Six questions about long-duration energy storage

energy storage
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Babcock & Wilcox (B&W) is actively engaged in advancing long-term clean energy storage technologies for both immediate deployment and long-term systems up to 100 hours. B&W is part of the U.S. Department of Energy’s National Renewable Energy Laboratory’s (NREL) Duration Addition to Electricity Storage (DAYS) Advanced Research Projects Agency-Energy (ARPA-E) team.

This project focuses on developing an innovative electric particle heater and pressurized fluidized-bed heat exchanger – a long-term thermal energy storage system that stores energy up to 100 hours, and other technologies to allow power producers to store solar or wind energy to generate continuous, reliable, grid-scale power. B&W’s proven and established pressurized fluidized-bed boiler technology is an ideal choice for advancing this technology to commercial operation.

To learn more about long-duration storage, John Meier, Director of ClimateBright Babcock & Wilcox, answers six questions.

Why is long-duration energy storage important?

JM: We need long-duration energy storage because renewables are becoming a larger part of the energy mix, and renewables like wind and solar aren’t available for power generation all the time. Energy storage is needed to bridge those gaps when the sun is not shining and the wind is not blowing to provide consumers a reliable and resilient electrical grid.

What is thermal energy storage?

JM: Thermal energy storage is the process of storing renewable energy in a high-temperature material, such as sand, ceramics, or molten salt. Sand is being used in the NREL DAYS long-duration energy storage project. Sand is an ideal abundant low-cost material since it is chemically stable over a large range of temperatures. The thermal energy in the sand can be later converted back into electricity or steam.

Our current design includes B&W’s pressurized fluidized-bed heat exchanger and will be able to generate up to 135 megawatts of power for up to 100 hours (four days) from stored clean thermal energy with zero CO2 emissions. By facilitating long-term storage of zero-carbon, renewable energy, this technology enables power producers to deliver power to the grid 24-hours a day, including during periods of peak demand, or when solar or wind generation are not optimal.

Why is sand a beneficial energy storage medium?

JM: In terms of availability, sand is plentiful, inexpensive, and environmentally friendly. Sand is also a great energy storage medium. Think of walking across a sandy beach on a hot day. When you walk on your bare feet, you can really feel the heat of the energy stored in the sand. And the sand will hold that energy for a very long period of time.

How does the NREL DAYS technology work?

JM: A sand battery, as these energy storage systems are sometimes called, uses electricity to heat sand via heating elements. The heating elements are arranged in a formation that allows the sand to flow through, coming into contact with the elements and heating it up to 1200°C.

The heated sand is stored in an insulated silo. When we need to recovery the energy, the sand is moved from the silo into B&W’s pressurized fluidized bed heat exchanger. This is a direct contact heat exchanger that blows air up through the sand, causing it to behave like a fluid. The air passing through the sand absorbs the heat from the sand. The pressurized and hot air is then used to drive a gas turbine to generate electricity.

How long can the heated sand be stored for use?

JM: The sand can be stored and used for more than 100 hours. Since sand is inexpensive, adding more thermal storage capacity is incrementally inexpensive. Thermal energy systems such as these can provide 10s to 100s of megawatts of electrical power output.

Are there benefits to thermal energy storage vs. batteries such as lithium ion?

JM: The greatest benefit of thermal energy storage is duration. The current cutting-edge battery technologies such as lithium ion or zinc provide energy for 4 hours – if you want 8 hours, you need two of them at double the cost. Thermal energy storage can provide energy for power generation for hundreds of hours with only the incremental cost of sand to increase the duration of storage capacity.

About John Meier

John Meier is the Director of ClimateBright for Babcock & Wilcox, a leader in energy and environmental products and services for power and industrial markets worldwide. 

Starting with B&W in early 2022, Meier currently supports the commercial advancement of ClimateBright, B&W’s comprehensive suite of carbon capture, hydrogen and other decarbonization products and services designed to help utilities and industry aggressively combat greenhouse gas emissions and climate change while producing clean energy.

Meier has over 18 years of experience controlling emissions from coal-fired utilities and is a subject matter expert in the field of mercury emission reduction with several US patents and numerous publications in the field.  Currently, Meier is responsible for assisting clients throughout Europe and Asia Pacific in developing their decarbonization pathway whether through fuel switching, carbon capture technologies or production of low-carbon fuels with B&W technologies.  While originally from the United States, John currently lives and works in Berlin, Germany. 

John Meier will host “Long Duration Energy Storage: Opportunities and Challenges for Scale-up” at Enlit Europe on 30 November, 2022 at 2:30 p.m.

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