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.

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.

Best video I've seen discussing this topic. Well done.

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 !

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

I was sceptical when my installer suggested optimisers back in 2013 but now having the data for every panel (occasional shading depending on the time of year) each panel varies by quite a degree in terms of output even in non-shaded conditions (i.e. two adjacent panels in summer for example) - if it was a single string, the whole array would have been pulled down by the weakest panel and thus over the lifetime of the array this could well add up to 100s of kWh - in close to 10 years this is very apparent and so I’m glad I went with them - I’m squeezing every W out of each panel so they have paid for themselves in their gains from my calculations…each to their own however. That said, back in the FiT days, the upper limit for the highest rate was 4kWp so there wasn't as trivial as adding more panels - even then the added cost for the panels and mountings might outweigh the benefits of the optimisers/u-inverters imo Bit long winded but, I have data from the first 4 years - the install was intended as a bit of an 'experiment' as my installer was explaining the virtues of thin-film panels over mono-crysytalline - they can have better low light output and better peak performance but at the expense of being bigger panels (hence more cost to install) - I suggested we went 50/50 on the same roof and I share the data with him - 1.95kWp Solar Frontier and 2kWp of LG - the difference has been pretty self evident though the LGs actually perform marginally better in low light (slightly better yield on dark days), the SFs better in peak conditions due to the 'light soak' effect. Solar Frontier did a case study at the time (not sure if still on their site) though I calculated gains of around 4-5% for the same kWp (they claim 10%) By way of example, on a crappy day in January 2016 my best thin film managed 133Wh, the worst 65Wh, the LGs were 96Wh and 82Wh respectively. On a good sunny day in July same stat - SF 2.4kWh vs 2.2kWh and LG 1.72kWh vs 1.65kWh so there is variation between panels - similar to the performance of microprocessors where they are categorised for sale depending on bench testing - for the thin-films at least this is very apparent, the LGs are much closer but again over a lifetime, those few Wh add up - I want to harvest every electron I can and on balance between cost and material input for the optimisers, they seem to be doing their job! (as an aside, I noticed quickly that the SF panels wouldn't 'come online' until they reached around 10-12W of power versus the LGs which started at 2-3W - I shared the data with SE and they sent over a newer version of the optimisers that were on the thin films as they have a Vp higher than monos - that solved the 'low light' problem as they all come on at around the same time now - it was a faff to replace but fortunately it's a bungalow so I just said to my installer that I'd do it myself rather than them get scaff back up etc)

Interesting conclusion; one of your cons is actually our pro. We went for microinverters. The reason being resilience and redundancy. As I understand it, a single microinverter or panel failure will have an impact only on that single element. The rest of the array will function the same. The microinverters are also separate from our battery system, so there's no single point of failure that could bring the whole system down. The microinverters having a 25 year warranty also gave us greater confidence in the reliability of those parts. Our roof is really hard to access. So a failed panel, inverter or wiring damage (damn birds) would be a huge expense. So, whilst the microinverters do indeed give more points of failure, a single failure can wait until we have another good reason to access the roof as the overall impact is minimal. It also means a battery inverter failure wouldn't impact solar and vice versa. There's also a chance that I'm wrong and I've spent the extra money for no reason, lol.

Gary, it is always such a pleasure to get the alert that you have a new video out.

Loving your content Gary. Very clear and to the point. Keep them coming.

Really appreciate the hard work and depth of information you provide in your videos. An invaluable source of knowledge, thank you.

Very clear presentation Gary. Well done. Subscribed

Best video yet Gary 👍

Another fantastic video thanks Gary! Your graphics and commentary is superb. Greetings from South Africa.

A very informative video that helps to clarify the pros and cons.

Well explained, thanks from all of us and great initiatives

Another great video. Informative and unbiased.

Super presentation love the voice tone + explanations !!! BRAVO

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!)

Fantastic video and well explained and illustrated.

Best and easyest to understand video about this topic. I've just subscribed. Thank you for your work 👍

This is helpful. Seems to me that in most cases it's far better to simply buy more panels (as long as they fit) for a roof, rather than optimizers.

Without a doubt, the best explained series of videos on solar PV! Thank you Gary

Good explanation and analysis of the pros and cons. Thank you.

Really well explained. Great job.

Excellent and so very scientific. Many thanks Gary!

Very clear and detailed explanation. Thanks!

Thank you Garry, the way you explain and present it is just invaluable! We need more heroes like you on KZfaq! 👍🏻

Brilliant content as usual Gary. This is the true spirit of the internet.

Fantastic video to help understand what's going on with string, micro, optimizers, etc. Thank you!

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 was incredibly useful thanks. Great to get the technical detail. Cheers.

Excellent explanation. Best video on KZfaq explaining how they work and the pros and cons.

Thanks again Gary- so much useful information!

Excellent presentation. Nice and simple: the way true understanding always is.

Thank you - terrific explanations and perfectly accompanied by the simple graphics. You have a new subscriber.

Thank you very much indeed Gary; really well made, clear, easy to understand, I’m formative video.

Great information Gary, very clearly explained, thank you

Wonderful. Great information clearly explained, thanks bud!

Thank you for an well presented (and correct) explanation of solar shading.

Thanks for this, I saw the NRG Solar video, but it just raised more questions. It's all much clearer after you explained how the bypass diodes work.

Very informative. Thanks Gary

Great video Gary!

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

An excellent presentation!

As having no experience in this field you’re videos have given me a better insight to what I need to know before I make a final decision on what to install,I wish to thank you for making it a lot easier to ask the relevant questions,excellent videos

Love the explanation...well presented.

Thx. Great. Very clear and educational. I have been searching this and now the yt algorithm keeps popping up these vid s about string vs optimized panels. This one is very good!

This is a must watch video. Thanks a lot.

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.

Another very informative video - thanks very much.

I've just read through most of the comments on this excellent presentation/video. There is really very little I could add. Extremely informative, challenging & clarifying supplier based information; excellent graphics. I suppose in summary, I feel in safe hands, without a hidden agenda. Thanks very much 🙏

Thanks Gary. This video is a model of clarity. I have recently been mulling over the question of optimisers but, aside from generic 'marketing-speak', I had found very little in the way of hard information. My gut feeling was that, for my installation, optimisers would offer little benefit and your helpful video has backed this up and saved me quite a bit of cash 😀.

Excellent video, thank you. I was fretting about cable shading on my newly installed array, and couldn't understand why my panels were still generating when some of the stuff I'd read said they wouldn't. This has explained it in simple to understand language. Thank you.

Very well explained,thank u sir!

Thank you so much Gary. Very useful 🙏

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.

Excellent content well presented - thank you

Very professional. Thank you.

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.

Great video, thanks!

Thank you. A very timely video for me as I'm in the process of comparing various quotes at present. I have tree shading issues so have been querying why optimisers are in/excluded from various quotes and why some quotes are only including partially optimised Tigo solutions. This is probably as clear an explanation of all the regular systems as I've seen (several compare Enphase and SolarEdge but very few include Tigo in the mix, which is what most companies are using in their quotations). Keep up the great work.

Great simple explaination thanks.

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!

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..

very useful and informative indeed. Thank you.

Thank you for that very useful information. Great video as always A++

Well presented Gaz

Great explanation. Thankyou

Good job, Good explanation

I have to say that was a great video I had no idea that the solar panels with micro inverters had those bypass diodes which makes them much more immune to shading problems .

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!

Another brilliant video Gary. I look forward to seeing what you tackle next. I wonder if you'll get any feedback from SolarEdge/Tigo/Enphase?

Your channel is probably the best source of technical information about solar and battery systems on KZfaq right now, Gary. Many thanks for making such thorough and clear videos, I've learnt a lot from them.

Great research, thanks for sharing.

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.

Great really clear information. Excellent job!

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 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 microinverters is the only solution to reduce the impact of shading. However, your video 'Solar panels shading: Are optimizers and microinverters 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 microinverters 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

Great video!👍

Gary I send all my customers in 2 minds about shading to your video and encourage them to use your octopus referral code- thanks for your comprehensive research

I did a 2 panel test in series hooked up to a Bouge RV MPPT. Both panels getting full sun I covered one with a blanket. It took the watts to near zero for about 20 seconds but then the mppt adapted and gave about half of the 2 panel wattage. I think the whole panel has a bypass diode too that keeps one shaded from taking out the whole array. Two panels in Parallel reacted to one fully shaded panel a lot faster almost immediately halving without going to zero for 20+ seconds. This convinced me that parallel is best for small RV 12v systems. You never know when you will turn and have shade across a panel. Losing 20-30 seconds of power everytime would add up. I also saw an increase in heat for the mppt controller with the series due to higher voltage having to be downstepped to 14.4v. However Series is a must for higher voltage battery systems (24v or higher) or you can use higher wattage panels as an option.

Excellent, thanks.

Very helpful thank you.

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.

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 KZfaqr: 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?"

That was is a fantastic video. I have just been quoted for 3 strings, 4,4,6. One of the 4 will be shaded by a gable over time and they quoted optimisers for them. This makes sense no. I would imagine they will go from the simple aerial apology to the chimney over the day. This has given me more confidence in the company I have chosen. They have quoted them for a good reason and didn’t try and stitch me up by only adding them to the string that needs them. On to your next video now

Nice video, and well put together. I'd add 1 more con to your list of optimizers 1. A constant 2% efficiency loss at the optimiser itself, regardless of shading or direct sunlight. I feel that most PV systems do not require optimizers/micro Inverters, but they do have their place in more difficult roofs with unavoidable shading. Good survey and design mitigates the need for optimizers in most cases in my opinion.

Brilliant, just brilliant.

I installed a new solar panel system 4 1/2 years ago. I live in the Desert Southwest of the USA where solar panels are a virtual necessity to prevent the power company draining my bank account. At the time I knew very little about the architecture of different systems. Like the vast majority of consumers I relied on contractors to recommend the best approach. Based on the recommendation of my installer, I ended up with a string array with a SolarEdge inverter/optimization. I’m lucky enough to have a large South facing roof with the one panel shadowed by a chimney that partially blocks sunlight in the morning. I’m a chagrined to learn that I could have saved a significant amount of money by eliminating the optimizers. I suspect that my installer, who is a very nice guy whom I trust, follows conventional wisdom in planning systems. I am going to share this video with him because I think he would be interested in lowering system costs allowing him to be much more competitive in pricing.

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.

That is the best presentation of the pros and cons of optimization that I have seen. Thanks! SMA says they have a new MPPT routine for their string inverter that works as good as optimizers in some circumstances without the reduced reliability. Have you figured that one out yet?

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.

Very clear and informative. One advantage of microinverters is their ability to shut off power when the grid goes down. This is a safety issue and a requirement here in the US. If firemen need to go on the roof, series solar panels can present a dangerous HV DC.

Best Video so far! i found my problem! thank you

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.

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).

Very informative video. Thanks for that tip. I have 3 different solar power systems that I own. 2 on the RV's and one on our house. the house has the Enphase micro inverters and the RV's both have NPPT controllers. Only one of the RV's uses an inverter. On the one RV I have seen a low or no output situation, as the solar panels had not been cleaned in quite a while. I thought it very odd that with 800 watts of possible output that the controller showed only the low battery voltage. I think it was around 8V, not enough to power the inverter or even the LED interior lights. Now I understand why that happened. I have a video about my 3 systems posted, if you'd like to check it out. I'd be very interested in your evaluation of my 3 different systems. I guess now I have to go clean a few solar panels!

Great video 👍

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.

Great presentation, thanks for sharing, when you run out of ideas this topic can be extended to half cut cells modules and having strings in parallel how this is being affected. Having one bigger string or having 2 strings half the size in parallel. Again thanks for sharing:)