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Old 04-11-2017, 06:31 PM   #1
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Solar panels in series with no loss due to shading

A year ago when I installed my solar panels I did a lot of research and decided to install my panels in parallel, this meant not using the solar pre-wire in my Airstream because of the gauge of the wire (10 ga) and the energy loss it would cause.

Solar panels when run in series suffer when one panel in a series gets shaded and the other(s) don't, the shaded panel pulls down the solar production of all the other panels in the series.

Residential solar installations have this same issue and they have different solutions. One is microinverters connected to each panel but that doesn't work for the RV world since microinverters take DC and turn it to AC and we really want DC to charge our batteries.

The other solution is DC optimizers (aka maximizer), so imagine 2 panels in series one in the shade making 13v and the other in the sun making 18v because they are in series the entire string is pulled down to 13v. By attaching a DC optimizer to each panel both panels will produce 18v, although the shaded one will be producing less current.

So lets say you install 4 x 100w panels in series each with a DC optimizer bringing the string up to 72v and 5.5a. Assuming the wire length from your solar panels to your charger controller is 15ft over the factory Airstream 10ga wiring would result in a 0.22% voltage drop.

Tigo makes a retrofit kit, the TS4-R you could can use with just about any solar panel that you would put on an RV. Although you are adding $50 per panel to your install cost you don't have to buy and run thick 6ga wire.

http://www.tigoenergy.com/products/#smart-modules-ts4-r

In summary there are lots of considerations when installing solar on your rig and this gives an option for using the existing wiring without compromising power generation.
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Old 04-14-2017, 06:22 PM   #2
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Mgieselman,

Nobody else is biting so i'll go first. Have you done this mod yourself? I have noticed pretty pronounced solar drop off when one panel is shaded and this looks like a very interesting mod.

I think my AM Solar panels have a junction box on the rear the same size (just looking at it) as the units you are describing. It surely could not be as easy as changing out the back plate with electronics?
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Old 04-14-2017, 09:44 PM   #3
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Ohiobrits I think it's even easier than that, Tigo as well as SolarEdge offer retrofit kits. Basically you screw a power optimizer into the back of each panel then plug your panels MC4 connectors into the optimizer, then connect the optimizers in series with the last connection going to your solar charge controller. (See picture below.)

Tigo offers several different power optimizers, some have monitoring built in so you can monitor the output of each panel which is very cool. Another benefit is mixing panel sizes in a single series.

Now let me also say is I haven't done this, my panels are installed in parallel already so individual panel shading isn't an issue. The optimizers are designed for larger residential panels so you'd need to find one that can tolerate the lower voltage of the typical 100-160w RV panel.

AM Solar recommends cutting off the MC4 connectors and crimping directly to the wiring that runs to your combiner box. I didn't do that so I could replace a solar panel without cutting and crimping wire, but I could also add the optimizers although really no reason for me to do so now.

If I were doing a new install I would definitely look into this, it would be great to use the 10ga wiring and get per panel monitoring. I'm going to guess in a year someone, maybe Victron, will be making power optimizers for the RV/Marine market.
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Old 04-15-2017, 04:25 PM   #4
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Thanks for this post! I have been running numbers and combinations for a new 500w PV system for my 22 Sport. The narrow design and crowded roof leave me with limited design constraints, but your information about "the optimizer" gives me another option. The Optimizer sounds like a Solar Super Hero😉.
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Old 04-16-2017, 10:58 AM   #5
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Thumbs up series v parallel solar

We haven't replaced our old panel yet, I'm very glad I saw this. Watching.

Thanks!
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Old 04-16-2017, 12:34 PM   #6
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This is great. I've always wondered about running in series which allows the use of smaller gauge wire for the install (higher voltage ==> lower current).
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Old 04-16-2017, 02:54 PM   #7
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Beware of DC optimizer

Something to consider before buying DC optimizer.

FCC issues a Notice of Violation to Solar City for RFI Interference.

After an on-site visit and testing by an FCC Enforcement Agent interference caused by a Solar City solar array the FCC issued Solar City a Notice of Violation.

Testing by the FCC Agent showed that the interference does not stop until the optimizer is detached from the solar panel. Attempts by Solar City to add filters were unsuccessful and only resulted in a few DB of change.

The optimizer (as well as the rest of the system) is manufactured by Solar Edge. Fortunately the FCC is concerned about this issue and is actively working to resolve it.

The above is a synopsis from a QRZ.com forum.
https://forums.qrz.com/index.php?thr...erance.559331/

Hopefully not all DC optimizers have this problem as it seems as a good solution for some installs.

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Old 04-16-2017, 03:42 PM   #8
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anyone else tested these devices (; This is hilarious if you dont take it seriously
How to demonstrate innovative leading edge products

turbo encapulator
https://youtu.be/rLDgQg6bq7o

or the rockwell Retro Encabulator
https://youtu.be/RXJKdh1KZ0w
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Old 04-16-2017, 10:32 PM   #9
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Basically DC optimizers are DC to DC converters, so using optimizers all panels put out the same voltage regardless of the amount of sun hitting them.

Wikipedia has a good discussion:

https://en.wikipedia.org/wiki/Power_optimizer

Depending on optimizer design there could be RF issues, you would have thought SolarEdge would have done RF interference testing.
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Old 04-16-2017, 11:14 PM   #10
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Old 04-17-2017, 04:09 AM   #11
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I could not find any specs in their info about conversion efficiency.
It may do what it says, but if it is inefficient in the conversion, your total wattage will be worse than before.
If all you have to work with are undersized wires, it will give you more volts and less amps at a price.
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Old 04-17-2017, 09:28 AM   #12
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Using DC optimizers you are essentially putting an MPPT controller at each panel.

According to the SolarEdge data sheet their DC optimizers have 99.5% efficiency.

http://www.solaredge.com/sites/defau...tasheet-na.pdf

You also get the added efficiency of less transmission loss since the wires running to your charge controller are at a higher voltage.

Since each panel essentially has an MPPT controller attached at some point in the future you'll run the output of your panels into a battery charger as opposed to a traditional charger controller.

Here's a good discussion of DC optimizer/microinverters.

https://www.greentechmedia.com/artic...Solar-Question

Note that the above article is from 2012 so this technology has been around for a long time.
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Old 04-17-2017, 09:46 AM   #13
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That does not seem like a real world efficiency rating. It would be nice to see the conditions that brought them to that number.
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Old 04-20-2017, 11:33 AM   #14
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DC optimizers are currently not a solution for RV installations. Although Mgieselman described the DC/DC modules that need to be piggybacked onto each solar panel, there's also a hub at the end of the series connection that's required to tell the other modules how to compensate. I couldn't find a single supplier for a system that would be suitable for RV installation. I'd be happy to investigate if I'm wrong and report back.

Many folks on this forum already build series and series/parallel-connected solar panel systems in order to reuse the existing 10 AWG solar pre-wiring and make the DIY installation easier. You can do this successfully with an MPPT solar charger that's adequately specified for your configuration. Commonly available 12V solar panels for RVs include four bypass diodes that 1) allow the other power producing panels to continue to generate power even if one panel is obscured and 2) allow even a partially obscured panel to produce power in some circumstances.

I have four 100 W panels in a series/parallel configuration. My losses due to the pre-wiring are less than 2% in a 30' Classic and after two years of use, I'm very happy with the performance.
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Old 04-20-2017, 11:44 AM   #15
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interesting info as I am getting geared up to do solar install later this year or next year.
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Old 04-25-2017, 04:37 PM   #16
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Quote:
Originally Posted by alano View Post
DC optimizers are currently not a solution for RV installations. Although Mgieselman described the DC/DC modules that need to be piggybacked onto each solar panel, there's also a hub at the end of the series connection that's required to tell the other modules how to compensate. I couldn't find a single supplier for a system that would be suitable for RV installation. I'd be happy to investigate if I'm wrong and report back.

Many folks on this forum already build series and series/parallel-connected solar panel systems in order to reuse the existing 10 AWG solar pre-wiring and make the DIY installation easier. You can do this successfully with an MPPT solar charger that's adequately specified for your configuration. Commonly available 12V solar panels for RVs include four bypass diodes that 1) allow the other power producing panels to continue to generate power even if one panel is obscured and 2) allow even a partially obscured panel to produce power in some circumstances.

I have four 100 W panels in a series/parallel configuration. My losses due to the pre-wiring are less than 2% in a 30' Classic and after two years of use, I'm very happy with the performance.
alono, everything you have stated is true however I think there is a case for DC optimizers.

DC optimizers act as MPPT controllers on a per panel basis, this allows energy to be harvested in cases where bypass diodes would be "activated". DC optimizers can harvest with PV volage as low as 5v. There are conditions where panels connected in a series/parallel configuration will never get above the charge voltage of a battery where DC optimizers would. It's possible to park in partial shade and generate no solar energy to charger you batteries whereas DC optimizers would, imagine this over a week and there "could be" a huge difference.

I called Tigo Energy support at (408) 402-0802 ext.2 and was told that the hub is only required if you want per panel monitoring and uploading of data to the cloud. I specifically asked how the modules communicate and got a very fuzzy answer that they will adjust output voltage automatically. Not a very satisfactory answer.
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Old 04-25-2017, 11:13 PM   #17
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My understanding of DC optimizers is different. Let's take a simple example with three panels in series. If one of the panels becomes totally shaded, the DC optimizer for that panel will not produce any energy, but will operate in bypass mode. When this occurs, the hub instructs the other two panels to boost their outputs to try and reach a point where the DC/AC converter operates more efficiently. Now in the case of RVs, we don't need a DC/AC converter. In an RV installation there would already be a MPPT controller installed when using three panels in series. Since an MPPT controller is a DC/DC converter that can find the best operating point, I think the efficiency gains are questionable.
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