Researchers assess the value and role of long-duration energy storage technology in securing a carbon-free electric grid.
Nestor Sepulveda, Ph.D. ’20 says that “the overall question for me” is “how to decarbonize society most affordably.” He was a postdoctoral researcher at MIT and an MIT Energy Initiative (MITEI) member. He collaborated with a team for several years to determine which combination of energy sources would most effectively achieve this goal. Dharik Mallapragada is a MITEI research scientist. He says the group’s initial studies showed that energy storage technologies could be more cost-effectively used for extended periods than lithium-ion batteries.
Sepulveda and Mallapragada offer a detailed cost-performance evaluation of LDES technologies for transforming energy systems in a paper published in Nature Energy. LDES is a term that refers to a variety of emerging technologies that can respond to variable outputs of renewables. They discharge electrons for days or weeks and provide resilience to an electric grid ready to deploy large amounts of solar and wind power.
“If we want overwhelmingly to wind and solar power for electric — which is becoming an increasingly affordable way to reduce carbon emissions — then we must deal with their intermittency,” Jesse Jenkins SM’14, PhD’18, assistant professor of mechanical and aerospace engineering and the Andlinger Center for Energy and the Environment, Princeton University, and former researcher at MITEI.
The researchers examined whether LDES could be paired with renewable energy sources and short-duration energy storage options such as lithium-ion batteries to power a significant and cost-effective transition towards a decarbonized grid. LDES could even eliminate the need to have available-on-demand (or firm) low-carbon energy sources such as nuclear power or natural gas with carbon capture, sequestration, etc.
Sepulveda is a McKinsey and Company consultant. “The message here was that innovative and low-cost LDES technologies could potentially make a deeply decarbonized electric system more affordable and reliable,” he says. He notes that it is still better to have reliable, low-carbon energy sources.
Jenkins and Mallapragada are not the only coauthors of the paper. Aurora Edington SM ’19 was a MITEI research assistant during this research and is now a consultant with The Cadmus Group. Richard K. Lester, former head of The Department of Nuclear Science and Engineering, is MIT’s Japan Steel Industry Professor and associate professor.
Lester says, “As the world focuses more seriously on how to reach deep decarbonization goals over the next decades, the insights from system-level studies will be essential.” This work will benefit researchers, innovators, investors, and policymakers.
Performance and cost
The team was tasked with assessing the effects of LDES solutions in a hypothetical electric system that reflects real-world conditions. In this environment, technologies are not evaluated based on their attributes but on relative value compared to other energy sources.
Sepulveda says, “We must decarbonize at an affordable price to society. We wanted to know whether LDES can increase our chances of success while decreasing overall system cost.”
The team used GenX, an earlier electricity system expansion model developed by Jenkins and Sepulveda at MIT, to achieve this goal. The simulation tool allowed the team to assess the system impact of LDES technologies. This included technologies that are currently in development and those that could be. It also provides for the evaluation of alternative future low-carbon electricity grid scenarios. These scenarios will differ regarding the cost and performance of renewable generation, firm generation, and other electricity demand projections. Jenkins said that this study was the first to extensively use an experimental method that applied wide-scale parametric uncertainty and long-term system-level analysis and evaluated and identified target goals regarding cost- and performance for new long-duration energy storage technology.
The researchers reviewed long-duration technologies, some of which were supported by the U.S. Department of Energy’s Advanced Research Projects Agency–Energy (ARPAE) program. They then analyzed five key parameters, encompassing a range of chemical, thermal, and electrochemical approaches. These include pumped hydropower storage, vanadium-redox flow batteries, and aqueous sulfur flows batteries.
Jenkins explains, “Think about a bathtub. The parameter of energy storage capability is analogous to that of the tub.” Another critical parameter, charge capacity, refers to the size of a faucet that fills the tub. The discharge power capacity is the size of the drain. Each attribute can be sized independently in the most generalized LDES technology. Jenkins says that LDES technology can optimize an energy system that is more economically viable and produces a less carbon-intensive grid. The researchers discovered that energy storage cost is the most critical parameter.
Edington says, “for a comprehensive assessment of LDES technology design, its economic value to carbonized grids, nearly 18,000 distinct cases were evaluated.” These varied in load and renewable resource availability as well as northern and southern climates, various combinations of LDES technologies, LDES design parameters, and the choice of low-carbon stretched resources.
These are some of the key findings from the rigorous analysis by the researchers:
- LDES technologies offer more than a 10% reduction in the deeply decarbonized electricity system costs if the storage cost (the cost of increasing the bathtub’s size) is below $20/kilowatt hour. If the energy cost of future technologies drops to $1/kWh, and as high as 50% for the best combinations in space modeling parameters, this value could rise to 40 percent. The current storage capacity cost for batteries is approximately $200/kWh.
- LDES must cost less than $10/kWh to replace nuclear power. LDES must cost less than $1/kWh for all power options.
- It will be more challenging in northern latitudes for the firm generation to be displaced under any future cost and efficiency range of LDES technologies than in scenarios that include extensive transportation electrification. This is due to higher peak electricity demand due to heating requirements in colder climates.
Get actionable insights
The researchers believe that the insights they have gleaned from their research can be used to make an immediate impact.
Mallapragada says that LDES technology can help people see how their technology will fit into the future electricity mix. It’s a call to action in policy and investment for innovation. We show where technology gaps are and where we see the most significant potential for LDES technology development research.
LDES technologies are not all equal. LDES cannot be relied upon as the only way to increase wind and solar quickly in the short term or to allow a transition to a zero-carbon economy by 2050.
Sepulveda says, “We show how promising LDES technology could be.” “But, we also demonstrate that LDES technologies are not the only solution and can be used to complement firm resources.”
Jenkins immediately spots niche markets for LDES, such as areas with lots of solar and wind power and limited transmission to export this power. These locations allow storage to fill up when the information is exhausted and export power later while maximizing power line capacity. He believes LDES technologies will significantly impact the economy by the 2040s. Natural gas dependence might be eliminated.
He says, “We must develop LDES and other low-carbon technologies in this decade to offer real alternatives to policymakers.”
Jenkins is addressing this urgent need at Princeton and Mallapragada MIT. They are currently working to develop and evaluate technologies with the most significant potential for storage and energy fields to accelerate the zero-carbon goal. They are also making ARPA-E’s state-of-the-art GenX electric system planning model open-source for the public with support from MITEI and MITEI. Sepulveda says that if their modeling and research can help developers and policymakers determine the most effective designs, “We could have an affordable decarbonized system if things are done right.”