Effects of grid-scale electricity storage on system carbon dioxide emissions as power systems decarbonize

Grid-scale electricity storage (hereafter “storage”) could be a key technology for deeply decarbonizing the electric power system.1,2 However, the net effect of storage on system CO2 emissions largely depends on which... [ view full abstract ]

Grid-scale electricity storage (hereafter “storage”) could be a key technology for deeply decarbonizing the electric power system.^1,2 However, the net effect of storage on system CO₂ emissions largely depends on which power plants charge and are displaced while discharging the storage unit.³ Consequently, storage could actually increase system CO₂ emissions, as demonstrated by several studies using historic CO₂ emission and electricity price data across the U.S.⁴ Since studies have focused on historic or decarbonized power systems, how storage will affect system CO₂ emissions as power systems shift from historic to decarbonized systems remains unclear. This knowledge is critical to understanding the lifetime effect of storage on system CO₂ emissions and the timing at which storage would begin contributing to CO₂ emission reductions. To begin to fill these gaps, this research will focus on three questions. 1) Where, with respect to generator fleet composition, is the transition point from storage increasing to decreasing system CO₂ emissions? 2) When, for a given generator fleet trajectory, would storage have no net effect on CO₂ emissions over its lifetime? 3) How does the effect of storage on CO₂ emissions change when storage participates in energy versus reserve markets? To answer these questions, we will jointly apply two power system optimization models to the Electric Reliability Council of Texas (ERCOT) system. To forecast generator fleet additions and retirements over time, we will use a capacity expansion (CE) model that meets demand and reserve requirements by adding generators to an existing fleet while minimizing fixed and variable costs. To determine detailed system operations and system CO₂ emissions with and without storage, we will run the fleet output by the CE model in a unit commitment and economic dispatch (UCED) model that meets hourly electricity demand and reserve requirements while minimizing total energy and reserve costs and enforcing unit-level constraints. Via scenario analysis, we will test the sensitivity of our results to several factors, including natural gas prices, wind and solar capital costs, and storage unit type. Additionally, to compare how the effect of storage on system CO₂ emissions changes with storage operations, we will consider scenarios in which storage provides only energy, only reserves, or energy and reserves.

REFERENCES

(1)     Mileva, A.; Johnston, J.; Nelson, J. H.; Kammen, D. M. Power system balancing for deep decarbonization of the electricity sector. Appl. Energy 2016, 162, 1001–1009.

(2)      Sisternes, F. J. De; Jenkins, J. D.; Botterud, A. The value of energy storage in decarbonizing the electricity sector. Appl. Energy 2016, 175, 368–379.

(3)      Arbabzadeh, M.; Johnson, J. X.; Keoleian, G. A.; Rasmussen, P. G.; Thompson, L. T. Twelve Principles for Green Energy Storage in Grid Applications. Environ. Sci. Technol. 2016, 50, 1046–1055.

(4)      Azevedo, I. M. L.; Hittinger, E. S. Bulk energy storage increases United States electricity system emissions. Environ. Sci. Technol. 2015, 49, 3203–3210.