG or renewable energy policies or research approaches.
In developing new REopt capabilities, National Renewable Energy Laboratory (NREL) engineers Kathleen Krah and Amanda Farthing have been researching applicable policies and data sets needed to make the tool usable for stakeholders across the United States.

According to Krah, “It’s been interesting to learn about the emissions rates and factors—especially where the data is coming from and the renewable energy and emissions modeling and accounting approaches.” The REopt team currently leverages the U.S. Environmental Protection Agency’s Avoided Emissions and Regeneration Tool (AVERT) for regional hourly grid emissions profiles and allows users to assume a fixed annual percentage change in emissions rates, applied to each timestep. In the future, the team hopes to incorporate NREL’s Cambium data sets, which contain projected long-run marginal emission rate estimates through 2050 for the contiguous United States.

Farthing says the team was surprised by the relative cost of health-related emissions impacts compared to CO2 emissions impacts, explored in a forthcoming study. “They’re both significant and part of the national conversation, but health-related emissions costs aren’t as frequently discussed as a social cost of carbon. It surprised me that those costs ended up being so substantial.” By default, the location-specific health costs in REopt currently draw from the Estimating Air pollution Social Impact Using Regression (EASIUR) model developed at Carnegie Mellon University. Looking forward, the team would like to explore more detailed health impacts by accounting for the expected location of marginal power plants and their proximity to communities.

Tailoring Analysis to Individual Clean Energy Goals
REopt users can tailor their analyses to help them pursue different types of clean energy goals. These include, for instance:

Percent renewable electricity targets, to help users answer a question such as, “How do I achieve a 25% renewable electricity target at my site at the lowest cost?”
Percent climate emissions reduction targets, to help users answer a question such as, “How do I reduce my site’s CO2 emissions by 50% with an investment in distributed energy resources, relative to current operations?”
Climate and/or health emissions costs, to help users answer questions such as, “How does the cost-optimal system change if I consider the costs of climate and health emissions?”
New REopt capabilities address a growing desire to assess the climate and health impacts of buildings’ energy use, and the emissions savings that can result from investment in distributed energy resources.

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