Sizing Victron MPPT Controller

[john61ct]

A/B testing is easiest to do before final install, both sides should be done within a few hours, trying to control all the other factors as much as possible, two batts at the same 50% SoC, same insolation, angles etc.

An object sitting on the panel casts a harder shadow. From farther away it is much more diffuse, less of an effect. Cloud cover is an extreme example on the one hand, bird poop on the other.

Victron MPPT should IMO be matched with higher-voltage panels so they don't need to be series'd, 16Vmp is likely too low.

[GTom]

Originally Posted by john61ct

A/B testing is easiest to do before final install, both sides should be done within a few hours, trying to control all the other factors as much as possible, two batts at the same 50% SoC, same insolation, angles etc.

An object sitting on the panel casts a harder shadow. From farther away it is much more diffuse, less of an effect. Cloud cover is an extreme example on the one hand, bird poop on the other.

Victron MPPT should IMO be matched with higher-voltage panels so they don't need to be series'd, 16Vmp is likely too low.

The results are interesting for a longer run, but indeed can be influenced by many factors: true controller-analytics has to be performed quickly (<1hour) in order to mitigate any changes in insolation (angle, atmospheric transmission) AND panel temperature(!).

16V is very close to the 14.x used for charging, I would be interested 17V and upwards. I suspect that the advantage of adding more voltage diminishes after a certain point.

[TheThunderbird]

Originally Posted by Davidhoy

This! Multiple MPPT controllers gives you many advantages.
1. Redundancy
2. Parallel panels reduce effects of shading
3. Locate the controllers close to the batteries, and you can run smaller gauge wires from the panels to the controllers.
4. Redundancy ;-)

I personally have two SmartSolar MPPT 100/30 controllers, but I have two big 350 watt panels, so I do have one per panel.

-David

dead friend, point 2) has nothing to do with number of controllers... :

[TheThunderbird]

100/30 stands for 100V 30A working limits
Thus, have some panels in series and you

- can use possibly the 100/20
- gear up Voltage, with a benefit in transmission losses, low sun situations (Noelex said!), MPPT performance v PWR

I DONT BUY the alleged difficulties claimed for the re-wiring, which should come shorter indeed, and simpler too! :-)

panel output is 19 - 21 V, 2 of 3 in series can easily go


PS this is out of an acclaimed installer of fiction-deka solar power systems

[john61ct]

Originally Posted by GTom

I suspect that the advantage of adding more voltage diminishes after a certain point.

For Victron MPPT my understanding is that efficiency improves until Voc is somewhere well over 40V

Don't get within 10% of the rated max though.

And not to make that the highest priority in panel selection, incremental improvement only.

Panel efficiency in watts per total square area is very important in a mobile context, as is simple dimensions to maximize roof space usage.

[Davidhoy]

Originally Posted by TheThunderbird

dead friend, point 2) has nothing to do with number of controllers... :

But I'm not dead yet... ;-)

https://www.youtube.com/watch?v=UPatfgoNBRo

[Bleemus]

So I have four Kyocera 140 watt panels at 22v Voc in parallel going to a Victron 100/50. Lets assume for this question that there is no shading.

Am I better off having two pairs of panels in series at 24 volts go to a buss bar then to SC or keep in parallel?

And, yes, I am aware I would be better off with 4 controllers.

[travellerw]

Originally Posted by Bleemus

So I have four Kyocera 140 watt panels at 22v Voc in parallel going to a Victron 100/50. Lets assume for this question that there is no shading.

Am I better off having two pairs of panels in series at 24 volts go to a buss bar then to SC or keep in parallel?

And, yes, I am aware I would be better off with 4 controllers.

If we are assuming no shading (or very little shading), then series panels make more sense for a couple of reasons.
1. Higher voltages can use smaller wires and have less losses. Your panels could run in series with a %3 loss on 5AWG cable. 3AWG for a 2% loss. (assuming 40ft round trip).

2. Higher voltages usually mean the MPPT controller is more efficient. However as has already been pointed out there is a limit to this and you would be over that.

Personally, I don't think you would be better off with 4 controllers. I think your best bang for the buck would have been 2 100/30 controllers and breaking your panels into 2 banks of 2 panels in series (again assuming no or very little shading). This would give you some redundancy and a good balance of performance and cost (cheaper wire,only 2 wire runs, only 2 controllers to buy).

People will disagree with me and argue for 4 controllers or that parrallel is the way to go. However, our real life experience with series panels has convinced me its the way to go (with limited shading). We have lived and cruised full time for over 2 years now and all our banks are in series. However, our installation has very limited shading (mast, stays, haylards) for only the early part of the day.

[GTom]

Indeed, one advantage (~50V working Voltage vs 17V) may compensate for the occasional inefficiency due to partially shaded panels in your stack.

I collected a few arguments pro & con / few controllers vs many:
(-) 1. if you happen to buy a large panel (e.g. that 370W LG) for your tilting davit mount, you're out of lack, the well respected 75/15 will miss 20+% of the power (correct me if you can use two controllers for a single panel)
(+) 2. Price speaks for the 75/15 though: these are 2.5-3x cheaper than the 100/30.
(-) 3. Wiring speaks for a single controller: obviously more controllers need more wiring, more wire glands, more mess.
(+) 4. Multiple controllers = Redundancy. Though you can keep a 50$ PWM controller in a Faraday cage and just use it until the mailman arrives with your nice new blue box. I can imagine, it sucks if it happens 200 miles West of the Cape Verdes, but I have no knowledge of any boats that sunk mid-Atlantic, because her solar efficiency was 20% down...
(.) 5. Partial shading: here a lot depends on your bypass & blocking diodes too.

[noelex 77]

Originally Posted by travellerw

We have a small bank (200W) of cheap Chinese panels (HQST brand). They have a VMP of 16V so essentially 12V panels. They are connected to a Victron 75/15

Thanks for the report. It would be great to see a lot more reports such as this from people that have tried parallel and series connection, especially with the Victron controllers.

Is the Vmp of 16v you are mentioning from the specifications (in which case it is very low) or from real life measurements (in which case it is lower than average but not so unusual )? As the Victron controllers have a higher than normal start up voltage, I think this lower Vmp was the likely cause of you measuring series connection as better when most people report the opposite.

It would be good to have more real life examples, but I would recommend some caution teeming up the Victron controllers with those “12v” panels that have a low Vmp when wired in parallel, especially in hot climates where there is not much airflow under the panels.

[noelex 77]

Originally Posted by john61ct

Victron MPPT should IMO be matched with higher-voltage panels so they don't need to be series'd, 16Vmp is likely too low.

Two “12v” 100w panels are the same as one “24v” (72 cell) 200w panel so your statement does not completely make sense, but I agree a Vmp of 16v is a little low for the Victron controllers.

However, with the limited space, high efficiency panels are a great bonus on a boat. A small number of high voltage panels are also high efficiency panels and recommending these is good advice.

[travellerw]

Originally Posted by noelex 77

Thanks for the report. It would be great to see a lot more reports such as this from people that have tried parallel and series connection, especially with the Victron controllers.

Is the Vmp of 16v you are mentioning from the specifications (in which case it is very low) or from real life measurements (in which case it is lower than average but not so unusual )? As the Victron controllers have a higher than normal start up voltage, I think this lower Vmp was the likely cause of you measuring series connection as better when most people report the opposite.

It would be good to have more real life examples, but I would recommend some caution teeming up the Victron controllers with those “12v” panels that have a low Vmp when wired in parallel, especially in hot climates where there is not much airflow under the panels.

The 16Vmp is from the specs.. In real life, I actually see lower than that.

Turns out I didn't actually switch that bank back to series (thought I did) and it has been running that way since February. Absolutely no problems with those panels teamed up to a Victron controllers. They have been performing just fine for almost 2 months, besides a performance loss (that bank has never broken 165W in the last 2 months). Those panels have never been hot when I have checked them.

However, I'm a little confused. I don't think "most people" report better performance on parallel than series. Sure, if the boat has loads of shade then parallel is a smarter config. On a lightly shaded boat, series just makes sense.

What I would love to see, is someone take 4 idential panels into an empty parking lot or unshaded space. Hook 2 up in series, then 2 up in parallel. Both solar banks hooked to their own LFP battery that is cycled the same every night (e.g 100Ah pulled every night). Then catalog the data for a month. That is data I would like to see.

[noelex 77]

Originally Posted by travellerw

The 16Vmp is from the specs.. In real life, I actually see lower than that.

Thanks. That certainly explains why you have found series better. A panel with a specified Vmp of 16v on its own, or in parallel, is too low to use with a 12v battery bank no matter what type of controller is used PWM or MPPT.

The results with a typical “12v” panel with a much higher Vmp would have almost certainly favoured parallel conection at least with most controllers.

[noelex 77]

Originally Posted by travellerw

However, I'm a little confused. I don't think "most people" report better performance on parallel than series. Sure, if the boat has loads of shade then parallel is a smarter config. On a lightly shaded boat, series just makes sense.

I agree. The question of whether series or parallel connection is best is not entirely clear cut , but by far the overwhelming reports from people that have tried both on a boat is that parallel is superior.

Originally Posted by travellerw

What I would love to see, is someone take 4 idential panels into an empty parking lot or unshaded space. Hook 2 up in series, then 2 up in parallel. Both solar banks hooked to their own LFP battery that is cycled the same every night (e.g 100Ah pulled every night). Then catalog the data for a month. That is data I would like to see.

More experimentation would be great, but with no shadows, series and parallel connection and for that matter the results with single or multiple controllers should be very close to identical (providing all options are wired correctly). The few experiments that have been reported confirm this.

[GTom]

Originally Posted by noelex 77

More experimentation would be great, but with no shadows, series and parallel connection and for that matter the results with single or multiple controllers should be very close to identical (providing all options are wired correctly). The few experiments that have been reported confirm this.

Provided you have at least 18V Voltage to work with