Underground facilities built for storing electric energy in the form of gravity and buoyant energy are described herein. In one embodiment, the facility is disposed in a thixotropic fluid beneath the ground surface and houses water to maintain a positive buoyancy and a piston having a bulk density greater than the water. In another embodiment, the underground facility is configured as a buoyant capsule arranged in a cylinder filled with water, where the cylinder is sealed except for openings in a bottom half of the cylinder to allow near unimpeded water flow from a location inside to a location outside of the cylinder. In another embodiment, the underground facility is configured as a negatively buoyant capsule.

Individual honeycomb shaped modules used in an assembly for underground storage of storm water and other fluid storage needs. Modules are assembled into a resultant honeycomb shape for maximized structural strength and material use efficiency. Internal hexagonal or square shaped modules are assembled and encased by external hexagonal or square shaped modules. Internal adjacent modules are in direct fluid communications with one another through a channel-less chamber. Internal hexagonal or square shaped modules drain into external hexagonal or square shaped modules chamber where fluid is either stored or drained. Assemblies include various top and side pieces along with access ports for entry into said assembly.

Individual square shaped modules used in an assembly for underground storage of storm water and other fluid storage needs. Modules are assembled into a resultant square tilling shape for maximized structural strength and material use efficiency. Internal square shaped modules are assembled and encased by external square shaped modules. Internal adjacent modules are in direct fluid communications with one another through a channel-less chamber. Internal square shaped modules drain into square shaped modules chamber where fluid is either stored or drained. Assemblies include various top and side pieces along with access ports for entry into said assembly.

Individual honeycomb shaped modules used in an assembly for underground storage of storm water and other fluid storage needs. Modules are assembled into a resultant honeycomb shape for maximized structural strength and material use efficiency. Internal hexagonal or square shaped modules are assembled and encased by external hexagonal or square shaped modules. Internal adjacent modules are in direct fluid communications with one another through a channel-less chamber. Internal hexagonal or square shaped modules drain into external hexagonal or square shaped modules chamber where fluid is either stored or drained. Assemblies include various top and side pieces along with access ports for entry into said assembly.

Individual square shaped modules used in an assembly for underground storage of storm water and other fluid storage needs. Modules are assembled into a resultant square tilling shape for maximized structural strength and material use efficiency. Internal square shaped modules are assembled and encased by external square shaped modules. Internal adjacent modules are in direct fluid communications with one another through a channel-less chamber. Internal square shaped modules drain into square shaped modules chamber where fluid is either stored or drained. Assemblies include various top and side pieces along with access ports for entry into said assembly.

A nitrogen blanket system for small fuel tanks is disclosed that includes tank empty-space pressure control for sealed tanks that can hold pressure. The system includes a fuel tank storing some volume of fuel, such as diesel fuel. The remaining empty volume is filled with nitrogen by the disclosed system. The nitrogen blankets the liquid fuel and fills the remaining space in the fuel tank to prevent the accumulation of moisture and thereby prevent corrosion within the fuel tank.

A natural gas energy storage system can comprise a high-pressure subterranean reservoir and a low-pressure subterranean reservoir. The high-pressure subterranean reservoir and the low-pressure subterranean reservoir can be configured to respectively receive and contain high-pressure natural gas and low-pressure natural gas. Said reservoirs can be coupled by a natural gas compression assembly and an energy recovery assembly to generate electricity. The natural gas compression assembly can be configured to recover natural gas from the low-pressure subterranean reservoir, compress the same to produce the high-pressure natural gas, and inject said gas into the high-pressure subterranean reservoir, during surplus periods. The energy recovery assembly can be configured to recover a portion of the high-pressure natural gas from the high-pressure subterranean reservoir, expand the same to generate energy and produce the low-pressure natural gas, and supply said gas into the low-pressure subterranean reservoir, during deficit periods.

A nitrogen blanket system for small fuel tanks is disclosed that includes tank empty-space pressure control for sealed tanks that can hold pressure. The system includes a fuel tank storing some volume of fuel, such as diesel fuel. The remaining empty volume is filled with nitrogen by the disclosed system. The nitrogen blankets the liquid fuel and fills the remaining space in the fuel tank to prevent the accumulation of moisture and thereby prevent corrosion within the fuel tank.

Individual four-sided shaped modules used in an assembly for underground storage of storm water and other fluid storage needs. Modules are assembled into a resultant four-sided tiling shape for maximized structural strength and material use efficiency. Internal four-sided shaped modules are assembled and encased by external four-sided shaped modules. Internal adjacent modules are in direct fluid communications with one another through a channel-less chamber. Internal four-sided shaped modules drain into four-sided shaped modules chamber where fluid is either stored or drained. Assemblies include various top and side pieces along with access ports for entry into said assembly.

A method for subsurface gas storage including injecting a hydrogen stream into a subsurface reservoir for storage during periods of low sales demand, mixing the hydrogen stream in the subsurface reservoir with a stored gas, and removing the hydrogen from the subsurface reservoir during high sales demand.