Can energy Storage operation be clean?
REducing system emissions while retaining revenue
Eric Hittinger, Rochester Institute of Technology, 585-475-5312,
Laura M. Arciniegas, Rochester Institute of Technology,
Overview
Energy storage is frequently mentioned as a necessary complement to increasing amounts of variable renewable electricity generation from wind and solar. Furthermore, bulk energy storage[1]is a valuable tool that can aid electricity systems in several important ways: integrating renewables, managing peak demand, reducing the need for new transmission, and providing short-term balancing. However, when used to maximize revenue, the operation of energy storage tends to increase electricity system emissions [1].
In this work, we use a linear programming approach to determine the optimal operation of grid-level energy storage, but apply increasing “carbon fees” to determine how storage operation, emissions, and revenue shift when carbon emissions gain more weight as a decision criteria. We find that, in most regions of the US, storage-induced emissions can be reduced significantly (50% or more) with a small effect on annual storage revenue (10% or less).
Methods
This research models the economic operation of grid-level energy storage at locations throughout the United States, using a perfect-information linear programming approach. CO2emissions resulting from the operation of the energy storage are calculated using the Marginal Emissions Factor (MEF) approach developed by Siler-Evans et al. [2].Two decision criteria are involved: annual revenue and annual CO2 emissions associated with storage operation. These are combined into a single objective function by applying a “carbon fee” to the net CO2 emissions (However, importantly, neither generators nor storage is forced to pay this fee, which simply affects the decision-making of the storage device).
Results
As the CO2 fee increases, storage can respond in two ways: shifting the periods of charging/discharging to hours with lower net effect on carbon emissions, or curtailing the overall operation of storage (note that a storage device that never operates has both zero net revenue and zero net emissions). Our results show that storage initially reduces emissions primarily by shifting charging/discharging periods, which has a small effect on revenue, and only curtails operation when the carbon fee is very high. As a result, the effective cost of emissions reductions is consistently lower than $20/tonne of CO2 for up to 50% reductions.
Figure 1: Annual revenue and emissions of a bulk storage device in 22 eGRID regions of the US. Each line corresponds to a storage device in one region, at varying carbon fees ranging from zero (in upper right) to infinity (lower left). While profit-maximizing storage (the rightmost point of each line) consistently increases system emissions, the low initial slopes show that emissions can be reduced with little effect on revenue.
Conclusions
While storage-induced emissions are a likely outcome of new storage deployments, this effect can be mitigated at low cost if storage operates with concern for its net emissions. An important remaining question is how to achieve this outcome. The easiest method would be an actual price on carbon emissions, which would affect the dispatch of existing generators and, indirectly, the emissions associated with storage. Alternately, storage could be constrained to operate during certain periods or in conjunction with certain marginal low-emissions generators. Regardless of the approach, this work shows that storage emissions are not a necessary result of profitable storage operation, but occur when the emissions effects of storage are neglected completely.
References
[1] Hittinger, E., Azevedo, I.L., Bulk Energy Storage Increases US Electricity System Emissions. Environmental Science & Technology, 2015. 49(5): 3203-3210
[2] Siler-Evans. K., Azevedo, I.L., Morgan, M.G., Marginal emissions factors for the US electricity system, Environmental Science & Technology, 2012 46 (9), pp. 4742–4748.
[1]"Bulk energy storage" refers to energy storage that charges and discharges over the course of hours. These high-energy, low-power energy storage technologies include pumped hydro, compressed air energy storage, and some types of chemical energy storage.