The Impact of Electricity Storage on Energy Sector Emissions

The composition of the U.S. electrical power system reflects competing objectives, as investments are driven by ratepayers who demand access to electricity that is both low cost and reliable. Maintaining generation ready for fluctuations in demand currently requires the inefficient use of generation assets, driving up total energy system costs. During the night, low demand for electricity can force the underutilization of wind farms and baseload coal-fired plants. During the day, load-following natural gas-fired plants are often operated at partial capacity so they can be ramped up to track changing demand. One means to address these two issues is electricity storage. Electricity storage technologies are capable of shifting surplus low cost nighttime electricity to times of higher daytime demand. Whether time-shifting electricity storage technologies may enable lower energy system costs depends upon the parameters of these technologies and future conditions. In this study, a least-cost optimization energy model (MARKAL) managed by U.S. EPA is used to explore the potential future role of electricity storage under varying conditions. Scenarios model a stricter national renewable portfolio standard (RPS), varying natural gas prices, and a national limit on CO2 emissions from the energy system. Scenario results are analyzed to discern the impact of electricity storage on generation output and on the associated energy sector emissions of CO2, SO2, NOx, and PM10. Four trends emerge when examining the impacts of time-shifting electricity storage on the national energy system. First, electricity storage enables an increasing utilization of baseload generation and a corresponding decreasing reliance on daytime load-following generation. Second, and to a lesser degree, nighttime natural gas-fired generation increases, making use of existing capacity. Third, the overall decreasing natural gas use by load-following generation leads to the increasing use of natural gas in the industrial sector. Fourth, the use of time-shifting electricity storage does not result in net increases of electricity output from renewable power sources. The impacts of these four trends on generation investments and emissions vary by the future conditions modeled. In many instances the use of electricity storage results in a less expensive energy system with higher emissions of CO2, SO2, NOx, and PM10.