Solar The facts about shading on your solar panels

[Boots in Action]

At last, I have found a definitive answer on what really happens when one of your solar panels or portion is shaded. There has been a lot of info and technical data posted on this forum, but now an independent test by none other than Adam Welch is available. His is the best explanation and demonstration of how shade affects multiple panels whether connected in SERIES or in PARALLEL. At the 2.50 minute point, he explains the problem simply and how losses can be reduced and the benefits of using Schottky diodes instead of the standard silicon rectifier type most commonly used on solar panels. Schottky diode voltage drop of 0.163 volts is less than one third of standard silicon type which has a 0.543 voltage drop. This confirms my upgrade as being very beneficial with my 3 folding panel setup with each panel now having 2 Schottky diodes in place of the two silicon types. He even introduces an even better type to reduce voltage losses, but getting close to the ultimate would be too hard to incorporate on my panels. From this story, it would appear that connecting multiple panels in SERIES will result in less possible voltage losses than connecting in parallel with leakage losses back through the standard silicon diodes. Something for the "Tech Heads" to think about anyway. Well worth watching!!!

 

[Boots in Action]

but now an independent test by none other than Adam Welch is available

Just one other point that some may have missed. Note that when first testing with the two panels in SERIES, the MPPT controller was able to use the extra voltage (approx 39 volts) to produce 75 watts. When both panels were connected in PARALLEL , the best each panel could produce was 27 watts for a total of 54 watts at approx only 15 volts. There is approx 30% difference when connected in SERIES and using the higher voltage to gain the extra AMPS. When one of the panels was covered, only 15 odd volts was available and so less volts meant less amps. Only a MPPT controller can do that and Adam Welch was always using a MPPT controller. The big advantage for those using a PROPER MPPT controller!!!!!

 

[jazzeddie1234]

He leaves a key thought to last - weighing up the permanent losses across the series diodes in the parallel panel configuration vs the occasional losses when one panel is fully shaded. The second panel is never fully dark in normal usage with some light preventing any back flow.

Its always interesting to read the panel voltage range of an mppt controller because those with buck converters need at least a few volts above the battery to operate whereas the buck boost ones can function even when the panel output is very low (such as in the evening) . This design is used in dc dc units but then you have to watch out for their conversion efficiency

 

[Boots in Action]

He leaves a key thought to last - weighing up the permanent losses across the series diodes in the parallel panel configuration vs the occasional losses when one panel is fully shaded. The second panel is never fully dark in normal usage with some light preventing any back flow.

Its always interesting to read the panel voltage range of an mppt controller because those with buck converters need at least a few volts above the battery to operate whereas the buck boost ones can function even when the panel output is very low (such as in the evening) . This design is used in dc dc units but then you have to watch out for their conversion efficiency

Good technical info there @jazzeddie1234 . I agree with your first paragraph and the same would apply for me with three panels in series. When I have my portable panels connected (in series), they are therefore not too far apart, and it would be possible for perhaps one and maybe even two to be partially shaded and the remaining one to be in full sun. So the benefits of Schottky diodes does help in those cases.

I guess my MPPT controller must have the buck boost components as conversion efficiency is rated at more than 98%. In the early morning (very early - say first light), I have noticed that voltage comes up first before current is available. At that time, 3 panels in series gives me around 39 volts and only 0.2A. But as light increases, so does voltage, and amperage especially when panel voltage reaches 44 volts or more. When battery is fully charged and controller in FLOAT mode, panel voltage gets as high as 55 to 56 volts whilst still providing 3 or 4 amps to carry any light loads connected.... mobile phone, LED lights being charged, fridge fans etc. I have FLOAT VOLTAGE on my controller set at 13.8 volts, and MAX CHARGE VOLTAGE at 14.6 volts. These settings are fully temperature compensated as I have a temperature sensor from controller taped to the top of 120ah AGM close by. In hot conditions, I have seen battery temperature up as high as 30C and other times in the cold as low as 12C. There sure is some sophisticated circuitry in those controllers!