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Old 12-07-2016, 10:31 AM   #1
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Micro-Inverter vs Power Optimizer

Researching the solar system now and I know that I do not want my solar panels in series. With the curved roof, my pannels will be in multiple orientations and I don't want this or shading to impact my entire system. This means that I need to install either micro inverters or power optimizers on the back of each panel. The question is...which one.

Micro inverters convert the DC to AC at the panel. However, I would then need to convert back to DC to charge my batteries...and then convert from DC to AC when there is no sun to run my AC items like the fridge.

Power Optimizers condition the DC at each panel so the power can be combined in its DC state before you do whatever you want (either send through inverter or directly to the DC charge controller to feed the batteries)

I'm leaning towards the Power Optimizer right now...but what are your thoughts?
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Old 12-07-2016, 11:07 AM   #2
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Neither?

How many watts and volts are the panels in question? Just wire the panels in parallel to a bus bar and connect that to the charge controller. Charge controller runs straight to the batteries. Inverter pulls directly from the batteries.
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Old 12-07-2016, 11:50 AM   #3
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Only issue is that shade on any of the panels will reduce the efficiency of all the panels in this setup. That is what I am trying to avoid. Both the micro inverters and the power optimizers allow the panels to operate independently of each other.
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Old 12-07-2016, 12:02 PM   #4
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Only if you wire them in series is that true. If you want to increase voltage then you wire them in series. If you want to keep each panel independent and have the current increased then you wire them in parallel.
Panels wired in parallel are independent in that if one is completely shaded it has no effect on the other panels. Your total array output is reduced, of course.
I have my panels wired in parallel. One can be completely shaded and the other can be producing full power.

Here's a 2-second google search page I found on the subject: How to Wire Solar Panels in Parallel or Series | HES PV Blog
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Old 12-07-2016, 12:34 PM   #5
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Makes sense...so is there any benefit to the micro-inverters or power optimizers?

Also, I'll be charging a 48v battery bank. I'm leaning towards keeping my panels wired in parallel (300w, 25amp, 12v) and using a 12v to 48v DC/DC converter? Thoughts?
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Old 12-07-2016, 12:49 PM   #6
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I'll chime in again here..

No, I don't think there's any benefit to using micro-inverters or power optimizers on a small scale solar array that isn't grid-tied. It would also be added complexity, which is often not a good thing.

Uh oh. So your panels are 12v and you want a 48v battery bank.. Hmm.. Well, you could maybe use a DC step-up converter, but it'll take some fiddling with and, again, adds complexity. A problem I see is that with the varying output of the panels a step-up converter will be constantly cycling off and on. I would expect it to burn out quickly.. Have you been able to find a reasonably priced step-up converter that can handle the necessary watts? All this extra stuff just makes me think it's going to be unreliable.

You'd be better off using higher voltage panels and an MPPT charge controller. I don't know of any charge controllers that can take a lower voltage and increase it on their own. It's usually the other way around. I have a Tracer MPPT charge controller that can take up to 100 volts input and charge a 12 volt, 24 volt or 48 volt battery bank.

Honestly, with those low-voltage panels the most direct solution is to put them in series, despite the shading issues you'll encounter. Otherwise it might be worth putting them in parallel and going with a 12 volt battery bank.
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Old 12-07-2016, 12:59 PM   #7
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Learn something new every day and I really need to stop making assumptions. I just assumed that solar panels were 12v DC. Time for more research

Thanks
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Old 12-07-2016, 01:09 PM   #8
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As Jazty said, your plan is too complicated, inefficient, expensive and potentially unreliable. On any moving vehicle you need to keep it simple! If you have a 12V house battery bank, use grid-tie panels (about 30V and 8.5A each, and well less than $1 a watt) in parallel, with their combined current feeding a MPPT charge controller that will charge the batteries. This way one shaded panel doesn't cut the entire output, and the CC is working efficiently because it's stepping down voltage and stepping up current by only about a factor of two. The batteries' output then powers an inverter for your AC loads. Simple!

Micro inverters are for grid-tie systems, and not even all of them.

John
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Old 12-07-2016, 09:45 PM   #9
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Quote:
Originally Posted by PappySki View Post
Makes sense...so is there any benefit to the micro-inverters or power optimizers?

Also, I'll be charging a 48v battery bank. I'm leaning towards keeping my panels wired in parallel (300w, 25amp, 12v) and using a 12v to 48v DC/DC converter? Thoughts?
I sell solar for a living and microinverters are great for maximizing profits earned by big corporate solar companies when installed on otherwise low sun hour roofs. They're used mostly in private residential projects, producing just enough energy to save the homeowner their 20% or so on electric and with the federal rebates here in the US the company makes a killing. I would never fathom installing microinverters on my bus. Just install a heavy duty tilt system so you can angle the panels in the winter. The difference between an RV and a true residential install is that the homeowner is rarely going to want to get on the roof and adjust 20 panels. Even if you found a homeowner who was willing to get on the roof and tinker around, the liability that comes with 3rd party owned systems wouldn't allow it.

On your bus, however, get up there and tilt the 3 or 4 panels to the point that they get direct sun. Jazy is spot on in that if you're really concerned about shading, wiring parallel will overcome that concern.

Lastly, check out the 24v 305w Grade B solar panels selling on ebay. They put out something like 9 amps per hour, each, in optimum sun. ~$100 per panel, cosmetically flawed but otherwise work fine. If you can pick them up in Arizona on a desert vacation you save yourself freight shipping and can invest in a good MPPT charger so you don't have to worry about keeping the voltage the same on your roof and in your battery bank.
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Old 12-08-2016, 09:03 PM   #10
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Thanks J ,IJ and WW. I've copied your comments to my notebook as a reminder should I ever find myself in the position to build a true live in Skoolie. What you point out makes perfect sense.

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