panel converts sunlight into electricity, which in
turn drives the direct current (dc) pump. In this
way, water flows through the collector only when
the sun is shining.
The dc pump and PV
panel must be suitably matched to ensure proper
performance. The pump starts when there is
sufficient solar radiation available to heat the
solar collector. It shuts off later in the day
when the available solar energy diminishes. As in
the previous systems, a thermally operated valve
provides freeze protection.
Common appliance timers also may control solar
system operation. These timers must incorporate
battery backup in the event of power failures.
The timer is set to operate during a period of the
day when solar radiation is available to heat the
potable water. In order to avoid loss of energy
from the tank during overcast days, the collector
feed and return lines are both connected at the
bottom of the storage tank with a special valve.
During normal operation, natural stratification
allows the warmer water to rise to the top of the