The report “Glass Half Full: Building a Decarbonized US Power Sector” published by MIT Center for Energy and Environmental Policy Research assesses how much the current policy environment preserves the benefits of the prior policy environment, situates those modeled results within the real-world forces shaping delivery, and draws out what the findings imply for future policy priorities and public spending. The report further uses Energy Innovation’s Energy Policy Simulator (EPS) to compare two modeled scenarios of the US power sector: a current scenario defined by the OBBBA without the Biden-era Environmental Protection Agency regulations (“OBBBA scenario”) and a prior trajectory defined by the IRA with those regulations intact (“IRA trajectory”). The analysis focuses on the 2025-2035 window, when the gap between the scenarios grows fastest and today’s policy decisions can most directly shape the outcome. 

The analysis suggests:

  • The Glass is more than Half Full: across the three dimensions of power-sector decarbonization – clean electricity, fossil electricity, and emissions reductions and the substantial majority of the IRA trajectory’s benefits remain under the OBBBA scenario. The OBBBA scenario preserves 74 percent of new clean energy capacity, 71 percent of new clean generation, and 67 percent of emissions reductions that the IRA trajectory would have delivered relative to 2021 over 2025–2035. Fossil capacity barely diverges between scenarios (OBBBA scenario 4 percent above IRA trajectory), while fossil generation is 19 percent higher. 
  • The clean shortfall concentrates in a few mature technologies, with onshore wind comprising the majority of it and being the sole metric that fails the Glass Half Full test. In both scenarios, wind, solar, and storage account for all of the new clean capacity, and therefore all of the shortfall – because the model registers essentially zero new nuclear, geothermal, or hydropower under its cost and performance assumptions. 
  • The OBBBA scenario’s larger emissions come from higher fossil utilization and a dirtier fleet composition, not new fossil buildout. The clean gap is filled by running the existing fossil fleet more. Coal retires more slowly than it would have under the IRA trajectory’s regulations, while gas capacity is actually 3 percent higher under the IRA trajectory. 
  • These modeled results sit adjacent to real-world context that falls outside the model’s scope. 
  • The Glass Half Full result matters because it suggests that the next era of policy should seek to be additive to existing policy, not rebuild what was lost. The OBBBA–IRA gap is inherently limited: both scenarios have the same ceiling on how fast clean energy can be permitted, sited, built, and interconnected. Alleviating supply-side barriers, primarily through permitting reform and transmission buildout, would lift that ceiling, rapidly increasing deployment speed and lowering costs. 
  • The analysis directs policymakers’ attention to two goals. The first is to unleash clean energy supply and the second goal is to close the emissions gap. Both goals share a single answer: build.  The clean gap closes by building more renewables and storage, which compose the entire modeled shortfall. The emissions gap closes by building the clean firm capacity that the fossil fleet’s eventual retirement requires. Because the fossil fleet’s size is sticky and its output highly flexible, the only path to decarbonization is to build the clean generation that runs it less and the clean firm that lets it retire. 

Access the report here