With respect to last week’s shiur on cooking in direct sunlight, readers have asked for a final p’sak.

Some pointed out that they are accustomed to brewing iced tea in direct sunlight.

The halacha is that cooking in direct sunlight is permitted and therefore one may place an egg on a piece of paper and cook it in direct sunlight. Likewise one may place a cold cup of tea in the sun even though it might reach a temperature of yad soledes bo. [1]

It is prohibited to cook on an item that is hot from the sun toldos chamah (derivatives of the sun) such as the sidewalk, hot sand or the hot hull of a tank.

How does the halacha deliberate on hot water in a solar system?

It is a rather complicated issue and we will attempt to be brief.

How It Works

Cold water enters the hot water heater from the bottom (see diagram below) and from there travels to the sun/solar collector. The collector consists of several black-coated pipes, on a black background, all encased in a sheet metal tray covered with glass, which absorbs the sun’s rays and heats the water. The water then returns to the upper part of the water heater. When a hot-water faucet is opened, the hot water is released and is replaced by fresh cold water.

Several factors must be considered -

1)     Is water heated in the panel considered heated in direct sunlight or toldos chamah?

2)     Is new fresh water heated from the hot water inside the tank?

3)     Turning on a hot water faucet causes cold water to enter the tank: is this g’rama, [2] p’sik reisha [3] or a direct action?

 

• On the one hand water heated in the panel is heated in direct sunlight and yet the sun alone could not heat the water to such a degree were it not for the greenhouse effect and the various techniques used in the panel, thus making it toldos chamah.

• Cold water entering the tank mixes with hot water in the tank. The hot water is toldos chamah (because it was heated in the sun) and will heat the cold water. Making matters worse is that, most solar heaters are equipped with an electrical element that one turns on when there is insufficient sun, or if a lot of water is used before the replacement water can be heated by the sun. If the heater is turned on before Shabbos (and turned off before Shabbos) it is very possible that hot water is in the tank and cold water entering will be heated from toldos ha’ur – derivatives of fire, (the water heated before Shabbos) which is an issur d’oraisso.
• On the one hand, cold water entering the tank is via p’sik reisha, because one’s direct action is opening the hot faucet, which ‘causes’ cold water to enter the tank. On the other hand, the system is engineered to operate in this fashion and Rav Shlomo Zalman Auerbach preferred to consider such designs as a direct action and not as a p’sik reisha. (Similar to the light turned on in the refrigerator when opening the door of the refrigerator. He was inclined to say that it is called a direct action and not a p’sik reisha being that it was engineered to turn on when opening the door).

So what is the final ruling?

It is widely accepted [4] to refrain from using hot water from a solar system on Shabbos, mainly because the panel and piping heat the water and are toldos chamah. Also, considerations such as for an ill person etc. must be considered. One must ask one’s rav for a final ruling.

May one use a dishwasher on Shabbos?

Obviously one may not manually operate the machine on Shabbos. The question is whether one may set it on a timer to operate at a certain time.

Rav Moshe Feinstein ztz”l opposed using a Shabbos clock for anything but lights and many follow that custom.

Conversely there are many who do not follow that custom and set heaters and air conditioners on timers. A dish washer though is different!

In order for the dishwasher to operate one must shut the door – if this is not done it will not operate. It can be compared to turning on a light switch at a time when the power is off, which will cause the light to turn on. The poskim prohibit such an action. [5] Consequently it is ossur to shut the dishwasher when programmed to turn on. [6]

Another possible problem is that even if it is g’rama, there are opinions who say that cooking via g’rama is ossur mid’oraisso and water in a dishwasher cooks. [7]