Systems and methods for storing energy in gaseous form in submerged thin-walled tanks are secured to the ocean or lake floor but are open to the water at the tank bottoms and are configured to be filled with gas while submerged.A conduit operatively connected to the tanks provides flow from a surface source of an energy-containing gas to the tank interiors. Surface or subsurface pumping apparatus which may include piston-less pressure cylinders or have leveraged pistons provide a preselected flow rate of the energy-containing gas into the containment structure interior against a back pressure essentially equal to the static pressure of the body of water at the location of the tank to displace an equivalent volume of water through the open bottom. The conduit can be configured to allow heat transfer to vaporize liquefied gas prior to storage. Hydrogen gas can be generated and stored within the tank using Aluminum activated with Galinstan.