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Solar panels upgraded but no increase in watts in. Why?

OffgridJJ

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Jun 9, 2021
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I have a mobile trailer setup with 10x PV panels, a Midnite Classic 250 charge controller, 2x SMA Sunny Island 6048-US inverters, and a 48v GNB battery bank with C/6 540 AH. I'm upgrading the 250w panels to 330w panels and have currently changed out half of them (5 of the 10). I'm still getting the same watts in as previously. Why? What should I do to improve this?

The trailer was originally set up with 10 of the following 250w panels:
Boviet Solar BVM6610P-250
Vmp 30.1v
Imp 8.31A
VOC 37.5v

New panels:
SunEdison SE-R330BMC-39
Vmp 37.7v
Imp 8.77A
VOC 46.2v

Thanks, Everyone!
 
I would suggest that you change all of them before jumping to conclusions ;)
I don't know how exactly they are connected, but your older panels are the "weakest link" in your array, and as in electric circuits, they could bring down the voltage/amps of the newer panels (depending if connected in series or parallel).

This means that although in theory you have more watts in your array, in reality the older panels can actually act as "consumers" of that extra power (getting heated up too...) and therefor you have the same total output.
 
Are you running in series or parallel?
In series, the lowest amps panel will set level for entire string.

In parallel, the SCC controller will use the lowest Vmp for all panels unless the new and older panels are on separate controller. Need to have same Vmp for all panels. The amps are close but Vmp is probably running at 30v not 37.7v so you are losing that energy.

One way to test is to bypass if you can.

Hook up only old panels and see your watts out, then disconnect old panels and just run new panels and you should see increased power due to larger panels.

Hook them up together and you will get output lower than adding both together.

I did that test and realized panels of different manufacturers with different Vmp > 1 volt don’t perform together well.

Try the above test. It will at least confirm your new panels have potential to perform better if all panels changed to same.

Other option is to get second SCC for second string but you are in process of changing which is why I suggested you test output on just new panels to give yourself confidence that you will get more output once all panels are switch out.
 
I assume the array is wired as 5s2p
Your new panels are similar current, but higher voltage.
They are probably dragged down to lower voltage.

Try connecting just one string at a time, compare output power of old vs. new.

The Classic 250 puts out 63A max, 3024W at 48V, 3780W at 60V
250W x 10 panels = 2500W (STC), 330W x 10 = 3300W (STC). Either is good.




"VOC 46.2v"
You might be in danger of exceeding 250V max of the charge controller on a cold day. But I think it has "Hyper VOC", tolerates some over-voltage by disconnecting; check the manual to be sure.

I suggest getting a Sunny Boy GT PV inverter (choose one on the compatibility list) and AC couple the panels you've removed. Sunny Island + Sunny Boy makes a nice system.


Do these DC solar trailers have either a communication card to talk to the Classic or a battery shunt, so Sunny Island knows state of charge?
 
Your charge controller might have a setting that limits charge amps and you are hitting that limit.
 
Your charge controller might have a setting that limits charge amps and you are hitting that limit.
Agree with this comment - this is set thru the Config -> Advanced screen as shown here
1623864802642.png

Also if you're batteries are near or fully charged - the output is limited. You want to see Charge Status: BULK MPPT (as shown here) to ensure max thruput from PV -> Battery charging.
1623864997822.png
 
I assume the array is wired as 5s2p
Your new panels are similar current, but higher voltage.
They are probably dragged down to lower voltage.

Try connecting just one string at a time, compare output power of old vs. new.

The Classic 250 puts out 63A max, 3024W at 48V, 3780W at 60V
250W x 10 panels = 2500W (STC), 330W x 10 = 3300W (STC). Either is good.




"VOC 46.2v"
You might be in danger of exceeding 250V max of the charge controller on a cold day. But I think it has "Hyper VOC", tolerates some over-voltage by disconnecting; check the manual to be sure.

I suggest getting a Sunny Boy GT PV inverter (choose one on the compatibility list) and AC couple the panels you've removed. Sunny Island + Sunny Boy makes a nice system.


Do these DC solar trailers have either a communication card to talk to the Classic or a battery shunt, so Sunny Island knows state of charge?
The Sunny Island does show SOC, which is always around 0.4v less than the charge controller. I'm thinking about combining some of the panels to make a larger overall system but may need a new charge controller. Thinking of a 4s4p to get around 4kw solar reliably at 80% of rated watts. Unsure of the right charge controller for this or how to parallel the Midnite classic 250 with another. Also would need to use a combiner box. Anyone have suggestions and/or a good resource on how to do this?
 
Agree with this comment - this is set thru the Config -> Advanced screen as shown here
View attachment 53078

Also if you're batteries are near or fully charged - the output is limited. You want to see Charge Status: BULK MPPT (as shown here) to ensure max thruput from PV -> Battery charging.
View attachment 53080
It does go into bulk mode, so I think it is just the old panels bringing the system down.
 
The Sunny Island does show SOC, which is always around 0.4v less than the charge controller. I'm thinking about combining some of the panels to make a larger overall system but may need a new charge controller. Thinking of a 4s4p to get around 4kw solar reliably at 80% of rated watts. Unsure of the right charge controller for this or how to parallel the Midnite classic 250 with another. Also would need to use a combiner box. Anyone have suggestions and/or a good resource on how to do this?

My suggestion is get a Sunny Boy, use it to AC couple some panels.

"SOC", "0.4V less"
Do you mean Voltage? or State of Charge?

I'm curious - does the trailer have a battery shunt, which would have a sense cable wired to Sunny Island?
Does it have a data cable from Sunny Island to MNSICOMM to Midnight, which serves as a communication link?
One of these two is necessary for Sunny Island to know battery state of charge.


You can parallel multiple charge controllers.
Any kind would work if a shunt is used.
If MNSICOMM is used, should be another Midnight Classic.
 
My suggestion is get a Sunny Boy, use it to AC couple some panels.

"SOC", "0.4V less"
Do you mean Voltage? or State of Charge?

I'm curious - does the trailer have a battery shunt, which would have a sense cable wired to Sunny Island?
Does it have a data cable from Sunny Island to MNSICOMM to Midnight, which serves as a communication link?
One of these two is necessary for Sunny Island to know battery state of charge.


You can parallel multiple charge controllers.
Any kind would work if a shunt is used.
If MNSICOMM is used, should be another Midnight Classic.
I meant voltage, not state of charge. Not sure on the shunt/MNSICOMM. Not sure what a shunt looks like.
 
When charge controller is pushing amps to the battery, it would have somewhat higher voltage. As charge rate diminishes (late in the day less sun, or full battery), the voltage difference between SCC and battery/inverter would decrease. They can also have different calibration errors. Use a DMM to check voltage across battery, at SCC, at inverter.

A shunt is a gizmo wired in series with battery cable, typically on negative terminal. Fat wires will go to it, carrying full battery current. A small pair of wires will come from it and go to Sunny Island.

MNSICOMM would have data cable to Sunny Island and to Midnight.

If only used with PV feeding midnight, it would be possible to have neither device. Sunny Island would not know state of charge, only voltage.
If charged by generator or grid feeding Sunny Island AC input, or by Sunny Boy on Sunny Island AC output, in that case Sunny Island needs to know about all other DC charge sources and loads. So one of the two is necessary.

You can increase the amount of PV panels feeding the existing Midnight SCC, until it reaches its maximum. If that is the Midnight Classic 150 (96A output), that would be somewhere around 6kW of panels all oriented one direction, or 9kW with multiple orientations. Midnight Classic 250? That puts out 63A, so about 4500W (STC) of PV oriented one direction or 6750W multiple orientations. With a peak of about 3780W (63A x 60V) that can't keep up with the 11.5kW output of the inverters. You can expand a lot to support heavier loads.

With FLA batteries, there is a particular optimum charge current. I would expand DC coupled PV only up to that current. Any additional PV I would only install AC coupled (e.g. Sunny Boy), with Sunny Island programmed to hit that optimum charge current if power available. The extra AC coupled PV would be curtailed if not needed for loads, or allowed to produce when your loads need it.

My system has 405 Ah 48V AGM, and I changed Sunny Island charge settings from default to 85A, about 0.2C. That is maintained while PV supplies loads (oversized array). The default is 0.55C which is why I changed it.
 
1. This forum is awesome. Now that I'm using solar as my only power source, I've been learning a lot about it and it is fascinating!

2. @Hedges what is AC coupling? And how would this setup be wired?
 
Traditional DC coupling is PV panels feeding a charge controller, which charges batteries.
The inverter and DC loads draw from the batteries.
In most systems, no communication occurs, and each just watches battery voltage. Maybe monitors cycles to do an equalization charge occasionally.

AC coupling means you have a battery inverter which serves as a UPS (if grid tied), charging battery from AC and producing power from battery when necessary. If you attach a grid-tied PV inverter (e.g. Sunny Island, Enphase, others) to output of the battery inverter, it converts PV to AC and with the right features it adjusts how much power it delivers.
When the UPS is on the grid, frequency is 60 Hz and GT inverter delivers full power to the grid.
When off-grid, the UPS ramps up frequency. With the default settings of my Sunny Boys, they deliver 100% up to 61 Hz, then linearly ramp down to 0% at 62 Hz. Whenever there is a load fluctuation (A/C kicks on or off), the UPS supplies/absorbs the difference momentarily, and readjusts frequency.
The key feature to make this work is "frequency-watts", which is now an optional feature of UL-1741SA compatible inverters.

This document lists which SMA Sunny Boys are compatible with Sunny Island for off-grid and for grid-backup systems.

https://files.sma.de/downloads/SB-OffGrid-TI-US-en-22.pdf

Sunny Island was probably the first battery inverter to do that, now several other brands too.

You would wire Sunny Boy into the breaker panel on output of the Sunny Islands. If you do not ever feed it from utility grid, configure Sunny Boy in off-grid mode (or maybe called "island". If it is sometimes on-grid, you're supposed to configure Sunny Boy for "Backup = On All" or similar, and install RS-485 modules and run cable from master Sunny Island to all Sunny Boys. Some models of Sunny Boy don't have functioning "backup" or don't have RS-485 option, so support told me to set Sunny Boy for "off grid". I would get such instructions from them in writing and keep a copy before doing that, because it goes against their published instructions.

If you do both AC and DC coupling, definitely should have one or the other schemes to inform Sunny Island about DC charging by Midnight.

If your loads drain battery so low (80% DoD) that Sunny Island shuts off, Midnight will eventually recharge battery to 50% where Sunny Island will restart. I don't have any DC coupled PV so that would never happen. Instead, I have a "load shed" relay which disconnects my house from the panel with Sunny Boys at 70% DoD. That leaves enough charge to keep Sunny Island up until the sun rises again. Even with Midnight, you can do a load-shed relay so your AC coupled PV contributes and charging is faster, don't have to wait for only the DC coupled PV to get battery high enough.

The nice things with AC coupling is the additional inverter capacity helps power loads during the day, and Sunny Island controls their output so battery charge current can be a constant optimum, rather than varying so much.

See diagram with Sunny Boys on output of Sunny Island, by house (load shed relay not shown.)
This diagram also shows some new communication paths supported by the latest model Sunny Boys. I have older models.
That communication is optional.

 
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