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Old 10-25-2021, 06:47 PM   #1
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Can optimizers be used allow solar panels with different MPP to work together

I have 3 solar panels with around 18v mpp on my motor home. I would like to add another big one, say 400W. However, all the big panels are for higher mpp, for example 41V. I don't understand optimizers, but wondered if I could run my current 18V panels through an optimizer to come out at 41V and wire them in parallel with a new 41V panel.

Do optimizers have an adjustable setting for the output voltage, so I could set the output to 41V???


Appreciate any input I can get on how optimizers work, and whether this scheme would work.


Thanks
Ralph
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Old 10-31-2021, 09:06 PM   #2
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I am not sure what an optimizer is, but you already have a solar charge controller connected to the three existing panels.

What you need when you have "incompatible" panels is that you need an additional MPT solar charge controller. Be sure that it is rated for more than your MPP of the panels that you are hooking up. A Victron 100/30 would work well for your 300W panel. It will take up to 100V of panel Voc (open circuit) and will charge at up to 30A (360W into a 12V battery bank). The key here is that both SCC need to be set for the proper battery chemistry and voltage points.

You just hook the new SCC up in parallel with your existing controller. They will both provide current for the batteries.
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Old 11-01-2021, 05:17 PM   #3
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jkane,
First, thank you for responding. i was beginning to think I had posted in the wrong place and nobody would read it. Second, optimizers are dc to dc converters that are usually placed on each solar panel in a string so that each is locally optimized for shade, etc, not just an averaging optimization for the whole string that an MPPT controller would give. See https://www.solarreviews.com/blog/co...wer-optimizers , or any of many web sites describing them. The reasons I want to use them rather than an additional solar controller is that they are cheaper ($100 vs $200 to $300), they can be mounted on the solar panels so I don't need to find space inside for an additional controller, and no additional wiring is needed from the rooftop down the refer vent and over to wherever I would mount it, nor down to the batteries.
Some of my questions are: If I connected my old 18 MPPV panels in parallel to the the optimizer, what voltage would the optimizer output (18 V or something else)? Could I connect this output (whatever it is) in parallel with the 41 MPPV new solar panel (to keep the system voltage down so I don't shock myself) or would I have to connect them in series (in which case I would have to buy 2 power optimizers, one for the new panel and the other for the 3 older panels)? And are there any other stumbling blocks I don't know about?
Anyway, thank you again for responding, and if you run across from somebody who knows optimizers, let me know.
Ralph
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Old 11-01-2021, 06:23 PM   #4
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I use solar edge optimizers on my home solar system. They output around 60 VDC, at about 5 amps or so.

https://www.solaredge.com/sites/defa...-datasheet.pdf
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Old 11-02-2021, 05:49 AM   #5
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Originally Posted by ralphl View Post
jkane,
First, thank you for responding. i was beginning to think I had posted in the wrong place and nobody would read it. Second, optimizers are dc to dc converters that are usually placed on each solar panel in a string so that each is locally optimized for shade, etc, not just an averaging optimization for the whole string that an MPPT controller would give. See https://www.solarreviews.com/blog/co...wer-optimizers , or any of many web sites describing them. The reasons I want to use them rather than an additional solar controller is that they are cheaper ($100 vs $200 to $300), they can be mounted on the solar panels so I don't need to find space inside for an additional controller, and no additional wiring is needed from the rooftop down the refer vent and over to wherever I would mount it, nor down to the batteries.
Some of my questions are: If I connected my old 18 MPPV panels in parallel to the the optimizer, what voltage would the optimizer output (18 V or something else)? Could I connect this output (whatever it is) in parallel with the 41 MPPV new solar panel (to keep the system voltage down so I don't shock myself) or would I have to connect them in series (in which case I would have to buy 2 power optimizers, one for the new panel and the other for the 3 older panels)? And are there any other stumbling blocks I don't know about?
Anyway, thank you again for responding, and if you run across from somebody who knows optimizers, let me know.
Ralph
You need one optimizer for each panel, so it can be a lot more expensive than multiple SCCs. I have 2 SCCs that cost 2x$150 = $300. I have 4 panels, so $400 for optimizers and $150 for a single SCC.

Doesn't make sense for mobile because you never know what panel will be shaded.
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Old 11-02-2021, 09:20 AM   #6
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OK, I now know what solar optimizers are :-)

I have not been working on Home solar, so while I knew about micro-inverters I did not know about solar optimizers. Basically they are small MPPT controllers (DC Buck/Boost converters)

As HarryStone and corn18 mentioned, they will take you voltage output from each panel and provide 60V out. I concur with HarryStone, I think that I would only look at these in home installations. Also as corn18 mentioned, I think you need one per panel. Could you cheat? Maybe, it would depend on your panels. You might be able to hook your 20V panels up in series to one optimizer and then the other 41V panel to another optimizer. Parallel both of the optimizers (you can do this because they are both outputting 60V) and you are good to go.

However, I would still want to go about this differently. You did not mention your 20V panel specs, so let's assume that they are 100W each.

You could put the 3x20V panels in parallel, to a single MPPT controller (anything that handle 25V and does 20A - 30A of charging current). In parallel you don't lose output if any panel gets shaded (other than the shaded one). However, they will not produce enough voltage early in the day or late in the afternoon.

You could put the 3x20V panels in series, to a single MPPT controller (anything that handles 75V and 20A - 30A of charging current). In series you get usable power earlier in the morning and later at night. You do get much reduced power if a panel gets shaded.

Finally your 41V residential panel needs its own controller (anything that handle 60V and 30A - 40A of charging current).

I would do this, 2 MPPT controllers. and I would minimize the chance of shading happening on the panels. If you can see fit to do it, I would oversize the MPPT (for the 40V panel) if you think you might add more of that panel in the future.

The key here is that you can mix panels only if they have very similar values for Voc / Vmpp / Isc / Impp. If you don't match them you get really strange problems and poor performance. Anytime you add a new type of panel, you need to basically be a new string.

Cheers
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Old 11-02-2021, 09:23 AM   #7
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Quote:
Originally Posted by corn18 View Post
You need one optimizer for each panel, so it can be a lot more expensive than multiple SCCs. I have 2 SCCs that cost 2x$150 = $300. I have 4 panels, so $400 for optimizers and $150 for a single SCC.

Doesn't make sense for mobile because you never know what panel will be shaded.
Optimizers take the worry about panels being shaded. If one is partially shaded, it will still produce, and so will the others in the string.
And they are about 85 each, so a bit less than you mentioned.
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Old 11-02-2021, 09:53 AM   #8
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Optimizers take the worry about panels being shaded. If one is partially shaded, it will still produce, and so will the others in the string.
And they are about 85 each, so a bit less than you mentioned.
I love the concept and might get them for my 4 panels. Also nice that you can parallel 20V panels with optimizers and get plenty of voltage to the SCC.
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Old 11-02-2021, 12:21 PM   #9
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The Tigo TS4-A-O looks like the bees knees @ $46 each. Would accomplish what the OP needs.

https://tandem-solar-systems.com/pro...AaAjBwEALw_wcB
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Old 11-06-2021, 12:36 PM   #10
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I want to thank each of you that replied. That was tremendous!
First, my configuration. I have 2 matched 125W 17.5 MPPV solar panels, and one 210W 18.5MPPV panel, all 3 connected in parallel to a Morningstar TS45 MPPT solar controller. I have 4 Full River 6V 224Ahr AGM batteries connected in parallel/serial to give 12V.

I have spent a couple days playing telephone tag with salesmen for the Tigo TS45-A-O (thank you Corn18 for suggesting them). Here is what they told me as best I understood it:
1. The optimizers (TS45-A-O) should be connected in series to the MPPT solar controller.
2. A solar panel with just enough light to activate it will put out close to its MPPV voltage, but just a fraction of an amp. As the light intensifies the amps will increase, but the voltage will remain about the same.
3. When 2 or more solar panels with dissimilar MPPV outputs are connected in parallel, the panel with the lowest MPPV will drag the voltage of the other panels down to its voltage. The amperage will remain about the same, but the result is lower wattage for all the panels.
4. A TS45-A-O optimizer needs 16V input to activate it. An 18V panel may not be enough to activate and the optimizer would put out zero volts.
5. The TS45-A-O is made to work with MPPT solar controllers like my Morningstar controller. The MPPT solar controller and the optimizers won't "fight" with one another to control the voltage from the optimizers into the solar controller.

6. An optimizer connected to a single panel will output the MPPV voltage of that panel. In other words an optimizer on a 41MPPV panel will output 41V to the solar controller.
7. If multiple optimizers (on solar panels with different MPPV) are connected in series to the solar controller, the output feeding the solar controller will be the average of the MPPV of the solar panels. For example, 2 optimizers (one on an 18MPPV panel, and one on a 41MPPV panel) connected in series to a solar controller would output (18+41)/2=29.5V.
I came up with several options for how I might connect my existing solar panels with a new 350 plus wattage panel.
1. Connect the current 3 (about) 18MPPV panels in parallel into an optimizer. Place an optimizer on the new 41MPPV panel. Connect the 2 optimizers in series to my solar controller getting a 29.5V feed. Pros: shade on any solar panel won't affect the others; low voltage so I don't get shocked. Cons: 18V may not be enough to activate optimizer.
2. Connect 2 matched 17.5MPPV panels in parallel, then connect those 2 panels in series with the 18.5MPPV panel to get 36V. Feed 36V into an optimizer. Place a second optimizer on 41V panel and connect the 2 optimizers in series with the solar controller. Pros: 36V is sure to activate the optimizer, whereas 18V in Option 1 might not be enough; connecting the existing 18.5MPPV panel in series with the existing 17.5MPPV panels would give a little more wattage. Cons: Shade on any of the (about) 18MPPV panels could affect the output of all of them; output voltage to solar controller a little higher at 38.5V
3. Find a new high wattage panel at 36MPPV. Connect existing (about) 18MPPV panels in parallel/series as in Option 2, and connect the 36V output of the existing panels in parallel with the new 36MPPV panel. Forget about the optimizers. Pros: Save $100; fairly low voltage (36V); almost no rewiring required. Cons: Shade on any of the current 18V panels could affect output of other 18V panels due to series connection.
Problem: I don't understand wattage loss due to shading on parallel connected panels well enough to know if Option 3 (no optimizers) would work as well as Option 2 (with optimizers), or not.
I would like to hear anybody else's comments.
Ralph
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Old 11-07-2021, 12:46 PM   #11
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A couple of more notes on solar panel bypass diodes and optimizers that might be interesting:
This website has a good explanation of bypass diodes (and half cut solar cells): https://www.solarquotes.com.au/blog/...nal%20panel%3A .

I have come to the conclusion that optimizers don't provide much benefit on old solar panels without bypass diodes (most newer panels have 3 bypass diodes), if panels connected in parallel have the same MPPV. Where optimizers provide big benefits is with series solar panels, where without optimizers, shade on one panel would kill the output from the entire serial string of panels. Optimizers seem to also provide big benefits over parallel connected solar panels (with the same MPPV) when one of the panels has bypass diodes. Shade on one section of such a panel activates one or more of the bypass diodes and essentially changes the MPPV of the panel, causing a mismatch of MPPVs on parallel connected panels. In other words don't parallel connect panels with bypass diodes. My Option 3 listed in the above post would do just that and so won't work.
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Old 11-28-2021, 06:22 PM   #12
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Check me on this, but I believe that optimizers need a fixed voltage to "work into." I.e., the 60V is the voltage they are designed to feed into. My son's home system does not have an MPPT controller. Instead it has an optimizer on each panel and those feed into a "dumb" controller that simply aggregates the current (at 60V) provided by each optimizer.

What I'm getting at is that your MPPT solar controller may not behave well with the optimizers. It will try to reduce voltage to maximize power (voltage times current). As a wild guess, that would collapse the voltage on the optimizer outputs and they will then not do their thing.

Think of it like this ..... your solar controller uses your battery voltage as a reference and moves the input side voltage up or down to maximize power. The optimizers are similar, they use the fixed 60V provided by the dumb controller as a reference and move the input voltage up or down to maximize power from the associated panel. Without that fixed 60V from the dumb controller, the optimizers would have no way to apply a regulated voltage to the panel.

I have no direct experience but this is how I believe the optimizers work.
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Old 11-30-2021, 02:25 PM   #13
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hclarkx:
Thank you for your response. i appreciate people discussing this with me. I am trying to find a single solar panel at a reasonable price, but so far the freight is more than the panel price and I haven't found one nearby. So I haven't been able to experiment yet.
You mention 60V as a reference voltage for an optimizer. Where did you find that. I don't think there was anything in the Tigo specs about 60V. In my conversations with the salesman, he said the optimizer would output the voltage going into it. So, as I understand it, a 41V solar panel would cause the optimizer to output 41V to the MPPT controller. The 18V panels would cause that optimizer to output 18V to the MPPT controller. Since the optimizers would have their outputs connected in series, I would have thought the MPPT controller would get 59V, but the salesman said it would get the average of the 2 optimizers 41+18=58, 58/2=29V. Maybe the "averaging" is caused by the MPPT controller. The salesman also said that the Tigo optimizer is specifically made to work with MPPT controllers. So I guess I will have to do some experimenting, if I ever find a reasonably priced solar panel.
Thanks again.....
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Old 12-01-2021, 07:25 PM   #14
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Originally Posted by ralphl View Post
hclarkx:
Thank you for your response. i appreciate people discussing this with me. I am trying to find a single solar panel at a reasonable price, but so far the freight is more than the panel price and I haven't found one nearby. So I haven't been able to experiment yet.
You mention 60V as a reference voltage for an optimizer. Where did you find that. I don't think there was anything in the Tigo specs about 60V. In my conversations with the salesman, he said the optimizer would output the voltage going into it. So, as I understand it, a 41V solar panel would cause the optimizer to output 41V to the MPPT controller. The 18V panels would cause that optimizer to output 18V to the MPPT controller. Since the optimizers would have their outputs connected in series, I would have thought the MPPT controller would get 59V, but the salesman said it would get the average of the 2 optimizers 41+18=58, 58/2=29V. Maybe the "averaging" is caused by the MPPT controller. The salesman also said that the Tigo optimizer is specifically made to work with MPPT controllers. So I guess I will have to do some experimenting, if I ever find a reasonably priced solar panel.
Thanks again.....
There definitely could be more to it than my limited experience provides. I was referencing optimizers on my son's home solar system which IIRC are in parallel. It sounds like there could be other designs or newer ones.

IIRC there are optimizers that communicate with the central DC-AC device. Those would require matching the optimizer with the central device it's designed to work with.

In my mind it wouldn't make sense to have two MPPT controllers cascaded.

But, the optimizer should be controlling its input voltage (at the MPP) and I don't think there's a way to do that without a reference voltage on the output.

There are probably some good threads on optimizers on DIYSolarforum.com

https://diysolarforum.com/search/643...rs&o=relevance

I'll dig into this a bit more.

Please refresh my memory; what purpose where you hoping to achieve with an optimizer on each panel?
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