[bigiain]

They've got active/closed-loop control of the mirrors.

Right now, it looks like it's just using the camera feed to aim the reflected bright spot into the centre of the fiducial markers to align it with the oven window. If you wanted consistency temps, you could over provision enough mirror, then use a temp sensor in the oven to intentionally aim some of the bright spot outside the oven window - "wasting" that solar energy, but it was free anyway. (Maybe put a solar hot water system collector right next to the oven window, so any heat not needed for cooking could be used to make hot water for cleaning up after cooking?)

[remipch]

Yes, this is exactly how I planned to control the temperature : add a temperature sensor in the oven and implement a simple PID in the supervisor to do so.