Toronto Hydro’s new pilot project involves the world’s first offshore compressed air energy storage system, something that is monumental for the use of compressed air, a technology that currently has its primary usage in functioning machinery. With the challenges that exist with storing electricity and the large cost of sizable battery technology, compressed air’s current use and potential for storing energy could help to manage the use of electricity with different sources of energy.
Pneumatics is one of the two forms of fluid power, and like hydraulics, which uses a liquid to transmit power in a machine, it accomplishes the same task with a gas, which can be nitrogen or other inert gases, but is generally compressed air. Most pneumatic systems operate at pressures at 100 psi or less, which requires cylinders to be sized large to provide appropriate force. In comparison with hydraulic systems, these cylinders are very large and have very little pressure, but pneumatic systems are also lighter and provide more cushioning, or “give”. Pneumatics has several advantages over traditional electric motors; specifically, pneumatic machines are not limited by heat generation so they have no potential to overheat. Also, since the main source of power in pneumatics is gas, it can easily be released outside of the system without bringing any personnel harm.
Compressed air exists as a potential alternative for storing electricity that has been generated through either conventional or renewable sources of energy. The difficulty of storing electricity is managed with conventional forms by simply burning more fuel during peak hours of energy use, but for renewables, we are not capable of creating more sunlight or increasing the wind, so we generally need to use the electricity once it is generated. Through compressed air energy storage (CAES), electricity is used to compress ambient air, which is then stored in an underground cavern. When electricity from this source is desired, the compressed air is heated and expanded in an expansion turbine that drives a turbine to generate electricity.
Air heats up very fast when being compressed, but a great deal of heat energy has been lost through the walls of storage caverns in the past. This issue can be managed by either heating the high-pressure air in combustors using natural gas, which actually requires more energy usage, or by thermally storing the heat of compression before it enters the cavern and using it for adiabatic expansion extracting heat from the thermal storage system. For the offshore CAES system, when the stored air returns to land, waste heat is captured so that the system has an overall efficiency of up to 80 percent.
The two-year, one-megawatt pilot project is being carried out by Ontario-based startup Hydrostor, which, by working like a developer and not manufacturing anything, has costs that are far lower than any compressed-air energy storage startup. The company makes use of unique technology that fills underwater balloons with compressed air. The air can then be returned to land to generate electricity. The process Hydrostor uses to install balloons only requires a single tugboat. The balloons are pressurized to match the pressure of the ocean floor, so this installation would be more costly in areas that the ocean has greater depth. Despite any challenges that might exist with this technology being implemented in other parts of the world, it still serves as a viable alternative to battery storage for maintaining electricity, and this project will reveal the data needed to better understand it.
Standards for compressed air-based pneumatics machinery are written and published by the National Fluid Power Association (NFPA), an ANSI-accredited standards developing organization.