Energy storage is a key enabling technology in the exploitation of intermittent renewable energy resources such as wind and solar, meeting the fluctuations in demand. It is also critical for mobile devices from cell phones to vehicles.
Among various storage techniques, hydrogen and batteries have been advocated as promising media to store energy.
Hydrogen has the highest energy per mass of any fuel and the energy stored can be extracted using hydrogen fuel cells at high efficiencies while releasing no pollution. These have been demonstrated in passenger vehicles, buses, and forklifts. The low ambient temperature density of hydrogen, however, results in a low energy per unit volume. Conventional compression and liquefaction methods have inherent problems.
For batteries, electricity is stored and then released upon demand. There are many different types of batteries featuring distinct advantages related to specific applications. For mobile applications, the current mainstream Li ion batteries have high energy density. For load leveling related to electrical grid, batteries using naturally abundant elements such as Na and Mg are under intense investigation.