Plasmonic nanoparticles are found in a number of applications as efficient converters of optical energy into heat, e.g. cancer therapy of nanoparticle-laden tumors. More recently, aqueous solutions of plasmonic nanoparticles have proven the ability to produce steam with relatively high efficiencies upon solar illumination. We show in this report through modeling of the light transport in nanoparticle solutions that this effect originates in the optical properties of the nanoparticles. Strong optical scattering leads to multiparticle interactions that can concentrate light resulting in large temperature increases in the focused region. This model can be extended to all systems of dense nanoparticles in which light to heat conversion is crucial, e.g. photothermal cancer therapy and materials processing.