NOVELTY - The system (20) has a proton exchange membrane (PEM) electrolyzer converting water into hydrogen gas and oxygen. A hydrogen storage tank (64) stores the hydrogen gas generated by the PEM electrolyzer. A PEM fuel cell (30) combines hydrogen from the hydrogen storage tank with the oxygen in air. A multistage dryer and a float-operated automatic drain valve remove moisture from the hydrogen gas to 10 parts per million (ppm) water or less before the hydrogen gas enters the hydrogen storage tank. An electrolyzer coolant loop controls temperature of the PEM electrolyzer.    USE - Hydrogen fuel cell driven heating ventilation air conditioning (HVAC) and power system for powering a diesel-powered vehicle i.e. line haul sleeper cab lorry, during engine-off time and providing conditioned air and auxiliary power to a cab interior of the lorry, railroad locomotive and port equipment during engine-off time.    ADVANTAGE - The system is simple, efficient, retro-fit compatible, stand- alone, installed quickly and capable of rapid replacement of components when necessary. The system provides green energy solution to restrictions on running diesel engines, while the vehicles are parked. The system allows operators to comply with diesel engine anti-idling regulations. The system provides a source of energy that is environmentally friendly, non-pollutable and does not burn fossil fuels. The system eliminates exhaust from an internal combustion engine of the vehicle for purposes of operator comfort during rest periods. The system provides electrical power needs for a vehicle interior, while a main traction engine is off. The system facilitates hydrogen storage in metal hydride storage tanks that are inherently safer than storage of compressed hydrogen gas and cheaper than storage of liquefied hydrogen at cryogenic temperatures. The system eliminates harmful Environmental Protection Agency emissions during regular engine off intervals and reduces engine maintenance. The system allows an operator to activate the system to provide cab temperature conditioning, direct current power and alternating current auxiliary power without draining vehicle main batteries during engine-off-time.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a hydrogen fuel cell driven HVAC and power system with PEM regenerative hydrogen production.    Hydrogen fuel cell driven HVAC and power system (20)    Electrolyzer system (24)    High efficiency reverse cycle heat pump system (28)    PEM fuel cell (30)    Hydrogen storage tank (64)