On optimized solar-driven heat engines

Heat engines will usually be designed somewhere between the two limits of (1) maximum efficiency, which corresponds to "Carnot" or reversible operation, albeit at zero power, and (2) maximum power point. Each of these limits implies a specific dependence of heat engine efficiency on the temperatures of the hot and cold reservoirs between which the heat engine operates. We illustrate that the energetically optimal operating temperature for solar-driven heat engines is relatively insensitive to the engine design point. This also pertains to solar collectors whose heat loss can range from predominantly linear (conductive/convective) to primarily radiative. Potential misconceptions are also discussed regarding the maximum power point and the Curzon-Ahlborn efficiency of "finite-time thermodynamics.".