Batch
water heaters are simpler than any other water heating system, including
active, thermosiphon systems, or conventional water heaters. However, they provide
less hot water, usually only 15% to 40% of a family's yearly demand. Batch water
heaters combine the collector and storage tank in one box. The box has
insulated sides, a glazing cover and one or more tanks inside. If the box has
an insulating lid that can be "closed" at night or during bad weather,
the unit is called a "breadbox" water heater. On a sunny day,
sunlight travels through the glazing and strikes the tanks, which are painted
black or covered with a heat-absorbing material. As the tanks absorb the sun's
energy, the water inside heats up. This "preheated" water goes directly
into a conventional water heater.
Many
batch heaters are manufactured and sold commercially. However, because of the
simplicity of their design, some people build their own. Most of the materials
can be purchased at local hardware stores for between $300 and $600 (depending
on the design). The appearance of batch systems has been a major drawback, but
units are now available that fit into the roof structure and resemble a skylight.
Others can be enclosed within interior spaces, so they are less obtrusive and
are protected from freezing.
