Sometimes called a bread box system or integral collector storage system, a batch solar collector consists of one or more storage tanks placed inside an insulated box, usually with a glazed glass plate, facing the sun. The storage tank and the solar absorber act as a single unit and use the normal water pressure of your system, therefore there is no need for other expensive components such as pumps and controllers. A batch collector can be mounted on the ground or on the roof. Ground mounting usually makes for a very simple and cost effective installation.
Some batch heaters use a "selective" coating on the tank(s). These surfaces are good absorbers of solar infrared radiation but many DIY'ers will simply paint the tank a flat black colour to increase heat absorption. Batch collector systems are much cheaper than flat-plate collectors or evacuated tube collectors, but also deliver less energy per year and can not be used during winter months if outside temperatures reach freezing point.
Passive, batch solar water heater: Your household cold water, under normal pressure, is diverted into the solar collector during warm months of the year. The heated water then flows back into the existing hot water tank and into your home. As the normally cold water, has been preheated, the energy required by your hot water heater is greatly reduced. When night-time temperatures start to approach freezing, the taps to the batch heater are closed and the batch tank is drained. Note that using large amounts of warm/hot water first thing in the morning will reduce your efficiency. Try to wash the clothes/shower, later in the day with ANY solar heating system.
Cottage Batch Water Heater
Here is a very simple batch water heater used at our cottage, to shower off after coming out of the water. The tank was taken out of an old water heater and painted black. It's fed using a standard garden hose at the bottom of the tank. The heated water is then taken off the top of the tank, using a standard black garden hose. Very easy to setup and it does the job, since you only use the shower when it's warm enough to swim!
DIY Solar Water Heater
Here's a nice little project completed by Jake Teater that goes a step beyond the batch heater. Jake has used half inch tubing, placed inside fluorescent light tubes, painted black and covered with a sheet of glass. The whole thing is powered via thermal suction. Visit Jake's site for more info.
If I was making this collector, I would NOT use the fluorescent tubes, as the system works well without them, plus I would not want to work with the chemicals inside the tubes. Releasing the mercury vapor can't be good for you or the environment.
