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

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

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.

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

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

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

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

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

This is a must watch video. Thanks a lot.

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.

Very clear and detailed explanation. Thanks!

Thanks again Gary- so much useful information!

Excellent and so very scientific. Many thanks Gary!

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

Love the explanation...well presented.

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