Compressed Air Energy Storage (CAES)
Compressing air is a mature technology, and is an excellent and under-represented renewable energy storage option, especially when considering that many common engines and tools have been commercially engineered to utilize compressed air as an energy source.
For reference, an ordinary 18L diving tank could hold enough energy to run a regular LED light bulb for 15 hours at optimal efficiency.
0.018m3 at 4,400PSI = 4.83×10^6 in lbf (pound-force inches) or 546 KiloJoules = 151.7 Watt hours.
Not bad for a simple metal container!
Compression systems can be extremely efficient, but compressing gas heats it up. If this heat is wasted, compression systems bleed out a lot of energy and drastically lose efficiency. Most large scale compression systems reclaim this heat for other uses.
City-wide compressed air energy systems have been built since 1870. Cities such as Paris, France; Birmingham, England; Dresden, Rixdorf and Offenbach, Germany and Buenos Aires, Argentina installed such systems. Victor Popp constructed the first systems to power clocks by sending a pulse of air every minute to change their pointer arms. They quickly evolved to deliver power to homes and industry. As of 1896, the Paris system had 2.2 MW of generation distributed at 550 kPa in 50 km of air pipes for motors in light and heavy industry. Usage was measured by meters. The systems were the main source of house-delivered energy in those days and also powered the machines of dentists, seamstresses, printing facilities and bakeries. – Wikipedia.
// large scale underground CAES info coming soon