Q&A: Solar Water Heater on the Sabbath
Originally published:
This is an English translation (via GPT-5.4). Read the original Hebrew version.
Solar Water Heater on the Sabbath
Question
In your opinion, is heating water in a solar water heater considered cooking by the sun itself (direct heating of the water), or cooking by a derivative of the sun (heating the pipes in the collectors, which in turn heat the water)? With respect to the laws of cooking on the Sabbath.
Answer
https://www.kosharot.co.il/index2.php?id=53328&lang=HEB
There is room to dispute his claim that cooking the water itself is considered the sun and not its derivative. As far as I know, the sun heats the system, and it heats the water. But I haven’t checked it just now.
The water is definitely heated directly by the sun, and one can view the pipe as a container rather than as a derivative of the sun. The issue is that there is also the collector and the glass surface (which functions like a greenhouse), which also contributes to heating the water, and that is certainly called a derivative of the sun.
The question is whether one can view the whole system as cooking by the sun or as its derivative (something like “this and that together cause it”)?