A novel energy efficient variable aperture mechanism for a cavity-type solar receiver is presented. A 10 kW, solar simulator was used to experimentally test the receiver with and without the aperture mechanism and while the mechanism's blades were uncooled and water-cooled. An in-house model of the system was developed by coupling a Monte Carlo ray tracing to a two-dimensional heat transfer analysis, which was then experimentally validated at three different solar simulator power levels, four different feedstock gas flow rates, and eight different aperture sizes. Using the validated model, it was determined that approximately 60% of the receiver's input power is lost through radiation, which was mitigated by optimizing the receiver's fixed aperture size. It was observed that the receiver's temperature non-uniformity decreases as the aperture size reduces and its temperatures peak at a certain optimum aperture size, which decreases as the input power level increases. As for the aperture mechanism, water-cooling the aperture mechanism had no apparent impact on the receiver's temperature distribution. Furthermore, the aperture mechanism did not demonstrate the same desirable behaviors as varying the receiver's fixed aperture size, such as obtaining peak temperatures at certain smaller sizes. Nevertheless, the aperture mechanism was shown to be a very promising technique to regulate a solar receiver's temperature and compensate for intermittent solar irradiance since the results showed that the aperture mechanism can regulate the average temperature within the range of 475-800 degrees C and while capturing and recovering 54% of any surplus power it intercepts.