Sunday, December 9, 2018

MIT Researchers Develop Renewable Energy Storage System Using Liquid Silicon

    Researchers at MIT have released a conceptual design for a renewable energy system capable of storing extra electricity from solar and wind power that could be released back on demand.
    The design involves storing excess electricity in the form of heat in large tanks of molten silicon and then converting the light from the glowing material back into electricity when required. The engineers investigating this design state that such a system would cost significantly less than lithium-ion batteries, an alternative method to store renewable energy. Furthermore, it is estimated that this system would cost half as much as pumped hydroelectric storage, the cheapest form of grid-scale energy storage currently used.
    This design is based on an existing model of renewable energy called concentrated solar power. Unlike conventional solar plants, concentrated solar power utilizes fields of huge mirrors that concentrate sunlight onto a central tower. There, light is converted into heat that is eventually turned into electricity.
    Concentrated solar plants store this heat energy in big tanks filled with molten salt heated at temperatures exceeding 500 degrees Celsius. When electricity is needed, this salt is pumped through a heat exchanger that converts the heat into steam which in turn powers a electrical turbine.
    What sets this system apart involves a few factors including the following:
- Silicon is used instead of salt as it has the highest heat tolerance on record. This tolerance creates a more efficient system that can still be stored safely in graphite tanks that withstand corrosion.
- Instead of mirrors and a central tower, the storage system converts electricity generated by a renewable source (let it be sunlight, wind) into thermal energy through joule heating (by passing current through a heating element)
    The following is an excerpt from MIT News detailing the concept in action:
    The system would consist of a large, heavily insulated, 10-meter-wide tank made from graphite and filled with liquid silicon, kept at a “cold” temperature of almost 3,500 degrees Fahrenheit. A bank of tubes, exposed to heating elements, then connects this cold tank to a second, “hot” tank. When electricity from the town’s solar cells comes into the system, this energy is converted to heat in the heating elements. Meanwhile, liquid silicon is pumped out of the cold tank and further heats up as it passes through the bank of tubes exposed to the heating elements, and into the hot tank, where the thermal energy is now stored at a much higher temperature of about 4,300 F.

    When electricity is needed, say, after the sun has set, the hot liquid silicon — so hot that it’s glowing white — is pumped through an array of tubes that emit that light. Specialized solar cells, known as multijunction photovoltaics, then turn that light into electricity, which can be supplied to the town’s grid. The now-cooled silicon can be pumped back into the cold tank until the next round of storage — acting effectively as a large rechargeable battery.

     “Even if we wanted to run the grid on renewable right now we couldn’t, because you’d need fossil-fuelled turbines to make up for the fact that the renewable supply cannot be dispatched on demand,” said Asegun Henry, the Robert N. Noyce Career Development Associate Professor in the Department of Mechanical Engineering. “We’re developing a new technology that, if successful, would solve this most important and critical problem in energy and climate change, namely, the storage problem.”

Read the full press release at: http://news.mit.edu/2018/liquid-silicon-store-renewable-energy-1206

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