In this research, the effects of the novel movable cover on reducing heat loss and overheating protection of a cavity receiver for parabolic trough solar collectors were studied. The heat loss tests were carried out at different inlet temperatures and mass flow rates. A three-dimensional heat transfer model was developed and validated by the test data. Effects of ambient temperature, wind speed, inlet temperature, rotation angle of the collector and on-off state of the movable cover on heat loss were investigated. The heat loss of turning off the movable cover was less than that of turning on it. The heat loss reduction rate varied from 6.36% to 13.55%. Three tests of collecting solar energy all the time (control group), overheating protection with the methods of rotating the reflector and turning off the movable cover were conducted under similar weather conditions. The results showed that both the overheating protection methods were effective. However, the method of turning off the movable cover avoided rotating the reflector and re-tracking the sun later. The presented novel movable cover improved the thermal performance of cavity receivers remarkably in a simple way. (C) 2018 Elsevier Ltd. All rights reserved.