The intermittency of solar photovoltaic and wind-based power plants places a significant burden on natural gas power plants, requiring that they ramp up and down quickly to compensate for unexpected changes in renewable electricity supply. Natural gas plants operate most efficiently with the lowest emissions per unit power at their peak output, not while operating at part power or while ramping up and down in power substantially. At high turn-downs ratios, or under fast ramping rates, these plants exhibit increased fuel consumption, higher greenhouse gas and air pollution emissions, lower longevity, and higher maintenance costs. Gaia Energy Research Institute (Gaia) proposes to develop thermodynamic, techno-economic, and environmental impact models to identify how to best integrate a new type of long-term storage device, reversible fuel cells, with natural gas power plants to reduce these impacts and improve their performance. A main technical objective of the Phase I project is to develop system designs for integrating hydrogen-based reversible fuel cells with natural gas power plants in an efficient and cost-competitive way. Another main objective of the Phase I project is to down-select to the most cost-competitive, effective configurations for integrating the reversible cells with these gas plants, and to finalize a system design configuration to be implemented in Phase II. Gaia proposes to identify optimal ways to integrate 3 different types of reversible fuel cells with natural gas plants through computer simulation of the (1) thermodynamics, (2) economics, and (3) environmental impacts of these cells with gas plants. Gaia will (1) Gather relevant engineering, economic, & environmental performance data; (2) Develop thermodynamic, techno-economic, and environmental impact models; (3) Develop design scenarios, run simulations, and search for optimal configurations; and (4) Down-select to the most optimal configuration for demonstration in Phase II. Gaia will identify optimal designs for integrating these three cell types with natural gas plants. These optimized design configurations will reduce emissions in the U.S. by millions of tonnes per year. They will breathe new life into natural gas power plant assets, by allowing these plants to smoothly transition from natural gas fuel to 100% renewable H2 over time. The intellectual property from this work will be licensed to benefit gas plant operators globally.