Bypass VS Blocking Diodes in a Solar Power System

today we're going to talk about the difference between a bypass diode on a solar panel and a blocking diode in a combiner box a lot of people are confused what they're used for so today we're going to go over that so first every solar panel on the market has a bypass diode or multiple diodes you can find these diodes by opening up the junction box on the back of your solar panel and inside this panel we have two diodes and what a diode does is allow current to flow in only one direction so first the number of diodes will tell you how many strings of cells you have on this panel so for this one we have two strings and each diode is wired in parallel to each string and this will ensure that even if this panel is shaded the rest of the panels that this is connected in series to will still produce power so the bypass diodes bypass this panel if it is shaded or if it's not producing enough current but if you're a beginner you might be curious as to what a series string is so these solar cells are wired in series so they can produce a voltage high enough to be used to charge a battery or to run an inverter and on this panel we have two series strings so that it can create 20 volts open circuit when you connect this panel to a system like a 12 volt battery this will actually drop to 16 volts which is the perfect voltage to charge a 12 volt battery so we have two strings to create this voltage in the first string if you look at how these cells are wired is right here and then it connects to this one this one this one and it creates a string all the way through up until here so if any of these cells on this string get shaded that bypass diode will allow current to flow past this string because if this is not producing enough power it will actually bring down the string so the bypass diode allows it to be bypassed and because these cells are in series if even a single cell is shaded it will wipe out the power producing capability of this string so whether you shade one cell or all of these cells that bypass diode will still be activated and will bypass the string also if you shade this whole panel then both bypass diodes will allow both strings to be bypassed so if the panel gets shaded it will not reduce the output of the whole string that this is connected to if i did not have these bypass diodes and i had other solar panels connected in series with this one and one cell got shaded all three solar panels would not produce any power but because we have bypass diodes if this were to get shaded the other two panels would still produce power so bypass diodes are very important for shaded cells now let's talk about blocking diodes because they're entirely different in the first difference of a blocking diode versus a bypass diode is the bypass diode is in parallel configuration with the series string with a blocking diode it's in series configuration with the string so this is a combiner box and it has two blocking diodes on the top and this can allow for four individual strings traditionally in the olden days a blocking diode was used to ensure that the battery was not being discharged at night because you can think of a solar panel as a large light emitting diode if you connect it directly to a battery the energy will actually flow out of the battery and into the large light emitting diode but the light that is emitted by a solar panel is not a wavelength that we can see it's not within our visible light spectrum and back in the olden days these blocking diodes were very important so you wouldn't discharge your batteries but nowadays you don't need them because most solar charge controllers ensure the current will not flow out of the battery from the solar charge controller so these are pretty useless in that regard today but blocking diodes have a second job that they can accomplish and they can be very useful for some solar panel array configurations so the number one use case is if you have arrays that are facing different directions you can use a blocking diode to ensure that when those strings are in parallel the voltage of one will not bring down the voltage of another so let's imagine we have a roof and on the east side we have a solar panel array and on the west side we have a solar panel array and what will happen is in the morning one of your arrays will produce more power than the other array because they're connected in parallel the lower producing array will actually discharge some of the energy produced by the higher producing array also the voltages will not match and whenever you have something in parallel you want the voltages to match so you can actually lower the voltage of both arrays if one of them is underperforming so what a blocking diode does is ensure that this does not happen it allows current to flow in only one direction from each string and typically we'll have one blocking diode for each string but in this combiner box we have two strings for each blocking diode so if you have an east roof you would put it on these two if you had a west roof you would put it on these two that way there is no fighting and the current will flow from each array in an equal fashion so over the course of the day you will actually produce more power when you have blocking diodes rightfully implemented but if all of your solar panels are facing the same direction and tilted in the same way then there is no point in using a blocking diode it's nice to have a combiner box that does have it but keep in mind there is voltage drop across any diode which is not much but it will lower the energy producing power of that array by a couple watts but over the course of a day when used properly a blocking diode can significantly benefit your system but keep in mind that the reason we see blocking diodes in a combiner box is because we assume that people are putting their strings into parallel but if you only have a single series string and you're connecting it to only one mppt solar charge controller you do not need a blocking diode at all we only use a blocking diode when the strings are connected in parallel if you have single series strings you should never use a blocking diode ever and in my systems if i have two separate arrays that are facing at the sun at different times of the day i will actually have personally separate mppt solar charge controllers i do not like to use blocking diodes unless the combiner box is far from the solar charge controller in that instance it will save money on wire so then i'll use a combiner box but if i can i personally like to have different solar charge controllers for each array that's facing the sun differently or at a different tilt angle but if they're all facing the same direction in the same tilt get a combiner box and hook up multiple strings and you will be good to go that's pretty much it a bypass diode will bypass a string of cells and ensure the maximum output from your panel and a blocking diode traditionally was used to avoid discharging of the battery but nowadays it's used specifically for instances when two arrays are connected in parallel let me know if you guys have any questions in the comments section below and i will talk to you later bye

Channel: DIY Solar Power with Will Prowse

Views: 181,358

Keywords: off grid solar, will prowse, diy solar, rv solar

Id: -x_6OLdAods

Length: 7min 9sec (429 seconds)

Published: Wed Jun 23 2021