Confused - How many panels for my Victron 150/35

[Jimbo-hf]

My current setup:
2 * 250 Watt Panels in SERIES, (Panel Specs:- Voc: 37.3, Vmp: 30.1, Isc: 8.78, Imp: 8.31)

These 2 panels feed a Victron SMART controller 150/35 which then feed a
DIY (LiFePO4) 4 * 3.2v prismatic cells (12.8v NOMINAL), with 4sDALY BMS.

Now I've used a calculator on the Victron site and it only recommended 2 PANELS for my controller, charging a 12v battery.

Now I understand to ADD the VOC for the panels and ensure < than 150v. I also understand that the controller will MAX output 35Amps to the battery.
With this in mind I ask the following questions (I apologise in advance, this is my very first system & I'm still learning and trying NOT to make errors that may be dangerous or costly)

1) If my battery is 100% SOC, where does the excess energy from the panels go? Is it dissipated as heat via the fins on the back of the Victron controller? Does the controller simply stop pulling energy from the panels (is that such a thing? I watched a Youtube video that said this WAS the case) Do the panels remain in a high charge state and thus start to degrade and is this dangerous/damaging?

2) I'm in the Southern Hemisphere and Spring has just begun, so my 2 panels rarely produce their maximum energy CONSISTENTLY. With this in mind, can I ignore the Victron sites calculator, and just add more panels, providing I remain < 150v? For instance 4 series panels (250 Watt Voc 37.3) = 149.2v which is < 150. Is that TOO close? Or would I be better doing 2S2P config? I realise my controller will MAX at 35A, however I would like the system to be able to be at MAX for longer throughout the day using greater solar collection. Is this safe to do, even if the battery reaches 100%SOC early in the day?

(P.S. This system is on an off grid shed, powering a beer fridge (24*7), lights and a TV, but may be used for tools if I can get more power. F.Y.I. I have ordered 2 more Victron 150/35) and have 10 additional panels at my disposal. Also considering building a 48v 310Ahr prismatic cell battery)

 

[chrisski]

1) If my battery is 100% SOC, where does the excess energy from the panels go? Is it dissipated as heat via the fins on the back of the Victron controller?

Mop need to worry where it goes. THe solar panels are like batteries (DOn’t store energy of course) that only provide power when needed. THis is not a wind or hydro system where you need to do something with the “excess power.”

2) I'm in the Southern Hemisphere and Spring has just begun, so my 2 panels rarely produce their maximum energy CONSISTENTLY. With this in mind, can I ignore the Victron sites calculator, and just add more panels, providing I remain < 150v?

To a degree. Remember now that you’re leaving winter warmer panels put out less volts, so even though total power may not be the same because days are shorter, voltage of these panels will increase in cold weather, so don’t “flirt” with the 150 VDC limit or the coldest day of the year could have panels put oiut over 150 and theb the SCC could be toast.

Also, remember the 35 amp limit is amps out, not amps in. So wattage will double between 12 and 24 if you keep amps steady as voltage goes up, and then double again once you go to 48.

If you’ve had your panels set up and have been getting good data about charging amps, a better way may be to add another parallel string for more amps into the SCC to approach the 35 amp limit. I added a Victron 100/50 with 600 watts of panels set up 3S2P expecting 36 charging amps on a 12 volt system, so I did not purchase a 100/30. I found that because of shading and the panels flat on the roof, I have never seen more than 25 charging amps. I plan on adding an additional string to make this 3S3P and get to a total of about 36 real charging amps from that SCC. I can do this because I have collected data and victron lets you install panels to “Overamp‘’ the controller. I certainly could not overvoltage it.

 

[Jimbo-hf]

Mop need to worry where it goes. THe solar panels are like batteries (DOn’t store energy of course) that only provide power when needed. THis is not a wind or hydro system where you need to do something with the “excess power.”

To a degree. Remember now that you’re leaving winter warmer panels put out less volts, so even though total power may not be the same because days are shorter, voltage of these panels will increase in cold weather, so don’t “flirt” with the 150 VDC limit or the coldest day of the year could have panels put oiut over 150 and theb the SCC could be toast.

Also, remember the 35 amp limit is amps out, not amps in. So wattage will double between 12 and 24 if you keep amps steady as voltage goes up, and then double again once you go to 48.

If you’ve had your panels set up and have been getting good data about charging amps, a better way may be to add another parallel string for more amps into the SCC to approach the 35 amp limit. I added a Victron 100/50 with 600 watts of panels set up 3S2P expecting 36 charging amps on a 12 volt system, so I did not purchase a 100/30. I found that because of shading and the panels flat on the roof, I have never seen more than 25 charging amps. I plan on adding an additional string to make this 3S3P and get to a total of about 36 real charging amps from that SCC. I can do this because I have collected data and victron lets you install panels to “Overamp‘’ the controller. I certainly could not overvoltage it.

Thank you for your timely reply Chrisski. So if I understand you correctly, the better option is 2S2P or even 3S2P (which you suggested)? As that would double the input amps and remain safely under the VDC limit of the SCC?
Also, I could just add 1 more panel to go from 2S to 3S and that too would be safe?

 

[MisterSandals]

P.S. This system is on an off grid shed, powering a beer fridge (24*7),

Red alert, priority project!

I would like to add a little thinking outside the box to the excellent info chrisski provided.

Since this is a stationary setup and you appear to be wanting to maximize your SCC there is another solution. You could face several panels in series east-ish (enough panels to get to your 35A charging) and several panels west-ish. Connect east and west strings in parallel. This will get your charging earlier in the day at 35A and hopefully at maximum until late in the day.
So instead of 35A for 5 hours, maybe you get 35A for 10 hours? Double, no?

 

[Jimbo-hf]

Red alert, priority project!

I would like to add a little thinking outside the box to the excellent info chrisski provided.

Since this is a stationary setup and you appear to be wanting to maximize your SCC there is another solution. You could face several panels in series east-ish (enough panels to get to your 35A charging) and several panels west-ish. Connect east and west strings in parallel. This will get your charging earlier in the day at 35A and hopefully at maximum until late in the day.
So instead of 35A for 5 hours, maybe you get 35A for 10 hours? Double, no?

PMSL, yeah I thought the Beer Fridge would inspire a reply or two I also use the empty cans to determine the angle the panels should be tilted. Multi-purpose ;-) Yes you are quite right, I intend to have panels on the west and east side. Just taking baby steps right now, so as to learn at each step.

 

[MisterSandals]

Yes you are quite right, I intend to have panels on the west and east side.

F.Y.I. I have ordered 2 more Victron 150/35) and have 10 additional panels at my disposal.

So with 12 panels 250W thats 3000W of solar.
You will then probably be constrained (no info on your battery Ah) on how many amps your batteries will accept at any one time.
But this will be a serious amount of power. Spreading it out from early morning to late in the day will help keep the amps down. You can probably have a east, north and west SCC and array.

Just build arrays as chrisski indicated and you'll be solar rich.

 

[Jimbo-hf]

Brilliant. I just quickly added 1 more panel RIGHT THEN, to make it 3S. I need to get more solar mounts to add to that. Bloody plague lockdown issues where I am. Yeah, my curent 4S primatic cell battery is rated at 230Ahr (1c Nominal), however I get closer to 240Ahr from it. Once summer hits, I'm hoping to run a small air conditioner, to keep the consumers of the beer fridge COOL, hence I'm planning on upgrading to a 16S 310Ahr prismatic cell battery, and then get a 48v Victron Inverter. This Solar stuff is so addictive

Thanks for all your help, along with chrisski. I love learning this stuff, then making it happen ;-) Now If I could just stop staring at the victron app to see how many watts I'm getting hehehe.

 

[FilterGuy]

So with 12 panels 250W thats 3000W of solar.
You will then probably be constrained (no info on your battery Ah) on how many amps your batteries will accept at any one time.
But this will be a serious amount of power. Spreading it out from early morning to late in the day will help keep the amps down. You can probably have a east, north and west SCC and array.

Just build arrays as chrisski indicated and you'll be solar rich.

If both east-facing and west-facing panels are on the same controller, be sure to put blocking diodes on each string.

Also, I recently wrote up an overview of over-paneling MPPT controlers

Overview of Over-paneling an MPPT controller

To get to the paper, click on the orange button at the top of the screen. There is a misconception that putting more panels on an MPPT controller than the controller is able to use will damage the controller. However, in almost all cases it is...

diysolarforum.com

 

[chrisski]

I have successfully over-paneled by 80% on a small build. I have a small 25 ah lithium pack, 600 wh that I have a 15 amp SCC and 15 amp BMS with the intent of it producing power like this diagram from the resource linked above with good success:


The only thing I will add is that this over paneling must be set up to fall short of the BMS's cutoff, or max amp input for the battery. I found that my SCC current limitation would have brief excursions above the 15 amp limit, 15.1 amps, which would trip the BMS. The same would apply to a lead acid battery that can only take a small percentage, 13%, of the total amp hour capacity when compared to Lithiums.

These limitations applied to me because I had a certain wattage I wanted to pull out of the lithium battery and immediately replace it to keep the overall size of the battery bank down, so running high C-rate, .6C, relative to the battery bank for hours on end.