Not reaching peak anymore...

Panels do age over time, with a degredation of output.  Wouldn't expect it to be hugely significant though.

Regardless of that, solar panels will produce significantly more power in colder weather.  You can see this from the solar panel datasheet, where the voltage, current and wattage temperature coefficient ratios are provided (usually in percent per degree Kelvin).  The significant increase in solar panel voltage can cause system failures (due to overvoltage!) if not accounted for during design.

Also worth keeping in mind that the power monitoring in the MPPTs may not be super accurate--and this could also explain the discrepancy you're seeing.  (Even my expensive Morningstar Tristar TS-MPPT-60 registers a significantly higher amperage on the readout than I actually measure with a clamp DC ammeter, easily off by a whole amp.  Not sure which one isn't reading right!)

The MSBs are consistent...ly wrong with the figures they display.  The degree varies from unit to unit, but probably no proper calibration and using the cheapest parts they can source no doubt is the cause.  But in my experience at least they are consistent in that if the unit reads X watts under a set of conditions it will still read X watts under those same conditions in a few months time.  It may be the poor MPP tracker algo in the MSBs showing it's head.  I have 2 v117 (with some version of v118 firmware loaded) and a v119 and they all have issues to some degree with finding and holding onto MPP - ie, they might find a knee point and track that instead of doing a full sweep and finding the real MPP etc.

If the panels individually can produce enough voltage to let the MSB attempt to find MPP and also charge a battery, even if that means temporarily hooking it up to a reasonably discharged 12V battery so that the battery can sink all the current the MSB provides, hook up each panel individually to the MSB and compare the power output of each one.  This assumes no shading and all in the same plane.  That'll at least let you know if one panel has reduced output compared to the others.

What make, model and age are your panels, Busky?

3 hours ago, TheButcher said:

What make, model and age are your panels, Busky?

They are Panasonic 330W panels.  about 3 years old..  But the panels in question sat in my garage for about a year and a half... So I assume they don't really degrade if they are not in sunlight? This is the data from today..  Max is 1.2kW.

Here is from June when I started keeping this data..

<fileStore.core_Attachment>/monthly_2022_01/image.png.af3712a4307b576fd7c408e814760aea.png

Here is the same day zoomed in on the peak:

<fileStore.core_Attachment>/monthly_2022_01/image.png.002b4b33bbf033cdb517860d8850506a.png

So It looks like it's getting a higher power after it's re-tracking..  But I also swore it was steady state over 1.5kW when I first started using one of the MSB's before I got the data acquisition going...

Panasonic panels would definitely not be showing that sort of age related power reduction at 3 years old.  The curve in image 2 is what I'd expect to see in a system where the charger and what ever is on its output is not being maxed out, ie the charger is taking everything the panels can provide.

The flatness in the first image is what I'd expect to see if the panels are exceeding either the charger's abilities, that could be panel watts out or it could be thermal limiting in the controller but I don't know if the MSB does that, or it could be that what ever is on the output of the MSB is not capable of accepting any more current.  If the charger / load is being maxed the panel voltage will go up so graphing panel voltage at the same time as watts produced would be a good way to track that.

I'm guessing you have cloud going past in the last 2 images.

A word about solar charger limiting.  If the unit is rated at 40A at it hits 40A you might think that's maximum wattage right there.  But it isn't.  Maximum wattage is a function of that 40A multiplied by the output side voltage.  If the output voltage is being held down by a load your wattage will be lower.  28.4 * 40A = 1136W, 26.5 * 40A = 1060W

1 hour ago, Busky said:

They are Panasonic 330W panels.  about 3 years old..  But the panels in question sat in my garage for about a year and a half... So I assume they don't really degrade if they are not in sunlight? This is the data from today..  Max is 1.2kW.

//content.invisioncic.com/g308908/monthly_2022_01/image.thumb.png.042bc78fdeef1cd1c6b8d8eca50cfa3b.png

 

Here is from June when I started keeping this data..

<a href="/monthly_2022_01/image.png.af3712a4307b576fd7c408e814760aea.png" title="Enlarge image" data-fileid="1045" data-fileext="png" rel="">

//content.invisioncic.com/g308908/monthly_2022_01/image.png.af3712a4307b576fd7c408e814760aea.png

Here is the same day zoomed in on the peak:

<a href="/monthly_2022_01/image.png.002b4b33bbf033cdb517860d8850506a.png" title="Enlarge image" data-fileid="1046" data-fileext="png" rel="">

//content.invisioncic.com/g308908/monthly_2022_01/image.png.002b4b33bbf033cdb517860d8850506a.png

So It looks like it's getting a higher power after it's re-tracking..  But I also swore it was steady state over 1.5kW when I first started using one of the MSB's before I got the data acquisition going...

 

Ah, but here's something to keep in mind: I am assuming your panels are on a fixed array.

The sun is significantly lower in the sky in the wintertime than in the summer (at least in the Northern hemisphere).  From a direct point-of-view, the panels are getting LESS actual sun in the wintertime due to the LESS-than-perpendicular angle.  This will result in reduced power output.

At least from my guesstimates, a 15-degree angle (0-degree being flat on the ground) tilt is good for summertime.  Wintertime is best at closer to a 60-degree angle (IIRC, could be wrong!)--and if your panels are at 15-degree angle, they're basically tilted away from the sun in the wintertime.

But something to keep in mind: if it's cloudy, the best panel angle is flatter (i.e. closer to 15 degrees), though then snow likes to build up on them.  So many compromises!

Way too easy to forget that people live further away from the equator than I do 😇

Yes it's fixed..  I believe they set it for optimal at the equinoxes.. So not optimal for winter or summer..  Somewhere in between.  I really did think I saw above peak in the cold when I first got the panels..

I wish I had a high voltage DC-DC  so I could manually find the MPPT.  My RD power supplies only handle max of 70V input..  So I'd have to test each panel individually!

I could also "rent" a panel tester from amazon and test individually also.. 

<fileStore.core_Attachment>/monthly_2022_01/image.png.dbfceff00e22d23c74e38d1ebcca4a29.png

I think the flatness is more coming out of shade at the "top" of the curve...  I never come close to fully charging the batteries.. So the MPPT *shouldn't* be throttling..

Ugh..  I wish  I wouldn't have fried my other 40A MSB...  Maybe I'll "rent" a victron 150/35A.  to see if I could get more out of my panels...

I think there's a prime version..  I do hate doing that!  And at ~$350..  it's not too bad....

Next time I'm home with full sun I'll re-power the MSB controller to see if that does anything I guess...

Jim

I would suggest using an external meter to measure the actual power flow.  There's a chance the MSB might be mis-reporting the actual current.

You can sorta guesstimate the "maximum power point" voltage--in my experience, the MPPTs usually either run at close to the actual power point, or they yank the panels all the way down to battery voltage.

At least with firmware v117 pulling the solar panels off the MSB charger for 30 seconds or so then reconnecting would cause it to attempt to find MPP again, but from experience it could still find a false knee point again and park there.  If you have a bench/lab power supply with current limiting (important that it has this) you can attach it to the MSB's PV input.  Depending on the exact firmware version* the voltage the charger needs to see above the battery voltage before it goes into MPPT mode varies but 6V over is pretty much a safe bet.  That'd let you determine input power pretty accurately and indicate if there is something awry electrically with the MSB and/or output figures reported.

*the end user can not determine the exact version of the firmware installed.  only the major version, 116, 117, 118, 119 number is available.

Depending on the exact firmware version* the voltage the charger needs to see above the battery voltage before it goes into MPPT mode varies but 6V over is pretty much a safe bet.

MSB V118  works  good  for lithium ion  car ev  battery  64v  setting .  It is the only cheap  solar charger  on ebay or in the world  that go to 64 v .   PowMr  only go to 58v  max  and not  work  for ev car battery .   

That's probably really the only thing going for the MakeSkyBlue chargers, they are cheap, but there's a good amount of free gotchas included.  If they work for a person's application that's fine by me but some of those gotchas will leap out at the worst possible times.

What happens if you accidentally, or due to circumstances, run your lithium battery down to the point where the BMS cuts off output?  With the MakeSkyBlue you are now dead in the water as the MSB will turn off and will not turn back on until it sees > 9 or so volts on the battery input, ie no matter how much solar input power you have it will not start to charge the battery again so if off grid is the game and MSB is the chosen charger an alternate way of charging the battery to wake it up is needed.  Granted most off-gridders will have an alternate source such as a generator but it's still something that pretty much all MSB owners are not aware of.

What happens if you accidentally, or due to circumstances, run your lithium battery down to the point where the BMS cuts off output? 

Diaster and  say bye bye to my  MSB v118  and   120 dollars .    I  have a ebike  67v  plastic charger  always plug in to each  string of  ev car battery  to make sure the voltage stay above 44 v .   So  the  3  MSB  is still  working  for a year now .  

I  have 13 strings  of ev battery  so a lot of  67v ebike charger .    I  check the ebike charger  and  they  fail  also  but also cheap to replace at 12 dollars .  I  do not  recommend ev car battery  or  wire  battery in parallel  to anyone .    I  have a generator to  charge the battery  but  I  can not  use  because  I live in the city and can not make noise at night  .    

Unless you live down here. I went out and looked at mine at noon. The 4 100 Watt panels on the shed were putting out 394 Watts at 78°. The 6 on the container roof, not so much. The ones on the container are nearly flat which works well in the summer. The 4 are hooked to a 30 Amp while the 6 are hooked to a 60 Amp MSB. The 60 Amp will cut back to float while the 30 Amp holds the load.

This method is not possible with later versions of 118 and all versions of 119 it seems.  They changed the tracker behaviour at some stage.  With a current limited power supply attached the MSB will chase all the way down to 0 watts output and sit there for several seconds before climbing all the way back up.  Repeat cycle ad infinitum.  They seem to be monitoring PV side voltage and wanting it to decrease/increase while adjusting current flow rather than looking for maximum power output directly.