These tanks hold 90 cubic metres of air compressed to 300 bars.
I can't do the math to get the tank size
Just using PV = nRT, if temperature stays the same, 90 cu.m at 1 Bar is about .3 cu/m. at 300 Bars (90/300), or about 2 ft x 2 ft. x 2 ft. Reasonable enough.
Actually compressed air is an excellent way to store and tap energy, similar to, and almost exactly the same as, heat, which is why a lurker like me speaks up, and why the Indians consider it. Pressure (N/sq.m) is also energy per cubic meter (N-m/cu.m.). Altho like heat and the Second Law, there has to be a sink, (lower pressure) for the energy to flow. In this case 300 Bars and decreasing, to one Bar atmosphere, a calculus problem in regulating the volume flow for a constant energy flow (power).
Equating this pressure (300 Bars) and volume (.3 cu.m.) results in a stored energy of about 2.5 kwh. That's about what? 3 to 4 12 v. batteries. Not a lot but more than enough to get around the golf course a couple times.
None of this of course has to do with acquiring the pressure in the first place, about which I can offer no numbers.
"These tanks hold 90 cubic metres of air compressed to 300 bars.
I can't do the math to get the tank size"
Pretty simple. 90 m^3 / 300 = .3 m^3, or 300 litres, or 10.6 cubic feet. Not terribly big, a cube about 2.2 feet to a side. Or a cylinder 2 feet in (inside) diamater and about 3.4 ft long. Somewhat bigger (by about 5 or 6 times) than a typical gas tank.