Power Storage Loop
Short Abstract for IEEE SusTech
A long, continuous loop of low-cost steel tubing moving at high speed in a vacuum tunnel can store enormous energies with high efficiency and low losses. Power storage loops can scale from kW-h to TW-h capacities, with system costs proportional to the square root of energy storage capacity. This energy can provide on-demand peaking power for the grid, as well as absorb the unpredictably random output of wind and solar generation.
Flywheels depend on the mechanical strength of expensive carbon fiber - the energy storage capacity is less than the volume of the moving rotor material times its tensile strength. Loop storage uses magnetic deflection of moving steel tubing in Tesla-scale turn-around fields. While magnetic field pressure of is hundreds of kiloPascals rather than GigaPascals, it can bend and turn steel rotors 180 degrees over kilometer scale arcs.
Induction motor and generator efficiencies increase with speed, well above 99% above a kilometer per second.
A steel rotor , in a sideways attractive magnetic field averaging 1 Tesla, is deflected with a force of 8MN per meter, accelerating 80000m/s2 sideways. If the rotor is moving at 2,000 meters per second, it can be turned 180 degrees by a 1.6 kilometer diameter magnet (with cross sections on the order of 1 meter). This rotor stores 320 Gigajoules per kilometer.
If the rotor travels ballistically for 30 kilometers between the end magnets in a meter-scale high-vacuum tunnel, the rotor can store 20 Terajoules of energy, more than 5 Gigawatt hours. Energy can be added or drawn off with linear induction motors, perhaps one percent per revolution if drawn from multiple locations, so the system can charge or discharge over 20 minutes.
These are enormous energy scales, vastly exceeding the 25kW-h of one five-ton Beacon Power flywheel assembly. And ordinary steel, even if diamond-coated to reduce surface erosion from residual gas and small particles in the vacuum, is far cheaper than exquisitely formed carbon fiber.