Research Publications

Generation of and demand for electricity must match in real time for the electricity grid to operate reliably. To correct for mismatches, system operators deploy a suite of ancillary services, including power system reserves, the focus of this work. The uncertainty of variable resources has potential to create larger mismatches, in turn, requiring reserves to increase with the increase in variable generation. Traditionally, conventional generators provide required reserves, but this can decrease their efficiency. Grid-connected distributed energy storage (ES) is widely seen as an attractive alternative for providing grid reserves due to its responsiveness, flexible, and its potential to increase traditional generator operating efficiencies. To fully understand the environmental impacts of ES for reserves, we coupled life cycle assessment data for battery materials, manufacturing, and end of life (EOL) with a unit commitment and economic dispatch model to simulate power system operations. We determined generator commitment and dispatch by solving an optimal power flow problem for eight grid configurations, with different percentages of wind, solar, coal, and natural gas. We solved the power flow problem with and without ES to determine the changes in generation from each resource attributable to ES. Upstream and EOL environmental impacts were calculated using Argonne National LabÉ__s BatPaC model and their Greenhouse gases, Regulation Emissions, Energy use in Transportation (GREET) fuel cycle model. We found using lithium-ion batteries for reserves actually increased life cycle and operating greenhouse gas, SOx and NOx emissions in nearly all cases examined when using an IEEE 9-bus test system under a variety of assumptions and system configurations. This contradicts common assertions that ES decreases average electricity emissions when combined with variable renewables. The only scenario with consistent reductions life cycle environmental impacts included significant renewable energy curtailment in the case without ES. More specifically we found that grid mix has the most substantial effect on life cycle environmental impacts, driving changes in generator dispatch, in turn, effecting fuel upstream environmental impacts and combustion emissions. In all cases, environmental impacts from dispatch surpass the upstream and EOL environmental impacts of the lithium-ion batteries themselves. Capacity degradation and efficiency degradation had the second largest impacts to grid mix. Our initial assumption of 90% round trip battery efficiency contributed more to environmental impacts then generation mix for at least one grid configurations in all impact categories. To improve the environmental impacts of ES for power system reserves policies need to focus on integration requirements and research should focus on reducing capacity and efficiency degradation, as well as, improving overall round trip efficiency. The next steps in this research include assessing the integration of a variety of strategies into the unit commitment and economic dispatch problem to mitigate environmental impacts of integrating ES. These strategies will include, emissions pricing and capping, as well as, monetizing the health impacts of emissions, which considered location of generation, populations, temporal and spatial dispersion of pollutants to more equitably monetize the impacts of emissions as they effect human health.