Reducing the operating temperature of photovoltaic modules increases their efficiency and lifetime. This can be achieved by reducing the production of waste heat or by improving the rejection of waste heat. We tested, using a combination of simulation and experiment, several thermal modifications in each category. To predict operating temperature and energy yield changes in response to changes to the module, we implemented a physics-based transient simulation framework based almost entirely on measured properties. The most effective thermal modifications reduced the production of waste heat by reflecting unusable light from the cell or the module. Consistent with previous results and verified in this work through year-long simulations, the ideal reflector resulted in an annual irradiance-weighted temperature reduction of 3.8 K for crystalline silicon (c-Si). Our results illustrate that more realistic reflector concepts must balance detrimental optical effects with the intended thermal effects to realize the optimal energy production advantage. Methods improving thermal conductivity or back-side emissivity showed only modest improvements of less than 1 K. We also studied a GaAs module, which uses high-efficiency and high-subbandgap reflectivity to operate at an annual irradiance-weighted temperature 12 K cooler than that of a c-Si module under the same conditions.