Table of energy storage traits




Flywheel purpose, type Geometric shape factor (k)
(unitless – varies with shape) 		Mass
(kg) 		Diameter
(cm) 		Angular velocity
(rpm) 		Energy stored
(MJ) 		Energy stored
(kWh) 		Energy density (kWh/kg)
Small battery 0.5 100 60 20,000 9.8 2.7 0.027
Regenerative braking in trains 0.5 3000 50 8,000 33.0 9.1 0.003
Electric power backup 0.5 600 50 30,000 92.0 26.0 0.043

For comparison, the energy density of petrol (gasoline) is 44.4 MJ/kg or 12.3 kWh/kg.

High-energy materialsedit

For a given flywheel design, the kinetic energy is proportional to the ratio of the hoop stress to the material density and to the mass:

could be called the specific tensile strength. The flywheel material with the highest specific tensile strength will yield the highest energy storage per unit mass. This is one reason why carbon fiber is a material of interest.

For a given design the stored energy is proportional to the hoop stress and the volume:

Comments

Post a Comment

Popular posts from this blog

History

Image
The principle of the flywheel is found in the Neolithic spindle and the potter's wheel, as well as circular sharpening stones in antiquity. The mechanical flywheel, used to smooth out the delivery of power from a driving device to a driven machine and, essentially, to allow lifting water from far greater depths (up to 200 metres (660 ft)), was first employed by Ibn Bassal (fl. 1038–1075), of Al-Andalus. The use of the flywheel as a general mechanical device to equalize the speed of rotation is, according to the American medievalist Lynn White, recorded in the De diversibus artibus (On various arts) of the German artisan Theophilus Presbyter (ca. 1070–1125) who records applying the device in several of his machines. In the Industrial Revolution, James Watt contributed to the development of the flywheel in the steam engine, and his contemporary James Pickard used a flywheel combined with a crank to transform reciprocating motion into rotary motion.
Read more

Flywheel

Image
A flywheel is a mechanical device specifically designed to use the conservation of angular momentum so as to efficiently store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, if we assume the flywheel's moment of inertia to be constant (i.e., a flywheel with fixed mass and second moment of area revolving about some fixed axis) then the stored (rotational) energy is directly associated with the square of its rotational speed. Since a flywheel serves to store mechanical energy for later use, it is natural to consider it as a kinetic energy analogue of an electrical inductor. Once suitably abstracted, this shared principle of energy storage is described in the generalized concept of an accumulator. As with other types of accumulators, a flywheel inherently smoothes sufficiently small deviations in the power output of a system, thereby effectively playing the role of a low-pass filt...
Read more