TABLE OF CONTENTS Energy storage systems are tailored to the type of fuel being used or to the mechanical, chemical, thermal or electrical form of energy directly stored. Liquid fossil fuels that will be used as feedstock for the engine include gasoline, liquefied petroleum gas (LPG), natural gas (NG) or hydrogen. Mechanical storage systems include flywheels, plus pneumatic (hydraulic) and elastic mediums to store energy in its kinetic and potential energy forms, respectively. Hydraulic storage systems generally use pneumatic means such as a nitrogen bladder as the actual storage medium with the hydraulics as the actuation system.
A taxomomy of energy storage systems has been done that shows the relative energy density of the various media [1]. Table 10.1 is a summary of these fundamental energy storage systems.
| Energy storage technology | Energy density gravimetric (J/kg) | Energy density volumetric (J/m 3) |
|---|---|---|
| Nuclear fusion | 3.4 10 14 | 2.37 10 16 |
| Nuclear fission | 2.89 10 12 | 1.0 10 17 |
| Reformulated gasoline | 4.4 10 7 | 3.3 10 10 |
| Ideal battery (Li-F) | 2.19 10 7 | 1.89 10 10 |
| Fuel cell (Li-hydride) | 9.2 10 6 | 8.6 10 9 |
| Lead acid battery | 1.6 10 5 | 4.6 10 8 |
| Flywheel | 5.3 10 4 | 8.1 10 8 |
| Compressed gas at 35 kpsi | 10 10 4 | 3.0 10 8 |
| Rubber spring | 6.2 10 3 | 6.2 10 6 |
| Electric field in Mylar [*] |
