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Old 06-03-2018, 03:51   #31
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Re: MPPT vs PWM cotrollers?

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Please do not take offense, but if you are considering "saving" $100 by using PWM when outfitting your multi-thousand dollar boat, you might as well give up now. MPPT is just so much better that there is no argument. Are you also going to photocopy charts, and use your phone GPS for navigation?

Regards Michael
If that was intended for me, I didn't know the practical difference, now 1-2 victrons are on my order list for the same price I see PWM's in the local stores. I usually don't assume the "more expensive = better" rule, but ask before.
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Old 06-03-2018, 15:16   #32
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Re: MPPT vs PWM cotrollers?

My research indicates that for smaller installations (200w) PWM is more efficient. This was from 2 different solar supply firms.
For higher wattage installations or if there is significant partial shading then MPPT with higher voltage panels is more efficient.
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Old 06-03-2018, 18:21   #33
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Re: MPPT vs PWM cotrollers?

PWM can be a little more efficient depending on the panels (lower voltage) and (pretty rare) specific environmental conditions.

99% of the time not.

That is defining "more efficient" as "extracting more charging power" from the same panel(s) in the same conditions.

Cost is not irrelevant though, and that is the PWM advantage.

But I agree in a marine context very rarely would saving a little money be worth giving up MPPT's greater power output.

It has nothing to do with the total size of the install in watts. Yes higher *voltage* panels are completely wasted with PWM.
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Old 07-03-2018, 13:53   #34
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Re: MPPT vs PWM cotrollers?

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Yes higher *voltage* panels are completely wasted with PWM.
Found this: Apparently the larger the voltage is, the larger the advantage mppt has.


In this context, I was wondering if it makes sense to use multiple smaller (e.g. 100W) panels in series instead of a larger one (e.g. 300W). For other reasons (easier to avoid shade, redundant if a panel dies) the series of small panels wins.
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Old 07-03-2018, 14:22   #35
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Re: MPPT vs PWM cotrollers?

No, best to buy panels that already run at the higher voltage.

Series'ed panels are especially crippled by even a little shade over just a small area of one panel.
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Old 07-03-2018, 14:33   #36
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Re: MPPT vs PWM cotrollers?

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No, best to buy panels that already run at the higher voltage.

Series'ed panels are especially crippled by even a little shade over just a small area of one panel.
=better to have a large 300W panel, 20% shaded, vs 3x100W panels, one of them 10% shaded? (on one controller of course)

I'll keep that in mind, so far I was leaning towards a pair of 160-200W, but there might be a place for a 330W panel under the boom - a constant ~20% shade.
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Old 07-03-2018, 14:45   #37
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Re: MPPT vs PWM cotrollers?

At the time I did my solar for the boat is was far cheaper to just add another 100 watt panel that gave 4.5 amps for $100 ish then to buy a $150-$250 MPPT controller that gives 1.5 amps more under bulk charge.

Myself I use multiple 12v panels as it seems that one is shaded nearly all the time when on the hook. Added benifit is I can run it manually with a disconnect if the charge controller takes a bath.

There is no question that a GOOD MPPT controller will provided 12-15 percent (sometimes more) more power. But if your charged up (over 90% SOC) by 1 pm anyway, it does not really make that much difference in the real world.

Mind you a poor MPPT or PWM controller is so much junk. I purchased a $40 MPPT controller years ago. When I opened it up is was just a PWM controller and did not have the circuitry of a MPPT unit. Tried it for a week and went back to my then cheaper pwm controller that had better set points and charged the bank better.
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Old 07-03-2018, 15:02   #38
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Re: MPPT vs PWM cotrollers?

I decided for the controller, I'll use Victrons - the original question is answered . Panel configuration comes next. (Brand is not crucial, all rigid panels live 10+years anyway... ) Apparently size, even mounting (shade, angle) matters for controller efficiency...

Speaking of mounting: I have yet to see a tilting panel in real life - especially one that keeps the panel always perpendicular to the sun. Mounting flat means 10%+losses even on the equator = a smaller controller (e.g. a 75/15 for 300W) wouldn't show any real life losses compared to a more expensive one.
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Old 07-03-2018, 15:08   #39
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Re: MPPT vs PWM cotrollers?

You don't want to place panels where you know they will be shaded.

Certainly never where it would be shaded even just a little bit *all* the time.

One set on P side shaded, S side not is fine.

10% shade can kill most of the actual charging output.

If you must put multiple panels per SC, parallel is better than serial, but 1:1 is best.
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Old 07-03-2018, 15:53   #40
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Re: MPPT vs PWM cotrollers?

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You don't want to place panels where you know they will be shaded.

Certainly never where it would be shaded even just a little bit *all* the time.
Right, the panels stay on the shore, settled
I don't want to start building an arch - but maybe a smaller project, like a strong pole...
The other alternative is to use long panels on the two sides, wired to a "port" and "starboard" controller.

Quote:
If you must put multiple panels per SC, parallel is better than serial, but 1:1 is best.
This also speaks for larger/higher voltage individual panels. Should have bought a bigger boat...
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Old 08-03-2018, 07:49   #41
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Re: MPPT vs PWM cotrollers?

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Series'ed panels are especially crippled by even a little shade over just a small area of one panel.
I really can't agree with this, at least not for my panels.

I connected my 3x80watt panels in series as, living in the UK, I thought the higher voltage on poor-light days would give the the MPPT controller a fighting chance.

I was, however, concerned about all the reports on the forum warning against such a configuration, so whilst I was on a swinging mooring with a cloudless blue sky (and no mast shadowing on panels) one day last May, I though I'd find out for myself.

I firstly turned off the fridge, radio etc as I didn't want them kicking-in half was through the test. The remote display of my MPPT controller was indicating it was providing 8A at 14.2V. I then covered one of the panels with a dark green bath towel. The output current from the controller dropped drastically, then after 30 seconds or so it reconfigured itself (MPPT doing it's stuff I guess) and the controller output was providing 5.8A at 13.6V.

So, the shading dropped the power output from 113.6w to 78.9w (interestingly only a 30% reduction), but absolutely did not cripple the whole bank.

I know not where the opinion that 'series panels are killed by shading' comes from, maybe before the days of bypass diodes? But I suspect it no longer applies with modern panels, not that I'm an expert on this. It would be useful if others could try it and see what results they get.

Incidentally, I'm not having a go at john61ct, just thought I'd convey my personal findings
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Old 08-03-2018, 08:08   #42
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Re: MPPT vs PWM cotrollers?

If you will just be coastal cruising on the weekends and on vacations, PWM Controllers work just fine since we don't have a lot of power requirements

I think my main power usage is for the lights and the fan I run at night during the summer.

During the sailing season, I have a 60 watt panel sorta mounted on my Aft Lazarette Locker and a 20 watt panel inside the port lazarette that I bring out when I need it like at anchor etc

Right now though, I only use the 20 watt panel to keep the batteries charged at the dock. The 60 w panel is below since I'm about to do some painting as soon as it's warm enough

I have three PVM controllers at this time. Two that I paid $12.00 for and the newest one I paid $18.00 for which has float adjustment.
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Old 08-03-2018, 08:20   #43
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Re: MPPT vs PWM cotrollers?

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I know not where the opinion that 'series panels are killed by shading' comes from, maybe before the days of bypass diodes? But I suspect it no longer applies with modern panels, not that I'm an expert on this. It would be useful if others could try it and see what results they get.
Probably the opinion roots from bad experience with earlier stage of MPPT programming? What kind of controller are you using/has it received firmware/programming updates in the past 1-2 years?

@thomm225: depends, not all coastals have access to shore power at the end of the day. Living on a swinging mooring, low-cost quays, etc...
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Old 08-03-2018, 08:42   #44
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Re: MPPT vs PWM cotrollers?

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Total power produced increases with lower temperatures, some panels go **over** Voc rating on clear cold days with reflected light. So 75/15 don't put more than 65W. I
Victron quote a maximum of 220w for the 75/15 in the latest manual in a 12v circuit and 200w in the slightly older manual. The manual does say that if you exceed this then the MPPT will hold the maximum chage to 15A. I have my 75/15 connected to a 150w solar panel without any ill effects.

So who stated a limit of 65w to you?

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Old 08-03-2018, 08:44   #45
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Re: MPPT vs PWM cotrollers?

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Found this: Apparently the larger the voltage is, the larger the advantage mppt has.


In this context, I was wondering if it makes sense to use multiple smaller (e.g. 100W) panels in series instead of a larger one (e.g. 300W). For other reasons (easier to avoid shade, redundant if a panel dies) the series of small panels wins.
Good chart but its inaccurate as it assumes a battery voltage of 24v which minimizes the advantage of MPPT. With a more normal battery voltage of 12V that line where the MPPT is of advantage move way down the graph extending the MPPT advantage even further!
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