Beginner w/8 100W 12v panels in series to chg 2 LiPo4 12v batts: 60Amp MMPT or PWM for shade?

[Pi Curio]

I find this HQST 150V 60A !! also very interesting. Looks great too. https://hqsolarpower.com/60a-negati...charge-controller-with-bluetooth-lcd-display/

It supports 12/24/36/48V and up to two SCCs in parallel.

Woopping 900W @12V for 200$ ish at sale.

Would love to try it out. If its good, would make it a lot easier to recommend a more economical yet capable quality SCC within a certain budget.

 

[El Tigre]

I went and drew up (over some pics I found) what I THINK are some options...


I could start with Option A (2S2P) as someone suggested and, if it seems to work out, then expand to either Option B (4S2P) for 800 watts or even 5S2P for 1000 or 4S3P for 1200W (IF MY CALCULATIONS ARE FLAWED PLEASE LET ME KNOW...I'M VERY MUCH A NEWBIE).

SO, regarding controller choice:
1. I admit to a little penny-pinching but I was wondering if, based on the above voltages and wattages, I couldn't use the Renology Rover 20A SCC
https://www.amazon.com/Renogy-Charg...e+controller+lithium+mmpt,aps,151&sr=8-3&th=1
or some other reasonably priced SCC for any of the above described combinations (except the 4S4P with it's 32Amps)?
2. Also, I'd read that for a series-wired setup an MPPT is best and that for parallel wiring (supposedly also better for shady areas) that the cheaper PWMs are better. But (?) for these mixed environments (2S2P for example) I wonder if it matters as much (and which is even better If I, as described above, wind up with Option B). I wonder if I might be about as well with a cheapo PWM)?
3. (if anybody is still reading this far; sorry) Finally, what is the "Victron energy Lynx distributor... 1000 DC that is shown in all the pictures above at the lower far left of each of the drawings just above the battery? Is that just an inverter or is it something else (It's never shown hooked up to anything at https://shop.explorist.life/shop/al...charging-wiring-kit-9x-100w-12v-battery-bank/
Thank you!

 

[Rednecktek]

SO, regarding controller choice:
1. I admit to a little penny-pinching but I was wondering if, based on the above voltages and wattages, I couldn't use the Renology Rover 20A SCC
https://www.amazon.com/Renogy-Charg...e+controller+lithium+mmpt,aps,151&sr=8-3&th=1
or some other reasonably priced SCC for any of the above described combinations (except the 4S4P with it's 32Amps)?

I think there's a key piece of information you're missing about SCC's. When you see a rating on them like 20a or 60a, that's the maximum OUTPUT to the batteries at system voltage. So, a 20a SCC on a 12v system can pump 20a of current at 12v, or 240-ish watts MAX. If you throw 10 Gazillion watts of panels on a 20a SCC you can only get about 240 watts out of it and into your batteries. A 20a SCC on a 24v battery can pump 480 watts. That's why we've been pointing you towards the 60+ rated SCC's. If you're going to run 800w of panels to a 12v system you'll need 800w / 12v = 66.7a of SCC to fully utilize those panels. Granted the numbers aren't that exact and you almost never see full panel rating, so a 60a would be the absolute smallest you should go on this system.

2. Also, I'd read that for a series-wired setup an MPPT is best and that for parallel wiring (supposedly also better for shady areas) that the cheaper PWMs are better. But (?) for these mixed environments (2S2P for example) I wonder if it matters as much (and which is even better If I, as described above, wind up with Option B). I wonder if I might be about as well with a cheapo PWM)?

Nope, PWM's and MPPT work in different ways. The MPPT is based on watts in = watts out where your 1200w of panels (as rough example math) which are coming into the SCC at 120v and 10a gets converted via dark voodoo magic to 12v and 100a going to the battery. They're basically smart DC-DC transformers.

A PWM on the other hand just cuts off any voltage coming in that doesn't match up to the battery. So, say you have the same 1200w array at 120v and 10a, the PWM is just going to cut off any voltage above the 12v the battery needs and give you whatever amperage is left over, so 12v @ 10a or 120w. That's a MASSIVE loss of potential power.

About the only place PWM's are really useful is if you have a couple of small panels that output close to the battery, like most normal 100w panels that like to run at 15v Imp. Going from 15v down to the 14v a battery needs to charge isn't much and a couple watts here or there are nothing. When you get above about 300-400w though those losses start to really add up and makes dropping the cash for a proper MPPT a might better value. By the time you're in those panel ranges you usually have higher voltages from your panels and can do things like strings.

As an example in my pump house I have 2x 100w " panels almost exactly the same as yours on the roof to provide some DC lighting inside and power a diesel heater. I have a 20a MPPT on that system because it was a gift. Perfect world I might see 85% of what the panel says it can do minus pollen and dust, so call it 170w maybe from those panels. If I had used a PWM controller on there I might only get 78% of the panel's theoretical output, or 156w maybe. Was the extra 15w worth spending almost $100 on a proper MPPT? No. I wasn't going to see $100 more power generated in my lifetime.

Now, on the utility room where my current bank of WallyWorld DC29's lives to feed the 12v bus, lights, heaters, etc on the cabin itself I used a pair of used 208w panels from a pallet buy. Those panels are putting out about 36v each at 6a-ish so I put those on a 40a MPPT (40a * 12v = 480w-ish). Even going 85% max that's about 355w I could see out of those panels. If I had used a PWM that just cut the extra voltage off to the 14v my battery likes that would be 14v * 12a = 168w or less than a single panel. In that case getting over double the power out of the same panels made the cost of the MPPT worth it.

3. (if anybody is still reading this far; sorry) Finally, what is the "Victron energy Lynx distributor... 1000 DC that is shown in all the pictures above at the lower far left of each of the drawings just above the battery? Is that just an inverter or is it something else (It's never shown hooked up to anything at https://shop.explorist.life/shop/al...charging-wiring-kit-9x-100w-12v-battery-bank/
Thank you!

That's like a fancy bus bar and fuse block, you can ignore it. It was just in the pictures for people who like to spend extra money. ?

 

[Mattb4]

Once again the panels are not 12vDC. The ones you linked in your OP were 21.6vDC at Voc (and as I mentioned more likely 23vDC) and 18vDC at max production. Your voltages will continue to be wrong until you understand this.

And also as others have mentioned your amps charging are going to effect your potential wattage. W=VA

 

[El Tigre]

Thanks for that Matt. In your earlier post you mentioned:
The specs for the HQST panels list Voc as being 21.6vDC. More likely you will see up to 23Voc from them. That means if you wire 8 in series your voltage would be 8 X 23 = 184vDC Too high for many SCC. Well over the 100vDC the Renogy lists for max PV.

Since you have shading issues you will want to run some panels in parallel. To stay under 100vDC you would likely go to 3S3P
I modified the earlier sketch I sent earlier...


Which probably still shows my lack of understanding. I figured that if the panel was actually producing 23v instead of the 12v earlier assumed then the current must be 100W/23 or 4.4A. If that's wrong, then some of the others are too. In the likely case that something is wrong in the pic would you let me know which numbers need to be changed to what?
Thanks again.

 

[El Tigre]

Anybody have an opinion?
Thanks!

 

[Mattb4]

Thanks for that Matt. In your earlier post you mentioned:
The specs for the HQST panels list Voc as being 21.6vDC. More likely you will see up to 23Voc from them. That means if you wire 8 in series your voltage would be 8 X 23 = 184vDC Too high for many SCC. Well over the 100vDC the Renogy lists for max PV.

Since you have shading issues you will want to run some panels in parallel. To stay under 100vDC you would likely go to 3S3P
I modified the earlier sketch I sent earlier...
View attachment 143195

Which probably still shows my lack of understanding. I figured that if the panel was actually producing 23v instead of the 12v earlier assumed then the current must be 100W/23 or 4.4A. If that's wrong, then some of the others are too. In the likely case that something is wrong in the pic would you let me know which numbers need to be changed to what?
Thanks again.

Notice the specs for Isc or short circuit current of 6.5a. Now look at the operating current of 5.56a at 18vDC. The panels are rated for operating voltage and current 18v X 5.56a = 100.08w This is the panels rated wattage under test conditions. Voc means there is no load being placed on panel. Voltage can reach and exceed 21.6v when solar radiance reaches or exceeds the test conditions. Very important for sizing your SCC because high voltage that exceeds the SCC specs can damage it. But understand that as you load a panel the voltage drops.

A 100w panel can indeed produce more than 100w under the right conditions. More often conditions are not up to the test conditions though so it is most likely that you get about 75-80% of rated wattage.

Incidentally the STC rating of a solar module is determined by carefully controlling light and temperature in the testing environment. The light source in the laboratory is calibrated so that precisely 1,000 watts per square meter of solar light falls on the photovoltaic panel. This is important to know for spotting some of the fake claims out there for solar panel wattage. Take for instance if you have 21% efficiency for a panel. Thus a 1 sq meter panel can deliver 210w. If you see a panel advertising 300w but only measuring 1/2 of a square meter in size it has to be a fraud.

 

[El Tigre]

OK, I think I got that. Lots of good advice. Thinking I might start out w/4 panels in 2S2P for 400 watts (left sketch below)
and expand later to 3S3P (right sketch) for 900W as shown below: (Did I get the numbers right this time?)

I've also been looking at SCCs and got good advice above..
"with these 100W panels Voc and Isc, a 3S 3P is as high as you can go within reasonable Renogy 100/20 Voc Isc limit safety margin."
and also that
"When you see a rating on them [SSCs] like 20a or 60a, that's the maximum OUTPUT to the batteries at system voltage. So, a 20a SCC on a 12v system can pump 20a of current at 12v, or 240-ish watts MAX".
I'm probably misinterpreting both; one seems to say that, with 3S3P, a 20 Amp SCC would charge my 12v 100Ah batteries fine (and they are nicely cheaper than the 60Amp SCCs!)
and the other suggestion seems to say that a 20 amp SCC can only charge 240W max. My confusion makes this last decision difficult.

Since I obviously don't have sense enough to interpret 2 good explanations, let me just ask,
for the 2 phases described in the 2 sketches above (the 2S2P w/11.12A and the 3S3P (later) with 16.68A, do I need a high-amp SCC and, if so, how high?
I'm looking at this 60A Renology: https://www.amazon.com/Renogy-Solar...+charge+controller&qid=1680720261&sr=8-4&th=1 for $289.99 and
also at a 20A Renology Rover for $79.95 that might be easier on by budget...but if it won't efficiently put the panel power into the battery, of course I will choose a larger one.

So:
1. Is the chart above still full of erroneous understanding?
2. I'm ready to buy an SCC; your advice is appreciated.
I think I would have given up without all your help.
Thanks!

 

[Pi Curio]

OK, I think I got that. Lots of good advice. Thinking I might start out w/4 panels in 2S2P for 400 watts (left sketch below)
and expand later to 3S3P (right sketch) for 900W as shown below: (Did I get the numbers right this time?)

I've also been looking at SCCs and got good advice above..
"with these 100W panels Voc and Isc, a 3S 3P is as high as you can go within reasonable Renogy 100/20 Voc Isc limit safety margin."

That only says that you could fit 9 panels in 3s3p configuration within Renogy 100/20 SCC limits if you wanted to.

But, the SCC can only provide 20A to the battery.
Not worth doing.

The whole point of my suggestion to start with 400W of panels was so you could get a Victron 100 50 smartsolar SCC or similar within the same total budget and avoid spending any more money on a new SCC again. With Renogy 100/20, it's highly likely that wont be the case.

and also that
"When you see a rating on them [SSCs] like 20a or 60a, that's the maximum OUTPUT to the batteries at system voltage. So, a 20a SCC on a 12v system can pump 20a of current at 12v, or 240-ish watts MAX".
I'm probably misinterpreting both; one seems to say that, with 3S3P, a 20 Amp SCC would charge my 12v 100Ah batteries fine (and they are nicely cheaper than the 60Amp SCCs!)

True, the 20A SCC can only utilize 280W ish @12v.

Why buying a 'bigger' SCC will save you money going forward and make the whole experience better from the get-go.

 

[Rednecktek]

When you see the numbers like 100/20 what that means is "I can take NO MORE than 100v of PV input from the panels, and output NO MORE than 20a." Those SCC's I listed above would be like saying 150/60 or 150/80 so more voltage input and a LOT more amperage output.

PVInput voltage is the maximum voltage it can take in before releasing the magic orange smoke. The amperage rating is the maximum amps @ whatever your system voltage is that it can put out.

That's why I was recommending those 80+ amp units. If you're putting in 800w of solar panel to a 12v system, that's like 67a (800w of panel / 12v nominal system = 66.7 amps going from the SCC to the batteries). And remember that's the MAXIMUM it can put out, so if you started at a 2s2p for 400w of panel, that's 400w / 12v = 34a of power so your SCC can do more down the road when you get more panels plumbed in.

 

[Pi Curio]

Would just add a bit of info to Rednecktek's well written explanation of how it all relates to the SCC limitations and its output in general where he for obvious reasons used easier to understand round numbers.

On top of that, in the real world, you can expect around 85% of panels rated power most of the time.

800W rated power, 800*0.85 = 680W.

680/12 = 56A
680/14= 48.5A
On average, 52A

So ideally, his suggestion is more than valid, that is an SCC of 60A + rating.

50A is on the limit, but manageable.

Was looking for what would be the best possible way to go about your build now, while keeping an eye on going forward, and without altering your stated budget, sort of speak.

While having two things in mind.
1. Looking to get 450W into the system from solar per your requirement in OP

2. Since it's a stationary build when you get to point of needing more power it's only logical to switch to a 24v battery arrangement for 2000W + inverter/load thus enabling up to 1400W solar with 100 50 SCC.

 

[Mattb4]

...

I've also been looking at SCCs and got good advice above..
"with these 100W panels Voc and Isc, a 3S 3P is as high as you can go within reasonable Renogy 100/20 Voc Isc limit safety margin."
and also that
"When you see a rating on them [SSCs] like 20a or 60a, that's the maximum OUTPUT to the batteries at system voltage. So, a 20a SCC on a 12v system can pump 20a of current at 12v, or 240-ish watts MAX".
I'm probably misinterpreting both; one seems to say that, with 3S3P, a 20 Amp SCC would charge my 12v 100Ah batteries fine (and they are nicely cheaper than the 60Amp SCCs!)
and the other suggestion seems to say that a 20 amp SCC can only charge 240W max. My confusion makes this last decision difficult.

Since I obviously don't have sense enough to interpret 2 good explanations, let me just ask,
for the 2 phases described in the 2 sketches above (the 2S2P w/11.12A and the 3S3P (later) with 16.68A, do I need a high-amp SCC and, if so, how high?
I'm looking at this 60A Renology: https://www.amazon.com/Renogy-Solar-Charge-Controller-Adjustable/dp/B07PXJPSTY/ref=sr_1_4?keywords=renogy+charge+controller&qid=1680720261&sr=8-4&th=1 for $289.99 and
also at a 20A Renology Rover for $79.95 that might be easier on by budget...but if it won't efficiently put the panel power into the battery, of course I will choose a larger one.

...

SCC are rated based on charging power. So a 20a rating means that it will provide 20a at battery charging voltage (Note: battery charging voltage is higher than battery nominal voltage). So as example you are charging a 12vDC battery at 20a 13.2vDC which equals 264w. That is what you draw from the panels. If the panels are supplying 264w at 18vDC they are experiencing 264w/18vDC=14.67a So one side of the SCC is at 20a and the other is at 14.67a. Recall at all times that panels only provide power based on loads. No load the panels happily sits there at Voc doing nothing in full sun. Just like your homes 200a 240vAC service does not use all of it when you plug in a 13w lightbulb.

Why is this important? Sizing of wires and disconnects.

So if you want to use a 20a charger plugged into panels that can deliver much more than it needs you have over paneling. There are advantages to this and disadvantages. The subject is discussed other where on the Forum.

 

[Mattb4]

...I need to run as much as 450 watts during the day ...

Hopefully the panel and SCC setups are understood and now it is time to move on to just what it is you need to power your loads.

Every load has a running wattage (or amperage) and a starting amperage to be concerned with. As they run it adds up into power used denoted by watt-hours. An example is a 13w LED bulb. It uses 13w when on. If you leave it on 30 minutes it has consumed 13w X .5hr = 6.5wh it draws very little starting current above 13w. Anything with a motor however will draw far more starting current (can be as high as 5-11 times running current) and that must be allowed for when sizing your inverter.

So looking at your statement of needing 450 watts you can see that it is inadequate. 450w is a instantaneous amount. To get your load requirements you will need to add up all the things you intend to power over the day and for how long.

Moving on. Power stored in a battery (batteries are not power sources) is measured in amp-hours. For instance a 100ah deep cycle battery has the ability to deliver 100ah in 20 hours of discharge. That works out to 5amps for every hour of the 20 hours. 5a X 20hrs = 100ah, 100ah X 12vDC = 1200wh. If you draw the battery at a higher rate than 5a the total watt-hours drop to less than 1200wh due to the Peukert effect.

I hope this helps on your PV journey.

 

[El Tigre]

Thank you for all that info. Yes, regarding the load, I will, at least for some periods, need to run a small window air conditioner whose cooling watts are low (200-450) but whose starting amps are much higher. However, this is just for a few seconds and I've run that same unit just off of my 100Ah 12v LiFeO4 battery for longish periods through my 2000W Sine Wave inverter without any problems at all (amazing little Midea 8000BTU Inverter AC). So, I'm thinking that, as long as the heaviest starting load is already easily handled by my battery and inverter for longish periods just off the battery then it will be ok if the SCC isn't delivering that much right at the moment of starting the AC. However, for longer periods of use I would certainly need the larger array at right below. That said, a newbie should always ask, "Duh, is that right?"



Regarding the choice of SCC:
As noted above by Dynamic Daxo,
800W rated power, 800*0.85 = 680W.
680/12 = 56A
680/14= 48.5A
In average, 52A
So ideally, his suggestion is more than valid, that is an SCC of 60A + rating [will work].
However, if the sketch at right is where I want to get to (900W) it might be more like (because I have significant shade at times of the day) an average of 65% of the rated power. So, with that higher gross power and more pessimistic net power, calculations like the ones above might be:
900W rated power, 900*0.65 = 585W
585/12 = 48.75A
585/14 = 41.8
in average, 45.3A [Amps to the SCC]

---

So, my panel performance assumptions (that are lower than Daxo's due to shade that I didn't mention)
seem to make a (theoretical) 54v / 45.3 SCC enough for now. A 100 / 60 SCC would seem to leave room for even further expansion.

Possibilities:
1. Renology 150/60 (if I read their specs right) $285.00 (ouch)
https://www.amazon.com/Renogy-Solar-Charge-Controller-Adjustable/dp/B07PXJPSTY/ref=sr_1_4?keywords=renogy%2Bcharge%2Bcontroller&qid=1680720261&sr=8-4&th=1
2. HQST 150 / 60 MPPT Solar Charge Controller (suggested by someone here) $200
https://hqsolarpower.com/60a-negative-ground-mppt-solar-charge-controller-with-bluetooth-lcd-display/

3. Other suggestions?
Thanks again !

 

[Mattb4]

You might consider the MakeSkyBlue SCC at 60a. (aprox $90) It can be found on Amazon, Ebay or direct at https://makeskyblue.com/products/60a-mppt-solar-charge-controller-w-wifi?variant=31426587918470. I am presently using a 30a MSB SCC for 800w of panels as a supplement to my other array for battery charging. However it is at 24vDC battery so it pretty well can utilize all the watts.

Please keep in mind the panels Voc rating. You seem to want to use Vmp and it is a bad habit to get into. Voc can kill your SCC.

 

[Black Pearl]

Renology 150/60 (if I read their specs right) $285.00 (ouch)

Here's one of the nice price point Sigineer SCC's I mentioned earlier. Its 200 bucks shipped. It has a similar/ comparable bigger brother that's about ~50 dollars more. Sigineer SCC's seem to have some advantages when compared to let's say a Renogy rover 60 - as per their own literature.

12V 24V 60 Amp MPPT Solar Charger Controller LED PV 150V

Model #: DS2460 Free shipping to the USA, Canada & Puerto Rico by courier. The DS2460 solar charger controller features LED screen, unlimited parallel capability, automatic battery voltage recognition from 12Vdc to 24vdc, wide PV input range up to 150V, various battery charging algorithms...

www.sigineer.com

Here's a screenshot from the owners manual (PDF) of the linked SCC above.

 

[Rednecktek]

Please keep in mind the panels Voc rating. You seem to want to use Vmp and it is a bad habit to get into. Voc can kill your SCC.

This!

I have a couple of the PowMr 60a SCC's that have worked for me for many years, but I've never been close to maxing them out. Knowing what I know now I probably wouldn't buy them again but they do turn Solar DC into battery DC which is all I wanted out of them at the time.

Also, even though you have some shading issues, always do your math assuming full direct sun. You don't want to assume the trees will protect your equipment and have something burn up. If anything it will help to be a bit oversized. Much like anything else in the world, just because it's rated to hit 250mph doesn't mean you want to drive 250mph all the time.

That Sigineer is also a good unit, definitely don't go for anything less than 60a. Better to spend $300 now on a good SCC that will let you expand and support a larger array than to spend $120 now AND $300 later if you can do it.

 

[El Tigre]

You might consider the MakeSkyBlue SCC at 60a. (aprox $90) It can be found on Amazon, Ebay or direct at https://makeskyblue.com/products/60a-mppt-solar-charge-controller-w-wifi?variant=31426587918470. I am presently using a 30a MSB SCC for 800w of panels as a supplement to my other array for battery charging. However it is at 24vDC battery so it pretty well can utilize all the watts.

Please keep in mind the panels Voc rating. You seem to want to use Vmp and it is a bad habit to get into. Voc can kill your SCC.

Just to be sure, do you mean that I should be using Voc (for panel voltage in the sketch below) (which is 21.6v) instead of Vmp (which is 18v).
(It seems plausible to use the higher value to be conservative for the protection of the SCC but I just wanted to be sure.)

 

[Rednecktek]

Just to be sure, do you mean that I should be using Voc (for panel voltage in the sketch below) (which is 21.6v) instead of Vmp (which is 18v).
(It seems plausible to use the higher value to be conservative for the protection of the SCC but I just wanted to be sure.)

Yes. The VoC is what will fry your SCC if you go over so you should use that for your math. Be aware that a panel will produce more voltage when they get colder. It's not much but it does add up when the snow falls. If you keep your panel voltage around 20%-ish lower than the limit then you're good to go anywhere outside of Alaska.

All those linked SCC's support 150v VoC so with a VoC of 21.6v, you could easily do 4s2p which keeps you well below the voltage limit and doesn't require fuses or a combiner box which simplify things a lot.

 

[Black Pearl]

you could easily do 4s2p which keeps you well below the voltage limit and doesn't require fuses or a combiner box which simplify things a lot.

Yep, that's how my first build was set up, and it was very beginner friendly.

I would have used that Sigineer I linked if I had known about it, assuming it existed as is several years ago. Seems it didn't - I digress.

The ability of being able to over panel with more and more duplicates of series strings into parallel is a really cool hack.