DC coupling scenario

[Bhilton]

Hello,

I recently purchased a solar inverter kit, growatt 3500tl lvm-us and a SOK 48v 100ah, with 4 PV modules (each module rated for 380-405w at max 36.6v).

It appears the combined 4 PV modules are not quite good enough to reach the Growatt 3500's startup voltage of 150vdc.

I called Growatt and their US support confirmed that 150v from the PV array is required, he said sometimes it'll work with a little less (I assume this has to do with Voc vs. closed circuit).

That leaves me in a bind because my 4 modules produce a max combined Voc of 146.4v. That might be enough to startup the growatt 3500 during a super optimal environment, but not good enough in my (inexperienced) mind. Side note: I've reached out to the store I purchased the kit from, I'm waiting for a response.

I am trying to avoid buying a 5th panel due to lack of mounting locations and lack of stock for a matching panel, they are out of stock right now.

If I used a victron mppt charge controller rated at 150v PV input and 35amps, I could charge the battery with it and while the all in one growatt inverter wouldn't do any PV charging, it could still act as my AC input from my generator when required. So long as I don't max out the SOK battery input amperage by having 2 different chargers running at the same time, that would work right?

Anyone know what the minimum PV array voltage needs to be for the victron 150/35 to charge? *edit* I just found out, it charges when PV is at least Vbat + 5v.

I also wondered, in the above scenario with the generator NOT running, if the Victron mppt is charging the battery and the growatt has an AC load, does the growatt utilize the power coming in from the Victron and the battery at the same time or how does it pull power?

For example, the Victron could be throwing 30amps at the battery in excellent sunny conditions, and then I power on say 10amps of AC devices, where does the power draw from, victron or the battery?

Thank you,
Bill

 

[sunshine_eggo]

If I used a victron mppt charge controller rated at 150v PV input and 35amps, I could charge the battery with it and while the all in one growatt inverter wouldn't do any PV charging, it could still act as my AC input from my generator when required. So long as I don't max out the SOK battery input amperage by having 2 different chargers running at the same time, that would work right?

Sorta. 146Voc is too close to the 150V limit for safety. In cooler weather, you'd blow the controller.

You might be able to use them in 2S2P config, but you would likely have trouble hitting peak output in hotter temps.

Anyone know what the minimum PV array voltage needs to be for the victron 150/35 to charge? *edit* I just found out, it charges when PV is at least Vbat + 5v.

Yep.

I also wondered, in the above scenario with the generator NOT running, if the Victron mppt is charging the battery and the growatt has an AC load, does the growatt utilize the power coming in from the Victron and the battery at the same time or how does it pull power?

Depends. The MPPT follows battery charging rules with bulk/absorption/float. If in bulk, the charger is already putting out max, so the battery is getting less charge (or no charge if load is > MPPT input). In absorption, or float, if a load pulls the voltage down, the MPPT will add power to keep the battery at the float voltage. As long as the load doesn't exceed the max available MPPT power, then the MPPT is effectively powering the load.

For example, the Victron could be throwing 30amps at the battery in excellent sunny conditions, and then I power on say 10amps of AC devices, where does the power draw from, victron or the battery?

Yes.

Hopefully, my description above allows you to answer this question. If not, let me know.

 

[Bhilton]

Sorta. 146Voc is too close to the 150V limit for safety. In cooler weather, you'd blow the controller.

You might be able to use them in 2S2P config, but you would likely have trouble hitting peak output in hotter temps.



Yep.



Depends. The MPPT follows battery charging rules with bulk/absorption/float. If in bulk, the charger is already putting out max, so the battery is getting less charge (or no charge if load is > MPPT input). In absorption, or float, if a load pulls the voltage down, the MPPT will add power to keep the battery at the float voltage. As long as the load doesn't exceed the max available MPPT power, then the MPPT is effectively powering the load.



Yes.

Hopefully, my description above allows you to answer this question. If not, let me know.

Haha yes it makes sense, thanks!

My follow up question, I could use two victron 100/30's and put 2 PV modules in each one too right?

Since two panels would be max 73.2 voc and a victron 100/30 could easily handle that?

 

[hwy17]

146 VOC is perfect for a Midnite Classic with HyperVOC. Those can tolerate the voltage excursions but still operate optimally on the regular VOC.

When DC power is generated and consumed concurrently, it flows proportionately over the bus bar and does not have to go "through" the battery. Reality is a little more complicated, because DC is not consumed smoothly it's an erratic pulse, but the answer is it works fine.

 

[Bhilton]

146 VOC is perfect for a Midnite Classic with HyperVOC. Those can tolerate the voltage excursions but still operate optimally on the regular VOC.

When DC power is generated and consumed concurrently, it flows proportionately over the bus bar and does not have to go "through" the battery. Reality is a little more complicated, because DC is not consumed smoothly it's an erratic pulse, but the answer is it works fine.

Thanks! Can you share a url to the one you are speaking of?

 

[1201]

For example, the Victron could be throwing 30amps at the battery in excellent sunny conditions, and then I power on say 10amps of AC devices, where does the power draw from, victron or the battery?

Thank you,
Bill

It's going to come from the charge controller. You'll see 10a going to loads and 20a going to battery

Haha yes it makes sense, thanks!

My follow up question, I could use two victron 100/30's and put 2 PV modules in each one too right?

Since two panels would be max 73.2 voc and a victron 100/30 could easily handle that?

Whats the vmp? Will your vmp be above vbat +5v?

If so then you could

 

[hwy17]

Thanks! Can you share a url to the one you are speaking of?

https://www.amazon.com/MidNite-Solar-Classic-Charge-Controller/dp/B01LY1J9XO

Category Products - MidNite Solar's

MidNite Solar Category Products.

www.midnitesolar.com

 

[Bhilton]

It's going to come from the charge controller. You'll see 10a going to loads and 20a going to battery

Whats the vmp? Will your vmp be above vbat +5v?

If so then you could

I was looking further and the victron 100/30's only appear to be 12/24v. It still seems like the least expensive to get two victron 150/35's rated for 48v as opposed to a larger victron 250 or even the Midnite solar.

My PV modules (4 of them) are the 395MS ones below.

 

[sunshine_eggo]

Haha yes it makes sense, thanks!

My follow up question, I could use two victron 100/30's and put 2 PV modules in each one too right?

No.

You could go 2X 100/20, which can do 48V.

Since two panels would be max 73.2 voc and a victron 100/30 could easily handle that?

Your Vmp may be too low to effectively charge 48V in warm conditions.

ANY panel that has a similar Isc/Imp value could be used in series with your 4S panels to get you the minimum voltage though that doesn't address the mounting issue.

A better option would be to get 4S 72 cell panels that are closer to 45-50Voc

 

[Hedges]

If this is the data sheet, "MPPT range 120VDC ~ 225VDC"
And you noted 150V minimum to start up.

If you can pick up one more panel, anything of similar current, you should be able to make it work with 5s.
Check local listings, Craigslist etc., for used ones and try to pay about $80 to $120 for a 400W panel, or less for lower wattage.
Less money than separate SCC and more power produced. Just DIY some manner of mount for it.

https://us.growatt.com/upload/file/SPF_3000-3500TL_LVM-US_Datasheet_EN_202212.pdf

 

[Bhilton]

There are just so many cons to me adding another panel, maybe I will go that route

If this is the data sheet, "MPPT range 120VDC ~ 225VDC"
And you noted 150V minimum to start up.

If you can pick up one more panel, anything of similar current, you should be able to make it work with 5s.
Check local listings, Craigslist etc., for used ones and try to pay about $80 to $120 for a 400W panel, or less for lower wattage.
Less money than separate SCC and more power produced. Just DIY some manner of mount for it.

https://us.growatt.com/upload/file/SPF_3000-3500TL_LVM-US_Datasheet_EN_202212.pdf

Ok, I ordered another panel, very similar specs.

My 4 panels are Pmax 395w, Voc 36.6v, Vmp 30.6v, Imp 12.91A, Isc 13.77A.
My new one is Pmax 405w, Voc 37.15v, Vmp 31.18v, Imp 12.99A, Isc 13.78A.

I'll be doing the 5.5 hour drive back to the cabin in around 10 days. I'll change the Growatt option 001 from "Ut1" back to "Sbu" before I leave home.

When I get there with the new panel, I'll connect it do the other 4 panels, connect the Growatt and battery, watch the display and cheer when it shows over 150v, then I'll plug the fridge in to keep the beer cold, and cross my fingers that it can "start up" solar charging!!

I only hooked it all up last weekend and with 4 panels I was only getting 135 to 142volt on the Growatt display (around 14C / 57F temp outside). I've yet to see it charge from solar - so I am hoping it is that silly 150v growatt "start up" requirement.

 

[sunshine_eggo]

When I get there with the new panel, I'll connect it do the other 4 panels, connect the Growatt and battery, watch the display and cheer when it shows over 150v, then I'll plug the fridge in to keep the beer cold, and cross my fingers that it can "start up" solar charging!!

If we'd known this was a mission critical application, we would have had you fixed sooner...

 

[Bhilton]

If we'd known this was a mission critical application, we would have had you fixed sooner...

Next time I will title the thread "Need help chilling my beer"

 

[Bhilton]

@sunshine_eggo

I brought a 5th panel up to the camp last weekend and I have successfully witnessed Solar charging and I did not have to run a generator at all.

The battery and solar kept the fridge going and the beer was cold all weekend.


After running it all last weekend, I have a follow up question. Some details first, my PV panels are in a temporary spot, I have lots of trees to cut down and I am building a new camp and will place the panels on the roof (some day...).

I have 5 panels that are rated for 36v and 13A wired in series.

Even when some small portions of the panels are getting partial shade from trees, I am seeing 150 or over 160 volts coming into my Growatt.

Is it normal to have a huge fluctuation in charging amps?

My SOK battery screen would often show a small amount of current like 0.8A to 3.6A going to the batter.

I was not monitoring it super closely but each time I looked, the current was low.

Once I saw it getting up to over 18 amps.

I'm curious - with the voltage staying fairly consistent, at around 160 volts (plus or minus 3v), is it possible that my panels location and angle to the sun and clouds, etc would impact the amount of available current more than the voltage?

E.g. I would see roughly 160v and it would be charging at 1A , but other times I would see it charging at 4A or higher, but the voltage was still roughly 160v.

Thank you!

 

[Hedges]

Slight clouds do make significant impact.

Besides actual current demand from the system, some SCC make large excursions to see if there is a different maximum power point.

At charge current near max available power, I would expect 1A vs. 4A to move voltage a fair amount. But if 13A at 150V available (1950W), the difference between 1A at 60V (60W) and 4A at 60V (240W) would hardly change PV voltage at all.

Look at the I/V or W/V curves for a panel, very steep near max voltage.

 

[Bhilton]

Slight clouds do make significant impact.

Besides actual current demand from the system, some SCC make large excursions to see if there is a different maximum power point.

At charge current near max available power, I would expect 1A vs. 4A to move voltage a fair amount. But if 13A at 150V available (1950W), the difference between 1A at 60V (60W) and 4A at 60V (240W) would hardly change PV voltage at all.

Look at the I/V or W/V curves for a panel, very steep near max voltage.

Thanks Hedges!

I will have more of my own test data once I go back to the camp and cut more trees down and re-locate panels to a better angle, etc.

Here is the data sheet for my 400W panels: https://static.csisolar.com/wp-cont...asheet-HiKu6All-Black_CS6R-MS_v1.7_AU-±5W.pdf

I was getting anywhere from 157v to 163v (the times when I looked at the voltage indicator on the Growatt display).

That's roughly 32v coming in from each panel.

Shouldn't I get much more than 1 to 4 amps if I have 32v per panel coming in?

OR say if 4 panels had really good sun, but the 5th panel was 3/4 in the shade due to a tree branch, we can assume it was producing a very low amount of current and that 5th panel would cause resistance for the other 4 panels and lower my overall current significantly?

 

[Hedges]

36.8 Voc, 30.8 Vmp, 12.99A Imp
A panel running at 32V will drop well below 13A, don't think it would be 1 or 4A. But that's in full direct sun, while cool.

You've got curves right there indicating about 32.5V is Voc at 65C. 4A is full sun at 45C, a reasonable temperature.

Probably you're getting less sun.

A panel partially shaded will either knock down current from all series connected panels (so their voltages rise), or will get bypassed through diode if MPPT selects higher power operating point.

Without shade, panel temperature, voltage, current would let you compute illumination. Or there are devices for that. First make sure it performs as expected with no shade.

 

[Bhilton]

36.8 Voc, 30.8 Vmp, 12.99A Imp
A panel running at 32V will drop well below 13A, don't think it would be 1 or 4A. But that's in full direct sun, while cool.

You've got curves right there indicating about 32.5V is Voc at 65C. 4A is full sun at 45C, a reasonable temperature.

Probably you're getting less sun.

A panel partially shaded will either knock down current from all series connected panels (so their voltages rise), or will get bypassed through diode if MPPT selects higher power operating point.

Without shade, panel temperature, voltage, current would let you compute illumination. Or there are devices for that. First make sure it performs as expected with no shade.

Ok, I think I was dealing with multiple factors, both clouds at random times and probably always had a panel with some shade from tree tops.

I will know more next time I am there when I eliminate the shade variable.

Sorry about the curve, I'm not sure I understand the panel curve in the sheet. I'm looking at the one chart sideways Watts / sq meters? It looks like the current drops the closer it is to 36volt? Why wouldn't the current be at its peak at the peak voltage?
The outdoor temp last weekend was 23C at peak of the day.


Can you elaborate on the diode scenario? I have panels in series and connected to the Growatt 3500TL-LVM, data sheet is here https://us.growatt.com/upload/file/SPF_3000-3500TL_LVM-US_Datasheet_EN_202212.pdf

 

[Hedges]

Outdoor temp, but panel in sun is hotter.

Current is maximum at zero volts. Current is zero at maximum volts.
Under any amount of sun, the model of a PV panel is a current source in parallel with a stack of diodes. Diodes have an exponential I/V curve. At zero volts, they conduct zero amps, so your DMM measures maximum current. If you had a variable resistance load, as voltage approaches Voc, current through diode starts how low then rises exponentially. At Voc, the diodes shunt away Isc worth of current, leaving zero for you.

Those curves are I/V, current vs. voltage. Power is current x voltage, so if you find a W/V curve it will be 0W at 0V, 0W at Voc, curved between those with peak watts around 0.8 x Voc.