Illustratively, an electrical generator includes a photovoltaic element which converts light produced by a surface into electrical power, the surface located in thermal communication with exhaust gases produced by an exothermic chemical reaction; a heat exchanger which takes at least a majority of thermal energy in the exhaust gases, after the thermal communication, and transfers the thermal energy to air input to the reaction; a catalytic converter, inside the heat exchanger, located to ensure that at least most of the exhaust gases are communicated into the catalytic converter and that heat generated by operation of the catalytic converter is transferred to the air input to the reaction; a sensor in the heat exchanger, located to monitor the reaction before the exhaust gases are communicated into the catalytic converter; a sensor located to sense after the exhaust gases are communicated into the catalytic converter, whether the catalytic converter is functioning properly.