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Old 04-16-2020, 11:30 PM   #1
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micro inverters solar

Has anyone installed a solar system on the top, using micro-inverters and bringing down 110V to a charger?
My idea is to start building my solar farm on the rooftop with individual micro-inverters, in parallel. It purpose will be mainly to charge my two banks 840 AH.
I would start with two panels and add more gradually up to 6 panels.
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Old 04-17-2020, 05:28 AM   #2
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Hmmm! You are going to take about 17v DC from a panel, and feed it to a micro inverter that converts it to AC. Then feed it to a charger that charges your batteries. There is a lot of inefficiency in that circuit.

Don't know how efficient the first step is, maybe 95% but the second step is usually only 80% for the charger. Just look at any charger's specs: voltage x current in vs voltage x current out.

I understand micro conrollers where each panel has its own controller that charges batteries, but not with AC in the middle. I don't see the point of that extra step.

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Old 04-17-2020, 06:03 AM   #3
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Has anyone installed a solar system on the top, using micro-inverters and bringing down 110V to a charger?
My idea is to start building my solar farm on the rooftop with individual micro-inverters, in parallel. It purpose will be mainly to charge my two banks 840 AH.
I would start with two panels and add more gradually up to 6 panels.

Short answer is No, use the solar to charge via DC straight to the batteries.



Solar devices like micro inverters and grid tied inverters generator AC output directly from the connected panels. But there are a few caveats.


Most of them are intended for grid tie, and require stable, pre-existing AC power that they can sync up to. If there isn't a pre-existing source of AC power, they will never even turn on. This is because they are designed to follow and push AC power, not create AC power. So if you just connect a micro inverter to a charger, most likely nothing will happen.


This is all a consequent of how a grid tied inverter deals with varying output from the solar panels. It does that by first synchronizing with the grid power, then it pushes all the power it has into the grid. The grid can absorb as much or as little as the inverter wants to provide, and the grid makes up the balance of whatever is needed to power you loads. It just becomes a matter of how much current flows in which directions.


But if there were no grid, all the solar inverter could do is create an AC output, wait for loads, and attempt to power them. If it couldn't power them, then it's only option would be to turn off. The only way for you to keep power on would be to regulate your loads. So getting back to your charger, you would have to constantly adjust it's output to limit power consumption to keep the micro grid running. That's not practical.


There are, however, products that let you do part of what you describe, but that I think are still not practical for your goal. With some products, you can run a battery powered inverter to create AC. Then you can connect something like a micro inverter to the AC output of the inverter, creating a so-called AC-coupled system. Now the battery inverter acts a bit like the grid, though with much less capacity. Plus, the micro inverter power can ONLY be used to supplement power to loads. It's can back-feed through the inverter to charge the batteries. You could now plug your battery charger into this micro grid, and to the extend that the solar products all the required power, you could charge your batteries. But if the solar isn't enough, and there will always be times when it isn't, the charger will continue, and draw any remaining power requirements from the inverter, which is getting it's power from the very batteries that you are trying to charge. At a minimum you would be wasting a bunch of the solar power, and worse case you would drain your batteries instead of charging them.
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Old 04-17-2020, 06:12 AM   #4
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Short answer is No, use the solar to charge via DC straight to the batteries.
Great explanation. Thank you for clearing this out. I did not think about this aspect.
The goal was to avoid heavy wiring coming down.
In that case, I just have to go with DC+Charger.
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Old 04-17-2020, 07:11 AM   #5
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Great explanation. Thank you for clearing this out. I did not think about this aspect.
The goal was to avoid heavy wiring coming down.
In that case, I just have to go with DC+Charger.
Most solar controllers sold for consumer use are DC+Chargers, like Victron's.

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Old 04-17-2020, 09:54 AM   #6
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The other goal of a microinverter string is to decouple each panel from the system so if part of the system is shaded it doesn't lower all the output of the system, they do a good job of this. There are mircoinverter systems designed to work off grid also. MI systems are the highest output systems in solar energy currently. All being said I would stick with a standard DC controlled system , I planned to add this to my boat in June until all the virus issues.
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Old 04-17-2020, 12:17 PM   #7
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, I planned to add this to my boat in June until all the virus issues.
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Do you have hardware list you plan to install already?

Yes, shading problem reducing was one of the goals with the MI idea.
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Old 04-17-2020, 01:21 PM   #8
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There are, however, products that let you do part of what you describe, but that I think are still not practical for your goal.
What do you think about this product:

https://www.samlexamerica.com/produc...l.aspx?pid=575

This can take the solar controller directly and charge/invert without batteries involved.
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Old 04-17-2020, 02:14 PM   #9
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LeoKa

If your intent is to charge your house batteries I think you need to look into MPPT controllers. They are designed to efficiently interface between solar panels and your battery bank without going through a separate charger. This will minimize system losses. Another advantage of a MPPT controller is that you can series configure your panels (if shading is not an issue) which will reduce the size requirement for the wiring between the panels and the controller which should be mounted as close to the battery bank a reasonable. Like Hollywood I'm going to be installing a system later on this spring. The system I'm putting together will be using a Victron 100/30 BlueSolar controller.
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Old 04-17-2020, 03:16 PM   #10
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What do you think about this product:

https://www.samlexamerica.com/produc...l.aspx?pid=575

This can take the solar controller directly and charge/invert without batteries involved.

That's an interesting twist. Other than the extra DC input for charging, it's functionally equivalent to many other inverter/chargers from Outback, Victron, Mastervolt, Magnum, etc. I have heard of Samlex, but have no direct or even second hand experience with them.


I think for solar the extra DC input won't help or won't be the preferred way to do things. It has a limited acceptable voltage range, which will seriously limit the panels that you can use. Plus, it doesn't have MPPT capability which I think is especially important on a boat where you need to extract max power from every sq meter of solar panels that you can fit. I think you would be much better off with a dedicated MPPT charge controller for your solar.


You expressed concern over wire size. Keep in mind that larger panels in the 300-400W size run around 60-70V, and only put out 5A or so each. That doesn't take much wire. Put the charge controllers near the batteries, and run the high voltage wires down to them. Just treat them like AC wires due to the higher voltage. ABYC calls for all connections to be in enclosures that require a tool to open. That tool can be nothing more than a screw driver. You can also wire the panels in series and further reduce the current running through the boat.
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Old 04-17-2020, 03:23 PM   #11
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LeoKa

If your intent is to charge your house batteries I think you need to look into MPPT controllers. They are designed to efficiently interface between solar panels and your battery bank without going through a separate charger. This will minimize system losses. Another advantage of a MPPT controller is that you can series configure your panels (if shading is not an issue) which will reduce the size requirement for the wiring between the panels and the controller which should be mounted as close to the battery bank a reasonable. Like Hollywood I'm going to be installing a system later on this spring. The system I'm putting together will be using a Victron 100/30 BlueSolar controller.






I'm doing very similar. I'm using four Solarex 360W panels, each with it's own Victron 100/20 (100V, 20A output) MPPT charge controller. The charge controllers are only about $125 each, so worth dedicating one to each panel to get max shading immunity, and get the most out of the limited panel space that I have available. Voltage from panels to controllers are 70V nominal, 95V or so max, so just under the 100V rating on the Victron. They have higher voltage units if you want to wire panels in series, and higher current like what LeoKa is using if you want to parallel a couple of panels.
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Old 04-17-2020, 03:48 PM   #12
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I think for solar the extra DC input won't help or won't be the preferred way to do things. It has a limited acceptable voltage range, which will seriously limit the panels that you can use. Plus, it doesn't have MPPT capability which I think is especially important on a boat where you need to extract max power from every sq meter of solar panels that you can fit.
Good points and observations. I do want the expanded voltage range for the panels, as I want as large Wattage as possible.
MPPT is also I want to have.
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Old 04-17-2020, 03:51 PM   #13
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I'm doing very similar. I'm using four Solarex 360W panels, each with it's own Victron 100/20 (100V, 20A output) MPPT charge controller.
What is the efficiency of those panels?

There is a company in Swiss land, which makes panels with over 25% efficiency. I could not find any price on them.
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Old 04-17-2020, 07:30 PM   #14
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What is the efficiency of those panels?

There is a company in Swiss land, which makes panels with over 25% efficiency. I could not find any price on them.

About 22% sticks in my head.
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Old 04-17-2020, 10:19 PM   #15
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About 22% sticks in my head.


What are the prices you see for it?
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Old 04-17-2020, 10:25 PM   #16
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This repeats from some replies above, but if you either run higher voltage panels, or put lower ones in series (in series volts add up while amps stay the same), then you can run thinner wire without seeing as much voltage drop (voltage drop calculators can help you make choices once you input wire length and etc.)

An MPPT controller can take the higher voltage in and output the ~13-14 volts you need for a 12-volt house bank.

You do have to pay attention to the ratings for controllers, and for switches, and breakers between the panels and the controller if you are running higher voltage on that leg, but there are options. Also know that at dawn in cold weather panels will put out a bit more than rated voltage so don't cut it too close.

There are other considerations, but not to bog down for now I leave them out.
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Old 04-18-2020, 06:56 AM   #17
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What are the prices you see for it?

I'm glad you asked, because I don't like the answer.



First, I misspoke earlier. The panels I have specified for the build are the SunPower X-Series, not Solarex. I should have checked. They rigid mono-crystalline panels, not the flex panels.



I haven't purchased them yet, so did a quick search and it looks like getting them may be difficult to impossible. I can't find anyone selling them. My guess is that they are only selling in bulk to large installations. So I may end up with a different manufacturer. I won't be buying until mid to late fall, so won't decide until then.
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Old 04-19-2020, 09:27 PM   #18
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I thought the Sunpower weren't available on the market, but could only be supplied AND installed by one of their authorized dealers?
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Old 04-19-2020, 09:32 PM   #19
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I thought the Sunpower weren't available on the market, but could only be supplied AND installed by one of their authorized dealers?

I can believe that based on not finding any for sale.


I found an equivalent from Panasonic that I will probably use instead. There are others too, but the Panasonic shape is a better fit for me. It's 21% efficient as opposed to 22%, so the same in all practicality.
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Old 04-20-2020, 01:09 PM   #20
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I can believe that based on not finding any for sale.I found an equivalent from Panasonic that I will probably use instead. There are others too, but the Panasonic shape is a better fit for me. It's 21% efficient as opposed to 22%, so the same in all practicality.

Take a look at this one:

https://platt.com/platt-electric-sup...x?zpid=1448021

I am not sure, if you can buy Panasonic without an installer.
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