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Old 04-25-2021, 10:24 AM   #1
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Sizing Charge Controller To Panel Array

This guys YouTube Channel is helpful for solar stuff in general. Yet, these two links are directly related to sizing your charge controller to your panels.

While the YouTube video goes into a lot of math and is at a fast pace, it really does a good job of explaining the ins and outs of sizing the charge controller.

The link to his calculator makes all the math really simple, because, well, it's a calculator.

Hope this helps.

Video -

Calculator - https://www.explorist.life/solar-cha...er-calculator/

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Old 04-25-2021, 06:36 PM   #2
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Best approach is no "array" but a 1:1 ratio between SC and panel.

For example Victron 75/15 is great value for a panel rated 200W, up to 300W if you get the panel cheap enough.

For MPPT efficiency, only consider big panels rated at say 40+ Voc, forget those puny nominal "12V" ones.

Shopping around locally, or driving to pick them up is best if looking to buy less than a pallet load at a time, otherwise shipping costs as much as the panels.

Ideal is to buy leftovers off a nearby professional installation, commercial projects etc.
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Old 04-27-2021, 08:39 AM   #3
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Best approach is no "array" but a 1:1 ratio between SC and panel.

For example Victron 75/15 is great value for a panel rated 200W, up to 300W if you get the panel cheap enough.

For MPPT efficiency, only consider big panels rated at say 40+ Voc, forget those puny nominal "12V" ones.

Shopping around locally, or driving to pick them up is best if looking to buy less than a pallet load at a time, otherwise shipping costs as much as the panels.

Ideal is to buy leftovers off a nearby professional installation, commercial projects etc.
Hi John. If you would I'd appreciate the science / economics behind what you're saying. I'm not arguing, I'm just ignorant on the subject beyond the basics.

Thanks.
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Old 04-27-2021, 08:52 AM   #4
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Hi John. If you would I'd appreciate the science / economics behind what you're saying. I'm not arguing, I'm just ignorant on the subject beyond the basics.
The industry is certainly going this route for grid tie already, search "micro inverters", although they usually do two panels per inverter to achieve 80V+, which is much easier to step up to 120V/240V than 40V. Imagine large systems where you can monitor the performance of every panel individually ( you can't do this when you combine them all at a single point ) it has some advantages.

There are advantages but I don't think its a one-size-fits-all solution. Definitely worth considering as an option. I think his argument is, if any single panel sees shade, it wont affect the charge output of the others because they are not strung together but rather completely independent. Also, the economics works out around the same buying several smaller MPPT versus a single large MPPT, and from that you inherently gain some redundancy

The downsides as I see it, if I had 5 charge controllers I'd need to reference all 5 to get an idea of what my total solar input performance was like, or use a shunt somewhere designed to get that information. Kind of a pain. I'm going to need two controllers soon so its a problem I'll have to deal with one way or another.
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Old 04-27-2021, 11:47 AM   #5
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Hmmm. That's interesting.

I agree with the "One size doesn't fit all." statement.

Technology and "bleeding edge" are always offering new stuff and methods, but simplicity is also something to consider in the overall scheme of what an individual's needs are.

My solar needs are pretty simple and minimal compared to many others, yet I'll look into the mini inverters to assure I'm not missing the boat.

Thanks!
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Old 04-27-2021, 01:00 PM   #6
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Micro inverters are really for AC grid tie systems AFAIK, there's often no battery bank to charge either.
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Old 04-27-2021, 03:49 PM   #7
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I'm just putting it out there since the way Victron prices there is now little extra cost for optimizing other than space / wiring.

Multiple panels per SC you take an efficiency hit the MPPT unable to fully optimize

any little bit of shading bird poop, a leaf, dust can disproportionally impact total watts output.

Also with 1:1 you can use different panels, sizes to maximize filling the roof when there's other stuff up there like vents.
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Old 04-27-2021, 04:08 PM   #8
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I researched micro-inverters. Pretty cool. I think my only concern from a roof top install is the number of wires that need to come into bus.

But, if one used high wattage panels at 24v, while there would be more wires, they would be smaller. Higher wattage panels means fewer panels too.

Maybe even use a version of a weather head (cap) to bring the wires in would be a good solutions.

Since my bus is RE, I could run the wires from the roof into the engine compartment. With smaller wires I could have a little longer run to the batteries, which are only about 10' from the RE compartment.

Hmmmm...interesting.

Yet, I'll still need to convert to 12v for my furnace and refrigerator. I could do that at the appliance so I keep my wire runs small diameter.
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