Blocking and Bypass Diodes in a Solar Panel Systems

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 where we’ve been making renewable do-able
since 1999.

66 thoughts on “Blocking and Bypass Diodes in a Solar Panel Systems

  1. when the cell is shaded, the current drops down, like pinching a garden hose. the cell will have static voltage but reduced current flow. the bypass diode completes the circuit in a loop for the panel. I understand just hard to put into words.
    If a seller says that these are blocking diodes when they are not, I have to wonder why. and there are many.

  2. Dear altE Store. I have seen some PV systems which use capacitors right after the DC breakers. It is claimed that these capacitors are used to make the fluctuation of the voltage and current from the PV panels to the controller more smooth. Please, explain this to us. Many thanks to your other videos.

  3. hi, i wounder does the diode need to be higher then the battery outputs. i got a solar panel that produces 21 volts and up to 1.3 amps and i wounder do i just need a diode that is litter bit higher than the solar panel or a diode that is higher that the battery?

  4. oh, i see you only need a diode the can handle oneway amps and volts, and it doesn't matter about the other direction right

  5. just checking because the the amps on the battery is high, and how do you what kind of battery do you use because in some battery doesn't show me the amps hour

  6. Hi..I have a panel output of 150 watt with 8.5 amp approx, also I have diode of 6amp and 3ampCan I use it both in order to save panel from reverse current

  7. Some PV panel manufactures states the bypass diodes that is in their panels. how to select blocking diode for a given panel?
    for example for a 260W panel

  8. If I have (12) 320 watt panels : 4 strings of 3 parallel panels feeding into one charge controller, and half of the panels (the eastern most) receive full sunlight an hour after the western most panels, do you think I should add blocking diodes to the eastern panels to prevent the eastern panels from sucking current before they get light ? —- your video sort of suggest I should

    Midnight Classic's string program suggests their Classic 200 will work with this 12 panel configuration- thus my question.

    I guess the other option is to buy 2 charge controllers and have the western most panels on one, and the eastern most on the other….

  9. Hi Amy, interesting that you bring up the two parallel system issue. I have a 600W wind turbine with a MPPT controller and will be adding the Renogy 600 W  6 panel system with the 60 amp MPPT controller going to the same 12 V battery bank. I would think that with two different MPPT charge controllers running in parallel to the batteries that each would have diodes blocking backflow, thus negating the need for additional blocking diodes. Am I doing the right thing or are there other precautions I should take ?   Thanks   Jim K   RV Prepper

  10. Can MOSETs used be safely as blocking diodes for 12V parallel panels?. IRF 1404 has 4mOhm resistance so at 10 amps only 40mV voltage drop.

  11. Hi, do you mind tell how can I charge different type same voltage battery in parallel connected to Hybrid Inverter. when the batteries can also be charged by grid when solar is not enough.


  13. I have an HQST Mono Flexible solar panel that just stopped working. Is there anything I can do to the junction box (?) to make it work again? Thank you

  14. would you like to make unbreakable transparent solar module which is lighter than glass.
    i can make for you if interested.

  15. This is a well done informative video.
    Question- looks like I blew the diodes in 2x 100W panels. I am guessing by disconnecting them in full sun or an intermittent short I created when installing a transformer on the load side of my 2x Morningstar SunSaver controllers. Still seems odd as the controllers are full featured and I would have guessed they would protect in this scenario.
    If I replace the diodes is it possible the panels will still work?

  16. hi, i am make my only solar panel and i want to know how to pick the right blocking diode? i am boosting the voltage from 7.5 to 13.0 volt with a boost converter. and i plan to increase the amperage from .2 Amp to 3.5 Amps. So how do i calculate to get the right diode to charge a 12 volt car battery without a charge controller ?

  17. Is that a Genasun boost charge controller..? I have a question about the diodes. With a flexible solar panel rated at: 19v, 6.7a, 120w, how many OMS should the diode read if working properly..? (or does it matter how many amps the panel is rated at, do the diodes all read the same when tested..? (How do the amp rating affect reading the multimeter..?

  18. hi solar queen, want to know plz that can we connect small AND big solar panels With same voltage but different in watt's in series by putting A. by pass diode With small Panel? plz reply thanks

  19. i have two 100w 12v solar panels. each panel has a imax of 5.72A. and diode rating of 12a. and 10A fuse rating. if i wire 3 of these together in parallel to try and create a 300w. 12v panel will they destroy themselves? seeing as how the current together could rise to over 15Amps which is higher than the diode and fuse rating?

  20. if we remove all the diodes from the Panel And measure the volts from the leads coming out from junction box, what would be the reading? will it be same as normal? or less?? plz comment.

  21. Texas Instruments makes an "active diode" (FET) that has a very small forward voltage drop (0.026V) at 8A, and can handle up to 15A.

  22. I've been thinking and guessing a lot of things about solar panels and diodes, I'm glad I found this video confirming my ideas, thanks !

  23. Very well explained. Thanks alot. Could you maybe make a video for using fuses instead of blocking diodes in the case of shading on parallel PV panels. Thanks again

  24. Hi, how can we know if blocking diode is present in the solar panel just by looking at it? I am layman. I have been given a task to identify whether a blocking diode is present in the solar panel or its part.

  25. You mentioned in your video, that it is best to install separete charge controllers for each string of panel, although it is more expensive. What do you mean by that? Do you have a video on this subject? Thanks.

  26. I removed the blocking diode between my solar cells and my battery so now at night, my solar panels make sunshine by using power from my batteries.

  27. Hello! do you have any videos on which kind of bypass diode(Amps/Volt) to be connected in parallel with series of solar cell (Amps/Volt)

  28. my name is Bobby. my profile picture here is of my girlfriend Patty who she sadly passed away from heart failure about 17 years ago. you did a very great job on your video on blocking diodes. i do have a question i like to ask you,, i understand that a blocking diode lets electricity travel one way but blocks it from going the other way,,,, i do understand that in the blocking mode that the diode blocks most of the electricity but there is a little voltage loss of some electricity passing through,,,,,,, now here is my question,,, could i use 2 diodes or better yet even 3 or even 4 diodes in series and have less of a voltage loss,,, or is that something that by using 2 diodes in series will be a bad idea.

  29. at a later date,, when i start building my home built micro camper i to tow behind my moped scooter,, i am going to be wanting to order some solar panels. i subscribed to your youtube cannel and i clicked on liked.

  30. Suggesting i have say 4 panels in series, say 100w 12v, and i wish to add bypass diodes for each, would each need to be rated the same, and how much, and why?

  31. i have a solar panels installed there and recently i have installed hybrid system with generator and now my question is that when there is bright sunshine the solar mppt modules get burned ? so what could be the reason ?

  32. I have a 100 watt mono,panel I blew out one of the 2 diodes, what do I replace this with ?? Blocking or by-pass diode??

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