Appropriate MPPT for 4x panels on 24V system?

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sean-cattee asked Feb 27 2023 at 10:06 AM

Appropriate MPPT for 4x panels on 24V system?

My question is that I'm not sure what setup would be best if I have 4 of the following panels:

https://voltaconsolar.com/solar-panel/mono-crystalline/410w-mono-facial-solar-panel-rs41-410m-e3.html

The online calculator suggests at 2S2P I should be using a 150/70 for a 24V system.

I have bought a Cerbo, and would like to connect the solar controller to it, is there a particular type (E.G Blue solar/Smart solar) that I would need for this?

Thanks in advance - I'm new to all this stuff, I figured it's best to ask those who know rather than make a costly mistake.

MPPT Controllers cerbo gx solar sizing

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Answer 1 · 2023-02-27T10:17:46Z

Alexandra answered · Feb 27 2023 at 10:17 AM

@Sean Cattee

You will also need a ve direct to ve direct cable to connect the cerbo to the mppt.

The smart solar allows you to program it with your phone.

The blue solar you will need either the ve direct to bluetooth dongle to program it or the ve direct to usb (with laptop or otg) you can also use the ve direct to usb to connect to the cerbo.

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Answer 2 · 2023-03-01T14:45:08Z

astrayan answered · Mar 01 2023 at 2:45 PM

Don't be surprised if you only get 48-52A. You are charging up to 28.8V, and the panels will be 85% efficient when hot, after a few years.

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Answer 3 · 2023-03-03T13:55:06Z

Alexandra answered · Mar 03 2023 at 1:55 PM

@Sean Cattee

Irradiance and temperature will affect what the panels yeild. Higher panel temps you see lower voltages, colder means higher. And sunshine is not a shiney as you think ;) .... So you may see more or less depending on conditons.

I think @Astrayan is getting a bit ahead of things here.

I have a 150/70 on a 24 system and I see the 70A full output often.

Power (or wattage) is voltage x amps...

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sean-cattee commented · Mar 03 2023 at 5:08 PM

As a resident of England I don't have particularly high expectations, if I clock in over 1kw I'll be a happy bunny.

I recently found that 12/24v MPPTs exist in the Victron range and they're significantly cheaper, so that's a bonus! I have no expectations to go higher than 24v due to the cost of batteries.

I figured;

410w × 4 = 1640w

1640w / 24v = 68.3A

1640w / 28.8v = 56.9A

Not accounting for inefficiency, these are the "perfect" conditions I'll never achieve, so in theory they're the worst case scenario in terms of peak power which is well within a 150/70's capabilities.

Thanks once more :)

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astrayan sean-cattee commented · Mar 05 2023 at 2:03 AM

The main reason to run these small sand-filled blue things conservatively, if that they can get a bit hot, which degrades the lifespan. I was talking to my solar guy, and he was still using PWM, because he reckoned MPPT got too hot. With Victron, you can limit the current, so I run my 100/50 at or below 42A. Since Power = I.I.R, you get a big cut in heat, by dropping the current a bit. 40A out of a rated 50A = 64%. But the 100/50 model is anomalously cheap, so you can waste it. When solar was all PWM, the authorities actually told you to run them at 75% capacity, because solar surges could occur, when the sun poked through a hole in the bright clouds, and the panels are cool. You had to waste the rating. So peak current from solar occurs when the sun is straight on, and the battery voltage is low (13.4V). In britain, the sun comes through a lot more air, and the panels are mostly cool, so you make up for it a bit. I favour overloading the MPPT, but limiting it a bit, so it doesn't get too hot for long. You may need to overload the MPPT, if you get a lot of cloudy weather. I had 3 Jinko 275W panels (STC 825W) outputting 720W in 2018, but now I just checked them, and I'm getting 610W. My place destroys panels.

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astrayan astrayan commented · Mar 05 2023 at 2:19 AM

actually scrub that comment about the Jinkos. I just managed 690W, but it's difficult to contrive the 14.2V conditions, and it's a cooler day, maybe.

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kevgermany ♦♦ astrayan commented · Mar 05 2023 at 6:39 AM

Don't mix up Victron with other brands. As standard Victron will recommend panelling up to 30% more than the MPPT max output. And as long as Isc limits are observed it's ok to exceed that.

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kevgermany ♦♦ sean-cattee commented · Mar 05 2023 at 6:49 AM

My panels give close to 100% peak in the south of Germany. Last summer in southern England I was getting a max of 80%. In Scotland I was down to about 50% max.

When cost/benefit is considered go for the smallest MPPT that will work. Don't consider PWM, UK conditions are going to cut power output a lot. If you don't intend to increase the number of panels, a 50A controller would be good. But the 70A model gives upgrade headroom.

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Appropriate MPPT for 4x panels on 24V system?

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