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Page15
PV7-PV14 manual.doc
Please Read!!
IMPORTANT: USING or NOT USING
BLOCKING DIODES ON YOUR PV CHARGING SYSTEM?
There has been a great deal of discussion in the solar electric industry over the use of blocking diodes.
In an effort to clarify the topic
Flexcharge
TM USA has called, met with, or gathered information pertaining to the use of diodes from
several solar panel and equipment manufacturers to verify the following information.
The following is a condensed version of the information to assist you in designing a failure resistant system.
What is a blocking diode?
A blocking diode is a one-way valve for electricity. The band on the case of the diode is the output, which should be installed towards
the battery in the positive wire from each solar panel. There are two primary types of diodes,
Schottky
(sensitive to damage but low
loss type) and
Silicon
(tough, but higher loss type). They are rated by the amount of current that can pass through them in amps, and
the amount of voltage they can withstand backwards.
What is the function of blocking diodes in a solar system?
1
To prevent the flow of electricity into the panels when the panels are not making electricity, and to prevent voltage spikes in
the system from reaching the panels, They also prevent interaction between each solar panel in the system. Without diodes a
shaded panel and substantially reduce the output of the entire system.
2
To prevent a damaged panel which has shorted (a common type of failure) from draining the battery system, or drawing
power from the remaining good panels.
There are primarily three types of solar electric panel technologies being used today.
1)
SINGLE CRYSTALLINE
2)
POLY CRYSTALLINE
3)
AMORPHOUS
How should blocking diodes be used with each type of panel?
SINGLE CRYSTALLINE
panels are glass covered rigidly mounted panels. They have a low nighttime back flow of power from the
batteries. The loss at night is actually a little less than the amount of loss you get by adding a blocking diode to the panel. You will
get more out of your panel if you do not using blocking diodes on these type of panels,
On multiple panel arrays, blocking diodes
should be used
,
especially
on unattended remote systems, to guard against a failed panel. Because they are glass covered, a stray
falling branch, hailstones, a child with a rock, or bored hunter could bring the entire system down by damaging only one panel.
Diodes help protect the rest of the system from these hazards.
POLY CRYSTALLINE
panels are also glass covered rigidly mounted panels. They have a slightly higher nighttime draw of power
from the batteries when compared to single crystalline panels. The loss at night is near equal to the loss you get by adding a blocking
diode to the panel. You may or may not get more out of your panel by using blocking diodes on these type of panels,
On multiple
panel arrays
,
blocking diodes should be used
,
especially
on unattended remote systems, to guard against a failed panel. Because
they are glass covered, a stray falling branch, hailstones, a child with a rock, or bored hunter could bring the entire system down by
damaging only one panel. Diodes help protect the rest of the system from these hazards.
AMORPHOUS
panels are a very different when compared to the other types of panels. They have a fairly substantial nighttime draw
of power from the batteries when compared to single crystalline panels. The loss at night is higher than the loss you get by adding a
blocking diode to the panel;
in addition,
these type panels could actually draw enough power from the batteries at night to damage
themselves if diodes are not used.
To compensate for the diode loss, most amorphous panels have a higher operating voltage, to
make up for the voltage drop losses of the diode.
Blocking diodes should be used on all systems when panels have been connected in series to charge 24V, or
higher voltage batteries, or when using an inverter on the system. Inverters can cause voltage spikes as high as
60 volts on the DC positive wires. This is enough voltage to damage most solar panels.
In conclusion; blocking diodes should be used on all systems except, one panel single crystalline 12V systems. If your
system is so marginal that using, or not using diodes will make the difference, consider adding another solar panel to
your system.
