NOVELTY - An energy system comprises a fuel cell stack for generating electricity from hydrogen and an oxidant to form a chemical hydride hydrogen generation system comprising a storage mechanism, a reactor, and a first pump mechanism; a first connection between the chemical hydride generation system and the fuel cell; and a heat transfer circuit.    USE - As an energy system for mobile applications.    ADVANTAGE - The energy system is capable of responding in real time to the fuel (hydrogen) needs of the fuel cell (referred to as load following ability).    DETAILED DESCRIPTION - An energy system comprises a fuel cell stack for generating electricity from hydrogen and an oxidant to form a chemical hydride hydrogen generation system comprising    (a) a storage mechanism for storing a chemical hydride solution comprising a solution of a chemical hydride solute in a solvent; a reactor containing a catalyst for catalyzing reaction in the chemical hydride to generate hydrogen; and a first pump mechanism connected between the storage mechanism and the reactor in a first circuit for circulating the chemical hydride solution through the storage mechanism and the reactor, so that the chemical hydride reacts to generate hydrogen in the presence of the catalyst;    (b) a first connection between the chemical hydride generation system and the fuel cell for supplying hydrogen to the fuel cell; and    (c) a heat transfer circuit including second connections between the chemical hydride generation system and the fuel cell stack, for circulation of the chemical hydride solution through the fuel cell stack to effect heat transfer between the fuel cell stack and the chemical hydride solution.    An INDEPENDENT CLAIM is included for a method of operating a fuel cell stack and chemical hydride hydrogen generation system with a reactor including a catalyst for generating hydrogen for the fuel cell stack and controlling the temperature of the fuel cell stack and the chemical hydride generation system, comprising supplying a chemical hydride solution to the reactor, and permitting the catalyst to catalyze reaction of the chemical hydride solution to generate hydrogen; supplying the hydrogen to the fuel cell stack and supplying an oxidant to the fuel cell stack, for generation of electricity; and circulating the chemical hydride solution through the fuel cell stack and the chemical hydride generation system, to effectively transfer heat in between.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of the energy system.    Fuel cell stack (3)    Storage mechanism (5)    Reactor (20)