Why does shading over one solar panel reduce the output of the whole string? - Page 1
Forum section: electronics / general

author: Malvineous
author_rank: Contributor
timestamp: January 01, 2018, 07:54:34 am
content: Hi all,I've been reading up about solar, and one thing confuses me (well lots of things do, but you have to start somewhere!)From what I have read, if you have a string of identical panels in series and one of the panels becomes shaded, the power output of the whole string drops to match the shaded panel. In other words, if the panels are producing 8 A each and one becomes shaded and drops back to producing only 4 A, all the other panels in the string also drop back to supplying only 4 A each as well. It's like each panel also acts as a current limiter, only passing up to whatever current it happens to be producing at that moment, and no more.This confuses me because I was under the impression that the panels worked like unregulated power supplies, producing as high a voltage as possible (up to the Voc / open circuit rating), and then as power is drawn from them the voltage drops until the Isc / short circuit current is reached, by which time they are presumably at an extremely low voltage but at their full current rating.If that's correct, then when one panel becomes shaded and it limits the current through the string of panels, shouldn't that make the voltage of the other unshaded panels increase accordingly from the reduction in current? Shouldn't this result in the inverter seeing an increase in total voltage across the string, since the panels are all in series? The inverter would presumably draw more current, dragging the voltage down low again but getting the extra power from the unshaded cells.Apparently it doesn't work like this, but can anyone point out where my misunderstanding is? If the unshaded panels suddenly can't deliver half the power they are generating, where does it go?

author: tszaboo
author_rank: Super Contributor
timestamp: January 01, 2018, 09:49:11 am
content: One image is worth a thousand words.mod: they remove the linked picture of course.

author: capt bullshot
author_rank: Super Contributor
timestamp: January 01, 2018, 12:09:01 pm
content: The drop in power output depends on how the load (inverter) handles the MPP algorithm.Usual PV panels have one (or multiple) reverse diodes installed. Either one diode for the hole panel or e.g. 3 diodes for each third of the number of cells in the panel. The purpose of these diodes is: if one or more cells is shaded, the generated current drops for this cell. If other cells / panels are unshaded, they still can supply the full current.The inverter can now try to still draw the maximum current from the non-shaded panels, this will drive the shaded panel into reversed voltage. The reverse diodes now start to conduct and reverse voltage drop across the shaded panel is limited to the diode drop. If the diodes wouldn't be there, the solar cells would see a quite high reverse voltage and may overheat due to this. So the diodes protect the shaded panel from overheating / damage.Now, if one panel (or part of the panel) is shaded, these cells deliver less current. The inverter can now either draw this reduced current and keep the voltage across the shaded panel - this results in a gross reduction of delivered power, or just continue to draw the full current from the non-shaded panels. Due to the reverse diodes, the voltage across the shaded panel drops to zero (or a bit negative), reducing the total output of the string by just the amount of one panel.So it's up to the MPP algorithm in the inverter to try lower voltages and see if there's more power available to maximize to strings power output. Some inverters do, others don't ...

author: capt bullshot
author_rank: Super Contributor
timestamp: January 01, 2018, 12:11:22 pm
content: Quote from: Malvineous on January 01, 2018, 07:54:34 amIt just heats up the panel, since the power isn't taken away from the panel.Quote from: Malvineous on January 01, 2018, 07:54:34 amYes, voltage rises, but just a little bit (see the MPP diagrams above)

author: Seekonk
author_rank: Super Contributor
timestamp: January 01, 2018, 12:32:12 pm
content: It actually doesn't take much to turn a panels output to crap. MPPT of a big string is just about as bad an idea as a PWM controller. The world is going to micro controllers for each panel.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: January 11, 2018, 08:36:34 am
content: The reason is that a solar cell acts as aforwardbiased diode when illuminated. That is why they never give more than 0.7v or so. It follows that a dark cell can be driven into reverse bias by the others in series with it. Since the PIV of the reverse biased junction is more than the panel o/c voltage, no current will flow.Exactly the same mechanism as the 'bully boy effect' in which reverse voltage will destroy a weaker NiMh or lithium cell in a series chain if you don't have a charge balancing circuit. Except that with the solar cell no harm is normally done.

author: f4eru
author_rank: Super Contributor
timestamp: January 12, 2018, 05:38:34 pm
content: An example :There are two power maximas, and often the mppt will select the wrong one, depending on it's software.Quoteit's a bad idea only if:- the panel string can be partially shaded by an obstacle- the MPPT is not smart enough- the installation of micro-inverters or local MPPT's is financially viable, which is often not hte case.

author: f4eru
author_rank: Super Contributor
timestamp: January 13, 2018, 06:55:42 pm
content: QuoteWhat's the problem with a PWM controller

author: Malvineous
author_rank: Contributor
timestamp: January 13, 2018, 11:32:54 pm
content: Many thanks for the detailed replies! That makes so much more sense now.I hadn't considered that when the current drops, the voltage of the panel can only rise so far before it hits the Voc and even before then the available current at any given voltage starts to rapidly drop, just as a result of the way solar panels work.Per-panel solutions (e.g. microinverters or DC-DC solar optimisers) make a lot more sense now. On this note, is it naive of me to think that a cheap constant-current DC-DC converter will do a similar job to a much more expensive solar optimiser? Ignoring for a moment that these cheap converters don't do MPPT tracking, they take a range of input voltages and produce a constant output current. If the output of these were all connected in series, then presumably you'd have a constant current at varying voltage, even as panels became shaded, with the voltage range no longer being a problem?The reason I ask is that I'm thinking about trying out cheap second-hand panels as a bit of an experiment, so they will all be different specs making a direct series string of them impractical. Because it's "for fun" so to speak (and unlikely to be grid connected), microinverters won't be any good (too expensive and they all must be grid-tied) and solar optimisers aren't so practical either (they either need a special inverter to control them or they are too expensive for this kind of project.) But if I could somehow combine a cheap MPPT device with a DC-DC converter...

author: f4eru
author_rank: Super Contributor
timestamp: January 14, 2018, 08:40:41 am
content: It really depends on your configuration!If you have no shading ( tree, obstacles), then you can skip the microinverters.If you have two roofs at different angles, you have to put them on separate MPPTsetcetc...

author: Seekonk
author_rank: Super Contributor
timestamp: January 16, 2018, 09:00:44 pm
content: If you have any shading, everything turns to crap fast. MPPT ain't going to save you except in a really long string and parallel strings are just lost. A lot of opinions from people that have never used solar. Being off grid makes you look at every watt.

author: mcbota
author_rank: Newbie
timestamp: July 01, 2022, 09:51:05 am
content: Hello. I have a problem which I cannot solve it and I ask you your help , please. On one string from my two strings PV system, consisting of 14 panels of 400 W, 37 Voc, after the system starts, about one hour later, the voltage decrease to about 220 V, the current on string increases much higher than normal (like something trying to adjust the drop of voltage), stays so for about three hours and then come back to the normal voltage. Looking at the position of the panel I observed that it is a little bit shaded. Is this the effect of the shadow that the inverter tries to adjust it by increasing the power? It is for any help to try to put that shaded panel somehow to the end of the string?. Thanks!

author: Berni
author_rank: Super Contributor
timestamp: July 01, 2022, 09:59:22 am
content: This happens because solar panels are simply current sources with a zenner diode in parallel.When one gets in shade it stops pushing current trough it, since they are in series this drops the total current.The fix for this are so called "Optimizer Modules":https://www.solaredge.com/sites/default/files/se-p-series-commercial-add-on-power-optimizer-datasheet.pdfThese modules sit between the solar panel and the series chain. They monitor each individual panel and bypass the current past it when it gets shaded. Additionally they also monitor the performance of individual panels and send that information over powerline communication back to the solar inverter. These are typically only seen in modern large solar arrays that operate with a series open circuit voltage in the 200 to 1000VEDIT: Additionally these modules enhance the safety of the system since the inverter can command the whole array to shut down by disconnecting all panels. Leaving the formerly 1000V wires perfectly safe to touch even during mid day sun. Making maintenance safer.

author: trobbins
author_rank: Frequent Contributor
timestamp: July 02, 2022, 12:31:46 am
content: One would hope that the MPP used in the inverter can move to the actual MPP of the string. The MPP of a string of panels is a series combination of voltage and current curves from each panel (as the inverter only sees the resulting series sum of panel voltages, and the sole current level through all panels).If the string comprised just the shaded panel, then the MPP would be at a lower current and voltage than for an unshaded panel. If the string comprised 2 panels, one shaded and one unshaded, then the resulting MPP is likely to be at a V and I that is between the two individual panel MPP's (if the inverter can resolve the best V-I MPP, and not lock on to a local MPP related to one or other of the 2 panels). If the string comprises more and more unshaded panels, then the MPP moves more to a V,I operating point that is closer to just if it had unshaded panels, but modified such that the total series string voltage is lower by an amount related to the section of shaded cells that are diode bypassed (eg. typically circa 12V or multiples).

author: fourfathom
author_rank: Super Contributor
timestamp: July 02, 2022, 01:27:49 am
content: It seems to me that discussing MPPT is likely confusing the OP. The question was about shaded panels in a series string, and to understand what is going on I suggest that the OP just look at the panel characteristics (the basic V-I curve) and then consider the V-I curve of a string of panels with and without partial shading. At this point one can calculate the maximum power point of the full string to see what a MPPT controller might do with it.Note that the panel is not a constant-power device, but is much closer to a voltage-limited constant-current source. The V-I curves will show this.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 02, 2022, 01:57:18 am
content: I wonder if anyone has tried to implement a sub string MPPT using MOSFET switching, with a single series inductor for the whole string. Doing it per panel should be relatively easy, it could also be done with multiple MPPT zones per panel or at an extreme, per cell using MOSFETs etched right onto the back side of the silicon.An open hardware implementation of the per panel type would be interesting.

author: ledtester
author_rank: Super Contributor
timestamp: July 02, 2022, 02:24:55 am
content: Quote from: Berni on July 01, 2022, 09:59:22 amFesZ Electronics just did a video on this last week:Modeling Photovoltaic Cells - Theory 1/2 - FesZ Electronicshttps://youtu.be/uV_z1ptufa4Quote from: Malvineous on January 01, 2018, 07:54:34 amAt about 10:15 he talks about this phenomena.

author: fourfathom
author_rank: Super Contributor
timestamp: July 02, 2022, 04:28:54 am
content: Quote from: Malvineous on January 01, 2018, 07:54:34 amThe *current* in the string drops to whatever the shaded panel is delivering. Since in practice the panel voltage stays fairly constant, shaded or not, the available power also drops proportionally.

author: mcbota
author_rank: Newbie
timestamp: July 02, 2022, 05:05:35 am
content: Thanks for all your answer. This is the situation in this morning, after the drop of the voltage. Normally it has to be above 400 V and around/under 1A, at this hour, on that string, being 14 panels. And this voltage and current stays for about two-three hours.Later edit: the second picture is made after that period of time passed and the voltage became normal on that string.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 02, 2022, 08:00:45 am
content: Quote from: Malvineous on January 01, 2018, 07:54:34 amObviously this is confusing, because it is a total and utter made up lie. It does not work that way. For example, I have a string of 10 panels where I get 1 to 2 completely shaded panels in late afternoon. No such effect.Sometimes it is just people who have no idea what they are talking about trying to be "helpful" but actually doing harm. Sometimes it's a microinverter or "optimizer" FUD BS market guy.I'm surprised such bullcrap is seen in this thread, too:Quote from: Berni on July 01, 2022, 09:59:22 amNo it won't, so the rest of the post is BS too.How can people be so oblivious to such commonplace urban myth so that they keep writing responses happily assuming it was true, instead of shooting it down as the very first thing?In reality, shaded panel cannot produce the same current, that much is true. This causes the voltage to change, look at the U-I curve set of the panel. The voltage tries to gonegative, and current starts flowing through the bypass diodes installed in the junction box.As a result, shaded panel production goes to zero, but rest of the panels keep producing optimally, assuming non-broken MPPT algorithm.Actual panels usually consist of 3 "sub-panels" (with 3 bypass diodes, too), so that if you partially shade 1/3rd of the panel, only that part goes to zero, and rest of the panel keeps optimal production.This is also why microinverters and "optimizers" rarely make economic sense: if you have say 10 * 300W panels, each producing 300W for 3000W total, and you partially shade one of them to production potential of 30W, in a microinverter system you could have 9*300W + 1*30W, and with string inverter you could have 9*300W + 1*0W. It is simple as that. However, string inverters tend to have a few %-point better efficiency than micros, this evens out the difference in typical installation where there is only very minor shading. Microinverters are recommendable when there is a lot of shading, sometimes half of the panels, or the panels are not in the same plane but point in whatever directions.

author: Marco
author_rank: Super Contributor
timestamp: July 02, 2022, 09:56:05 am
content: Quote from: NiHaoMike on July 02, 2022, 01:57:18 amCan only work if you give each panel a time slot. Seems a lot of trouble to save some inductors.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 02, 2022, 01:48:48 pm
content: Quote from: Marco on July 02, 2022, 09:56:05 amConceptually, take a bunch of buck converters (without output capacitors and with independent inputs) with the outputs in series and a single large inductor would be the same as many smaller inductors. At the extreme of per cell MPPT, having one inductor per panel (or one inductor per string) would be a substantial savings over each of the 70 or so cells in a modern panel having its own inductor.Where things get interesting would be developing an algorithm for each of the MPPT switchers to sense the ripple and try to minimize it. Probably the easiest would be to have the charge controller provide a timing reference and each switcher to slowly vary its phase shift at a pseudorandom rate until it settles down to a minimum ripple level.Come to think of it, a per cell MPPT wouldn't even a proper MPPT algorithm, as it could detect the cell temperature and light level to figure out what the Vmp should be.

author: Berni
author_rank: Super Contributor
timestamp: July 02, 2022, 02:19:50 pm
content: Quote from: NiHaoMike on July 02, 2022, 01:48:48 pmYou would need an inductor at each panel if you wanted to MPPT each panel individualy.What you are trying to regulate is not the voltage at the end of the string. It is the voltage across the actual solar panel. If you PWM the panel onto the series string you get either full current or 0 current trough the panel. This would give you an average of the two extremes in the panels IV characteristic. What you actually want to do is hold the operating point at the maximum power level. So for this you would need an inductor at the panel so that on one cycle the panel is charging the inductor with energy, then once switched over the inductor and panel are sending energy back out to the string. Changing the PWM duty cycle moves the inductors operating point up and down and so also rises and lowers the current trough the particular panel. Do this for every panel individually and each string will be operating at ideal current and voltage, the series string has the current flowing trough all of it, just that shaded panels are adding less voltage to the series string.This is what these solar optimizer modules are. Here is the insides of a SolarEdge brand one from a presentation:Here is the full presentation. It explains how the optimization works and a bit how the communication to the modules works:https://www.glavaenergycenter.se/wp-content/uploads/2018/11/solaredge.pdf

author: Siwastaja
author_rank: Super Contributor
timestamp: July 02, 2022, 03:03:30 pm
content: The problem with both "optimizers" and microinverters is that they still increase complexity and cost too much.Most installations that do use them, only use them because of serious misconceptions and false data they are marketed with. Of course, there are some legit cases, too.I do believe that microinverters will eventually win, but that will be after more rigorous integration, cost reduction, and reliability improvements. What I really mean, inverter becomespart of the panel, so you just basically have a sleek panel with AC output.It's worth noting how important the suitable, weather-proof DC power plug (MC4 and similar) was to the proliferation of solar installations. We also need the same to happen with AC power. These things need to happen:* Microinverter is integrated with the panel,* Output is with weather-proof, safe AC plug anyone can plug in (no electrician needed legally),* Pre-made wiring harnesses are made in different shapes, so that electrician only does one connection in house fuse box.I hope this happens soon. In the meantime, good old string inverter seems the best option, or maybe microinverters in special cases such as panels all over the places in random directions, severe shading, etc. Or very small installations where you only have a few panels. Modern cheap string inverters have evolved and support two strings (2 x MPPT) which reduces the gap to microinverters in partially shaded installations.In any case, this is a completely different discussion, and more like micro-optimization. For the OP, it is most important to realize they have been fed completely wrong information. In actual reality, string inverters, microinverters and power optimizers usually all work well, and differences in production is small, except in some pathological cases. The problem with pathological cases is, if you are having so much shading, total output will be low in any case, and hence spendingmoremoney for the system is even worse. Best course of action would be to find a better location. The problem is psychological: you like PV a lot but don't own a suitable spot. In this case, you could mentally or even financially support others to do the installs in optimum locations.

author: fourfathom
author_rank: Super Contributor
timestamp: July 02, 2022, 03:34:08 pm
content: Quote from: fourfathom on July 02, 2022, 04:28:54 amAs Siwastaja states, bypass diodes can "bypass" a shaded panel, or a shaded section of a panel (this depends no how the bypass diodes are configured). I should have mentioned that. How well this works depends on the number of panels in your string, and I suppose your controller.I am used to boat installations where we typically have 2/3/4 panels and the voltage reduction when a panel section is bypassed is a significant fraction of the full string voltage. On my sailboat I have three "12V" panels, with per-panel MPPT controllers. The shadowing problem on a sailboat is so bad that connecting the panels in series would not be a good idea, and the wire lengths are relatively short so there's one less compelling reason to go serial. Home rooftop installations often have many panels in series, and shadowing typically isn't as severe as on a sailboat.But I still think that one should first understand the behavior of a solar cell, then a panel (without diodes), then a string of panels. *Then* see what adding bypass diodes will do.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 02, 2022, 04:00:08 pm
content: I don't think mental modeling / understanding of the panel without bypass diodes does any good, because the diodes will practically be there for a very good reason. Unless you really want in-depth understanding of the semiconductor physics.This is like "what if your car engine missed one spark plug, how would it perform?" when considering fuel economy of different driving styles, or comparing different cars.

author: Berni
author_rank: Super Contributor
timestamp: July 02, 2022, 05:14:30 pm
content: Microinverters per panel are not a very good idea.The job of the inverter at the end of the chain is a lot more involved than these optimizer modules. The inverter is a isolated DC/AC converter, so it uses much more advanced typologies with enough safety to be directly connected to mains. It needs to survive the surges it might see and must operate at much higher voltages, at the same time the single panel would provide a fairly low voltage so a lot of steeping up would have to take place on a per panel basis. There is also more smarts in the inverters as they need to monitor and sync to the grid while also reporting status back to a command and control center (aint nobody got time to go check a little LCD on it every day). Since they work at 50/60Hz a significantly higher amount of energy storage needs to happen inside the inverter, tho this is often partially mitigated by using 3 phase mains. However 3 phase is not the solution for microinverters as you need a lot more wiring and complexity to do this. Already running single phase mains to each module would be significantly more complicated than just series connection.Optimizer modules at the panels minimizes the extra complexity to the minimum required for doing a panel by panel MPPT. They work at low voltages and do not require any isolation, making the switchmode topology inside significantly simpler while also dealing with only DC (So almost no energy storage required). These topologies have fewer parts, are smaller and run at very high conversion efficiency (reduces part cost, material cost and heatsinking requierments) To work they require the minimal of microcontroller brains while also providing insight into individual panel performance as a free bonus. At very low panel output they can easily let all the power pass straight trough by switching the appropriate transistors in the DC/DC converter. This wastes very little power, but across the whole string enough power might be collected for the big boss inverter on the end to harvest some useful power. Often a single optimizer module might handle multiple panels too, so you don't need quite that many of them. These modules also make it practical to have much longer series chains, this allows higher voltages to be used on the system level, this reduces the already lower copper wiring requirement by allowing thinner cables to be used with less loss. Sure this means more voltage to deal with for the inverter on the end, but it is already dealing with 400V AC mains anyway, so 1000V DC is not that far off.That being said optimizer modules are not default best solution for everyone. They do provide an extra layer of cost and complexity that might not always be justified in the particular solar installation. Going for simplicity the oldschool long chain of panels with a single big boy inverter is the most simple you can do. If you have an array of new identical matched panels that never gets partially shaded, then that simple setup is all you need, you won't see any extra energy production from installing these optimizer modules.

author: bdunham7
author_rank: Super Contributor
timestamp: July 02, 2022, 05:36:45 pm
content: Quote from: Siwastaja on July 02, 2022, 03:03:30 pmThese things already exist in practical form, although the second is not likely to be recognized legally in many jurisdictions as they simply won't allow user installs without a permit and inspection. My microinverter installation doesn't have integrated micros and I'm not sure I agree with that being an unequivocally good thing in the long term unless the 'integrated' module is separately replaceable. The premade AC wiring harness in various configurations is what I used 10+ years ago, although it is usually a bit more complicated than just connecting it to a breaker.I realize that costs and regulations are different now and also different in other places, but micros were economically the best plan for me 10 years ago even without considering the safety, detailed data and reliability issues.One thing you about your earlier post: If you have panels that are lightly shaded or just dirtier than others--say 5 of your panels are putting out 200W and 5 of them the full 300--a plain string inverter will have to either draw full current and thus bypass the 5 lower-power panels and produce 1500W or reduce the current and produce 2000W. And then it has to be smart enough (Global MPPT) to find the correct solution. Microinverters or optimizers will do per-panel MPPT and produce 2500W. Whether that matters depends on your installation, but mine is certainly not a 'marginal' installation as I have a nicely pitched roof facing due south in southern California--and I do get some benefit from micros over string, something like 10-15%.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 02, 2022, 05:47:00 pm
content: I would assume the MPPT getting stuck at local maximum would be a solved problem long time ago, in popular production string inverters that get installed (e.g., Fronius, Huawei, etc.)At least my Steca is able to find the global maximum, and it's a decade old product already.

author: fourfathom
author_rank: Super Contributor
timestamp: July 02, 2022, 05:48:59 pm
content: Quote from: Siwastaja on July 02, 2022, 04:00:08 pmSuit yourself. Different panels have different bypass diode configurations, and I think it makes a difference.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 02, 2022, 07:19:30 pm
content: Quote from: fourfathom on July 02, 2022, 05:48:59 pmEducate me, is there going to be any other "configuration" than just varying the number of cells per each diode, or the physical shape in which the cells are arranged, which is of course interesting if we have horizontal or vertical shadows.In any case, if the bypass diodes exist at all in the module (as they practically always do, of course), I can't see how the whole string could be brought to the near zero production of the shaded module.

author: fourfathom
author_rank: Super Contributor
timestamp: July 02, 2022, 09:07:11 pm
content: Quote from: Siwastaja on July 02, 2022, 07:19:30 pmOK, the 36-cell panels I have used have two bypass diodes (18 cells per section). I just found a Panasonic 335W panel with 96 cells and four bypass diodes (24 cells per section). An array of the old 36-cell panels will likely have less power reduction during partial shading than one with the 96-cell panels.Of course there are going to be valid reasons why you would prefer one panel design over the other, and for rooftop applications partial shading probably isn't at the top of your list of issues. But on a sailboat partial shading will be one of your primary concerns. And yes, I know that sailboats are a microscopically small volume consumer of solar panels, but it matters to me.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 02, 2022, 11:46:03 pm
content: Quote from: Berni on July 02, 2022, 02:19:50 pmIt can be done with capacitors across the inputs so the output will switch between Vmp and zero/bypass. It would be quite easy to have the frequency high enough that only film capacitors would be needed. In the case of the per cell MPPT, the low voltage would allow the frequency to be increased even more so that the capacitance of the cell itself serves that function. There only needs to be one inductor per string which can be shared with the boost stage that comes into play at low light levels.Quote from: Siwastaja on July 02, 2022, 03:03:30 pmMain weakness I found with them is that unlike DC systems that are able to output power as long as there's sunlight, AC systems have the problem of not being able to start up without some other power source providing voltage. I'm sure part of that is the safety aspect of making the output touch safe when not connected, but having all of them agree on the phase without something providing a timing reference probably isn't that easy to solve.

author: trobbins
author_rank: Frequent Contributor
timestamp: July 03, 2022, 12:12:27 am
content: From a general perspective, I'd suggest we are only really discussing issues in the domestic or small commercial/rural or niche markets. Large installations either don't have shading designed in to their layout, or use string inverters where only a small % are subject to some form of shading and that has been 'designed in' to their business case. Even for many domestic installations, a competent PV designer has assessed the site setup as not losing significant annual energy due to shading. And I'd suggest that many who think they have a shading problem have not adequately assessed the actual measured loss or their particular consequences of any such loss. Even the OP doesn't have an actual installed system to assess and is only starting on his journey to becoming aware of what is required to be a competent PV installer/designer.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 03, 2022, 07:36:50 am
content: Quote from: trobbins on July 03, 2022, 12:12:27 amIt's a good idea to simulate with a tool such as PVGIS (https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html), using a horizon file.Partial shading might look nasty to the eye, but it could still be just a few % in annual production.If you have a decently sized string inverter where minimum voltage of MPPT does not become a problem, and the MPPT algorithm handles global maximum - both assumptions are true with modern string inverters - even if you shadehalfof your panels, you won't lose that much of production. For example, you get 5*300W + 5*0W instead of 5*300 + 5*50W. And if the panels are shaded for more than an hour or two per day, it makes absolutely no financial sense to install those panels at all.Spot shading within one module is then dependent on the module, and microinverter or optimizer cannot make it magically better.I have an issue where 6 out of my 10 panels are shaded around 7am-8.30.am by a tree, coupled with misdimensioning the inverter, one designed for normally 16 panels. Now this ratio 4/16 is just too small so minimum voltage is not satisfied and MPPT cannot track below 200V, so production is very minimal. Still not a big deal in annual production. But this has started to bug me lately, because this happens to be the most expensive hour in the Nordic spot market.

author: Alti
author_rank: Frequent Contributor
timestamp: July 03, 2022, 09:17:43 am
content: Quote from: Siwastaja on July 02, 2022, 08:00:45 amI believe this is the consequence of misinterpretation/extrapolation of marketing claims of PV market players that advertise optimizers and microinverters.What they claim is that in a traditional string:A: shading one panel to0%results in Pstring =100%(implicit)B: shading one panel to50%results in Pstring =50%and now OP et al. extrapolated A and B, adding another claim to that:C: shading one panel to100%results in Pstring =0%Since this is an advertisement, IMHO it is to be reasonably expected that Joe Average without technical background understands B is true only in very specific narrow case selected for the benefit ofbatterizeradvertizer.http://www.gsmlimited.com/wp-content/uploads/2013/09/Solar-Edge.jpg

author: Berni
author_rank: Super Contributor
timestamp: July 03, 2022, 10:42:01 am
content: Quote from: NiHaoMike on July 02, 2022, 11:46:03 pmAh yes a capacitor like this could work.Tho in practice this means that you are putting sharp high frequency square waves on the series string. In a typical installation this string has quite a large loop area as it snakes around panel to panel with the return then taking the shortest route (rather than retrace the string back along the same path). This means that we might not even need an inductor on the end since the string itself is likely going to have a self inductance that comes close to the miliHenry range. However making this pass EMI regulations is another thing. Just laying out a small low power DC/DC converter in a wrong enough way can make you fail EMI compliance tests pretty badly. So sensing square waves in such a long string might make it transmit more RF power than a WiFi router.

author: Berni
author_rank: Super Contributor
timestamp: July 03, 2022, 10:56:33 am
content: Quote from: Alti on July 03, 2022, 09:17:43 amYeah this picture is completely wrong.What happens instead is that when a panel gets slightly shaded the other panels keep pushing the same current trough it. As a result the slightly shaded panel that might be producing 50% full power starts sliding down its IV curve rapidly, since it can't maintain a voltage at this high of a current. As a result the array pulls the panels voltage to 0 and then down into negative where the pass diodes catch it. As a result the panel that would be otherwise producing 50% of power is actually burning a few % of power into heat on the pass diode. So not only is it not producing any power, it is burning a bit of the power that other panels produced.The reason shading within a panel is not as bad is because there are also some parallel connected cells in there, so the cells can help each other out a bit. Also shadows tend to be pretty fuzzy from a distance. Certainly does affect them but MPPT can still milk some usable power out of them.Would have expected better from a big solar electronics manufacturer like SolarEdge, but then again the actual technical details of why partial shading is bad is not as simple of a topic even for tech minded people on this forum (Hence we have this thread) but now imagine trying to explain this to the typical end costumer that works as an accountant at the local bank and calls an electrician to wire up a wall outlet. There goal is to sell you there fancy solar tech after all.

author: tautech
author_rank: Super Contributor
timestamp: July 03, 2022, 11:04:47 am
content: Dave did a recent video on this:

author: Siwastaja
author_rank: Super Contributor
timestamp: July 03, 2022, 01:04:19 pm
content: Quote from: Alti on July 03, 2022, 09:17:43 amYes, that attachment is an outright lie. It is not some kind of exaggeration or "optimal" case, it's total bogus and would belong to the "dodgy technology" section. There is no way I could buy any product from this kind of company. In fact, this is a scam that should be handled by the authorities.No wonder this misconception lives so strong.

author: Alti
author_rank: Frequent Contributor
timestamp: July 03, 2022, 02:57:20 pm
content: Quote from: Siwastaja on July 03, 2022, 01:04:19 pmI tend to disagree, you misinterpret the advertising claim (B), expecting this property to hold in all but exceptional circumstances. That is not a lie but the way advertising works. A shift of a wonky MPPT due to partial shading results in output power drop whether you like it or not. Yes, that requires high noon, no clouds, primitive and greedy MPPT, string must include only three panels, shading must cover 50% of cells gradually, etc, etc.. But it is a fact, narrow case, not a lie.I attach some SolarEdge claims.These vary from 50% shading / 50% Pstring to 10% shading / 90% Pstring but the overall concept is identical. I suppose percentage varies country by country.https://www.solaredge.com/solutions/residential/system-benefitshttps://swb-herten.de/solaredge/And a pdf in Polish.solaredge-najlepsze-rozwiazaniePV.pdf(2504.14 kB - downloaded 56 times.)Quote from: Siwastaja on July 03, 2022, 01:04:19 pmExtrapolation.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 03, 2022, 03:23:23 pm
content: Well, they use words "typical" or "traditional" to describe practically nonexistent systems. Competitors on the market do not perform as described. This is the part where the scam is.This is not OK, like it or not. In marketing, descriptions of "typical" competitor systems must be realistic. You don't need to do careful analysis to find average or median system, but you can't take a malfunctioning system, or something that has not been sold in years. You also can't cherry-pick some special edge case without mentioning it.FUD is one of those marketing tricks that really piss me off. If you don't have a viable business case on your own merits, you should be improving your product or doing something else, instead of lying about how your competitors perform. And this is the problem with microinverters and power optimizers: they usually offer very little production gains. Thus, manufacturers have no otherfairoption but to accept they are filling in a niche. I know it is tempting to try to sell these to everyone, but that easily escalates into iffy marketing or outright lying.Power optimizers are in specially tight spot, because at least with microinverters, you have the obvious use case in very small systems, or systems that are very distributed by nature: two panels here, three panels there, one panel over there. Power optimizers still require the string inverter, and it needs to be aspecializedone - only on PowerPoint made by an engineer it is a "simpler one".

author: Alti
author_rank: Frequent Contributor
timestamp: July 03, 2022, 03:40:34 pm
content: Quote from: Siwastaja on July 03, 2022, 03:23:23 pmSo in your opinion 50% shading/50% Pstring claim is exaggerated and unrealistic?SolarEdge 60% shading/40% Pstring.http://www.elektromuench-ulmen.de/html/solaredge.htmlOT(or maybe not): Pictures of claims are excerpts from marketing materials from SolarEdge, it is quite tricky to reach the original pdf's from their servers, these are just pictures with no text to search for. If anyone knows how to find original documents - please attach pdfs.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 03, 2022, 03:51:06 pm
content: It's not an opinion, it's a simple fact. Anyone with a PV system can observe this, me included. I just observed it a few hours ago as my output was around 80% of normal with two panels out of ten shaded pretty severely. I will observe it again tomorrow, and every day, as the chimney shades first one, then one more panel in the afternoon. (Knowing what exactly is "normal" is of course challenging, as the illumination angle gets worse to the non-shaded panels at the same time, too. But you can obviously see there is no any kind of dramatic reduction.)That 40% 40% 40% 40% 40% 40% is not going to happen in actual reality, it makes absolutely no sense, PV systems do not work that way. Totally made up.Really it is 0% 100% 100% 100% 100% 100%. Or to be exact, a tad below 0% because of the Vf of the bypass diodes, but this is not much. Can also be over 0% if shadowing is very light, in which case all the others might be a tad below 100% (like 98%).The best thing optimizers or microinverters could offer for me would be the per-module monitoring which could be very interesting.

author: fourfathom
author_rank: Super Contributor
timestamp: July 03, 2022, 04:15:12 pm
content: Quote from: Siwastaja on July 03, 2022, 03:51:06 pmI know, I'm going on and on about sailboat installations, but similar shading across multiple panels really does happen, and this is one reason why we consider shading sources when we look at panel array orientation. I've got three panels where the shadow of the boom would fall on all three if I had the panels arrayed fore and aft. Instead, they are arrayed port to starboard so the shadow only hits one panel, or at most two partially. The same issue arises with the mast and to a lesser extent the shrouds and stays. A flagpole might create a similar shadow on a terrestrial installation, but the shadow would be much less severe -- not a 40% situation.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 03, 2022, 04:19:24 pm
content: Yes, panel orientation matters if you have straight line shadows or something like that.It's worth noting though this is orthogonal to the string vs. micro discussion. If you have such shadow shapes, it is worthwhile to build the right configuration, micros or string.

author: bdunham7
author_rank: Super Contributor
timestamp: July 03, 2022, 05:34:27 pm
content: Quote from: Siwastaja on July 03, 2022, 01:04:19 pmIt's not that bad. The case they show is a simplistic version of whathappensmay happen if the string inverter doesn't have global MPPT, the global MPPT is not enabled or as in your example, the loss of one or more panels results in the string voltage going below the MPPT threshold voltage. But in their simple example, even if the global MPPT was available and working, the output would be 0 + 100 +100 or 2/3 full capacity, whereas the per-panel optimizers would make that 50 + 100 + 100 or 5/6 full capacity.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 03, 2022, 07:07:38 pm
content: Very strong "may happen". And this isn't relevant because global MPPT algorithm is needed in any case. All modern string inverters have it, but those optimizers need it too because they are also dealing with series strings like it or not (within a module) which is still susceptible to non-monotonous power curve.I don't understand why people try to somehow justify the wrong claims by trying to come up with some rare edge case in which their claims are true.This is like claiming opamps are bullshit and you need our new xyzqwerty-amp because typical opamps suffer from phase reversal every day in every circuit, while in reality phase reversal only happens in certain cases, and only with some ancient opamps easily avoidable.

author: bdunham7
author_rank: Super Contributor
timestamp: July 03, 2022, 08:39:04 pm
content: Quote from: Siwastaja on July 03, 2022, 07:07:38 pmBut you've provided a specific example of this very thing happening to you!QuoteI can't speak for Solar Edge, but a microinverter system like mine would not have that issue at any power level. And global MPPT or not, the micro based system generally outperforms the string in shading situations--just not as much as the simplistic example that offends you. It has to choose between two generally non-optimum solutions and the non-optimumness of those solutions is not rare, it is normal. Now whether that bit of additional power is worth any additional cost, that is another issue--and a more important one, IMO.

author: Alti
author_rank: Frequent Contributor
timestamp: July 03, 2022, 08:45:47 pm
content: A marketing masterpiece. Or at least a clever one, an example of resources well invested IMHO. Either investing into improving a product, or hiring consultancy agency, marketing specialists and analysts for shading claims.. I'd say that this direction might have been based on the fact 98% of the decision makers won't/don't care how PV works, these SolarEdge presentations are clear, simple and convincing and target Joe Average.What puzzles me is: why have they gone only to 60% shading claims and stopped there? I think SolarEdge won't ever go as far as: X% shading/(100-X)% Pstring, for any X, as in OP but why 60%? Is this 60% some "decency level" that should not be crossed?

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 03, 2022, 09:15:12 pm
content: Quote from: Berni on July 03, 2022, 10:42:01 amSome filtering would probably be necessary to limit the slew rate, but it would be much smaller than the smoothing inductor since it only needs to reduce the radiated EMI (30MHz and up) to acceptable levels.

author: fourfathom
author_rank: Super Contributor
timestamp: July 04, 2022, 12:52:35 am
content: Quote from: NiHaoMike on July 03, 2022, 09:15:12 pmThe FCC may not care about radiated EMI below 30 MHz, but you're going to have radio amateurs showing up with pitchforks and torches.

author: Marco
author_rank: Super Contributor
timestamp: July 04, 2022, 08:50:03 am
content: Quote from: Siwastaja on July 03, 2022, 07:07:38 pmThey might have some way to regulate the current down to make the string voltage more efficient for the inverter and to allow bypass of a subset of the optimizer DC/DC converters. In theory though simply for putting maximum power on the string DC link a nearly constant current output works just fine. Can output arbitrary power.That's not really MPTT any more though, but minimum converter losses tracking.

author: Berni
author_rank: Super Contributor
timestamp: July 04, 2022, 09:36:39 am
content: Quote from: NiHaoMike on July 03, 2022, 09:15:12 pmNot sure how it is with FCC. The European CE standard also includes conducted EMI that includes frequencies below 1MHz.Quote from: Marco on July 04, 2022, 08:50:03 amWell yeah each optimizer module becomes it's own little mini MPPT.The only trick is that the MPPT can find the optimum operating point for each panel individually, so slightly shaded panels can still extract a good deal of power.If the MPPT is smart enough to find a global or local maximum is another thing. But the peak power point is going to be more prominently seen on a single panel versus a large array in series. On a large array the panels are all going to have a slightly different optimum operating point so the resulting IV curve is going to be more fuzzy as a result. Sure the panel itself is also made up from multiple cells internally, but they do come from the same batch and are physically close together so they are more likely to act similarly. So all in all the IV curve of a single panel should be sharper and less wavey, so easier for the algorithm to find the right spot.The big boy inverter on the end is basically a 3 channel D class audio amplifier that 'plays' 50/60Hz into the mains network. So it doesn't care about the precise voltage it is getting as long as it is within its operating range (Tho it likely is slightly more efficient around some ideal voltage)

author: Marco
author_rank: Super Contributor
timestamp: July 04, 2022, 09:55:23 am
content: I suspect if a lot of panels have near identical max power point, the optimizers bypass themselves to let the inverter determine max power point. Just to avoid double converter losses.

author: tszaboo
author_rank: Super Contributor
timestamp: July 04, 2022, 09:59:21 am
content: Quote from: bdunham7 on July 03, 2022, 05:34:27 pmActually, this is the answer. If an inverter tracks MPPT, and it uses simplistic approach, it might drop the entire string to 50% if one panel is shaded. Normally new inverters are smarter than this, and they have global MPPT, scan the panel array for optimal and work on that range, but some early inverters didn't do this. And it might be marketing, but otherwise the technology works.I have solaredge on the roof for the past year, and I'm very happy with it. It is more robust for panel failure, doesn't require global DC disconnector, and has a cheaper inverter than the more advanced 2 string inverters. So the total system cost is not that much higher. And unlike microinverters, the optimizers cost only like 40-50 EUR or so, and they can use the full power of the panels, unlike Enphase. Right now they make sense.On the other hand, I'm seeing more and more microinverters with something like 4 MPPT inputs. They seem to be the price/performance champions now, or the near future.

author: Marco
author_rank: Super Contributor
timestamp: July 04, 2022, 10:10:18 am
content: BTW on micro inverters needing more cabling, there have been commercial series connected micro inverters, with the whole string adding up to mains voltage AC.

author: Berni
author_rank: Super Contributor
timestamp: July 04, 2022, 10:20:34 am
content: Quote from: Marco on July 04, 2022, 09:55:23 amYep it does make sense to do it like that.The inverter on the end has to constantly follow the mains voltage on its output, so it rarely operates in its ideal PWM duty anyway. But the optimizer can try to run there internal buckboost at near 100% (or even just stay on to bypass it) since that's where buck converters are the most efficient. It only has to do a lot of work on the shaded panels where it has to step down the input voltage in order to get the extra current for feeding the series chain at whatever current it wants to run according to the fully sunny panels. (And even then the input/output ratio is not huge, so it is easier to make a buck converter efficient at it)The reason that these more complex ways make sense is because the panels are the most expensive part, so it might be beneficial to throw more electronics at the problem to make sure every drop of power is extracted from the panels. Maybe prices of solar panels will fall enough to a point where doing this does not make sense anymore.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 04, 2022, 11:39:18 am
content: Quote from: bdunham7 on July 03, 2022, 08:39:04 pmWat? No! I have shown an example where shading 12 panels out of 16 (design # of panels for the inverter) causes string inverter to fall below minimum voltage. Or more exactly, in my case ignoring the misdimensioning of the inverter, shading 6 out of 10. I may add that once two panels are cleared, with 4/10 shaded, full production commences no problem.They have shown two examples, where shading of (A) 1 panel out of 3, (B) 1 panel out of 6 fails the whole string.12/16 = 75%6/10 = 60%1/3 = 33%1/6 = 16.7%Completely and utterly different.Their optimizer will likely also fall below minimum voltage if you shade 45 of the 60 cells.This does matter. Their central claim is: shadingjust onepanel brings the whole string down. This is wrong, in realityshading most of the stringbrings the few remaining panels down. A huge difference because installations with one-two panels getting shaded for an hour-two makes total financial sense. But if you have most of your string shaded for a large part of the day, you should not be installing the damn thing to begin with. Especially not with their optimizers because it will only increase the cost and the system will still produce poorly.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 04, 2022, 11:59:45 am
content: Quote from: tszaboo on July 04, 2022, 09:59:21 am1) are you sure it doesn't require DC disconnector? I have not read the actual standards, but seeing the optimizers are non-isolated and suspect to failing short (or having configuration error, outputting a voltage), I would definitely want to have a DC disconnector to protect against arcing during maintenance work. In other words, I would not trust a software-controlled semiconductor switch in HVDC safety.2) how much did the inverter cost? You might not realize how cheap string inverters are today (have been for years), they are manufactured in huge masses by companies like Huawei. 2-string feature seems to now be the feature in the lowest-cost string inverters. You can get a 3kW inverters around 700EUR or so, depending on where you live and taxes etc.I am aware of the engineer reasoning that a PowerEdge inverter can be made simpler, and it theoretically can be of lower cost, but for that to become reality there has to be enough competition (so mix-matching different manufacturers must be possible, I don't know if it is) and large enough production quantities.Also DC disconnection switch is often a feature of string inverter. At least mine has the switch built-in.

author: tszaboo
author_rank: Super Contributor
timestamp: July 04, 2022, 12:47:56 pm
content: Quote from: Siwastaja on July 04, 2022, 11:59:45 am1) They had it up until a few years back, when they certified their system for safety. If the cables are disconnected, it drops the voltage to 1V/module.2) I have the 3500W inverter, which was 750EUR ex BTW. I looked at some prices now, SMA sunnyboy 3000 costs 1100 EUR, Huawei 940 EUR. The interesting part is, the 25KW Solaredge is only 1700 EUR. Maybe its covid prices.I don't think Solaredge will be the cheapest, but for me it was worth to spend extra ~5% on the system to get extra MPPT per panel, and the data. I get shading on the panels, plus the system is more flexible now.Mixing panels is definitely possible, you have like 3-4 different optimizers that can work together, they have different wattage.And I also get where you are coming from, at the beginning I was also doubting if it makes sense.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 04, 2022, 01:39:26 pm
content: Well, for +5% total cost it almost makes sense for just the monitoring alone.Reliability is hit-or-miss. Microinverters have some reputation of failing, which is understandable when you mount electronics in worst conditions (specifically heat) and increase the number of modules by 10x compared to a string inverter, so also increase failures by 10x. This can only be solved by very good engineering, and it is of course doable.You are looking at inflated prices now. 2.5-3kW inverters have ran as low as 500-600EUR at some point about 2 years ago. Panels have inflated a lot, too, for obvious reasons. The only comfort really is that price of energy has skyrocketed even more so PV is still more appealing than ever.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 04, 2022, 02:06:54 pm
content: Quote from: Berni on July 04, 2022, 09:36:39 amThat doesn't apply for the DC connection since the panels only connect to a charge controller or inverter specifically designed for that arrangement, no different than a PWM motor controller. The conducted EMI applies to where the system connects to the public grid and/or to third party devices that might not be EMI hardened.

author: Berni
author_rank: Super Contributor
timestamp: July 04, 2022, 04:45:31 pm
content: Quote from: NiHaoMike on July 04, 2022, 02:06:54 pmEven then if you wiggle one connection on a device it tends to end up on the other side as common mode noise instead. Both common and differential mode conducted noise is measured. The large array wiggling up and down has a lot of parasitic capacitance to its environment and so is capable of making a sizable common mode current. In the end it is not that hard to stick a few microhenries of inductance into the optimizer module, if it already has a MCU and beefy power electronics in it.I don't know what standards exactly solar installations have to abide by, but they do seam to be more stringent that regular household devices like a TV.Quote from: Siwastaja on July 04, 2022, 01:39:26 pmYep the monitoring part is about ease of maintenance later on. There is no need to check up on the system at all, as long as all the panels are performing well according to monitoring that means the system is working. Even if a panel is knocked out by a fault the rest of the panels keep working.Fact is that the inverter electronics are only a small part of the total system cost of a solar array. Most of the cost is in the panels themselves, so if you can use some extra electronics to squeeze more energy out of the existing panels you can actually save money since you can get the same amount of power from fewer panels.We do have a 13kW SolarEdge inverter and optimizer system here. These SolarEdge boxes is simply what most solar installation companies offer here and they work fine. I am sure you can save some money on a cheaper inverter, but you are going to be shaving singles of a percent off the total system cost with it.Microinverters are a perfectly valid solution. For small arrays they are likely the best solution even. But once you scale up to arrays with >30 panels they become a lot of unnecessarily duplicated electronics and mains wiring. Reliability also goes down indeed since you got 10s of little boxes doing pretty demanding power conversion in the hottest spot on a building while having to be cheap. Compared to a single big inverter that can put more money towards quality components (since you only need 1) while being placed in a nice cool dry shaded spot while having cooling fans to help keep it comfortable.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 04, 2022, 06:47:22 pm
content: For actual information about market shares, see the figure athttps://www.greentechmedia.com/articles/read/woodmac-last-year-saw-record-highs-for-the-inverter-marketAlso:https://www.solarpowerworldonline.com/wp-content/uploads/2019/12/image004.pngMicroinverters are totally negligible, but optimizers seem to have quite some market share, especially in US residential installations it seems. They are still small in the large scale of things, and even in households installations, in minority. The point I am making, if around you "everyone" is installing them, this is only a local exception to the general trend. For example, here no one has even heard about those things. Microinverters are at least a known thing.

author: Berni
author_rank: Super Contributor
timestamp: July 04, 2022, 07:40:30 pm
content: Yep it seams like only SolarEdge is pushing heavily into these local optimizer modules.This might be because they own a whole bunch of patents on the topic, so they might have a team of lawyers hunting down anyone who touches it:https://patents.google.com/patent/US8587151?oq=9088178Still regular oldschool series string inverters are perfectly fine. In the right cases with a well balanced array and limited shading they perform just as well.Also not saying that SolarEdge is absolutely everywhere, just in this corner of Europe they seam to be pretty popular in residential installations for whatever reason. Maybe they have some magical EU seal of approval that some others don't. I have no idea

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 05, 2022, 01:46:08 am
content: Quote from: Berni on July 04, 2022, 04:45:31 pmTie the inverter ground to the panel ground (already required by code), then the common mode current just circulates in a loop between the inverter and panels, never reaching the mains connection.

author: bdunham7
author_rank: Super Contributor
timestamp: July 05, 2022, 02:20:51 am
content: Quote from: Siwastaja on July 04, 2022, 06:47:22 pmI don't want to make this an interminable debate, but if you consider residential and small commercial (the only places any of this is realistically in play) thenin the US, SolarEdge and Enphase have the majority of the market. SolarEdge's share has increased dramatically in recent years and Enphase is second, but Enphase has pursued profits and shifted to a more expensive product with advanced features like battery backup, off-grid and so forth. What is available and cost-effective in your market may vary, and cost is the biggest factor driving most of these decisions--as it should be. But your market is small and not very sunny, so perhaps they aren't trying to compete there. Enphase makes and ships more inverter capacity every quarter than the entire installed solar capacity of Finland, so I think they'd dispute your 'totally negligible' comment. So your point about a 'local exception' seems to be correct.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 05, 2022, 06:10:05 am
content: Quote from: bdunham7 on July 05, 2022, 02:20:51 amStill, USA is a huge market but does not dominate in world-wide installations; otherwise the numbers would look different. Minority share in global market can only be explained by largest Asian markets not buying SolarEdge and Enphase nearly at all.'Murica however, this is where households have money at their disposal (big middle class), and where marketing works really well. For the similar reason cars must be large, PV systems must have some "premium" in them.Compare this to Finland where everything is expensive, you pay premium for crap and premium^2 for premium, middle class is taxed to death and are only able to support their lifestyles by getting more in debt. It is going to be the cheapest panels with the cheapest inverter.And there's nothing wrong in that, PV is most often money limited after all, so I think $/kWh (total cost of ownership per lifetime production) is the best metric. Also string inverters by the largest global players have the best track record for reliability, so there is no such compromise. It's like driving a Toyota instead of a Porsche, former is cheaper and better in getting reliably from A to B.And this is the thing: if your local PV installer works with SolarEdge and this is all they sell, they will give you a competitive price. If you ask them for other choices, they are either hesitant to install them at all, or quote similar price for lower-tier system. But it also works the other way around, if you ask if you can get a SolarEdge system here, price will be significantly higher because not many sell them.Ultimately, the problem with products like optimizers and microinverters is the economy of scales. It seems to me power optimizers have reached the point of being affordable enough that they are not necessarily a huge net loss. Have they reached this position by pushing the scale up by false marketing claims? Clearly yes. Is this morally right or wrong? I don't know, you decide.But one thing is, I think, undisputable: false marketing claims have done definite harm to the knowledge about how PV systems work, this very thread being the proof. I know the "one panel brings whole string down" misconception is ages old and notinventedby SolarEdge, but they sure have been feeding it.And for me, truth and understanding really matters. Those who fight against it only for their own financial gains, will never see business with me.

author: dirtcooker
author_rank: Regular Contributor
timestamp: August 13, 2022, 11:35:47 pm
content: Panel level optimizers only marginally improve performance in most cases. However, in USA at least, NEC code requires module level shutdown for panels installed on a roof. Since you are required to purchase MLPE, you may as well buy modules that do MPPT as well. Hi voltage dc strings are also less safe due to fire and shock hazards. NEC code requires arc-fault interrupters for systems over 80vdc. Converting to 240 vac at each module avoids this requirement.Longi and others have teamed with Enphase for their ac panels, which I think will be the dominant trend in the industry. I wonder how long that relationship will last. They don't really need Enphase for that. The technology is dead easy, so it is doubtful chinese panel makers will share profits for something they can easily do in house.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 14, 2022, 01:22:30 am
content: Quote from: dirtcooker on August 13, 2022, 11:35:47 pmCouldn't the same be achieved with mechanical relays? If an arc fault is detected, turn off all the relays.

author: nowlan
author_rank: Frequent Contributor
timestamp: September 25, 2022, 07:14:30 am
content: Micro and String Inverters in the Shade - Testing the True Impact of Shade on Solar PanelsFood for thought?note: does appear to be Fronius marketing.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 25, 2022, 03:15:38 pm
content: Thanks for posting the video, the result is completely as expected - a small localized shadow like a chimney is totally meaningless for total production in either per-panel optimized system, or string inverter system, because it only affects the one panel in either case. Contrary to the marketing claims (which always have emphasis on small shadows, based on the lie about string inverter going to zero or half or whatever thanks to that small shadow), microinverters / optimizers would give the best benefit over string inverter when panels are aimed at random directions so that they run at significantly different power points all the time.

author: Alti
author_rank: Frequent Contributor
timestamp: September 25, 2022, 04:53:00 pm
content: Quote from: Siwastaja on September 25, 2022, 03:15:38 pmAFAIK the furthest going shading claim was 60% shade/40% Pstring by SolarEdge.As for the attribution of the 100% shade/0% Pstring claim, this goes to OP and OP only, no reference for marketing involved provided so far:Quote from: Malvineous on January 01, 2018, 07:54:34 am