You have just enlightened me M8. I had seen the term blocking diode and bypass diode and assumed the two were the same. Thank you. I have been messing with off grid power for ~10 years and you just set me strait.
That is a really nice way to describe how things work. I already knew the basis but still really enjoyed watching your video. Totally agree that in your scenario you’re unlikely to require a diode. I wonder if I might though, as I’ll be building a solar fence where at times many panels won’t be in the sunlight so maybe that would yield different results. I’ll certainly film a test against that and see if it also works just fine without diodes. I’ll then also compare the diodes with Tigo optimisers as I haven’t really seen such a test but I think they go hand in hand when you look at how those optimisers work. Thanks for another good video!
You are right, in my first built east west 5KW unit I measured zero current running in the shaded part when the sun still was bright at the west side. Diodes produce losses, 0.7V siliciums
I would add only that a solar panel acts as diode ONLY in that when power is pushed to the panel it becomes an LED (light emitting diode), however the light emitted is not in the visible spectrum. Thanks for giving me some good laughs when you responded to people's comments though. Although I have a feeling those types of comments will never stop, lol. Great video, cheers. 😎
a blocking diode is only needed if one is using a low wattage panel direct to a battery with out a controller lets say for long time vehicle storage to stop the battery discharging into the panel
I have some doubts: 1, The solar strings act like 2 battery cell connected parallel (remember top balance!). Until there is a big enough load the current flows MOSTLY to load. 2, Parallel resistors. The MPPT (and LiFePO4 cells behind it) have very low resistance. The Solar panels have high resistance. So current is flowing through the panels too, but few: R = R1×R2 / (R1+R2) 3, Voltage difference: where there is a potential difference there is current (and bigger makes higher) 4, MPPT is a high frequency DC/DC converter. So it pulsates very fast (open-close) in the solar side. And every time it is open there is an OC (only path through lower V string). 5, You can have a string in East and one on West roof (angle >20). The East is already producing in early morning where the West panels are totally in dark. 6, You can have more than 2 strings parallel. Like 2s6p config for some MPPT's. If one of the strings is in shade then 5 strings will push current through it. 7, Use fuses for the parallel strings. If a short occurs then all the parallel strings production will be going through THAT (lower resistance). Making a big shiny arc (DC so constant arc).
Very good experiment and explanation. That confirms what i had thought regarding diodes and back current. Earlier today, i found som facts about solar cell tecnique, and read that a solar cell is a type of diode. But the current created by sunlight flows in back- direction of the diode/solarcell. That should explain why the solarcell does not block ” back-current” Back current in the way we ar speaking about will flow in forward direction thru the diode/solarcell.
Don't know why you tube said to watch this video but it did. I did. I use a blocking diode between each string in parallel. I don't know what the failure mode is for a solar panel but if it is shorted, I don't want 50 amps feeding it.
@@OffGridGarageAustralia I'd reply with "Yes". Not giving you an answer to either but knowing that I'm on one side or the other (or possibly both sides). :: Chuckles ::
RE: Blocking diodes. There is a case for blocking diodes for protection in case of "Fault". In the case where you have many strings in parallel, each string should have fusing or blocking diodes. In the event of Fault where cells go short circuit in a string - the parallel strings can drive "Lots" of current through the faulty string leading to fire and so on. A fuse or blocking diode saves this from happening. Solar cells are an interesting creature, they are PN junction so they are a diode, but when irradiated the electron flow is such that the diode action is "Biased" Off. They really are a gift to society. Enjoying your videos Andy :-)
Hey Andy. Good explanation on blocking diodes. I use three of them on my system, but it's very different than your setup. My system is on my Recreational Vehicle and i have three different sources of voltage/current to charge the batteries. I can use the onboard RV charger, i can charge from the tow vehicle, or i can charge from the Solar string. I found that i had to use a blocking diode for each of the three charging systems, as it was possible to be charging the batteries at night and the RV charger would pass current through the solar string. The biggest downside of the blocking diode is the .5v voltage drop that it creates, and the heat that has to be dissipated with the blocking diode. I have a large heat sink on the three blocking diodes to deal with the heat. Anyway, very different application that yours, and the blocking diodes allow me to use all three sources at the same time if i choose to quickly charge the system. Thanks Andy. Good stuff!
Thanks James, very good point and a different scenario. If you have panels with different voltage, you need blocking diodes, that is correct. You can get Shottky diodes which have only a 0.2V voltage drop.
Schottky diodes have a .4 volt drop. Use them for this purpose. Also, your solar charge controller should prevent current from going from your RV charger through the solar string but it depends on how you have it all connected. Seems to me you should only need one diode in the right place.
that may be true but show us a situation where one panel would be it total darkness while the other is in lighted area. even in shaded area the solar panel is still producing
All diodes and solar cells act like zener diodes when reverse biased. That includes all semiconductors acting like a solar cell to some degree when exposed to light. If you had thousands of LEDS you could make a solar panel. Although you would need many blocking diodes with one being in each small string, because they can only handle so much voltage before they try to conduct. That was some interesting trivia. Rectifying diodes also will have a much lower effective voltage drop if you put multiples in parallel. PN junctions are weird like that.
you're slightly wrong about all diodes acting like zeners, a zener junction will recover but a normal diode either stays shorted after rv breakdown or burn out
What blocking diode would you recommend for a 100watt 12 panel. I have shade problems currently and panels in different locations. A part number would be great. Great video.
Its best to have the blocking diode, as its not just shaded panels in a string, but also a faulty panel or cell can get very hot if its being back-fed from other parallel strings. Even thou most of the power will go to the charger/inverter some can back-flow through a dark string, if there is a fault, a lot of current can flow and the panels will get very hot. Did u know dark shaded spots on panels will destroy them as current is forced through the shaded cells and they get hot. Remember the roof is very hot as it is.
The diode at the back of the solar panel's black box is a bypass diode. Its function is to bypass the panel in case it got damaged (open circuit damage to be exact).
Blocking diode (function) will be in any good MPPT controller. Or ANY good controller, to prevent night loss. Installing directly in the panel array would be a waste, as they cause voltage loss, and extra expense.
Quite a bit of flickering...you might look into changing those lights...Maybe you get a LED driver (Power supply) and connect it to DC LED panels? The LED driver will make sure that you have a smooth DC Voltage without much ripple at the output. Alternatively you could use a DC-DC converter to dirve the LEDs with your battery bank directly.
Thank you, it’s fantastic to find a You tube site that is easy to understand and is interested in teaching the facts about the subject. Question, is it best to use lithium iron sulphate batteries? I have no experience in solar energy I’m hoping to set it up in my outside work shed.
Andy - interesting experiments, try totally shading the solar cell, then put it in full sunlight and see if the voltage required to back feed current through the solar cell changes? In theory the solar cells output voltage (what ever it is at the time of testing) has to be overcome by your power supply before any current will flow from your power supply? Your solar cell was under quite bright light so it could have been producing a voltage which would explain why it needed higher voltages to back feed current through the cell. Blocking diodes are only needed with parallel strings for example, when one string is facing east and another is facing west so they do not produce power at the same time of day! As your experiments clearly showed parallel strings on a roof in a east then west facing roofs would back feed without blocking diodes on each string. In situations like this it is better to have each string on separate MPPT inputs on your inverter then blocking diode are not needed. :)
When I connected the solar panel to the power supply to start the experiment, you could see the power supply did not show any voltage because the solar panel did not produce any power/voltage. if the panel would have produced say 3V under these conditions, the power supply would have shown these 3V. So the LED light above was not enough to trigger anything apart the 0.2V the power supply showed.
@@OffGridGarageAustralia Andy - what your power supply shows as a voltage will be largely irrelevant because it totally dependent on the impedance of the volt meter and power circuits in the power supply relative to the electromotive force (EMF) and current provided by the solar cell under its ambient light conditions at the time of testing! Presumably these are unknown but low, so if the power supply is actually NOT providing back current and the cell is in near total darkness but still producing its rated voltage when open circuit, when you apply back EMF with your power supply back current will only start to flow only when the EMF produced by the solar cell is overcome by the EMF of the power supply. Which is why you got the result you did with your experiment in my view. By the way, you are right solar cells and solar panels are NOT the same as diodes they act more like battery cells or capacitors than diodes! Blocking diodes exist in parallel string arrays because conditions relating to shading can and do occur that allow back current in a string to rob the total array output of power. Bypass diodes exist in panels to prevent partial shading of one or two cells causing cells to overheat and become a fire danger by becoming a resistive load in the string or panel. In a worst case scenario most of the energy produced by a string can be used to heat just one cell creating what is commonly known as a hot spot on the panel.
Hei Andy, have u tried to check the 5.5v mini solar power if it glows in the dark? If u feed it with 6v or over you'll have a little bit of surprise 😮😉...
Thanks - I was wondering about both of those diodes... answered my question completely!! People should do a little real research in the literature, not U-Toob, before throwing scat.
I can see blocking diodes being necessary in an RV/campervan solar system where let's say you park and a tree branch blocks the front of the vehicle but not the back.
Good video, very well explained re solar panels wired in series, but what about those wired in parallel? I have 3 panels (1x100W, plus 2x 160W) charging 12V AGM batteries for shed power. The 100W faces SSE, and both 160W panels face due South. One of the 160W panels is shaded each morning by a neighbours tree. Should I install a MC4 type blocking diode in the positive cable of each panel output?
I know this video is 3yo allready but I think the conclusion is questionable. Because: What happens if the solar controller or wires/conectors to it fails? They do from time to time! As you just proved the shaded string will become the load for the unshaded string. It even happens before you reach Voc. I bring this up because a installation case is to have 1 string pointing West and 1 string pointing East. Currently pv panels are a lot cheaper than (mppt) controllers. So it makes sense to install panels in a way that they will not have the same, by fare, incoming radiation during the day. So based on your test here I conclude that you should have blocking diodes (one on each string), when connecting pv strings in parallel, as a safety measure. PS: As pv panels has increased in size and power blocking diodes might allready be incorporated. So check your panels spec sheet.
*Blocking* *Diodes* are recommended when you connect a Solar Panel directly to the battery, without any Charge Controller. This prevents the battery from discharging through the Solar Panel(s) at night ...
@@MrSummitville It was a gift 10 years ago from my daughter. Surprisingly well designed learning tool/toy for the time. I know a couple offgriders that used them for years as their main electrical power source. Yes, they are wayout dated now, but if it works no need to throw them away. It can run 1 light in a shed or outhouse. I did have to open the panels up after 7 years... break the corners of the glass to resolder the leads back on. Lot of fun, minimally useful.
Andy, all along, I think the diode inside the solar panel was blocking diodes. You corrected my misconception. Thanks. You said it was not necessary to add blocking diodes since the charge controller had the lowest impedance. Yes, I totally agree with you. But if the battery was fully charged, and the charge controller was in float mode, then the charge controller would not take in any current from the panel. Then panel with a higher voltage will push the current into the lower voltage panel. In this case, will it hurt the lower voltage panel?
Simply said, bypass diode is connected between the terminals, blocking diode is connected in series to prevent back-current. Use a diode with lowest voltage drop for best performance
@@OffGridGarageAustralia if we're talking bout bypass, voltage drop does not matter. If we're talking blocking diode, i always choose schottky. The differential between schottky and ceramic one is not marginal. The performance loss is 1W on my 20Wp (schottky vs ceramic) and progress more as you catch the sun on stronger panels
I need to clarify something. The cell you have is 5.5 volts, assuming a diode turn on voltage is 0.6 volts that suggest a 9 or 10 cells in series. Let's say it is 9 cells or diodes. The proper electrical model would be would be 9 diodes in series where the bar is attached to the negative terminal ( or downwards on your drawing). This down ward direction is what limits the VOC ( open circuit voltage) of the cell. Multiple cells in series makes a panel. The curent from the panel is caused by the light, freeing electrons which flow in the reverse direction (or up ward direction on your drawing). Modeled as an ideal current source In analyzing panel performance you start with the standard diode equation then add a photo current current of a single cell. The panel performance is determined by the number of cells in series. The diode equation is an exponential where the temperature changes... change panel performance. I agree if you have strings where the panels have the same number of cells, the chance of turning all the downward diodes on is low. If your strings have a different number of cells in your string there may be a chance you can exceed the full turn on voltage of the dark panel. Panel fires do happen for this reason. The recommendation of most manufacturers is to use the same type of panels with the same number of cells and the same wattage. If your mixing panels wattage or type ...silicone or the film type blocking diodes may be in order. A better approach would be to use separate charge controllers for wattage or type panels. Multiple charge controllers can be hooked up to the same battery (bank). Don't let the math scare you, the analogy of a one way valve is correct for a power diode. For a solar panel it is more a one way valve with a very small leak. Rules of thumb for a silicone diodes for typical users. The one way valve is completely off with a forward biased voltage of 0.4 volts The one way valve conducts a current so small it can be called off at a forward voltage of 0.5 volts. The one way valve can pass a measurable current at 0.6 volts forward biased. The valve is partially open. Most solar panels sweet spot is 6.3 volts The one way valve is fully open if the diode is forward biased at 0.7 volts. The series resistance of a solar or power diode is so small it can be ignored or set to zero. The parrell resistance of a diode is so large it can be ignored or set to infinity. Ths 5 volt solar cell you used is really a module of 9 cells or diodes. If you look at the shadows on the front you can count the number of photovoltaic diodes. Good luck
What happens at night in total darkness? Isn't it possible (due to a fault in the Solar Controller) that the battery storage voltage & high current can backfeed into the solar panels and destroy them? Isn't this the reason why every Solar Panel has a diode across the (+) and (-), with the cathode facing the (+) terminal? Also, talking about diodes, if you are drawing any inductive load directly from a Solar Controller, it is wiser to install a blocking diode of a suitable size - simply to protect from back EMF reaching the Solar Controller, with possible resultant damage. This is my understanding, and I hope it makes sense.
Back in the early 90s i used 60 watt Solarex panels witch came with no diodes. I installed blocking diodes and ran straight to my batteries. No charge controller.
It's not necessary to have a blocking diode on each string if you have very few parallel strings. You don't want to run 80*ISC through one string because its shaded and you have like 100 strings in parallel.
It does not turn off the charge controller, there is no switch or relay. When the battery gets full and the charge controller reduces power it just drives the panels away from the maximum power point, into an inefficient area of the solar panel curve so to speak. It will not disconnect the panels though.
@@OffGridGarageAustralia thanks for the answer and for the time you spend to give us free learning content. You, Will Prowse, David Poz and Jehu Garcia are the best solar teacher in the globe!
added comment-just remembered 1 time i had ice drops stuck on panel in use when i had removed snow from but other did not and was not connected--this back current i now have an answer as to why 1 had ice crystals the other was smooth--live and learn
Please, anybody can help me to explain what is happening. I have a 24V setup with 16 lithium battery, a BMS balancer JKONG and a Powland Inver. My app show a 75% charge,432ah in the battery but the Voltage is down to 23v. ... The inverter is reading 22,1v and prepare to shoot down. Why??
Thanks for going over this, I like to hear the basics. I had not used any blocking diodes in my system and noticed that the combiner boxes that they sell come with them so always wondered if I should invest in one of those fancy boxes.
I think they are good for marketing. It all depends a bit on your circumstances and location. If you have a lot of shading during the day, yes, maybe (can you not just install more solar?). If you only have shading in the morning or evening, don't worry about it...
So here is my question. If I have 2X 120 watt panels in parallel (on a sailboat - so one may have shade) - should I put a 10 amp blocking diode on each positive before the combiner? So in a boat situation it is not only possible, BUT very likely, that one panel in parallel may be totally blocked by a sail shade..
100% agree with your explanation, but there is a scenario for the backwards current to occur: Off-grid system, batteries full, still plenty of sun, but a little latter in the day (meaning sun is at a considerable angle) If you have, let's say 2 strings of 3 pannels, but one of them gets completely block by hard shading (building, chamine, etc) at that time of day you will probably be subject to reverse current. This is not likely on grid-tie system, as the controller can get all the power available, but in off grid, if the batteries are full, it will block any current to go through, the voltage on the string exposed to the sun will rise to almost Voc and the path of least resistance will the the shaded string. Off course a "hard shading" is predictable and this can be mitigated.
That would be a very extreme shading. I don't think this is actually happening. And at such a scenario, the charge controller would drive the panels into an ineffective area of the curve anyway as the battery is full.
Great video, but I'm not sure why people are disputing this as blocking diodes are so cheap and they simply plug onto the end of a series string, so if you use them you simply eliminate any possibility of back feeding when shaded so I would rather know all of the power my panels are producing is flowing in the direction of my battery bank.
You are mistaken. You do need blocking diodes for older panels, which have a single PV surface. However, modern panels, have blocking diodes included in their internal construction, since you can shade half the panel and still get half the power. I have a bunch of thin film panels (the black ones, where the PV cells are thin and run through their entire length), which DO need a blocking diodes to run in parallel. I found out by experimenting, just like you did.
a diode have a p-n junction, a solar panel have a p-n junction regardless of whether its old or new, here is a challenge, show us one modern panel which have bloking diodes built in
Hi Andy, thank you for the follow-up experiment. Can you please do this easy experiment for us? I also see people started doubting your bypass diode explaination in the comments. In the previous video, you covered 2 of the 3 panels right? Since, the panels have bypass diodes, people will question shouldn't it be producing around 200W from the non-covered panel instead of a mere 30W total? However, as far as I understand your battery system is over 50V and a single panel's Vmpp is less than 40V, is that right? So, the panel can't change your battery, hence the low power output. But if you had covered only one panel, then the potential of the remaining two panels will be high enough to charge your battery and the panels should be able to push 300-400W right? Can you please verify this? Thanks.
@@MatejFabianek The usable power is only from one panel, his system requires at least 2 working panels. Obviously, the voltage we see is added with the voltage from the two shaded panels, and hence producing max 30W (V of panels should be greater than the battery V to charge). Anyways hope Andy will verify this easily and show us. Thanks.
do you replace the diode with the same number as the old one like [10amp Diode Axial Schottky Blocking Diodes for Solar Cells Panel,15SQ045 Schottky] [BOJACK 10SQ050 Schottky diode 10 A 50 V axial 10SQ050 10 amps 50 Volts for Solar Panel Parallel reflow Protection diodes] [Bridgold 25pcs 3Types Silicon Rectifier diodes,Package Including:10pcs 6A10 10pcs 10A10 5pcs 20A10] ok which one what volts going on and on
Blocking diodes used to be popular before the time of charge controllers and lithium batteries. Those days it was exciting to use a tiny 12v panel to trickle charge a lead acid battery and all that was needed was a blocking diode to prevent the battery to discharge overnight.... But then you already know this...
I'm sorry if I'm a newbie, but the way i understood is, blocking diode and bypass diode is the same, it's just the way it is connected that makes it a bypass or blocking. if its connected in parallel in between the + and - in a pv array then it acts as a bypass diode. if it's connected only in the + of the PV in a one way strean of power flow then it wll act as a blocking diode. am i correct? please respond.
Physically, they are the same diodes, that is correct. Yes, you're correct. Bypass diodes are across the single strings in a panel to prevent total power loss during shading, while blocking diodes protect the panels from current flowing backwards.
I have a question sir. I have all in one off Grid solar inverter which supports 3.5 KW panels. So there are 3 strings os 3 panels each that make up 3.5Kw. all 3 strings are parallel. Will it Be a problem If I place 2 strings iñ south direction and 1 string in West direction? Your reply will be appreciated. The reason for this is to get some power and try to keep the batteries topped up untill the sun goes down. Thanks
That depends on how many solar inputs the inverter has. If it has only one solar input, I would not recommend mixing strings which point in different directions.
Electricity and electronics (semiconductors) are mysterious for those who have not had training in the field. It seems as though the solar cell is acting like a diode with a reverse breakdown voltage equivalent to the open circuit voltage. Like a zener maybe. I wonder what the forward characteristics are. :) Polish beer is impossible to find here. Good stuff.
Exactly... his point is valid, but I think those defending their arguments from the previous video would say that it behaves exactly like a diode... just a really terrible one!
your experiment also pointed out another interesting point. it showed the large number of u tube viewers that never think past what they watch so will parrot anything they have heard without even thinking if it makes sense. I am reminded of the saying....the problem is not with people knowing things as it is with people knowing things that just are not so! I think it was the humorist Will Rogers who is known for saying this, ha ha ha get it i think it was..................................
Yes, that is correct. And you can argue and argue, they still don't believe you as many others still say the opposite. It's easier to flow with the stream and just repeat the same. Even not knowing if its true or not.
Love how you set the record strait. Too often these people that say things as gospel don’t get educated and continue to propagate rubbish. I hope it doesn’t cost you subscribes, it’s funny how some people don’t like to be corrected. 👍🏻👍🏻
But... this is why one should fuse each panel in a parallel string (depending on how many panels in the string). This is because if a short were to develop in one of the panels, the remaining panels in the parallel string would dump all their amperage into the shorted panel and cause a fire. The fuse should go right on each individual panel that is connected in parallel.
I have 4 panels 2x2 in series and both strings in paralel on both sides of my balcony. In the morning the sun is from one side than after 12 o clock fron the other. ON EACH SERIES strin one panel stoped working and I am wondering why. I do not haveb a blocking diode
The solar panel does act like a diode. You just exceeded the Peak Inverse Voltage (PIV) rating of the panel. Any diode will do the exact same thing. A curve tracer to analyze the breakdown is a fun tool.
Yeah I literally witnessed the panel acting as a diode as he was saying it doesn't act like a diode! I don't know, maybe I missed the point of his demonstration.
Love ur videos I've looked at a few my problem is my diodes are reading one way like they supposed to but my panels voltage is in reverse I'm getting a negative -00.1 when I test my panel
i once used a 1n4007 as a fan switch, just glued the diode onto the heatsink, the heatsink heats up, diode conducts,, allah fan switch... it did create a high pitch noise ...lol but the fan run keeping the heatsink cool
The comments from your viewers are correct many panels have both types of diodes installed in the junction some do not I know all of my panels have them trina solar and sun power
Everything emits IR light even the darkest parts of space. The light emitted is proportional to it's temperature. This is called black body theory or more properly "The Stefan-Boltzmann law".
i have combiner box in series solar panels 1-4 12v is 180w 2 + - 130w, 1 + - 100w, + - =wired ++++ - - - - in series one big panel 590w,7080w low sun light less w, 12v 200a battery 2400w sealed battery
i think I] will buy this one for 12v solar panel [Ltvystore 30PCS 15Amp Diode Axial Schottky Blocking Diodes Compatible for Solar Cells Panel,15SQ045 Schottky] if you think it is ok please [15a x 12v =180w] I think
I'm learning something. Thanks. So my questions is whether your observation regarding the blocking diode holds true between a full load and no load at the charge controller? Thanks again.
