Scientists from the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) have proposed to use silica sands – a stable and inexpensive material with prices ranging from $30 to $50/ton – as a medium to store excess wind and solar power.
The research team developed a thermal energy storage technology called Economic Long-Duration Electricity Storage by Using Low-Cost Thermal Energy Storage and High-Efficiency Power Cycle (ENDURING), which it defines as a scalable solution that can be deployed almost anywhere.
The baseline system, which is designed for a storage capacity of up to 26,000 MWh, works by heating silica particles through an array of electric resistive heating elements at a temperature of around 1,200 degrees Celsius and depositing them on insulated concrete silos for thermal energy storage.
“When energy is needed, the hot particles are gravity-fed through a heat exchanger, heating and pressurizing a working gas inside to drive the turbomachinery, and spin generators that create electricity for the grid,” the NREL researchers explained. “Once discharged, the spent, cold particles are once again fed into insulated silos for storage until conditions (and economics) are appropriate again for charging.”
According to them, the proposed storage technology could be deployed at a cost of between $2 and $4 per kWh and it could also be hosted by existing infrastructure from retired coal and gas-fired power plants. Furthermore, it may provide a continuous source of heat for industrial and chemical processes.
“Sand and concrete silos with refractory insulation are very inexpensive materials that can lead to low-cost energy storage,” said NREL researcher Patrick Davenport. “Traditional four-hour storage technologies don't scale well to the grid or city scale. Now that we are in need of large scale energy storage, this technology makes a lot of sense.”
The prototype heaters and heat exchangers for the proposed system are currently being tested under high temperatures.
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