household scale #energy storage to smooth out intermittency of common renewable power sources like #solar; #batteries are best. 10m³ of #lead-acid batteries weigh 19 tons and store 750 kWh (2.7 GJ), but they cost US$150/kWh (US$41/MJ). 360 kg lifted by 3 m is required to store 3 Wh (at 29J/kg at 3 m), about 500× less energy density per mass than lead-acid batteries, so gravitational energy storage is impractical. #Flywheel storage is practical at a multi-meter scale even with steel, but the construction is expensive. Compressed air at a multi-meter scale (10m³) is practical, but again expensive.
on 02015-11-16notes on #energy storage in #flywheel systems
on 02015-11-10figures on the #energy-density of different #flywheel designs. Discussion of #energy storage for I guess #solar?
on 02015-11-10#energy-density of a composite #flywheel can be up to about 400 Wh/kg, although the shape factor typically limits you to about 0.6 of that, about 900 kJ/kg.
on 02015-11-10a low-speed #flywheel built of steel rotates up to 10krpm, while composite flywheels rotate over 100krpm at over 1km/s.
on 02015-11-10The Bitterly carbon-fiber #flywheel, by US Flywheel Systems, spun in vacuum at 100krpm.
on 02015-11-10