Energy storage is widely cited as a solution to enable increased usage of non-dispatchable and intermittent renewable energy technologies such as wind and solar. While energy storage is essential to increase the penetration of the renewable energy, it may not be always inherently green and its environmental implications could depend on other factors such as the grid mix, energy storage capacity, and the effects of storage operation on the overall electricity generation.
If operated to maximize profit, in many grid situations storage will increase carbon dioxide emissions by enabling a high carbon emitting technology (e.g. coal) to displace a lower one. While some research has been conducted so far on emissions vs. energy storage, effect of bulk energy storage operation as a price maker on the total grid emissions has not been investigated.
This work models the deployment of large, non-marginal quantities of both bulk storage and wind/solar to determine their combined effects on system emissions. Two different grid environments are analyzed: a coal-heavy grid (Midcontinent ISO in the Midwest region) and non-coal grid (New York region), deploying storage as a price-maker. For the current grid mix in New York, adding storage can slightly reduce carbon emissions, while storage increases emissions in the Midwest region. We estimate that adding storage operated to maximize revenue in the Midwest region will not be carbon neutral until renewables reach around 18% of the generation capacity from the current 10%. Different operation patterns for storage could realize higher carbon reductions. For example, a carbon price on emissions from generators would shift operation to make energy storage carbon
neutral even with current wind and solar capacities. Sensitivity analysis shows that a slightly higher natural gas price ($5 per MMBtu) yields much higher storage-induced carbon emissions in both New York and the Midwest. In this case, storage in the Midwest will not be carbon neutral unless 35% of total generation capacity is from wind/solar. This illustrates that low cost, efficient natural gas generation is important to realize emissions reductions with storage under economic arbitrage.