U.S. Energy Storage Produces More Emissions, Not Less
The failure to put strategic thought into the use of batteries and other energy storage technologies in the United States means the technologies are enabling more fossil-generated electricity that produces more greenhouse gas emissions, veteran climate columnist David Roberts reveals in a recent post for Vox.
“In and of itself, energy storage is neither clean nor dirty—it is neutral, as likely to boost the revenue of fossil fuel plants as it is to help clean energy,” Roberts writes. So “if policy-makers want to use it as a tool to enable clean energy, they need to be conscious of its characteristics and smarter about its deployment.”
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That hasn’t happened to date, Roberts contends, citing a paper in the journal Environmental Science & Technology by Eric Hittinger of the Rochester Institute of Technology and Inês Azevedo of Carnegie Mellon University. And not for any reasons that are intrinsic to the technologies themselves.
“If deployed strategically, energy storage can do all the things boosters say, making the grid more flexible, unlocking renewable energy, and reducing emissions,” he explains. But two main issues complicate the picture.
First, storage is mostly used in the U.S. to buy low and sell high, delivering electricity during peak periods when it’s more expensive and profitable. So if a battery bank draws cheap power from coal plants operating overnight, when demand and prices are low, then sells it during the day when it can command a higher price, the transaction supports coal against a less carbon-intensive alternative (Roberts’ example is combined-cycle gas plants).
The second challenge is the proportion of the electricity produced by the original generator that is lost in transmission to and from the storage device. The “round-trip efficiency” of energy storage ranges from 40 to 90%, Roberts says. So even at a relatively optimistic 80% efficiency for lithium-ion batteries, it takes 1.25 megawatt-hours of generation to produce 1.0 MWh for storage.
The net result is that “the more energy that gets stored, the more generation has to increase to compensate for the round-trip losses,” Roberts writes. “If the generation that increases to compensate for the losses is more carbon-intensive than the energy that storage displaces, net emissions nudge up.”
Even when a battery stores renewable power, he adds, it doesn’t increase the amount of renewable power available, unless that power would have been shut out of the grid to accommodate other, non-renewable generators in the absence of storage.
The resulting picture is complicated for renewables and storage. “To avoid increasing emissions, it’s not enough that the energy stored is less carbon-intensive than the energy displaced. It has to be a lot less carbon-intensive,” Roberts states—20% cleaner in his example, just to break even. Current state policies “encourage storage without reference to timing or location”, leaving Hittinger and Azevedo to estimate carbon dioxide emissions from today’s storage facilities at 104 to 407 kilograms per MWh of delivered energy, compared to about 500 for gas plants and 950 for coal.
Roberts cites an Institute for Policy Integrity study that suggests three pathways to shift the system: pricing carbon to “internalize the externalities” for storage providers, eliminating barriers to introducing energy storage, and allowing storage to produce revenue from all the “value streams” it offers—from relieving grid congestion, to helping grid operators avoid costly distribution system upgrades. Hittinger and Azevedo “suggest revising the federal investment tax credit (ITC) to favour storage located next to renewables that are likely to be curtailed,” he writes.
Roberts says most observers see well-functioning energy markets as the best way to get storage right. “I am not opposed in principle to technology-specific public policies—far from it!” he writes. But he urges decision-makers to “put in place a market that values carbon, capacity, ramping, voltage regulation, and all the other services storage can provide, lower barriers to entry, set up transparent rules, and let profit-seeking companies battle it out. That market will be better at determining the proper amount and location of storage than any group of policy-makers.”