Regenerative brake system for a vehicle

A regenerative brake system for converting kinetic energy of a moving vehicle into usable mechanical or electrical power is disclosed. The regenerative brake system includes a generator operably coupled to at least one of the vehicle wheels. The system further includes a battery and a thermal storage system, each of which stores power generated by the generator until it can be efficiently used. The thermal storage system includes a heater that uses electrical power from the generator to vaporize a working fluid disposed within a storage tank. The thermal storage system further includes an expander to selectively expand the vaporized working fluid to convert heat from the working fluid into usable energy.