I read with interest the very recent paper by Pinilla et al., which discusses the utilisation of an apparently novel solar powered reactor for H2 (and carbon) production from thermal decomposition of CH4. The authors refer to their reactor as being adapted from a system previously reported in two of their earlier publications  and . When these references are pursued it is found that they both describe a “rotary bed reactor for CH4 decomposition” with process heat being supplied from a conventional stationary electric source. The reactor is described as a cylindrical (rotating) flow-type (volume 1000 cm3), though the precise routes of gas flow are, to me, unclear from the text or schematic. No mention is made in reference  of the reactor wall material though reference  states that this is “Kanthal”. It is not described whether the reactor tube is opaque, but it can be assumed that it is.