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Old 06-30-2020, 12:31 AM   #1
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Default Solar Panel Question ....

Just removed my fridge, 6 weeks until the other arrives.

In the process the guy asked about my solar panels, one of which was a 170 from Go Solar & other a 70 watt panel that I added later (manufacturer unknown).

Connected to a Victron MTTP 30/100 Controller.

All this was done by an installer I really respect who is an Electronic Genius.

I was sitting dumb & happy thinking my set up was more than adequate.

Then the guy stated "its a problem having both units going to one Controller, they each need a separate Controller otherwise the smaller unit is going to drive down your harvest - its a matter of simple physics..."

Is he correct or not?
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Old 06-30-2020, 03:10 AM   #2
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Depends on how they are wired. I believe the terms "series" and "parallel" that apply to batteries also apply to solar panels.

One way limits total output to the least productive panel (smaller limits larger/shaded limits panels in sun, etc). I think this happens from series wired panels, but I'm only going by what I've read.

Parallel wired panels are not affected and can combine the output from all panels (even of different sizes). Again, this is if I have it right.
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Old 06-30-2020, 03:19 AM   #3
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I know they go to the one Victron Controller but I don't know exactly how they are wired.

If its wrong, what am I losing everyday on average?
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Old 06-30-2020, 04:10 AM   #4
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I only know what I've learned on this forum, so I hope someone will be along to correct me if I'm wrong.

But if your panels are clean and in full bright sun, you should be getting up to 90% of total rated watts of all panels. If you are getting only 90% of your smallest panel, that could be what the person is pointing out. However, it seems odd that would be the case since when you added the smaller panel you should have noticed a decrease (rather than an increase) in solar output.

Are you mointitoring solar output via the Victron blutooth app. Some models have it standard. Others need an optional bluetooth dongle. They show about all the "real-time" charging information you could want.
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Old 06-30-2020, 04:28 AM   #5
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I have never checked the wattage per panel as you described. I have a suspicion that in fact my harvest did increase or I woild have said something.

My harvest today with a lot of driving was
380 watts with a P.Max high of 114 but somedays it has been as high as 234. On average its around 125-160.

Of course that depends on how much draw that day.

I do know that my batteries (2x100amp Lifelines) on average always reach an average of 5 hours in float at 13.4, 14.4 is absorb. Occasionally I will get 1-2 hours float.

I drive as well as solar.

I am using both the Victron BMV712 Smart Meter & I have the Bluetooth Dongle version of the Victron MTTP - the guy, like many, bought the uniy without the SMART/Bluetooth installed version - many people have made the very same mistake because of the way it is packaged.

Does this help?

PS. One thing I did at the beginning is remove the Maxxair shroud which allows you to keep the Fantastic Fan open at any time = too must shadow
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Old 06-30-2020, 11:09 AM   #6
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Default Good info here - Solar Panels - Parallel vs Series

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Old 06-30-2020, 12:10 PM   #7
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Markopolo has done some mixing of panels in the past successfully, so hopefully he can provide better detail for you.


The common statement is to not mix panels, but it does appear that there are circumstances where you can without major issues.


As mentioned by others, series wiring is out as the lowest amperage rated panel would limit the current and output.


If in parallel, the panels have to have matching voltage profiles, such as the maximum panel voltage and maximum power point voltage so the they are able to contribute their rated output when needed.


Also needed to consider is that if the panels have the more common now higher maximum power point voltage of about 17.7v you really should have an MPPT controller, which I think you already have.
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Old 06-30-2020, 01:58 PM   #8
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I just happened have an RV with two different wattage panels installed before I purchased it. I haven't done any testing of different configurations. The observed output was close to what would be expected when compared to a Solar Power Calculator.

Solar Power Calculator: Where RV Now? Solar Power

On a day with a clear, cloudless sky, put a 20A load on the system and use the solar output calculator to see if your output is what is expected. That would be a good starting point to see if any changes are needed.

Booster might have info on other, maybe better, solar power calculators.
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Old 06-30-2020, 02:10 PM   #9
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Quote:
Originally Posted by markopolo View Post
I just happened have an RV with two different wattage panels installed before I purchased it. I haven't done any testing of different configurations. The observed output was close to what would be expected when compared to a Solar Power Calculator.

Solar Power Calculator: Where RV Now? Solar Power

On a day with a clear, cloudless sky, put a 20A load on the system and use the solar output calculator to see if your output is what is expected. That would be a good starting point to see if any changes are needed.

Booster might have info on other, maybe better, solar power calculators.

That calculator looks like it would be fine for finding theoretical max power to horizontal panels. The others I had played with and posted about in the past were mainly ones that tried to estimate total energy harvest over the day at a given location and date, so a lot more complicated.


Good point on loading the solar for testing. If you don't load it down enough to have it run at it's max power point, you won't get accurate numbers. As always you need to look at watts being generated, or calc them, as the voltage will move around some and mess up the comparisons of just amps.
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Old 06-30-2020, 10:29 PM   #10
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Thank you - yes the Victron MTTP 30/100
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Old 06-30-2020, 10:39 PM   #11
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I think what is happening is that my batteries are by the best* Manufacturer: Lifeline

And that they never get stressed with the present Solar system.

As it is, I drove last night about 11.30pm a short way & therefore the lowest setting 30 minutes later was 12.73.

I drovw about 5 miles this am.

Partially in the shade now & my current is 49 watts.

Yield is 310 watts at 2.45pm with a P. Max high of 137.

But I was in bulk for 18% of time or 1 hour 45 minutes.

Absorb for 9% or 55 minutes.

And Float where I am now for 73% or 7 hours 45 minutes.
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Old 06-30-2020, 10:42 PM   #12
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For Marco Polo,

That might be beyond my technical expertise.

However, as soon as that fridge goes in there, I will be able to better gauge the solar power.

2.2amps, on average, 12 hours a day - 25 amps or 350amps per day were really drive the numbers up.
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Old 06-30-2020, 11:31 PM   #13
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Just spoke with my installer, he said there is a small compromise of about 10% at most & that gels with my #'s thus far.

He explains the deficit of series installation.

He said that he installed them in parallel versus series so that if one unit is not getting sun due to shadow, etc & one part is, I still get yeild.

He also said that ideally having two 170 watt panels going to one Controller would be perfect but I didn't have the space & that to install a second charge controller at this stage can be problematic in itself if there isn't synchronised communication between both.

I have the 170 & 80 watt panels & yet although the Power Max average this month is around 125-138 there have been highs of 234*, 220 & 202 plus a few lows of 99 & even a day of 60 but I still reached Float that day.

Knowing my averages I think that I am in a good place technically with the system, the telling part will be once the fridge is installed.

What do you guys who are far more technically savvy than I think with all the numbers I have provided?

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Old 06-30-2020, 11:33 PM   #14
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I was watching the figures last night & I could see something dragging 2 amps - looked feverishly until I determined it was the Verizon Phone Charger, which draws 2amps whether I am using 1 or 2 cords.
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Old 07-01-2020, 04:16 AM   #15
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4 Big Questions after watching the video DAVEBAD shared.

This guy says "do NOT use Parallel if you have mismatched panels ..."

And 170 & 80 is about as mismatched as you can get.

1. I do have a high quality Victron MTTP Controller - does that help?

My guy is an Electronic Guru rather than a RV Repaiir guy.

2. Who is Right & who is Wrong.

3. And does the MPPT mitigate my mismatch?

I just upgraded from a Victron MTTP 15/75 just because I noticed how hot it was getting & my guy said "this 75/15 theoretically is at the edge of its performance in certain conditions ..."

4. I was basing my Power Max figures in watts rather volts, is that a mistake ie; 170 & 80 = 250 & some days this month I have received highs of 234 which is more than 90% of 250 & other days of 202, 204, etc.
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Old 07-01-2020, 04:48 AM   #16
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Tried uploading photo, didn't work.

Instead, your answers to those 4 questions above will help me.
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Old 07-01-2020, 10:02 AM   #17
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Default Mixing Solar Panels

https://solarpanelsvenue.com/mixing-solar-panels/

Here is a good (long) article on panel connections and various outputs

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Old 07-01-2020, 11:51 AM   #18
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Quote:
Originally Posted by themexicandoctor View Post
Just spoke with my installer, he said there is a small compromise of about 10% at most & that gels with my #'s thus far.

He explains the deficit of series installation.

He said that he installed them in parallel versus series so that if one unit is not getting sun due to shadow, etc & one part is, I still get yeild.

He also said that ideally having two 170 watt panels going to one Controller would be perfect but I didn't have the space & that to install a second charge controller at this stage can be problematic in itself if there isn't synchronised communication between both.

I have the 170 & 80 watt panels & yet although the Power Max average this month is around 125-138 there have been highs of 234*, 220 & 202 plus a few lows of 99 & even a day of 60 but I still reached Float that day.

Knowing my averages I think that I am in a good place technically with the system, the telling part will be once the fridge is installed.

What do you guys who are far more technically savvy than I think with all the numbers I have provided?

Booster covered it: Match Imp (current or amps) for panels in series & match Vmp (voltage) for panels in parallel.

Your installer seems to have a good understanding of all this and I'd be confident that he did a good job given the space left from the first installation.

You've already seen near max possible output. I'd be happy with that.
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Old 07-02-2020, 06:13 AM   #19
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Thank you Marco Polo,

So am I naive reading the yield in watts versus the volts?
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Old 07-02-2020, 06:20 AM   #20
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DAVE BAD

Thank you - this was an excellent article indeed!
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