Active
Systems
Active systems use pumps to circulate water
or other heat transfer fluid through the system.
When sunlight heats one or more solar collectors
sufficient for water heating, sensors and a
controller activate a pump to circulate a fluid
- either potable water from the storage tank
or a food-grade antifreeze solution in climates
exposed to freezing conditions.
An
active system also has a flat-plate collector
on the roof and a solar storage tank which is
usually located in a garage or utility room.
An electric pump circulates the water between
the collector and the indoor solar storage tank
whenever solar energy is available and needed
to increase the temperature of the water in
the solar storage tank.
Passive
Systems
A passive water heater consists of a water tank
integrated into or located above a solar collector.
These systems are suitable only for warm climates
where there is no risk of freezing.
In
a passive system where the storage is separate
from the collector, as water in the collector
warms, water flows by natural convection through
the collector to the storage tank. Water gets
hotter as it progresses up through the copper
tubes, eliminating the need for gas or electricity.
