Classic 150 'Watts In' Not Adding Up

[Off_Grid]

Hi, this is my first posting here. Been off grid for 4 years now and don't think my set up has worked correct since day one. I have been living with it since it mostly works. I have a Magnum MS4448PAE with a Classic 150 charge controller and 8 6V Crown LA batteries. I have 12 275 watt panels in four groups of three. In full sun my watts in generally runs around 1800 watts, which seems low to me. If I isolate each group of panels, they generate 600 watts each. If I have any two groups turned on, I am generating 1200 watts. Any group of three generates 1800 watts. But when I turn on the fourth group, it stays at 1800 watts. What am I missing here? Shouldn't I be at 2400 watts with all four groups turned on? I know I went to school in Oregon, but my math isn't that bad. Any help would be appreciated. Thanks

[boB]

Looks like you are getting about 55%  of the nameplate rating of those panels no matter how many you use.  Yes, it is usually higher than that percentage but not always higher than around 85% of nameplate rating.  It is almost always less than 100% because the panels/cells are hotter than 25 degrees C which they are rated for at nameplate rating.  Standard Test Conditions or STC.

A couple of sanity questions...

Since you are using 48V nominal battery voltage, what is the typical  Voc of those PV panel strings ?

And/Or what is the typical PV input voltage that the Classic runs them at while in BULK MPPT mode ?

The reason I ask is that the Maximum power point voltage (Vmp) will be around 80% of the open circuit voltage (Voc) of the PV array.   Plus, if the Vmp is too low, then the Classic will need a higher PV voltage to get the most out of the array.


I'm sure that you know this but remember that when the Classic is in Absorb or Float, the power output WILL (almost) always be lower than the maximum that the PV array can supply.

boB

[Off_Grid]

Thanks for the reply boB. I'm pretty new to all this, so you might have to dumb it down for me.

Regarding your sanity questions, how would I go about measuring the Voc of my PV panel strings? Would I put a volt meter across the two wires coming in from each string? And would this be in full sun?

Right now in early morning (shaded panels) and in BULK MPPT mode the left side of the screen under 'IN' says 84.4V

Thanks again for the help

[Vic]

Hi, Off_Grid,

 1. You can see the last Voc reading the Classic has taken,  as follows:From the main Status screen, press the small white-ish button on the left, once, or probably, twice.  Voc should be on the lower left of the display.

 2. And,  am sure that you know, that the PV power that your PVs are making, needs somewhere to go (it needs to be used), so try to make your production comparisons, during Bulk.  You might need to increase the load on the inverter output to make this happen,  if the batteries do not need a not of charge currrent.

FWIW< Vic

[boB]

Vic has it right.  The power has to have somewhere to go..  So with that, when you see
a lower power level than the labels on your PV say you should have, then when you add up "12 275 watt panels" to get 3300 watts, you should not expect that much due to inefficiencies an such.

You might expect this once in a great while though and possibly more when it is cold out... IF it ever gets cold out and the sun is shining good.  But in general, the most you might see might be around 80% of that power so look for a maximum of about 3300 * 0.8 = 2600 watts or slightly more maybe.

You are seeing about 1800 watts which is around 55% or so.  This is definitely less than I would expect when sun shining is full and NO shading EXCEPT when the Classic is in Absorb or Float.  That is, except when the batteries are getting full.

The only time you should see around 2600 watts or so would be when the display shows BULK MPPT or FLOAT MPPT in the lower right corner.  MPPT means that the Classic is tracking the Maximum Power Point.

Another sanity check also runs around 80% and that is the IN volts (PV) should show from 75% to 85% of Voc which I think Vic showed you how to find.  You can find Voc either when the Classic shows RESTING or when pressing STATUS once from the main screen to the second or third status screen where Voc is shown in the lower left corner.

So, Try to post these when the sun is up and there is no shading involved.  Make a note of the time and make sure the panels are in full sun and no shading or PARTIAL shading.  Partial shading is when there are any lines or trees blocking just part of a panel or part of your solar array.

A very thin shadow across the PV solar array can make a huge difference on the power output and PV IN voltage when in MPPT tracking mode rather than Absorb or Float, too.

You might take some pictures of the LCD screen and note the shading or no shading conditions to help us understand better.

Thanks !  We'll get there !

boB


 

[Off_Grid]

The VOC is 99.6V by pressing the status button. I will post some photos of the status screen in a few of hours when the panels get in full sun. Thanks

[Off_Grid]

Here are some photos of the charge controller screen and panels shaded and in full sun.

[Vic]

Hi Off_Grid,  Thanks for the images.

The full-sun screen shot, shows that the Classic is in Absorb, where the battery charge current, plus any loads on the inverter, etc, will not show the maximum capability of your PV array, at that moment.

If you could look at your system, when the sun, is at right angles to the surface of the PVs (ideally, Solar Noon),  and if the Classic is in Bulk,  this will give you an idea of the performance of your PVs (with all of the Combiner breakers switched to ON).  If at that time of day, the Classic is in Absorb, perhaps you could plug a portable 120 VAC electric heater into the inverter/system,  and turn it on, this might be enough load on the system to allow the Classic to return to Bulk.

Also, if your PVs are not pointed at an Azimuth of 180 degrees for N. hemisphere, or 0 degrees for Southern hemisphere,  this can have a fairly large effect on max production capability of a PV system.

We do not know the Latitude of your location,  but the elevation angle of your PVs appears to be fairly steep.  This can reduce Summer power production, depending on just where you are, and, if it is even Summer there ...

FWIW,  your Voc and Vin values seem fine for a Classic, and a 48 V LA battery.   Vic

[Off_Grid]

My latitude is 42° 29' 20" give or take some. I cut all my lumber at a 45° and my posts are level so would figure my PV's are close to that. I could get an angle finder and adjust my runners to lower the angle if they should be closer to my latitude. My PV's are facing about 165° S-SE so not true south.

I checked the watts in at 1:00pm and it was in absorb at about 1560W. I powered on some stuff and got it to switch to bulk and the watts jumped up to 2300W.

[Vic]

My latitude is 42° 29' 20" give or take some. I cut all my lumber at a 45° and my posts are level so would figure my PV's are close to that. I could get an angle finder and adjust my runners to lower the angle if they should be closer to my latitude. My PV's are facing about 165° S-SE so not true south.

I checked the watts in at 1:00pm and it was in absorb at about 1560W. I powered on some stuff and got it to switch to bulk and the watts jumped up to 2300W.

Hi Off_Grid,

Thanks for the info.  To me, it looks like your system is performing well. Congratulations on that,  nice work!

Vic

[Off_Grid]

Thanks Vic for the help. Its nice to get honest advice. I had contacted some local 'experts' and their advice was to trash my entire set up and buy their shiny new solar system.

Just a few last questions. I know my property isn't ideal for off grid as it has too many trees. In the summer I only get about 5-6 hours of 100% sunlight. If I am unable to make it all night before the power goes out, is that a capacity issue? Is my system too small for that amount of sunlight?

[Vic]

Hi Off_Grid,

Questions:
Do you have the WbJr setup on the Classic?  If so,  this time of year, what is the Net Ah number early in the morning.  This number is most useful,  if the Classic has completed a full Absorb, and this Net Ah number will have been reset to zero on the day before.

EDIT: On the Classic, What is your Absorb voltage setting?
How is Absorb ended  -- Absorb time setting, or via End Amps (EA) ?  If it is End Amps, what is that EA value?
Is the Classic using the Battery Temp Sensor?
What is the battery temperature compensation setting on the Classic?
You do have heavy shading of your PVs, When is Solar Noon, and at what approximate time today, is all of that PV shading gone?<(end Edit)

What is the model number of your LA batteries? If they are Flooded LAs, the following would apply -
Do you have, and use a good quality Hydrometer, fairly regularly?
How often do you Equalize the batteries?

More later,  Vic

[boB]

Something I would love to do, sooner than later is to add software to actually measure the battery capacity in Amp-Hours.  It is easy to do, but doing it in such a way that doesn't mean "not charging" for a day+++  is harder than just letting the battery drain down to some low SOC%.

Measuring capacity can be done without that I think. 

Sounds like a great challenge !

boB