The ability to perform work using broad classes of energy conversion devices (e.g. batteries, solar cells, thermoelectric generators, fuel cells, etc.) depends on the energy provided by electrons as they transition from initial states to final states during a power cycle. Our laboratory investigates the performance of such heat engines when they are powered by non-equilibrium nanoscale optical phenomena, to reassess fundamental tenets in thermodynamics, photochemistry, and device physics. This talk will highlight several of our recent advances understanding and manipulating temperature in nanoscale plasmonic systems, for the goal of optimizing a variety of heat engines that are powered by sunlight.