AbstractResonant metal nanostructures exhibit an optically induced electrostatic potential when illuminated with monochromatic light under off-resonant conditions. This plasmoelectric effect is thermodynamically driven by the increase in entropy that occurs when the plasmonic structure aligns its resonant absorption spectrum with incident illumination by varying charge density. As a result, the elevated steady-state temperature of the nanostructure induced by plasmonic absorption is further increased by a small amount. Here, we study in detail the thermodynamic theory underlying the plasmoelectric effect by analyzing a simplified model system consisting of a single silver nanoparticle. We find that surface potentials as large as 473 mV are induced under 100 W/m² monochromatic illumination, as a result of a 11 mK increases in the steady-state temperature of the nanoparticle. Furthermore, we discuss the applicability of this analysis for realistic experimental geometries and show that this effect is generic for optical structures in which the resonance is linked to the charge density.