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John avatar image

Are 50vdc solar panels wasted on a 12vdc system?

Hi, I am just trying to get my head around this and wonder if someone can confirm it please?

For a 12-15vdc battery off grid system needing to charge through a charge controller via a solar panel array of course which the panels are rated at around 55Vdcmax.

With the cheaper Ebay MPPT controllers (link to example type bellow), they cut off the solar panels inputs if the solar panel voltages are above around 15Vdc, so effectively the panel would only charge the system when the panel voltage is within the 12vdc - 15vdc, effectively only for a VERY short time in the morning and again at sunset.

With a Victron charge controller like (link of example type below), to charge the 12-15vdc from the panels (55Vdc). Does the Victron charge controller cater for the full 0-55vdc from the panel or does it also have built in cut out solar voltage cut offs, resulting in the same issue as the cheaper Ebay charge controllers?

I guess I am looking to have some device which converts the 0-55Vdc to a more usable 12-15vdc range so as to charge the batteries. Is the Victron charge controllers able to do that, regardless of the voltage from the solar panels are producing?

Kind regards

John.


https://www.google.com/aclk?sa=l&ai=DChcSEwikvN3NkZ7nAhWBjY8KHc7qD1UYABAhGgJzYg&sig=AOD64_2zKdLOh-0DDQJdeH1s63koYtHLcg&ctype=5&q=&ved=2ahUKEwipx9XNkZ7nAhVE9XMBHb87AssQ9aACegQIGxBk&adurl=


https://www.victronenergy.com.au/solar-charge-controllers/smartsolar-100-30-100-50


MPPT - Solar Charge Controlleroffgrid
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Your google link does not work.

Looks like the cheapest PWM controller, that is guaranteed to boil your batteries.

Avoid.

4 Answers
warwick avatar image
warwick answered ·

6 panels is 1560Wp.

If you: 1. put two in series (120.18V @ 5.43A) in 3 parallel strings (120.18V @ 16.26A); and 2. you want to charge a 12V battery

Then, you can use a 150/100 (Max 1450W at 12V).

See the calculator at https://mppt.victronenergy.com/?locale=en:

7515-mppt-calc.png


mppt-calc.png (161.9 KiB)
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spirou avatar image
spirou answered ·

To simplify your problem... You're trying to empty an olympic size pool amount of water into two small buckets. And judging from your answers above you are quite out of your depth in that pool.

As others have said before, the panel voltage is not really a problem with a decent controller (not the PWM crap on ebay). The real problem is the mismatch between panel output and battery capacity. You will charge those 2 batteries in about 30min of early morning light and then what?

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archean1 avatar image
archean1 answered ·

Do a search for "difference between PWM and MPPT". A PWM charge controller only works with 12 v panels + 12 v batteries (or 24v-24v, or 48v-48v). An MPPT can work with higher voltage panels and 12v batteries and will effectively convert the extra volts into more amps at your required charge voltage. (The MPPT you posted an image of will also work with 24v batteries). Be careful of really cheap MPPT charges online... there is one brand that is called MPPT (as in its brand name) and it is actually just a PWM charger... quite the scam.

I do agree with other comments. You might find it safer and a lot cheaper (e.g., in terms of cable sizing) to run your batteries at 24v. With the money you save on cabling (and efficiency and safety), you could buy a reasonably efficient converter (e.g., buck?) to get a 12v power supply. You said you already have dual 120Ah 12v batteries, so maybe run those in parallel to get 24v?

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Running two 12 in series, not parallel will give 24v, an easy typo...

warwick avatar image
warwick answered ·

Yes, so check the datasheet for details but some of the MPPTs eg 150/35 support 12/24/48V (even 36V).

You can then provide any voltage as long as it is +5V above the battery voltage and it will regulate the panel voltage to what the battery needs.

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Hi Warwick, thank you for responding.

I was thinking it was the case, though am not sure when I read the specs as to it actually being the case. As it only says that the max panel input voltages are capable of over the 55Vdc, but it doesn't confirm it will actually operate the charging of the battery banks at say 12-15vdc under a panel input rang of say 0-55vdc (yes understanding it requires about 5vdc higher than the battery banks required so they charge as needed).

Its just a lot of money to spend IF it doesn't work as one, I, would assume it does.

If someone has done it, it would be of comfort to know it actually works.

thank you,

John.

See in the sheet below the notes at the bottom:

  • PV voltage must exceed Vbat + 5V for the controller to start.

  • Thereafter minimum PV voltage is Vbat + 1V.

7513-screenshot-2020-01-25-at-114941.png

Hi Warwick,

Yes, the actual charging voltage for the batteries isn't an issue, I understand how that part works to require charging batteries.

I'll try to explain my question a bit better.

My question is more as to IF the victron solar controllers will put out a constant charge voltage (MPPT) ideally to charge the batteries, when the input voltage to the controller from the solar panels varies anywhere from say 15vdc to 55vdc (depending on the sun of the daytime). As the Ebay type controllers have a Solar Panel voltage Turn off at about 14-15vdc and above. So the 55vdc panels wont work most of the daytime with said ebay controllers unless the panels are effectively in the shade and producing less than about 20vdc during the day. not practical of course.

Regards

John.



Per comment ABOVE the datasheet I shared:

  1. PV voltage must exceed Vbat + 5V for the controller to start.

  2. Thereafter minimum PV voltage is Vbat + 1V.

Hi John. Your panels will come with 2x voltage specs, Voc (open circuit) and Vmp (max power, what an mppt tracks). Can you quote those?

And yeh, some of that ebay kit is prepackaged landfill.

Hi JohnC,

I have tried to explain the question in more detail in a reply to Warwick, can you have a read and see IF that helps explain my question better?

Thanks,

John.

Hi JohnC,

here are the specs off of the panel. I have 6 panels in total I want to use off grid. (as my previous 2 x 12v panels have faulted with age). So I want to now use these panels.

Peak Power (Pmax) =260W
Max Power Current (Imp) = 5.07A
Max Power Voltage (Vmp) = 51.25v
Short Circuit Current (Isc) = 5.43A
Open Circuit Voltage (Voc) = 60.09V
Dimensions 1600 x 1056 x 40mm
Max System Voltage = 1000 VDC


Regards

John.

Yeh Johnno, that's what I wanted to see.

6x 260W panels = 1560W.

A big call into 12V batts, but a /100A mppt would likely suffice. You'd need a lot of paralleled 12V batts to handle all of that power though, and that's rarely/never recommended to parallel a lot of auto-size batts to do that.

So maybe step back and ask whether you really want 12V batts. Maybe 24V or even 48V would suit better? The panels won't matter, a Victron mppt will handle all. Panel wiring might need consideration though.

You're out of the realm of those landfill 'mppt's?' now, please dismiss them (at any level).

Have a play with this too: https://mppt.victronenergy.com/



If it was 48V, you could use a 150/35.

Hi Warwick,

I currently have 2 x 120Ah 12v batteries, which is fine for night time use when fully charged. I was hoping that I could use the excess generated from the panels in the daytime to run extras through the daytime while the sun shines on the panels and ensuring the batteries are charged for the night time. If the batteries are fully charged and the excess isn't used, are you saying it will damage something?

Regards

John.

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