We put the cooker to a more rigorous test today. Using a different pot, which I painted black, I put 1 liter into the cooker in the late morning. The results:
1 temperature probe coming down with heat stroke
1 semi-molten plastic bag
2 l of boiled water
1 l of very hot, but unboiled water
Apparently, the solar cooker works so well that the power input is too much for the small hand-held temperature probe, and it failed after about 15 min in the solar cooker. It had been inserted through a hole in the lid, with the actual sensor immersed in the water and the electronics and the display just above the lid. The sensor is good for up to 350degC, but not the handle that includes the electronics and the display. Back at the hab it was found that only the cover to the battery compartment had started to melt, but otherwise the probe is still intact and after minor repairs functional again. However, in lack of a working temperature sensor this morning, we were only able to measure the time it took to get the water to the boiling point.
The first pot of water boiled after 24.5 minutes, at 10:40 am local time. The water of the second pot got very hot, but did not boil within
45 min. I assume that this was due to the stronger wind during the second test. The third pot was put inside a plastic bag to reduce heat loss to the environment, and water boiled after 34 minutes. Towards the end of the test a distinct PVC smell developed around the pot and the plastic bag showed signs of melting in various spots.
The orientation of the cooker was adjusted a few times during the tests.
After each run, the heated water was transfered to the airlock and sent inside to the cooking team.
During the next days, I want to test the cooker during low light conditions - right after sunrise and inside the Greenhab.