Hi I’m Amy at the altE Store.
We got some requests for a video on diodes in solar systems from Clifton and Reverend John,
hi guys, so here it is.
A diode is designed to let current flow in one direction.
If you’re familiar with plumbing, a diode is the electrical equivalent to a check valve.
There are two purposes of diodes in a solar electric system.
Bypass diodes and blocking diodes.The same type of diode is generally used for both,
a Schottky barrier diode,
but how they are wired and what they do is what makes them different.
Bypass diodes are used to reduce the power loss solar panels experience due to shading.
Because current flows from high to low voltage, when a solar panel has cells that are partially shaded
the current is then forced through the low voltage shaded cells.
This causes the solar panel to heat up, and have severe power loss.
Those shaded solar cells become consumers of electricity instead of producers.
Bypass diodes inside a junction box of a solar panel provides a low resistance path
for the current to go
around a series of solar cells that have been shaded. The diode is wired in parallel with the cells.
Because electricity takes the path of least resistance, it is easier for the current
to go through the diode than through the shaded cell, so it does.
This minimizes the heat gain, and reduces current loss.
Most solar panels have bypass diodes built in these days, so you don’t have to worry
about that anymore.
However, if you have multiple solar panels wired together in series, and you consistently
have shading on one or more of the solar panels,
wiring a bypass diode in parallel across the shaded panel can prevent the current
from being forced back through the shaded panel and cause it to heat and lose power.
So it acts the same as the internal bypass diodes, but bypasses the entire panel instead
of the individual cells.
Blocking diodes are used to prevent your batteries from discharging backwards through your solar
panels at night.
Again, current flows from high to low voltage.
So during a sunny day, the voltage of a solar panel will be higher than the voltage of a
deep cycle battery,
so current will naturally flow from the panel to the battery. But at night, if the solar panel
is connected directly to a battery, without a charge controller,
the voltage of the solar panel is going to be lower than the voltage of the battery,
so there is a possibility of some backwards flow,
pulling power out of the battery. It won’t be as much as the flow during the day, but
there may be some.
As a result, in the days before charge controllers, people would put a blocking diode in series
between the battery and the solar panel,
only allowing power to go into the battery.
Nowadays, most solar systems have a charge controller between the solar panel and the battery,
and this charge controller prevents this backflow of electricity, eliminating the need for a
blocking diode.
However, there still may be some instances when a diode may be helpful, a couple come to mind.
If you have multiple parallel strings of solar panels that get shaded at different times,
a blocking diode in series will help prevent the power from the sunny string being forced
back up through the shaded string.
This is common on sailboats, with a solar panel on both the port and the starboard sides.
Depending on your tack, one of the solar panels may be completely shaded, and the other completely
sunny.
A blocking diode in series with each string will allow the sunny panel to output all of
its power,
and basically disconnect the shady panel. However, there are some disadvantages to this method.
There is a slight voltage loss through a diode, about ½ volt, so you will always be losing
a little bit of power through it.
A better, although admittedly more expensive solution, is to have a separate charge controller
for each string or panel.
Another example for a blocking diode is in a hybrid wind and solar system
that may have the power
coming from two different sources at two different voltages. Depending on the controllers used,
a blocking diode may be useful to help direct the current to the batteries, no where else.
Be careful where you put the diode in the system, you need to make sure it is not in
a bidirectional spot,
like where the current flows both into the battery and out to the inverter.
You also have to make sure the diode is designed for the right voltage and current to handle
the flow through it.
I hope this was helpful. Please like and share our videos, and if you have any requests,
put them down in the comment section.
We love to hear from you. Also, make sure to check out our website at altEstore.com
where we’ve been making renewable do-able since 1999.