The purpose of this invention is to capture concentrated solar radiation, converting the energy to chemical energy at a higher efficiency and lower cost than prior art. This is accomplished by operating a high temperature endothermic reaction such as methane steam reforming where the heat of reaction is largely or completely provided by solar energy. A spiral counter-cross flow arrangement of reaction channels and recuperative heat exchange channels enables efficient thermal spreading of inhomogeneous solar irradiation. The reduction of hot spots leads to lower OPEX and CAPEX through improvements to reactor's operability under high flux conditions and longer reactor life by reducing thermal stress, respectively.