<p>We compared 16 life-cycle environmental impacts, covering emissions to air, land and water environments, for three plausible grid-mix evolution scenarios between 2023 and 2050 in the ERCOT electric power system in Texas. All environmental impacts were assessed for local and global supply chains needed for each generation technology. Each generation-mix scenario was required to remain reliable over this period, as tested using an hourly cost production (dispatch) model in 5-year increments from 2030 to 2050. To isolate the impact of changing generation mixes, we kept all other key assumptions (e.g., demand growth and fuel prices) the same across the three scenarios. Results indicate tradeoffs across 16 environmental categories. Given global supply chains and different timing of capacity expansion and retirement under the three scenarios, these impacts were distributed temporally and spatially. Most impacts are local and realized in the short term, whereas climate change and ozone depletion are global and occur over longer term. Although many environmental impacts from wind, solar, and battery storage technologies were higher during the upstream phase (resource extraction and processing, equipment manufacturing, plant construction), thermal power plants that combust coal and natural gas exhibited significant impacts during the operation phase and, in some categories, exceeded impacts from wind and solar power plants over their entire life cycle. These tradeoffs are valued differently by host communities, which can delay and increase costs of projects and undermine the effectiveness of energy-transition policies.</p>