NOVELTY - A hydrogen generator comprises cartridge containing casing, pellets (40) containing hydrogen containing material capable of releasing hydrogen gas when heated, solid heat transfer members, hydrogen outlet valve (28), and hydrogen flow path from each fuel pellet to valve; compartment to removably contain cartridge, where compartment comprises housing comprising wall, hydrogen outlet, cavity, and heating elements (50) disposed within housing such that when cartridge is disposed within cavity each heating element is in contact with outer surface of casing; and an initiation system.    USE - As hydrogen generator in fuel cell system (claimed) such as proton exchange membrane fuel cell (PEMFC), alkaline fuel cell (AFC), phosphoric-acid fuel cell (PAFC), solid oxide fuel cell (SOFC) and molten carbonate fuel cell (MCFC); in electronic devices.    ADVANTAGE - The generator is inexpensive and easy to manufacture, safe to store and use, is able to produce a large total volume of hydrogen gas per unit of mass and per unit of volume of the hydrogen generator, is able to control the supply of hydrogen on an as needed basis, and is able to operate at or below a desired maximum temperature. At least a portion of the hydrogen generator in a fuel cell system can be replaced after hydrogen containing materials have been consumed. The generator is durable and reliable for a long period of time.    DETAILED DESCRIPTION - A hydrogen generator comprises a cartridge containing: a casing, pellets (40), each comprising at least one hydrogen containing material capable of releasing hydrogen gas when heated, solid heat transfer members, each in direct contact with but not penetrating the casing, a hydrogen outlet valve (28) in the casing, and a hydrogen flow path from each fuel pellet to the hydrogen outlet valve; a compartment configured to removably contain the cartridge, where the compartment comprises a housing comprising a wall, a hydrogen outlet through the housing, a cavity within the housing within which the cartridge can be disposed, and heating elements (50) disposed within the housing such that when the cartridge is disposed within the cavity each heating element is in contact with an outer surface of the cartridge casing and disposed so that heat can be conducted from the heating element, through the casing and to a heat transfer member, which can conduct the heat to a portion of the at least one hydrogen containing material not in contact with the casing, where each pellet is in contact with a heat transfer member; and an initiation system comprising the heat transfer members, the heating elements, and circuitry for conducting an electric current to the heating elements, where the electrical current can be applied selectively to at least one heating element for generating heat to selectively heat at least one pellet to initiate a release of hydrogen gas. The cartridge and the compartment cooperate so the cartridge can be inserted into the compartment only such that the heating elements and the heat transfer members are aligned for conducting heat from the heating elements, through the casing, to corresponding heat transfer members. Each heat transfer member includes a layer of pyrolytic carbon in contact with a pellet. In the generator, a layer of the thermally insulating material separates adjacent layers of pellets. The cartridge comprises device for maintaining contact between the heat transfer members and the pellets as the hydrogen generator is being used. An INDEPENDENT CLAIM is included for a fuel cell system comprising: a fuel cell battery; and the hydrogen generator. The portion of the initiation system is outside the hydrogen generator.    DESCRIPTION OF DRAWING(S) - The figure shows schematic view illustrating enlarged portion of the hydrogen generator.    Side wall of housing (14)    Lid (16)    Hydrogen outlet valve (28)    Opening (30)    Coupling (32)    Pellet (40)    Solid composition (42)    Heat concentrator (44)    Heating elements (50)    Central channel (52)    Guide plate (54)