The endothermic decomposition of natural gas is experimentally investigated using concentrated solar radiation as the source of high-temperature process heat. The solar chemical reactor features a vortex flow of CH4 confined to a cavity-receiver and laden with carbon particles that serve simultaneously as radiant absorbers and nucleation sites for the heterogeneous decomposition reaction. A 5 kW reactor prototype was fabricated and tested in a high-flux solar furnace with power flux intensities exceeding 3500 kW/m(2). The chemical reactor engineering, experimental setup, and test results are described. Maximum chemical conversion of CH4 to H-2 and C(gr) was 67% at 1600 K and 1 bar. Carbon formed was of nano-filamentary nature. The proposed solar hybrid chemical process conserves natural gas, reduces CO2 emissions, and provides a transition path to solar hydrogen. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.