Abstract The solar-driven steam gasification of different lignocellulosic biomass feedstocks was experimentally investigated with a 1.5 kWth continuously particle-fed solar reactor at high temperature using real high-flux solar radiation provided by a parabolic dish concentrator. Experiments were carried out with five carbonaceous materials under different biomass feeding rates in the range of 0.8–2.7 g/min at 1300 °C in order to optimize the synthesis gas production and composition. Increasing biomass feeding rate (at constant slightly over-stoichiometric steam/biomass ratio) noticeably promoted the syngas yields that reached up to 83.2 mmol/gbiomass. The syngas yield (especially H2) was more affected by the biomass feedstock (chemical composition) than by the particle size in the considered range (0.3–4 mm). The calorific value of the biomass was solar upgraded up to 24% through the syngas produced with a carbon conversion above 90%, thereby accomplishing efficient solar energy storage into the produced syngas. Increasing the biomass feeding rate inherently shortened the solar processing duration (for a given biomass amount). Thus, the solar energy input and the heat losses were reduced while the overall syngas production capacity was increased, which in turn drastically enhanced both the thermochemical reactor efficiency and the solar-to-fuel energy conversion efficiency with maximum values typically beyond 25%.