A practical high capacity and fast output energy storage solution is the “Holy Grail”, or missing link, in all renewable-energy systems.  Although not a strict necessity, as OA-Cities could also be connected to a national grid, it would certainly be comforting to know that your OA-City has an autonomous power supply not vulnerable to sabotage or terrorism.

 

BATTERIES – Recent years have seen great advances in battery technology, but they are very limited by their slow charge and discharge cycles.  They cannot quickly release the huge amounts of energy required to power thousands of homes, shops, factories, etc.   Batteries also have relatively short cycle lives and use a lot of scarce materials.  

Cryogenic energy storage is the use of low temperature liquids such as air or nitrogen as energy storage.

FLYWHEEL ENERGY STORAGE (FES)

Flywheel Energy Storage (FES) is a relatively new concept that is being used to overcome the limitations of intermittent energy supplies, such as Solar PV or Wind Turbines that do not produce electricity 24/7.  A flywheel energy storage system can be described as a mechanical battery, in that it does not create electricity, it simply converts and stores the energy as kinetic energy until it is needed. In a matter of seconds, the electricity can be created from the spinning flywheel making it the ideal solution to help regulate supply in the electrical grid.

Historically, flywheels have been huge steel structures with the majority of the weight distributed towards the rim of the wheel. However, over the last 30 years, scientific innovation has meant that flywheels can store more energy in less weight and volume, increasing their potential for energy storage. Newer flywheels are made from very strong composite materials and are operated on a bed of near frictionless magnetic bearings housed in a vacuum enclosure. This allows the flywheels to be spun at incredible speeds helping maximise the energy that they can store.

NASA scientists have managed to get flywheels to spin in excess of 60,000 revolutions per minute, which is nearly 2.5 times the speed of sound. The amount of kinetic energy that can be stored at this speed makes them ideal for replacing chemical batteries in the future.

There is also potential to use magnetic levitation as a way of prolonging the life of the flywheel energy storage systems. Since there is no friction on a system that is magnetically levitated there will be no wear on the system, so it is thought that these systems could last fifteen years or more as opposed to a chemical battery that may only last five years.