These slides use concepts from my (Jeff Funk) course entitled analyzing hi-tech opportunities to analyze how the economic feasibility of kinetic energy recovery systems is slowly becoming better through improvements in batteries, hydraulic pumps, and flywheels. Many of these systems are currently used in Formula 1 race cars because they enable these cars to achieve higher acceleration and longer times between pit stops. For consumers, flywheels may become the energy storage technology of choice for vehicles particularly as improvements in carbon nanotubes and graphene occur.
The rates of improvement for energy and power storage densities for batteries have been very slow and those of flywheels have been much faster. One of the reasons for the rapid improvements in the densities for flywheels is that improvements in the strength per weight of materials have enabled faster rotations and the storage densities are a function of rotation velocities squared. As shown in the slides, carbon fiber has about four times the strength to weight ratio and seven times the energy density of glass. Since carbon nanotubes have strength to weight ratios 15 times higher and graphene has ones 30 times higher than do carbon fiber, energy storage densities of 120,000 kJ/kg or 33.6 kWh are possible with graphene. This energy density is about 100 times higher than is currently available from lithium-ion batteries.