Blocking and Bypass Diodes in a Solar Panel Systems


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. hi I’m Amy at the alte store we got some requests for a video on diodes and 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 and solar electric systems bypass diodes and blocking diodes the same type of diode is generally used for both a Schottky barrier diode but how they’re 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 shet cells that are partially shaded the cart 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 these cells because electricity takes the path of least resistance

it’s easier for the current to go through the diode then 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 why are the 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 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 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 in the battery and this charge controller prevents the backflow of electricity eliminating the need for a blocking diode however there still may be some instances when a blocking 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 solar panel both the port and starboard sides depending on your tact 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 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 a half a volt so you’ll always be losing a little bit of power through it a better although admittedly more expensive solution is to have separate charge controller for each string or panel another example for blocking diode is in a hybrid wind and solar system that may have the power coming from two different sources and two different voltages depending on the controllers used a blocking diode may be useful to help direct the current to the batteries nowhere else be careful where you put the diode in the system you need to make sure it is not in a bi-directional spot like where the current is going 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 video and if you’ve got any questions or requests put it 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