Patent ID: 7669419

Claim:
A power supply system comprising: a) a utility electricity supply connectible to a load; and b) a back-up electricity supply also connectible to the load, the back-up electricity supply comprising: i. a vessel containing a volume of compressed gas; ii. a valve to release gas from the vessel at a predetermined pressure when the utility electricity supply fails; iii. a scroll expander connected to said valve to receive said gas when released from said vessel and having a rotary member rotated by the passage of said gas through the expander; iv. an electricity generator driven by said rotary member to provide said back-up power to the load; v. a dc power conditioning unit supplied by said generator; and vi. a power converter connected between the conditioning unit and the load, wherein the power conditioning unit includes at least one capacitor energy store that provides sufficient back-up energy to exclusively power the power converter and load both when the supply to the load is interrupted and when the power demand of the load changes until the back-up power provided by said generator matches the load requirement; and a regulator throttles the flow of the gas introduced into the scroll expander to a pressure which is determined according to the level of electrical back-up power demanded by the load.