Energy Storage Flywheels to Enable Renewable Energy and for Uninterruptible Power Source Service
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abstract
Energy storage facilities would help solve one of renewable energy's biggest challenges â its intermittency. Wind farms produce no electricity when there's no wind; solar farms produce no electricity when there's no sun. Linking the solar farm to the energy storage facility is likely to enable the solar farm to function like a traditional coal, nuclear or natural gas power plant â capable of reliably delivering large amounts of electricity whenever needed, based on customer demand. A flywheel energy storage battery is a ubiquitous, environmentally friendly, long life and efficient means of energy storage. The flywheel integral motor uses the solar farm's electrical output to spin it up to high rpm during times when demand for solar energy is low and supply is high. Its kinetic energy is converted to electrical power via its integral generator during times when demand is high and solar farm output is low. Energy density is a key measure of goodness for any means of energy storage. Batteries, fuel cells, flywheels and compressed air typically store in the range of 25 - 50 watt hrs per kg, based on total system mass. The limiting factor for flywheel energy storage is material strength since the flywheel will burst due to centrifugal stresses if spun at too high of an rpm, yet its stored energy varies as the square of the rpm. Therefore, the maximum specific energy density (SED, or the stored energy per unit mass) scales with the ratio of the strength of the material to mass density (specific strength). As such, novel materials with improved specific strength are desired to improve the SED of flywheels. In this proposed research, we address the need for high specific strength by developing novel composite materials reinforced with super strong carbon nanofibers - CNFs (theoretical strengths of 10-14GPa, far passing the inherent strength of carbon fibers ~6 GPa) with a microstructure composed of graphitic and amorphous carbon. The flywheel rim will be composed of wound CNFs yielding energy densities in the 200 kW-Hr/kg or higher range. Three major tasks will be performed including development of the CNF material and fabrication of the flywheel rim at TAMU, building a prototype flywheel system and spinning it at high speed in the existing spin pit of the LPI at TAMU, and total system performance testing at TAMU-Qatar with the flywheel powered by a solar panel array.
