Hi Nick - your comment has made my day! 😀 thank you! My next video will be a very short one talking about the difference between kW and kWh,…. and maybe a bit about voltage and current in there too - all using the water analogy 👍🏻
good video. When we set up our solar company, we had two systems installed. one partially shaded with microinverters, one with a string system also with shade. We demonstrate exactly what you are showing, but live in real life situations on our own home. Hearing from clients who have upgraded older string systems to Tigo and EnPhase is a real joy.
Thanks for watching my videos and taking time to comment. I’ll be doing a follow up on the shading one, and it sounds like you’ve great insight! If there’s anything you’d like me to cover in that, just let me know 👍🏻 All the best with your company! 😀
Great video, Gary. The time and care you clearly take to produce such professional presentations is definitely to your credit (not entirely sure about the start and end music, but hey that's personal taste!)
Hi Chas, thanks very much for taking the time to tell me this - it really means a lot. I agree about the music - it's a bit tacky and I'll change it before long! :-)
An excellent presentation. In fact that’s one of the best presentations on the subject of partial shading that I’ve seen. I was aware of the bypass diodes, but hadn’t considered the impact on the larger array. I think panels have evolved a little to include “half cut” cells. I think they run the bypass diodes up the middle of the panel, essentially doubling string number, and halving string length. It improves two attributes: - better partial shading performance - reduced diode hotspots, thereby improving panel life That diode heat loss can be a real panel killer. I did my own shading tests, which I think is in my Spring/June video this year. The direction in which shading is uncovered has a big impact on performance.
Coming from you, Anthony - that's praise indeed! Thank you. I might do a follow up on shading when I've collected enough feedback etc. and I'll be sure to include half-cut cells :-) And I remember your shading tests - I can't wait to be my own setup installed in January to do some of my own (I'll have relatively easy access to the panels as I have a number of Velux windows on my roof). I've had a bit of a nightmare with my solar journey, which started back in March! Let me know if you're interested to do something together on RU-vid at any time - I'd be game on for that.
Agreed, well presented. I’m breathing a sigh of relief knowing that I did do the right thing putting Enphase on my second array ( split across SE and SW facing roofs with chimneys ) Thanks
Direction of shade encroachment is indeed important. Most PV modules are wired as Gary illustrated so that the long edges each fall within one bypass diode zone. This is good for commercial ground mounted arrays facing South and with modules racked in landscape orientation. In that way the shade from the next most southern rack activates the minimum number of bypass diodes
how many strings can you break an array into? it seems like more wiring would be cheaper than optimisers or micro inverters, but there is a reason there are so many panels to a string and then the strings are in parallel; what are the limits?
Hi Scott, so it depends on your inverter. Most inverters only support two strings, but some can support three (or more). For each string, there is a minimum voltage level requirement before generation starts, so ideally, you want a lot of panels on each string to achieve that minimum requirement for longer in the day, especially if it’s cloudy. There is an upper limit on the voltage (and also current) which will be different for each inverter manufacturer.
one thing no one has touched on..at least in the extensive search on this topic that I have done.... the micro inverters are *VERY* useful if one has very limited room for panels and is running a 48v system. The micro inverters have a low voltage startup and being mounted onto each panel, can be used on most panels out there as the low voltage input range is fairly broad - so most panels have the voltage for them to work - then this AC is sent to an inverter like the Victron MultiPlus II and is used to charge the batteries connected to the victron inverter/s. If one tries to use a DC MPPT charge controller then one finds a "start up" voltage of 70-80+ volts - you cant get this from one panel. So if getting all you can out of *EACH* panel in a 3 or 4 panel setup that has shading issues through the day is *VERY* important to you, then a micro inverter is the answer. Note that what i have said above is for 48v battery systems. On a 48v battery system, even if you are willing to dedicate an DC MPPT controller per panel so that shading is dealt with, there are not many panels out there, that when used as a single panel system, produce enough voltage for the 48v DC MPPT controller to actually work. With 24v or 12v systems this is not a problem as a panel with 40v output has a high enough voltage to make a 24v MPPT do its thing. With a 48v system this problem is overcome as the micro inverter can accept just about any panels input voltage, convert it to AC and send it to the Hybrid inverter that then uses it to power its onboard battery charger. The added bonus is per panel monitoring.
@@GaryDoesSolar Gary, granted not many ppl would be looking for a microinverter to power 1 or 2 panels, but if one is doing just that (for example - on a sail boat) AND runs a 48vnom system then this is the best way. Its a very small niche to be honest but it does work.
Great video. We have optimizers and I am quite content with them. We have 92 panels on our apartment building. We have an east--west orientation with a raised edge around the flat roof and a chimney in the center. You can follow the output of each panel through an app and usually there are significant differences. If you have panels in different orientations, you have to make either separate strings, each with their own inverter or use optimizers/micro inverters. Micro inverters make sense if you don't have a large number of panels. It's not only about direct sunlight shading. In clouded weather (diffused light) all panels are affected differently by sources of shade and no cell will have 100% shading. Also, dirt on panels can reduce the output of some cells more than others. Long term if we have to replace some panels by non-identical ones, that will not give us any issues.
Agreed - having the ability to individually monitor a large array of panels is a great benefit to have! I'll cover some of the points you make here in a follow-up video I'm making, especially about non-identical panel replacement... thanks!
You forgot that you can make multiple strings with a main Inverter that support 1 ~ 4 string groups. Or use multiple smaller inverters (given that you have 92 panels) that each take 1 or 2 strings, and output in parallel. The problem with micro inverters as i see it, they are exposed to potential hot temperatures, constantly with no cooling. That will affect them, despite the claimed 25 years warranty, vs a larger inverter that has active cooling to keep everything nice and cool. Take it from somebody in the IT business, there is a reason why datacenters have AC, and servers are stacked with loud fans. Electronics , and yes, that micro inverter has electronics in it, will degrade faster. And wait when one or more dies and you want or need to replace it. Its one thing on a apartment building with easy access but normal homes where you may need to remove a bunch of panels to access the issue panels.
@@benjiro8793 We have optimizers, which have less electronics in it than microinverters. Our rooftop has good accessibility for replacing broken optimizers. Multiple string groups requires more cables, which is significant, because the inverter is in the basement. We may not have the most economical solution, but I am content with it. Electricity production is above expectations.
In Australia it is possible to get Enphase micro-inverters at only 10% more than a string inverter. One of the most important benefits not listed here is the increased reliability and longevity of micro-inverters; our local supplier recently switched to offering only Enphase micro-inverters for that very reason. There are also significant benefits for PV installation companies in terms of managing and storing stock. Having inspected several houses and businesses with non functioning solar systems, I believe the improved monitoring from micro-inverters is well worth that extra investment.
@@GaryDoesSolar Enphase IQ8 microinverter has a 1/500000 failure rate and will function accordingly for 25 years, longer of course but that is the limit of the warranty, works when the grid is down without the need for a battery. The options focus on in this video will have to be replaced at least once, possibly twice during the life of the array. Those are undisputed facts and serious considerations. The solar industry is pushing for a module life span of 50 years, None of the tech featured is capable of such a feat. String will die a natural death, the future demands innovation. Ultimately customer service is the reason Enphase is number one in the USA and hyper-growing in Europe.
Just food for thought to consider cost benifit is the ease of system diagnostics with the panel level monitoring that solar edge and enphase offer apart from Sma and fronius. The average homeowner doesnt have the knowledge to know when something is off at the panel level (diode issue, multi cell degradation). Also the fact that that enphase is modular system for reduced production loss with any defective equipment. Ive installed and serviced thousands of site between all manufacturers. There alot more after the fact to consider rather than just the unfront ideology.
Hi great video, I’ve some companies installing the optimisers in the loft ,by simply rooting the optimiser cable under the felt , so if any optimiser issues, being in the loft makes easy access and no need for scaffolding,
Not sure which products can ‘can cost the same as the panel’ but I know the basic Tigo is about £40. Interesting video though as my issue will be solid shadow from a chimney going right through an entire panel which suggests an optimiser will be pointless. Thanks for posting.
I think your best option would be to avoid putting a panel within that area, BUT I know that is very easy to say in a comment without knowing the whys and wherefores.
Another awesome video Gary.👍👍. The only benefit as far as I can see is the ability to check how each panel is working. Might be useful for the photon geeks? Have you seen the Australian RU-vidr: Off Grid Garage he demonstrates Hyundai shingled panels with a voltmeter and fries his voltmeter entitled "Hyundai Shingled Solar Panels - 15% better than other solar panels?"
Thank you!! Of many analyses I read and watched about this topic, you are the first to mention the difference between hard/intense shadow and diffuse shadow where the bypass diodes don't kick in. That's the missing link! We've got two nearby buildings higher than our (southern) roof and their (hard) shadows wander across our roof during winter. But there aren't any high trees, cables etc. nearby. So if I understand correctly, the most that I need is a decent mpp tracker and a clever orientation of the modules (because building covers up the lowest meter or less off the roof traveling from one side to the other, the modules (~1.7m x ~1m) there should be installed horizontally), correct? Now I just have to find out whether 1mpp tracker is enough (all modules go on one side of the roof).
Thanks Thomas - great to have feedback like this. Now, if your solar panels are of the half-cell variety (see part two of my shading videos) then you could still mount those panels in portrait format on the bottom row. And assuming you're planning to use a string inverter with two strings, you could ensure that all the panels along the bottom are on the same string, which will help with tracking. Alternatively, you could look at having optimisers on the panels along the bottom row - but given these problems are only during winter, I'm not sure that this extra expense would be justified. Good luck with whatever you decide! :-)
@@GaryDoesSolar Thanks a lot for the helpful reply! Yes, half-cell, and yes, inverter with 2 strings (and 2 mpp trackers), but I am also thinking about extending the setup to the garage in the not-too-far future, so will ask my electricion if it makes sense to then go for an additional (smaller, 1-string) inverter or whatnot.
@@GaryDoesSolar I'm sure it did as you can tell by the graphics and references you found to back up your explanation and reasoning and what people don't understand is the time ot takes to find what you are after and then to cros check what you have fojnd to make sure that it is correct. This takes ages. People in general just see the presentation and just assume that it has been grabbed and don't realise that research takes an incredible amount of time. Probably due to a lot of people just taken a source at face value and don't cross check. No, it is a very informative video as your others have been btw.
+1 for maybe looking at what happens with panels in parallel. As I understand it, this solves a lot of problems with shading in a series/string setup, but only if your inverter / charge controller works with the lower system voltage (due to the panels being in parallel rather than a series string)
Thanks Jamie. Certainly, parallel panels allows the current another route round in case of shading on one of the panels. I'm planning a follow-up video on shading in a couple of months and will try to cover this.
I installed SE optimizers on 50 300W panels to 2 inverters back in 2016, what a mistake, paid about $60 dollars per optimizer. However in the last 5 years, about 15 optimizers have failed. Mine was a self install ground mount so I'm able to get to each optimizer easily, but still a major hassle. And they used to send out replacements quickly, but not now, I had to wait 5 months for my last unit. Can't imagine the cost if I had to pay someone to do this, especially if it was a roof mount. So to get rid of them I'll have to buy 2 new inverters, but in the long run I think it will be worth it, since I'll most likely go with a hybrid inverter and add some batteries as a backup system.
Hi Donald - your experience with optimisers looks to have been awful, so thanks for taking the time to comment. This will help others in their decision making. Can I ask a question, when the optimisers failed, did they just take out the panel connected to, or did they affect other panels? I'm planning to make a follow-up video on shading soon, covering other aspects including reliability...
@@GaryDoesSolar well I use the SE app that shows my system and when I see a dark panel I know I have a problem, it either produces very little output or no output, in the app I can bring up the Optimizer voltage, and it shows very low volts like less than one volt, then take screen shots and send them to SE via the trouble reporting system. The other panels are not affected. Right now I have two more bad optimizers. After watching your video, I thought if I would have just bought a few more panels with money I would have saved, I would have been way ahead in terms of production. If you think about it when one fails it takes at least a month to get it back up and running, since this is in Hawaii everything just takes forever. Oh did I mention I've had to replace both SE inverters also. So far everything has been warranted. The panels I used are rock solid, never had an issue with them.
Hi Gary, very informative video thanks. I'm just in the process of designing a system at home and wondering if I needed optimisers. I'm still not 100% sure, can you clarify what your diagram shows at 16:45. If I have 2 panels out of a string of 6 that are not producing any current, without optimisers are the other panels still able to push current through the shaded panels? I thought if all the panel was shaded it would block the current.
Hi Kieron, great to hear you got a lot from my video 😀 So, in the video then: if there were no bypass diodes in the panels, any fully-shaded cells would completely block current flow in that panel and also for all the other panels connected in the same string. The bypass diodes essentially “detect” shaded cells then re-route (bypass) current around them - to the extent where if a whole panel is shaded, the three bypass diodes in the panel will simply bypass the current through themselves, avoiding all the cells in the panel completely. Hope this helps!
Very clear and informative: thank you. I had understood that optimisers did have a downside of 'stealing' one or two percent of the power from a cell permanently. So that while they may help in complex shading scenarios, they do extract a price to do so. Is that your understanding too? Best wishes. Michael
great video gary explained it a lot better than other ones. i do have a question to you or the viewers. so ive got a rooftop array already, runs fine. but im getting another 4 panels mounted onto side wall. that wall catches a lot of morning sun. can i get away with optimisers on just those 4 panels. they will be tied into the roof string and will effectively be "shaded" after lunch thanks in advance for any replies👍👍
Fantastic video Gary thank you. Please can you clarify what panel based optimisation actually does to PREVENT a bypass diode from "kicking in"? And if so, does string MPP tracking do this also? I might have missed this, but this wasn't clear to me. In fact it seems to me the main benefit of panel based optimisation is allowing each string to conduct maximum current by diverting partial current around partially shaded panels, thereby improving performance of non-shaded panels. It wasn't clear to me in the examples how optimisation would impact shaded panels. For example is it correct that an optimiser cannot fix the case of heavy shading as diodes have already "kicked in" and there is no current for the optimiser to track. And is it correct that panel based optimisation has no advantage over string based mpp tracking with respect to the individual panel performance (in the case of reduced current due to partial shading, but insufficient current to cause the diode to operate).
Thanks Richard. Ok, so a bypass diode will kick in if the current flowing into the cells that the diode is managing is circa 20% greater than those cells can collectively generate themselves (because of shading). What the optimiser does then is adjust the voltage in an effort to reduce the current so that it exactly matches the current those cells can collectively generate. Doe that help?
Gary Does Solar: What a brilliant video!!! I am subscribed, thumbed up the video and have shared it too! 👍👍 (please one on off grid 7.2kw system with battery storage)
Thank you 🙏 your subscription means a lot to me 👍🏻 I’ll add your suggestion to the work stack. I have to warn you though, there are about 15 items in the stack so far! 😳🤣
I am thinking of installing solar panels but each one going down to the control panel which is an extra metre or two each, reason is ease of maintenance being accessible at anytime, from the control panel they could be connected in series or parallel and easy to monitor each panel, I have worked out the voltage drop, just need to increase the cable size to reduce the drop
One of the main benefits of micro inverters is the flexibility. You can individually add panels and to subtract panels and change panels and have mismatch panels also have panels with multiple different angles and directions and do all sorts of things with micro inverters because every panel is independent
really insightful, thank you. I wonder if there is data available to help understand potential savings in some average shading situations. That could help people assess whether the potential % improvements are worth the additional cost required. My guess would be no in many cases though
Thank you. Now, I haven't seen any such data myself - in fact, it was hard to find any meaningful objective testing that had been carried out at all! NRG Solar carried out some long-term testing here, which seem to demonstrate that optimisers are not the holy grail that some manufacturers make out! Here's are a couple of links: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-UQ9Szhl1ceQ.html ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-6Ucb-f8YPuo.html
@@GaryDoesSolar You've doubtless heards, but Oct Go tariff go up to 12p from 7.5p, and the day rate is up from 38.x to 40p. Still worthwhile. They have made a new dedicated export tariff which gives 15p however. I've begun the SEG / export application process, which in itself can take a month or so. Worth bearing in mind when you get Solar. My system was fully commissioned (and paid for) mid September. Took just over 3 weeks to get all the HEIS / MCS DNO and other stuff necessary to apply. Bites into your payback period a small amount, but nothing too significant given it's moving into Winter. As part of the SEG process, you had to photo your smart power meter, showing total export. In the month since go live, 290kwh! If I had have been paid that was around a princely £13. If a normal customer is then buying my generated energy, that's around £130 if on a normal tariff. Daylight robbery if you'll excuse the pun!
Great to hear about your installation, Stuart! And yeah, there does seem to be a lot of daylight robbery going on! Would've thought that phrase would become literal again!!!!?
You say that there is no output difference on an unshaded array with or without optimisers. but optimisers are active electronic devices and must consume some power to operate. Another report I watched recently that looked into this question suggested that the optimisers take 2% of the power all of the time. If this assertion is correct, then it raises the question whether it is better to put up with shading for part of the day or the 2% loss all day.
Hi David, you raise a good point - yet another factor that should be considered! I’ll cover this in the follow up video I’m making - thanks for highlighting 👍🏻 😀
Very clear and informative video - thank you Gary! I have no knowledge or experience with solar panels, so please excuse my perhaps stupid question: Why do solar panels not have mini bypasses between each cell? Or would that drive the price of solar panels too far up?
In the example you pull a cloth accross 1 panel so the output goes to zero. Pulling a cloth accross a panel is causing no light (completly dark) on that panel. What happens with the output when the panel is laying in the shadow but with only diffuse daylight on it?
Worth watching this video on optimisers where I explain about diffuse shading in detail: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-I4czBPobtg0.htmlsi=qbpFaWgcxaKzpe0i
Great video once again Gary. One question, I have read that wiring in parallel rather than series also has an effect on shading, i.e wiring in parallel limits power loss similar to optimisers, have you an opinion on this?
Thanks for the kind words! Yeah, I did start to look into that, and decided that it would be too much to put in such an introductory video, and nearly all domestic installs are series only in any case. I don't have any particular view other than parallelism allows the current more flow options, in a similar way to the bypassing that the diodes provide.
@@GaryDoesSolar I believe that some inverters have 2 sets of connections for PV arrays, assume this is probably for 2 completely seperate arrays ie east and west, however I suppose if you have 1 large roof you could split the array electrically into 2 ? and have these connecting to the 2 PV array connections ?
Thanks for this video as I learned a lot from it but have some questions. In the shading events you mention in this video all light is removed from each string therefore turning that string off completely but in real life that doesn't happen. They may not get direct sunlight but may still get enough light to make some power even when in shade. To complicate matters the shade/sun will move across the panel during the day changing the percentage in shade. In my case in the summer up to 30% of my panels are in the shade in the afternoon (more like 80% in the winter) but those panels give reduced output rather than none. The panels are on a garage roof facing approx SSW but the gable end of the house shades this roof, a little in the summer and a lot in the winter. My location is far from ideal but was the best I could manage. I was advised to go with optomizers by the installers so am interested to hear what you think.
Hi Ali, thanks for your kind words. Ok, to your questions then: Yes, you're right - there will be ambient light, but that ambient light will likely be the same for all substrings. A bypass diode will kick in when there would otherwise be a notable reduction in the current (typically 20%) following through the substring it is managing. And partial shading on that substring could cause that. Ambient light won't avoid that. And you can see this in the example experiments in my video. For your situation, where there is quite a lot of shading, having optimisers would make sense, because each panel will be treated differently. And if your panels are half-cell or shingled, this will also help.
For price of this microinverters you could literally double solar array (usually you have plenty of place for it) which will outperfom any optimizer/microinverters.
@@GaryDoesSolar Here in europe i could buy 370w panel for 170euro, so 1. 20 panels + 20 inverters = 6800eur for 7.4kw theoretical peak system 2. 20 panels + 1 inverter = 4400eur with 8kw inverter 3. 10 + 10 inverters = 3400 for 3.7kw theoretical peak
@@W122ard1 Thank you - that's good to know. So it looks like Microinverter prices need to come down before they can compete with a basic string inverter system. But of course, when looking at the overall costs over 25 years (and string inverter replacements) the gap is lessened.
@@GaryDoesSolar It is also depend on what inverter we compare, because price for victron will overcome probably all microinverter )) But there are a lot of good reasonable priced inverter. Victron provide its full environment, but for me price for it too high.
Actually, that's straight-forward. Cloud coverage will affect all the panels, therefore there is no localised shading (that's all the bypass diodes and optimisers care about). That means all the cells will generate current at roughly the same level, depending on the amount of cloud cover.
Hi Gary, please help me with one simple piece of information. I have an 8kW Solar Mpp and 10 solar panels of 590Wp each. The inverter, in the description, is 2x4000W. My question is: can I put all the panels -5900Wp on a single input to the inverter? VOC is 42V for each panel - the inverter supports Max. 500V. Or how is it better to proceed? Please I wait for your answer ASAP. Thanks ,
Hi Felix, unfortunately, I'm not in a position to provide advice (not least because of potential liability issues - even if advice is given free - such is the world today). You're best to speak to an installer about that, or post a comment onto a solar forum (e.g. this one in the UK: facebook.com/groups/2197329430289466) Good luck!
Hi. Wow, well explained videos. Amazing. A Q please..I have been advised to have a 9 panel (415w) of approx 3.8 on my south facing roof and none on my north side, with a GE 3.6 inverter and 9.5 battery. Would this setup be advisable? Or worth adding panels to the north roof ( at a lower intake performance, due to indirect sun)? I am looking to a few eheaters. I have been told that I am low electric user at 3600 kw per year. Hope this make sense and thanks for your time.
Hi Neil, thanks for the kind words! Now, I can't give advise (as this would open me up to potential liability), but if you're in the UK, you might want to check out this forum on Facebook - it has 20,000 members and people ask detailed questions all the time and get great responses: facebook.com/groups/2197329430289466
What i know about solaredge and current in a string, is that in case of shading not the current is regulated but the voltage, so when shaded a panel will give the same current but with a lower voltage. The voltage of the optimizer (can go up to 60V) is not the same voltage as the voltage from the panel (max about 40V). In a string we have everywhere the same current, there is nothing you can do about that, so current is not bypassed around the panel.
Then I got a question to ask you why is my 9.74 amp 400 watt solar panel giving me 22 amps and on a good day it's giving me closer to 80 amps that's one 400 watt solar panel I have it hooked all by itself explain that to me or should I explain it to you.
@@GaryDoesSolar because every 10 watt is an amp I used to think it was every 13 Watts was an amp and that was explained to me when I was a little kid and that was explained to me in a book of electrical book before they start lying to you and my inverters tell me the same thing as well as my chargers that every 10 watts is an amp I don't understand what's the difference between amps and a Watts because of that but I do know volts pretty well that's why I don't understand how someone can use 10 amps and 1500 watts to run something because that don't make much sense to me then.
I am not sure where everyone is buying their systems and for what cost. But it is only about 20% more for Enphase where i am and they have a 25 year warranty in comparison to 10 or 12. That alone is worth the cost.
Hi Michael, for me, it's not the cost of installation that's the issue with microinverters - it's the cost to fix given the increased complexity on the roof leading to a greater chance of something failing over time.
So a typical solar panel has only a number of photovoltaic cells and three bypass diodes all wired together. Conversely, here is what the inside of an Enphase IQ8 microinverter looks like: static.seekingalpha.com/uploads/2019/12/16/38410276-15765300955164375.png As you can see, a thousand times more complex. Also, these warranties are only for product failure replacement. Enphase will likely send you a new one in the post, but only when you've sent the failed one to them to check first. And you will no doubt have to bear the access/scaffolding costs yourself. All that said, I actually really like the microinverter concept - so much so, that I'm going to make a video about them 👍
Why not put bypass diodes on each Panel that is in series with other panels? Then they would simply drop out and not affect the rest of the panels. Then you would not need to use microinverters.
I’m not sure I understand your suggestion. A panel is essentially three mini panel strips, each with a bypass diode already. Can you explain in more detail?
so in conclusion, if you do not have shading and only worry about long run degradation of individual panel, optimizer is no brainer. If you are facing shading issue, then either accept the lost or beef up more panel with optimizer. Otherwise you are forced between using microinveter or chopping trees, whichever cheaper.
Hi Gary. I have a query about the difference between the shading effect examples you’ve provided where there is heavy shading from a chimney stack & also the diffuse shading from a nearby tree. In the heavy shading example, optimizers won’t work because the bypass diodes have kicked in but in the case of the tree shading where the bypass diodes have also kicked in, the optimizers are still able to limit the current in this situation? From my understanding of what you had said, is that if bypass diodes kick in, optimizers can not reduce current or be effective at all? If you can clear this up for me please. Many thanks.
Yes, that’s in line with my understanding 👍🏻 for diffuse shading, optimisers can see the current being reduced in the panel, so will divert the remainder around the panel to retain the overall current for the next panel in the string.
Thanks Gary. However, I’m still a little confused as the example you use with the tree shading shows that without optimizers all the bypass diodes would kick in but with optimizers the current would reduce so that the output of panel reduces to 50%. In a previous example, if bypass diodes kick in at all, the optimizers cannot reduce the current because there’s no current to work with? If you can clear this up for me please. Thanks again for all the great support & advice you give. Karl
@@KarlCasey-up4gi Sorry for the delay in replying. "I’m still a little confused as the example you use with the tree shading shows that without optimizers all the bypass diodes would kick in" I would not expect the bypass diodes to kick in unless the tree (i.e. diffuse) shading was >20%. Can you tell me where in the video you're quoting from please? That will help me to understand your question - thanks!
Hi Gary. It’s 17’ 40” into video where the shading on the panels from nearby tree is 50% so bypass diodes kick in., however, you mention that with optimizers, there would be reduced performance but in the example you used with the shading from chimney stack previously, you said that if bypass diodes kick in there is no current with which the optimizers can work with. Therefore, if the bypass diodes kick in on the tree shading example, there should be no output from the panel even with optimizers, all being equal?
@@KarlCasey-up4gi Ah ok - I think I understand your question now. A bypass diodes kick-in when it detects that the current flowing through the substring it is managing will be reduced by more than 20%. For diffuse shading (like a tree) where the current flow would be reduced by half (example at 17m40s) the bypass diodes will kick in. But if there are optimisers fitted, each optimiser will reduce the current by half going into the panel - that means the bypass diodes won't kick in because each substring can easily handle half the current flow. In the previous example with the chimney, because at least one cell in each substring of the two affected panels is completely covered, there cannot be any current flow at all (see this video at 4m42s: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-9GvhDhCSJgo.html) and that means it doesn't matter what the optimisers might try and do, no current can flow at all in the affected panels. Hope that answers the question. Let me know if not...
Hi Gary [- Truly EXCELLENT video - concentrating on technical detail on how panels work and the effect of bypass diodes. As a professionally qualified electricaland electronics engineer- I think the solar trade in general needs far more of this excellent level of instruction. ( Sadly lacking -you only need to read some of the forums to see how poorly solar power is understood, Having taken many so called "solar installer courses" from well known manufacturers - this video mostly stands head and shoulders above those - in terms of accurate well presented technical detail - not so such as to baffle people - but more than enough to understand properly what is going on Excellent !
Thanks Don - I was careful not to draw firm conclusions one way or another. But I did want to get the point across that any improvements with optimisers are only marginal. If I had shading on my roof, I would like get optimisers for the affected panels, even just for the monitoring.
@@GaryDoesSolar Hi Gary. Thank you so much; these are fantastic videos which are so much easier to understand than just reading manufacturer's literature. I do have a question/observation. I've watched your earlier video 'How to choose SOLAR wisely and avoid costly mistakes' where you explain what each component does in a SOLAR system i.e. Solar panel, Invertor and batteries. In the Solar panel section, you mention that shading one panel will adversely impact all the solar panels in the series which suggests using optimizers and/or microinvertors is the only solution to reduce the impact of shading. However, your video 'Solar panels shading : Are optimizers and microinvertors worth it' you clearly explain that electronic protection measures are in place by having the bypass diode added to each array leg suggesting that optimizers and microinvertors are probably not worth the investment as the bypass diodes do a great job. Also, the cost of replacing the optimizer could be high for the reasons you explain. Maybe it's just me but I felt the videos slightly contradicted each other in the Solar panel sections. Let me know your views. Keep up the great work. Cheers
Misses out a lot about optimisers here. The string number lengths can be much longer, meaning that much more often you can have just one string down to the inverter. You can also parallel different length/orientation strings together (some conditions apply) Also orientation of panels in the string doesn't matter so much due to individual mppt. Open circuit voltage is only 1V per panel giving both panel signalling to an app for each panel's parameter indication and inherent arc fault fire protection.
Hi David, apologies - I thought I had replied to your comment already, but I see it’s not there. You’re right - on the earlier video I bought into the general perception that shading on one panel would affect all the other panels in the same string. Upon receiving a few comments for that video talking about bypass diodes, I decided to do some research myself, which concluded in the later video. It’s not really possible to modify videos once published but you can place correction markers, which I did. They may not always be displayed though depending on the device/app being used to view the video. Thanks for the kind words regarding my videos - much appreciated 👍🏻 😀
Hi Jeff, the features you describe are more advanced and I didn’t want to overwhelm the audience with what is essentially an introductory video into Solar PV shading. I’m now making a follow-up video though and will incorporate some of these into that. Thanks 🙏
I can’t imagine optimizer’s/microinverters operate at 100% efficiency. My guess would be in the range 98/99%, some maybe lower. That would be a permanent energy loss of approx 2 percent. Thus the question one should ask, assuming a 25 year solar panel lifespan, is if the following formula is true (or false) for a given installation: (cost of 2% energy loss over 25 years) + (cost of number of optimizers/microinverters * average failure rate per 25 years) + (replacement labor cost) + (cost of lost energy during microinverter failure) < (cost of lost energy during periodically shading)
Thank you for this video. Do you think on a house with quite a lot of shading from multiple trees (the whole moring and from 5pm) would be worth using optimizers? They will be south facing. And how much is marginally better as you said? Below 5% total extra or more like 20% for a shady situation like i have?
You’re most welcome, Roan. Ok, so without knowing your particular shading scenarios, I can’t determine what improvement you might get. Certainly, for free shading, optimisers will help, and the Tigo products are relatively cheap to buy and fit. Have a chat with a few installers (to get a reasonably unbiased view) and good luck with whatever you decide.
I manage about 10MW of rooftop solar across the UK. Of that about 20% is SolarEdge. It is entirely fair to say the the SE systems do produce more than an equivalent string inverter system. It's in the order of 1-2% if the SE system is entirely working. It is also the case that the SE systems have far more faults than all the other systems so the likelihood of us having a fully functional SE system is very low. Most of the time that's optimisers at fault, but they are also by far the most unreliable inverters we use and their support service is vastly worse than suppliers like SMA. Shame we can't actually buy any SMA kit at the moment!
That is quite an estate! 😳 Thanks for taking the time to share this insight. It’ll help people a lot in their decision making 👍🏻 I learned a few things too!
I must re-do my 'unshading' video at some point with something better than a scrap box webcam from another century: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-E9pcHZsnL7c.html you can hear the steps in power as parts of panels become unshaded. The built-in shading defences seem to work so well that the return on investment of additional equipment would be tiny. I wonder if there are lots of installations using panels with less of this kind of shade protection built in?
The video was well explained. I have a better understanding now. Still I have some concerns. (Time frame 16.01, what if the panels which are shaded is only having optimisers, will it give the same result, how mppt works in this case.) Does the optimiser in a panel will help that specific panel to improve the power output.
Thanks for your kind words, Amrutha. Yes, if only the shaded panels had optimisers, the output would be just the same as all the panels having optimisers. Each optimiser acts only on the panel it is managing, and it will bypass current around the panel if it is not performing as well as the others.
So if you were expecting getting horizontal shading from a neighbours roof, you would be better to have panels landscape, for the diodes to kick in, given the area each diode cover?
So actually; when using optimisers, one should remove the bypass-diodes, in order to be able to use the remaining power and generate more overall power!.
Quite frankly this is exactly what I have been looking for. Excellent presentation, and excellent communication. Having had solar for three weeks now, no micro inverters and the potential of chimney shading, this video has totally relaxed my worry about not asking for micro inverters. Thanks Garry - you have a new subscriber!
@@GaryDoesSolar same situation here. I'm glad I've not performed a costly installation of optimisers on my 7 year old system. As you point out, the extra complexity increases your chances of failure and the benifits while there are not so big as to justify the cost. Also, very nicely paced clear explanation with good illustrations.
There are other reasons you would want to go with solar edge optimisers, #1 being the ability to oversize your panels and get access to dc power to charge battery or ev. Absolute game changer that your string inverters cannot entertain unfortunately
Nice video, well presented. I do think you missed one aspect - in all your examples you are referencing a single serial string if panels. I think that it's fairly common to have parallel strings with (passive) combiners driving into a single charge controller/invertor. If one string is shaded it's voltage will be reduced, compared to the other (parallel) strings. It would be interesting to see how this manifests - I suspect that you would loose all of the power production from that string. It's also worth noting that if parallel strings are placed on different aspects of a roof that the same situation can occur... If at all possible panels should face same direction, or be wired on different charge controllers.
Thanks for the kind words. I'm getting quite a lot of interest in this particular video, and suggestions (including those you raise) for a follow-up video - so my plan is to work on that soon :-) I really appreciate you taking the time to comment
not sure when this video was produced, but it does not take into acount half cut solar panels. additionally the components thatare likely to go wrong are the string, mircr inverters and the optimisers. with string inverters they are normally in a loft or garage and therefore quite easy to get access to. With micro inverters and voltage optimisers they are normally mounted under the solar panels on a roof and thertefore the cost of scaffolding needs to be taken into account. regards Apollo Solar Energy ltd
Thanks for taking the time to comment, Philip. I cover half-cut cells in part 2 of the series, and go into depth on microinverters here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-q6t0AAi5Jws.html, including scaffolding concerns. All the best with your business :-)
@@philipholme9911 Yeah, and actually they're the next step on the way to shingled panels, which are becoming very popular. I talk about these in part 2 of the shading series here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ESpsdMFEFZo.html See what you think 👍
Hi I am looking into the world of solar and battery. Thanks for the advise I shall watch more from you. As a thank you I have joined octopus and used your feferal so fifty pounds should be coming your way
Nice explanation and definitely food for thought when deciding on the orientation of the panel based on likely hood of shading. If a wall or hedge is likely to shade the bottom of the panel late in the day it would make sense to have the panel in landscape orientation so only one string is bypassed and not all of them.
What I have found with my own testing is don't buy normal panels, buy half-cell split panels, or BF panels, as they don't souther nearly as much from shading, and even on an overcast day they produce nearly as much power as my 2 year old LG panels do in full sun, and they have expanded my day by almost 2 hours. Thanks for this video, I found it very helpful. Subed.
Very informative, thank you. If we ignore reliability of the bypass diodes for a moment, it looks like only part shading that does not trigger the bypass diodes is an issue in terms of generation (overall the system generating less than it actually could so to speak.) A quick search online suggests that bypass diodes can/do fail, and avoiding unnecessary load on them might be beneficial. In which case optimisers or micro inverters might have value in terms of long term maintenance/reliability, quite aside from slight increases in generation. HOWEVER, I am an amateur and quick searches online by amateurs often lead to mistaken beliefs… I have a house with quite severe local shading on much of the roof, that varies through the day and seasons, so have a more complex situation than anyone with no local shading issues. My feel at the moment is that I will be using optimisers or micro inverters.
As usual another extremely informative and useful video, I suspect it could save me a packet when we finally "take the plunge" early next year. However I suspect I'll be rewatching all of your videos before we make a final commitment . Thanks again Gary.
This is the first video I've seen to clearly explain the pros and cons of optimisers.I assumed I needed them. I'm not sure the benefit of individual panel monitoring and a small improvement in efficiency can justify the cost.
There are two more scenarios I can think of in which you can use optimizers: - you can have one string with some pannels placed at different angle on the roof or facing different direction - you can have pannels with different power output connected in one string I know that these are not good scenarios and should be almost always avoided, however they are possible with optimizers.
In addition to cons of optimizers (and microinverters) being cost and additional failure points, there is also lost efficiencies of having them in the system. For instance, the Tigo and Solar Edge optimizers are active devices which themselves consume power. So in a largely unshaded installation, the overall power output is typically greater without those parasitic device losses.
Very interesting and useful! Wish I had seen this before I had my system installed a coupe of years ago. I think the point about simplicity is very important. I just had one of the solaredge optimisers go and whilst solaredge sent a replacement for free it cost £150 + VAT to replace. (my installer has ceased trading - probably to wipe the slate clean - and it was just outside the 2 year insurance backed warranty) That's a big hit on the payback of a single panel, which is even worse when you consider the marginal benefit provided by the optimiser. solaredge optimisers do not seem to be that reliable? My panels are on a single pitch of a bungalow to easy access. Seems anyone with a high roof and difficult access should seriously consider if optimisers are worth it I was surprised that the optimiser can rescue nothing from a panel where the partial shading has tripped all the bypass diodes. Maybe we need to consider exactly how the shading will fall and select panels to minimise that issue? Do different panels have different diode orientation?
Sorry to hear about your bad experience with the failed optimiser. I agree, they provide only marginal benefit in many cases, against a high cost to fix in the event of failure. There doesn’t seem to be enough margin in the manufacturers’ products to allow for a better warranty payout :-(
Quite a good video. I'll add a few other points that need to be considered: * When designing a string without optimizers, make sure that there is plenty of voltage margin verses the optimal 'operating' MPPT range of the inverter. For example, if the inverter's optimal MPPT range is 300-500V, you don't want the total operating voltage of the string to be anywhere near 300V. You want it to be higher so partial shading does not reduce the voltage to the point where it leaves the MPPTs operating range. Of course you also have to make sure that the string's open-circuit voltage does not exceed the inverter's maximum voltage (for an inverter like this, typically 600V). So in this example, having the nominal operating voltage be, say, around 450V, would be ideal. * Not all MPPT controllers are the same. When partial shading occurs, it changes the voltage-current curve that the MPPT controller sees. Sometimes the partial shading can cause a 'double peak' on the curve where one peak produces far more power than the other. If the MPPT controller fixates on the wrong peak, system performance can degrade well beyond what it should. So, for example, SMA's high voltage string inverters will do a periodic voltage sweep (usually every few minutes) to make sure that the MPPT is servo'd on the correct peak. * In variable shading conditions... for example, foliage on a windy day, the MPPT point may move around more quickly than the MPPT can track, resulting in additional performance loss. Optimizers and micro-inverters are able to track these quickly-changing conditions far more quickly than whole-string MPPTs can. But in most cases, such effects are minor anyhow. * People often make the mistake of paralleling multiple strings into a single MPPT. This results in far worse losses under partial shading conditions because any shade will cause the combined MPPT point to be non-optimal for BOTH strings. Thus, when designing a string system, always be sure to give each string its own MPPT and do not use paralleling (i.e. don't use a solar combiner box to parallel 2+ strings together). In modern day, it is really easy to dedicate one MPPT to each string, but older string inverters often had only one real MPPT controller. -- * Also, note that micro-inverters have the additional problem of back-hauling 240VAC instead of 400VDC, which means either (a) higher losses on the return wires or (b) requires lower-gauge (thicker) copper wires to backhaul the same amount of power. -- The bypass diodes are typically schottky diodes, each with a 0.3V volt drop when operating. Solar panels typically have three such diodes so if a panel is mostly shaded you not only lose the power from that panel, the string as a whole would also lose another 1V on top of that (per mostly-shaded panel). Bypass diodes basically allow current to flow one way with a voltage drop of 0.3V to 0.7V. The solar panel itself develops a voltage across the panel which puts the bypass diode into reverse bias, which basically turns off the bypass diode. When shading occurs, the open-circuit voltage of the shaded panel is STILL LIKELY TO BE VERY HIGH, far more than 1V. However, the load on the panel (in shaded conditions) quickly drops this voltage as the panel is unable to support the current the other panels are generating, which takes the voltage below 1V and essentially turns on the diode, allowing it to conduct the other panel's current. -- So, generally speaking, it almost never makes any sense to use optimizers or micro-inverters, but one must still be a little careful when designing the string system to avoid the pitfalls mentioned above. The only situation where micro-inverters or optimizers make sense are in quickly-changing shading conditions because their individual MPPTs can react more quickly to the changing conditions. But that's it. I definitely prefer high-voltage strings over optimizers or micro-inverters. -Matt
Wow - this is great insight! Thanks for taking the time to share with me. I'm considering a follow-up video on shading in a couple of month's time - and if it's ok with you, I'll try to include this insight (with credit given of course).
Great analysis. Maximizing the MPPT voltage is the key it seems, which means longer (i.e. higher voltage) strings are better. This also has the effect of extending the operating (time) window of the system (i.e. inverter on/off) closer to the peaks of consumption (i.e. morning and afternoon) so producing more useful output. Optimisers actually reduce the operating time window by reducing the string voltage slightly (thus resulting in later 'inverter on' and earlier 'inverter off' times), even when completely unshaded. Bit of a chocolate teapot IMO.
@@whirled_peas Didi you get that backwards? The higher the voltage, the lower the losses, not the other way around. Losses are governed by P = I^2 * R (power = current squared times resistance). For voltage and current, transmitted power is P = I * V. So for the same power transmitted, the higher the voltage, the lower the current on the wire. But losses scale to the square of the current so if you hold power the same and cut the voltage in half, losses will increase by 4 times. For 400VDC vs 240VAC, the 400VDC line will 60% lower losses along the wires. Of course it depends which country you live in. In some countries the utility connection to the house might be higher. But in most it hovers around the 200-240VAC range. This is also why advertised efficiencies for micro-inverters and optimizers are usually somewhat disingenuous. For micro-inverters it is because they don't count the higher losses on the back-haul. And for optimizers it is because you still have to add-in the losses from the inverter that the optimizers are tied into (thus going through an additional conversion). -Matt
Hi Gary, As everyone else has said, this is another brilliant video - perhaps the best yet. The fact that you are very even-handed means, as you say, viewers can (and should!) make up their own minds on the subject. I've just placed an order for a 16-panel (8/8 east/west array)/5kWh battery system. At this time of year, we will have heavy shading on the west array (from about 2.30pm until about 5pm) from a large oak tree in a neighbouring garden. I've asked for Tigo optimisers on all of the west panels. We will have some shading on four of the east panels during the morning from a chimney. After some thought, I've decided to add optimisers to those four affected panels as well. I'm in discussion with Tigo at the moment about whether the Tigo Access Point (TAP) on the west array will be able to manage the additional four east panels. (The TAP connects to each optimiser by WiFi and is connected to the control gateway by a cable). When I started to watch your video, I wondered whether I'd specification the optimisers unnecessarily, but by the end my opinion is that for my situation I have made the right decision. Just a note on the point about costs: I've done a quick search for Tigo optimisers and the CCA (gateway) & TAP are available for about £60 & £400 respectively. Not an inconsiderable overall expense, but one which should, in my case, have a reasonably quick payback (I hope!).
Hi Phil - thanks for taking the time to comment in detail about your own situation. Yeah, I agree - optimisers are a good solution for you - and I would have taken the same approach. I'd love to hear how it all goes! :-)
Good video and well explained, one that I can point customers to!! been on about this for years, in these situations we parallel connect if some of the array will be shaded, we also combine series and parallel connections. Keep up the good work
Thank you so much! Yes, please feel free to share my videos with your customers. My next one will be explaining all the energy terms: kW, kWh, voltage, current, single phase, 3-phase, frequency etc.
Not a straight-forward question to answer as it depends on the kind of shading you have. Typical panels manage three separate zones, but the REC Solar Alpha Pure-RX panels manage 4, so I'd say it's ever so slightly more capable but my view is that I'm not sure it would make much difference in practice.
Great video. I might have added that the situation described applies to an array of identical panels mounted in essentially the same place which is probably the case for most new installations..
Gary, can you help me? I have 12 pieces Longi 450W half cut pointing SW and 12 pieces DAH 450W half cut, pointing SE. Both stings are connected to one MPPT(on other MPPTs I have panels pointing South). During all-day sunny day Longi panels reaches maximum 9 Amps, while DAH panels reaches maximum only 7.7 Amps. What is the reason?
Hiya, unfortunately, l'm not in a position to provide advice not least because of potential liability issues - even if advice is given free - such is the world today). You're best to speak to an installer about that, or post a comment onto a solar forum (e.g. this one in the UK: facebook.com/groups/ 2197329430289466) Good luck!
A very good quality presentation. It might be worth checking the minimum operating voltage of the string inverter, as this may come into play if the shading is across several panels stops it from operating all together. If you have dramatic shading, like I do on my garage and only space for 6 panels, then Enphase IQ7+ microinverters are the only real option. There is also something called sub-panel optimisation where by you can replace the 3 bypass diodes with a small circuit that will optimise each of the 3 strings of cells. These were in the form of the Jinko Cheetah Maxim optimised panels - which I believe are now obsolete. It is a pity they did not continue this idea with more panels. So I am looking at building some of the modules to retro-fit to a test panel, the IC that forms the heart of this is the Maxim MAX20800. This involves removing the silicon potting compound and diodes and fitting a small PCB and re-potting it to waterproof it and conduct any heat away. Its worth also mentioning that the panels do not need to face the sun to produce power, as I have mounted a panel on the west vertical wall of my garage to take advantage of the setting summer sun, but even in the autumn/winter when the panel does not get any direct sunlight, I can still see perhaps 160Whr on a part sunny/cloudy day with the sun bouncing off the clouds and 60Whr on a clear blue sky sunny day.
Hi Rob, thanks for the kind words. And thanks also for this detailed comment. Lots of information in there for me to work through, especially as I'll be making a follow-up video on the shading topic soon... I love it that you're not frightened to get stuck in on the bypass diode circuitry! :-)
Good explanation . Heard micro inverters have the advantage of energy loss while converting from DC to AC than string . Also in an ongrid system during a voltage fluctuation it will protect the solar cells from burnt off . Is it true Gary ?
Thanks. Now, I don't know if microinverters are overall more efficient than a string inverter. I guess it depends on the manufacturer in both cases. And for the voltage fluctuation, I'd expect both a string inverter and microinverters to be able to manage such conditions.
Our panels were installed 12 years ago and our installer went to the trouble of reducing the height of the top of our soil pipe and resiting our TV aerial. This means that our panels can never be shaded. Your video has explained why that was excellent practice. We were offered Solar Edge optimisers but neither our installer nor the manufacturer’s documentation could not explain what they did and why we would need them. I’m glad we didn’t buy them as you have explained why they would have been of little benefit with our installation.
The optimisers also provide arc fault detection, so fire protection and only provide 1V per panel open circuit so you can't get a fatal DC shock, you can also see each panel signals it's operating volts & amps on the Solaredge app, all besides each panel is doing its own mppt tracking.
Another method explained to help deal with this problem is to wire more parallel strings with less pannles in series. Not always ideal but it does work.
A benefit I see from optimizers is panel. By panel monitoring and arc fault detection and panel disconnections. Which are required on entire strings now in North America when over. 80V. However some hybrid controllers have afci on Pv protecting against this. The ROI of adding controllers could add 2-3 years of costs you have to recoup. Plus you will gaurenteed lost 1-2 controllers over at least 5 years.
Very informative video. Thank you But Several things 1. Are you saying its safe to have hundreds of volts on the roof? I would claim its not 2. What happens if the whole panel fails or the diodes? What happens then? 3. When the guy holds the obstruction over the panel you gloss over the fact that further down the line we have a system wide drop in power from one panel being slightly shaded. This seems significant. Thoughts?
Thanks for the kind words. My answers to the questions you raised: 1. Whether, it's AC or DC up on the roof, it's still hundreds of volts. DC is probably more dangerous given the possibility of arcing through bad connections. 2. Panel and diode failure rates are incredibly low compared to optimisers or microinverters - and as those rates affect everyone with panels, they're not a differentiator so can be discounted (in my view). 3. Could you tell me exactly where in the video this takes place please, and I'll comment.
This is a really nice overview of what the optimisers can and can't do. How often is shading extreme enough to actually trigger the bypass diode? Shaded but not bypassed seems to be where optimisers would work best. Even though they add cost they should reduce the fault finding time if a panel goes bad and can allow you to have different panel angles and positions without multiple string inverters.
Thanks Andy - great to get feedback like this. Now, I read that bypass diodes will typically kick in when they detect a 20% difference in current. And I agree, if my roof had shading, I'd likely put in optimisers on the shaded panels just for the monitoring capability.
It is very rare for a panel to go bad. The probability calculation is not in favour of oprimisers. Even with untriggered bypass diodes, the optimisers gain only
@@GaryDoesSolar the bypass diodes are Schottky diodes, and they block the current in reverse, and conduct when the is a potential on 0.1 V accross them in the forward direction. @ 10A, they will dissipate 1W of heat. This is a failure point of cheaper panels that use cheap under sized diodes. A 3 or 5w rated diode should be used to ensure longevity. The diode is simply a one way valve. From Wikipedia Schottky diode page: "... Reverse current and discharge protection Because of a Schottky diode's low forward voltage drop, less energy is wasted as heat, making them the most efficient choice for applications sensitive to efficiency. For instance, they are used in stand-alone ("off-grid") photovoltaic (PV) systems to prevent batteries from discharging through the solar panels at night, called "blocking diodes". They are also used in grid-connected systems with multiple strings connected in parallel, in order to prevent reverse current flowing from adjacent strings through shaded strings if the "bypass diodes" Effectively, if there is shading and the panel or string becomes effectively open circuit, the rest of the string, eg 300v, easily pushes past the 0.1v required turn on voltage of the diode, and current then flows past, bypassing the open string. Simple and effective.
