Solar Batch Heaters, also known as ICS or Integral collector-storage systems are one of the simplest solar water heater designs. They can also be one of the cheapest solar hot water systems. They once were know as a "breadbox water heater" by the do-it-yourself community!
A batch solar water heater can be as simple as a metal tank sitting in the sun. Most batch water heaters are made of one or more black tanks or tubes in an insulated glazed box that is aimed at the sun. A “glazed” box is simply a box with a glass or plastic cover or window that allows the suns rays into the box. The "glazing" helps keep the heat in and make the tank even hotter.
Cold water from your house under pressure first passes through the batch solar heater, which has been baking in the sun all day, which preheats the water and then continues to the regular home water tank or heater. In this way if the sun is not shining the normal water heater can provide the necessary hot water. In this way you always get all the hot water you need or want!
Batch solar energy water heaters produce very hot water! Temperatures can easily exceed 160 degrees which is much hotter than usually comes out of your tap. You can easily be scolded so to prevent that a tempering valve is usually installed that controls the temperature delivered to your tap by mixing in cold water.
Passive solar water heaters are best for households of two to four people where freezing is rare, although multiple heaters can be installed in series for more hot water capacity. But remember these tanks can be very heavy so it is best to make sure your roof can handle the load!
Solar batch heaters, or ICS systems are simple, reliable passive solar water heaters. However, they should be installed only in climates with mild freezing because the collectors itself or the outdoor pipes could freeze in severely cold weather. Some recent work indicates that the problem with freezing pipes can be overcome in some cases by using freeze-tolerant piping with a freeze-protection method.