New methods of thermal energy storage using hot sand

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An innovative new energy storage technology that uses hot sand is being developed as an alternative in the field of renewable energy technologies. This feeling of warm sand on the soles of the feet is what sparked an investigation into the ability of sand to absorb and retain heat, giving rise to new thermal energy storage processes.1

How sand is now a valuable tool for saving energy. Image credit: Khatib, H

Finding ways to store excess energy produced by renewable technologies is one of the main challenges researchers are trying to overcome. Teams from the National Renewable Energy Laboratory (NREL) and an Italian company, Magaldi Group, recently unveiled new systems to help solve this exact problem.

Endure the heat

NREL researchers named their system ENDURING; a systemic process used to superheat silica sand by taking excess heat from existing wind and solar technologies. Silica sand is subjected to extreme temperatures to generate steam for power generation.

ENDURANT is the abbreviated term for “economical storage of electricity for long periods of time using low cost thermal energy storage and high efficiency power cycle”.2 The system has been developed to solve the aforementioned problem with renewable technology; find an appropriate way to store excess energy when production exceeds demand.

ENDURING has the ability to store energy much like a battery and could be a revolutionary moment in the renewable energy industry. The silica sand is superheated to reach temperatures above 1200 degrees C. It is then introduced into the ENDURING system and transferred to a concrete silo which is insulated for long term storage.

When the stored energy must be released, the sand passes through a heat exchanger which supplies the turbomachines with gas under pressure; this, in turn, spins power generators which can then generate new electricity.

One of the most attractive features of the ENDURING system is its ability to be installed as part of the distribution network. In addition, this system could help phase out traditional coal and natural gas power plants and could even be placed on existing infrastructure at decommissioned sites respectively.

NREL estimates that a single basic system, ENDURING, can store up to 26,000 MWh of thermal energy; equivalent to the annual energy consumption of more than 400 households.

Additionally, the technology could be deployed at costs between $ 2-4 per kWh, making it a low-cost thermal energy storage solution.3

STEM

In Italy, the Magaldi group also heats sand as a viable thermal energy storage system that will consolidate excess solar energy. Based in Salerno, the company has developed its “Stem” system (Solare Termodinamico Magaldi / Solar Thermo Electric Magaldi), which will be used both in Italy and in other areas with a high concentration of solar radiation.

Using heliostats – devices containing one or more mirrors – the sun’s rays are deflected into a steel container filled with sand. The sand contained in these cylindrical steel containers is exposed to temperatures of around 600 ℃, which are then used to generate steam to generate electricity.

Compared to conventional solar panels, Stem can produce power under high temperature conditions as well as when there is little or no sunlight. In addition, the system is considered very environmentally friendly as it uses environmentally friendly materials and can be used at night for power generation.4

Alternative thermal energy storage solutions

Other systems are also under development for alternative thermal energy storage solutions. Ohio-based Echogen has also developed its own pumped thermal energy storage (PTES) system that uses a combination of sand, water, and carbon dioxide.

Echogen’s combined system transfers heat from a cold tank loaded with ice / water to a hot tank containing grains of sand using an electric heat pump. The heat is then stored in the sand and, if necessary, injected into a heat engine to produce electricity as and when required.

Echogen believes that PTES can provide a storage cost of $ 50-60 per 1 MWh for a 100 MW system. In contrast, Highview Power, a major competitor in long-term energy storage, currently offers a liquid-to-air system that operates at $ 100 per 1 MWh for a 100 MW facility.

While Highview aims to increase that figure to around $ 50 by 2030, Echogen’s calculations indicate that its PTES system will be 20-30% cheaper than Highview’s at 100 MW / 1 GWh on an equivalent basis.2

With the emergence of several innovative thermal energy storage solutions in the renewable energy sector, affordable energy could be poised to help improve grid resilience and promote the growth of alternative energy sources.

References and further reading

Khatib, H., (2021) How sand is now a valuable tool for saving energy. [online] AMEinfo. Available at: https://www.ameinfo.com/life/how-sand-is-now-a-treasured-tool-for-saving-energy/

Bellini, E., (2021) Wind and solar energy storage with silica sands. [online] pv magazine International. Available at: https://www.pv-magazine.com/2021/09/01/storing-wind-solar-power-with-silica-sands/

Balestrieri, G., (2021) Italian company turns hot sand into clean energy. [online] Inside the business community. Available at: https://www.businessinsider.com/italian-company-magaldi-group-sand-clean-energy-stem-thermo-electric-2017-4

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