Large photoelectrochemical reactors of various sizes, made of cylindrical photoanodes surrounding the counter electrode compartment, have been placed inside the glass tubes of either compound parabolic (CPC) or parabolic trough collectors (PTC, Helioman). Model pollutants have been destroyed at various solar light concentrations. Their oxidation rates have been found to be up to 1000-times higher than the values obtained with TiO2 slurries. Separation of charges is much better when the photogenerated electrons are collected through an electrochemical bias and, moreover, the continuous measurement of photocurrents makes it possible to directly monitor the efficiency of the whole system and thereby improve it.