A significant portion of the infrared solar spectrum is either unused, or wasted by inefficient solar energy conversion. In this paper, we show that infrared light harvesting can also be accomplished by dispersions of polar nanoparticles. Polar nanoparticle dispersions in a selective absorber may result in Solar Thermal Desalination (STD) systems that aim to maximize the solar-to-heat conversion efficiency by managing the thermal radiative and conduction losses. In noting that irregular dispersions of polar nanoparticles are less costly than regularly spaced nanostructures to manufacture at large scales, we describe the solar absorptivity as a function of a nanoparticle chain model determined emissivity and thermal conductance. The near-field interactions between nanoparticles are explained by modeling the nanoparticles as dispersed electromagnetic dipole oscillations that interact with solar light. An FDTD model of polar nanodispersions near an optical cavity is used to demonstrate infrared harvesting. With this model, we show that the infrared light-harvesting mechanisms of silica nanoparticles involve local and propagating surface phonon polaritons and varying the volume fraction changes radiation transport properties by several orders of magnitude. In discussing STD systems, we demonstrate a potential to use nanoparticle chains to create novel selective absorbers with tunable solar absorptivity.