EEVblog 1426 - WOW! This Problem DROPS Solar Output by 20% !

Dave tracks down why his old 3kW system that was moved was now showing a 20% drop in output power at the same time every day.
Is it inverter temperature, inverter mains voltage, solar panel cracking, dodgy connection resistance, or shading?

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[EEVblog]

Due to several requests I have created a 5min version of this video that allows you to share with people who don't want a 30min video:

[Billydevito]

I took my antenna down when I had panels installed because my guy said it would affect my power production.
I was sceptical, but I trusted him because he knows his stuff.
This video confirmed his advice.

[derek]

I see your problem...you need to install "wiggle wiggle wiggle yeah" inhibitors :D

[raysieber]

Unfortunately right at the start of this video I knew your problem. I was a radio tech from the mid 80 and worked for the police in Queensland. At the time the cells we were running at remote repeater sites were as low as 45W per unit and we used to have large strings of panels to keep sites alive (given there critical use). One particular site we had particular problems with during the Winter and it kept dropping out. We ended up at the site one day and were checking the current output from each cell trying to put a finger on the problem (previously we'd replaced all the cells and the Solrex regulator with no result) and discovered half the panels were low output. We then noticed the guyed wire from the 25 ft wind up Hills master crossed only the panels showing low output. Like a light bulb we'd found the problem after nearly a year of attempts to fix this repeater site. After a further trip we ended up building a new stand for the panels and moved the array away from the tower and the problem was solved. I do follow you on Twitter, I must have missed this series of tweets. Great video, wish we had YouTube in the late 80 :)

[nrdesign]

5:51 "one of the curses of being an engineer [...] is you know too much"

So much this - When watching a show, or an art installation you automatically start questioning every little detail and always wonder "how did they do it" instead of just enjoying the show's "magic" in awe like everyone else.

[Jinguapingi]

Did you update your SMA inverter with the latest firmware ? They introduced their "magic" shadefix algorithm (basically a quicker MPPT swipe) which greatly improves changing the MPP in case of shade. I'd love to see your update about it !

[SeanBZA]

Newer panels no longer have diodes, instead using a small IC that has an integrated power MOSFET, so that when current is detected flowing through the body diode the tiny bit of circuitry controlling the gate turns the MOSFET fully on, and shorts out the body diode and thus reduces power flow in the device. No power dissipation, and the energy to turn the MOSFET on is stored in a small ceramic capacitor using the normal off state voltage. Turns off the switch every few seconds, to both recharge the capacitor, and also check if the panel shading is transient and thus panel is back at full output.

[SeanBZA]

Rising voltage in evening is industrial and commercial customers reducing load, along with the home consumers reducing load from electric cooking, so the overall load in the area is dropping, and the input voltage from the power plant is essentially constant, so all those small reactances and resistive line drops add up.

[kristiansims]

Really glad you went on to explain what the bypass diodes were for, thanks!

[binaryglitch]

I know it's just semantics but impedances for AC on DC circuit's we call it resistance.

[HL]

I experienced this as a kid playing with some solar panels. Called it mouse effect after my plush mouse that if I put it on the panel, while only shading one of the cells in the panel, the output of the whole panel was nearly gone.

[Basement-Science]

Soo... Exactly what I suspected then.
When we installed a 3kW system many years ago on my dad's house, we put it into operation with the scaffolding still in place. There was just a thin shadow from the railing across half of the panels (essentially as thick as a water pipe). After we took the railing down, the output increased a solid 1kW just because that shadow was gone.
We were quite surprised the effect was THAT significant as well. But at least we figured it out immediately.

[rodrigomaero]

Now that was really interesting! Trap for (not so) young players!
I'd like to see an experiment, now that you have the micro-inverters I'd like to see how much dust affects power output. You could do this by washing one of the panels say every other day and see if it outputs any more than the rest.
Also temperature difference (this would be trickier). But I guess this wouldn't be an issue, if not manufacturers would sell a watercooled version lol

[redsquirrelftw]

I never would have figured partial cell shadows would be that drastic, that's pretty crazy.

[scottloftin]

Excellent discussion of solar panel architecture. Now I understand why one of my panels outputs exactly 2/3 the voltage of all the others, but the same current. A single bad cell or open internal connection will cause this even though all my panels are in full sun with no trees (or coax cables) nearby. Congrats on solving your problem. Every kWh is important.

[peterpetersen]

Effectively when a bypass diode kicks in, you get a second, but lower maximum in the MPPT curve. Not so sophisticated MPPT algorithms will get stuck on this lower maximum and do not search for the higher one. Would be interesting if a reboot of the MPPT controller helps, so it may search the whole area again an sees the higher maximum?

[chris-tal]

Wow, this looks to have a much bigger impact than it looks to the human eye at first glance. Nice eco-drive watch Dave! It's a pretty good idea on the battery side of things also you never have to worry about WR after a battery change. Love it myself!

[shadowpotatoe]

I have never seen anything like that, that's insainly extreme. I do not experience the same effect on my array. The shadow of a chimney moves across one of mine and is still not that bad

[keithrichardknight]

Your panels have 60 cells separated into 3 power generating columns protected with bypass diodes. It only takes a slither of shade to drastically reduce the current output of a column. If you know a shadow will traverse the entire panel you can consider reorienting to landscape and only impact one column of 20 cells.

[slypig]

On some of the Sunny Boy inverters, you have multiply inputs so you can divide your grid into smaller units. In that way shade will only drop output on that smaller grid. The drawbacks are higher cabling costs, and an isolators is needed for each circuit.