City-Scale Energy Storage With Molten Silicon

Molten silicon energy storage

A group of MIT, Georgia Institute of Technology and National Renewable Energy Laboratory researchers say their molten silicon energy storage design concept could help power cities – and be much cheaper than pumped hydro.

The Thermal Energy Grid Storage-Multi-Junction Photovoltaics (TEGS-MPV) system envisions the use of electricity sourced from renewables such as wind or solar power to heat silicon to extremely high temperatures.

The silicon would be stored in two 10-metre wide tanks made from graphite – a material that could withstand the temperatures required to run the system. One tank would be a “cold” tank containing silicon heated to almost 3,500 degrees Fahrenheit (~1,900 Celsius). This tank would be connected to a “hot” tank via tubes exposed to heating elements, raising the temperature to around 4,300F (~2,370 Celsius).

When electricity is needed, the silicon is pumped through an array of tubes that emit light. This light is then converted to electricity via specialised solar cells1. The somewhat cooled silicon would then be pumped back into the “cold” tank, ready to repeat the cycle.

“One of the affectionate names people have started calling our concept, is ‘sun in a box’, which was coined by my colleague Shannon Yee at Georgia Tech,” says Associate Professor Asegun Henry from MIT’s Department of Mechanical Engineering.

As you can imagine, the pump required to perform this work would have to be incredibly robust. It seems that challenge has been sorted, with the MIT team having already developed such a device that has the highest heat tolerance on record.

The researchers estimate the TEGS-MPV system would cost about half as much as pumped hydro storage and a single system could enable a small city of around 100,000 households to be powered entirely by renewable energy.

In-depth details of the team’s research have been published in the journal Energy and Environmental Science.

Molten Silicon Energy Storage – Australia’s Already There

The use of molten silicon for energy storage isn’t new – Australia’s 1414 degrees has been tinkering with the technology for some time. The South Australian company recently received a commendation in the 2018 Premier Awards for its SA Water GAS-TESS project, part of SA Water’s goal of achieving $0 net electricity costs by 2020.

1414 Degrees

The GAS-TESS system, which is currently being constructed at Glenelg Wastewater Treatment Plant, will burn biogas sourced from sewage treatment processes to melt silicon; with the stored energy later recovered as electricity. Should the trial prove successful, the technology could be implemented at other SA Water facilities.

In 1414’s various Thermal Energy Storage Systems (TESS’s) the energy from the latent heat is passed through an energy recovery system and a turbine to dispatch heat and electricity when required.

Footnotes

  1. At the scale involved, this would require *a lot* of solar cells – how many and how things would work at this end of things to make it viable isn’t really clear (to me anyway). In other related technologies, molten materials are pumped through a heat exchanger to create super-heated steam, which then powers a conventional steam turbine.
About Michael Bloch

Michael caught the solar power bug after purchasing components to cobble together a small off-grid PV system in 2008. He's been reporting on Australian and international solar energy news ever since.

Comments

  1. Ronald Brakels says:

    The molten silicon storage uses an interesting approach. Unfortunately it will be low efficiency, but if they used a steam turbine instead its efficiency wouldn’t be great either.

  2. Colin Woods says:

    I wonder if this could be used alongside gas-fired steam turbines – a gas-fired boiler and molten silicon boiler sharing the turbine/generator infrastructure?

    • Ronald Brakels says:

      Gas and thermal storage can definitely go together. There is a large concentrating solar power station in the United States that can operate off either solar heat or gas.

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