Solar Panel Shading (Part 1): Are Optimisers and Micro inverters Worth It?

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

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.

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

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

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)

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 !

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

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.

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

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

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.

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.

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

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

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

Our panels were installed 12 years ago and our installer went to the trouble of reducing the height of the top of our soil pipe and resiting our TV aerial. This means that our panels can never be shaded. Your video has explained why that was excellent practice. We were offered Solar Edge optimisers but neither our installer nor the manufacturer’s documentation could not explain what they did and why we would need them. I’m glad we didn’t buy them as you have explained why they would have been of little benefit with our installation.

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!

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.

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 🙏

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.