On a sunny day, sun transports power of 1000 W / m2 to us. If you have a lens with a front lens opening of 20cm2, this means 1-3 watts of energy in the form of light is transported to the sensor inside the camera.
On a dark cloudy day the above 1000W / m² shrink to 1/10th, i.e. 0.1 W to 0.3 W of energy is transported to the shutter and sensor.
Energy means heat, and thus temperature will rise inside the camera.
On the other hand: how much electrical energy could a sensor transform into heat?
Let's assume your camera has a battery of 8V x 1.2 AH of energy = 10 Wh. lets assume your battery drains after 1 hour of continous camera activity. Then within 3600 seconds the 10Wh of battery energy is consumed by camera processor and sensor. 10 Wh / 3600s = 10W
i.e. if you work continously with live view, electrical heating from circuitry is much higher than heating by light rays.