How three battery types work in grid-scale energy storage systems

Date: Mar 19, 2019

A typical lithium-ion battery system can store and regulate wind energy for the electric grid.

A typical lithium-ion battery system can store and regulate wind energy for the electric grid.

Back in 2017, GTM Research published a report on the state of the U.S. energy storage market through 2016. The study projects that by 2021 deployments of stored energy — a combination of residential, non-residential, and utility systems — will grow to over 2 GW, over 10 times greater than current levels. Such a drastic increase in deployment would, according to estimates, lead to an energy storage market worth $2.8 billion.

David Hart and Alfred Sarkissian of George Mason University studied grid-scale batteries in the United States and reported their findings to the U.S. Department of Energy in 2016. One major takeaway from the study stated that lithium-ion batteries accounted for about 95% of deployed systems in the grid-scale battery market. Since that time, however, redox-flow and zinc-hybrid ion batteries have emerged as significant technologies in the market.

Although utility-scale energy storage installations saw a slight drop in the first three quarters of 2018, the industry is expected to gain momentum this year. Storage systems may support renewable projects such as wind and solar, by regulating the variability of these energy sources and increasing reliability to deliver on-demand power.

There are performance-specific features and applications for each of these battery systems, however, the goal of energy storage developers is the same: to choose a battery application that will ensure an affordable, reliable, and efficient energy-storage system.

Lithium-ion batteries
Lithium-ion (Li-ion) batteries were introduced commercially by Sony in 1991 for use primarily in consumer products. Since then, they have become the most widely used battery technology for grid-scale energy storage. Lithium-ion batteries have the versatility to handle smaller-scale applications, such as powering electric vehicles, as well as grid-scale applications requiring megawatts of power for hours at a time.

Li-ion batteries get their name from the transfer of lithium ions between the electrodes, both when energy is injected for storage purposes and when it is extracted. Instead of metallic lithium, Li-ion batteries use lithiated metal oxides as the cathode (the negatively charged electrode by which electrons enter a device), and carbon typically serves as the anode (the positively charged electrode by which electrons leave a device). Unlike other batteries with electrodes that change by charging and discharging, Li-ion batteries offer better efficiency because the ion movements leave electrode structures intact.

Within the lithium family there are a variety of different chemistries and designs from numerous suppliers. Innovation and manufacturing volume have continued to yield improvements in cost, energy density, and cycle life.

For storage durations of 30 minutes to three hours, lithium batteries are currently the most cost-effective solution, and have the best energy density compared to the alternatives. For longer durations, lithium may or may not be the most cost-effective choice depending on the application, particularly when considering lifetime costs. Lithium batteries are also highly configurable into a variety of string sizes and battery racks to create a wide range of voltages, power ratings, or energy increments. This allows for application-specific designs that can range from a few kilowatts with a few minutes of storage, up to multi-megawatt solutions with hours of storage that may be used at a utility substation or a wind farm.

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