MPPT vs PWM cotrollers?

[wiekeith]

Originally Posted by GTom

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?

I think it goes back to the earlier days of solar panels and has been propagated as fact ever since.

I'm using a Tracer MPPT controller, not sure which model as don't I have the paperwork at hand, but it would have been suitably selected for 240w of solar (I've never updated the firmware). Probably worth mentioning, as I think has already been done on this thread, that the stated current rating of controllers often refers to the max it can output to the batteries, not the max from the panel array, which is a different thing.

[john61ct]

Originally Posted by Pete7

So who stated a limit of 65w to you

So sorry that was a typo, I was talking about max voltage "do not exceed 65V total with a 75/15"

Note that 220W max is on **output** and actually varies, derived from 15A so depends on voltage.

A 300W panel **input** would be safe, but some power "wasted" in optimum insolation conditions. Benefit is much higher average output, getting the bank full earlier in the day, etc.

[john61ct]

Originally Posted by wiekeith

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.

Yes in stable conditions and panels with bypass diodes the MPPT **may** be able to salvage more output than usual.

In many other scenarios I've seen 80% power loss from 20% shading.

Where the shade is moving it will be much more difficult for the SC to settle on a MPP.

Obviously if some shading is inevitable, so be it. But it is worth doing whatever you can to ensure it's either happening or not, not accepting it as a continuous issue.

Note also with the advent of LFP banks becoming more mainstream, having any dino juice charge source running regularly anyway can completely eliminate any need for solar at all.

[GTom]

Originally Posted by john61ct

A 300W panel **input** would be safe, but some power "wasted" in optimum insolation conditions. Benefit is much higher average output, getting the bank full earlier in the day, etc.

Is there a noticeable drawback under non-ideal conditions (let's say 10% insolation) if you use e.g. the 100/30 controller instead of the 75/15? Datasheets say they both have 10mA consumption.

[wiekeith]

Originally Posted by john61ct

Yes in stable conditions and panels with bypass diodes the MPPT **may** be able to salvage more output than usual.

In many other scenarios I've seen 80% power loss from 20% shading.

Where the shade is moving it will be much more difficult for the SC to settle on a MPP.

Obviously if some shading is inevitable, so be it. But it is worth doing whatever you can to ensure it's either happening or not, not accepting it as a continuous issue.

Note also with the advent of LFP banks becoming more mainstream, having any dino juice charge source running regularly anyway can completely eliminate any need for solar at all.

I don't understand what you mean by "**may** be able to salvage more output than usual" - could you expand on that?

I see what you mean about the moving shading though; if clouds, for example, are moving faster than the MPPT controller takes to re-adjust, then it will never adjust - a good point that I'd not considered. But surely that would also apply if the panels were in parallel? In which case, ironically, maybe a PWM controller would be more effective?

[Adelie]

Originally Posted by john61ct

. . . .
Note also with the advent of LFP banks becoming more mainstream, having any dino juice charge source running regularly anyway can completely eliminate any need for solar at all.

I see that as only being correct if you have the money for a really heavy duty alternator and charge controller or have moderate or low electrical needs.

Let’s say you motor on and off your anchorage daily totaling 1 hr per day.
With a standard 40-60amp alternator that means you make 40-60amp-hr electricity of which you get back 35-55amp-hr after going thru the battery.

I see a lot of people’s power budgets in the 100+ amp-hr range per day.
That means they need to run the motor an EXTRA 2 hours per day or pony up for a high output alternator and controller and probably serpentine pulleys and belts to handle the increased loads.

If you are sitting at anchor for an extended period or on passage under sail then that means running the motor when solar means you would do so infrequently or not at all.

[mikedefieslife]

Originally Posted by GTom

Is there a noticeable drawback under non-ideal conditions (let's say 10% insolation) if you use e.g. the 100/30 controller instead of the 75/15? Datasheets say they both have 10mA consumption.

Cost. The 100/30 is double the price.

[GTom]

Originally Posted by wiekeith

I see what you mean about the moving shading though; if clouds, for example, are moving faster than the MPPT controller takes to re-adjust, then it will never adjust - a good point that I'd not considered. But surely that would also apply if the panels were in parallel? In which case, ironically, maybe a PWM controller would be more effective?

The 30 seconds you mentioned sounds perfectly fine for a sailboat, I don't think you want to change course every minute.
Speaking of clouds, if there are many of them, you have diffuse light and not much partial shading. By no means am I advocating putting the first panel under the boom, but once the "premium spots" (arch/stern poles, sunny side) filled, I wouldn't be shy populating the top of the bimini and the foredeck. Panels there could help exactly when the most help is needed: under clouds...

[GTom]

Originally Posted by mikedefieslife

Cost. The 100/30 is double the price.

That's correct, however, if further upgrades are panned (even a tilting mechanism) it's not a waste of money to oversize the SC a bit. For =<300W flat panels I agree, 75/15's should be plenty, but efficiency growing, the "old" 270W panel size yields 330W, even 360W now and we don't know about the "day after tomorrow". What my concern is, 160W "small" panels - a 75/15 is an overkill for a single one but will definitely fall short for a tilted, non-shaded pair of them.

[john61ct]

Originally Posted by GTom

Is there a noticeable drawback under non-ideal conditions (let's say 10% insolation) if you use e.g. the 100/30 controller instead of the 75/15? Datasheets say they both have 10mA consumption.

Doubt it, those Dutch engineers likely optimize best they can

I just don't like paying that much more, and prefer the 1:1 that an $85 SC allows.

[john61ct]

Originally Posted by Adelie

I see that as only being correct if you have the money for a really heavy duty alternator and charge controller or have moderate or low electrical needs.

Yes of course investment is required no matter what *type* of energy source.

Just with lead we've been conditioned to think in terms of 5+ hours per day, 80% of which is at such low amps not worth burning dino juice.

LFP means just an hour or two a few times a week can give us all the juice we need to remain silent rest of the time if we choose, without bothering with a single pesky panel.

And there are very robust setups for not too much money if you have the HP, pump out kW rather than solar's puny outputs.

Not saying for everyone, just reminding of the option, from a big picture POV.

[missourisailor]

I think that it pretty much has been settled and shown, that MPPT does have advantages over PWM controllers.

Also most manufacturers, retailers and experienced installers recommend a controller for each panel to deal with shading issues. That, truth be told, all of us sail boaters have to deal with at one time or another.

To me the larger question is how to accomplish this “one controller per panel”, scenario?

Victron is the only major SC manufacturer’s that makes one that is truly water proof. But it has placement restrictions. So this means that all of the controllers must be located below deck, out of the weather.

Also, most cheaper ones have no battery temp terminals and rely on physical SC temp. Meaning that they need to be placed near the batteries.

All of this means that you must run wires all the way from the panels to the SC’s. Which are located near the batteries.
In my case that is 5 sets of 10ga, duplex wire, over 25 feet each.
That’s the small problem.
The larger one is how to get them through the deck in a water tight fitting. Lots of solutions as there are hundreds of water proof fittings to choose from. But most suppliers only recommend 1 cable per fitting, meaning five holes in the deck. Something that I’m really not ready to do.

So, even though one SC per panel is ideal, for me it’s not realistic.
Meaning that I’m going “old school” and wiring the panels in parallel using blocking diodes to help counter the effects of shading. All panel wiring will be routed to a “above the deck” junction box which will contain the diodes. From the junction box, two 4ga cables will be routed through the deck to the SC. A SC that has an external battery temp probe like the Blue Sky 3000i.

Now a question for the gaggle.

Will using one Schottky diodes (with their 3/10th of a volt drop) per panel, really make that much of a difference on my 17.1Vmpp/5.9Impp panels ?

Simple math tells me that at rated current, they will still be capable of supplying 99watts vs 101 watts. Assuming I did not bone something, I’m willing to live with a 2 watt loss.

[noelex 77]

Originally Posted by missourisailor

Also, most cheaper ones have no battery temp terminals and rely on physical SC temp. Meaning that they need to be placed near the batteries.

This is annoying. I think the best solution is to disable the temperature compensation and alter the charging parameters manually.

Lead acid batteries installed close to waterline will not alter temperature a great deal and a few periodic changes to compensate for the different seasons is all that is usually needed in practical terms.

The charge parameters can be easily done via bluetooth and battery temperature can be measured with an IR thermometer.

Originally Posted by missourisailor

Will using one Schottky diodes (with their 3/10th of a volt drop) per panel, really make that much of a difference on my 17.1Vmpp/5.9Impp panels ?

Blocking diodes achieve very little in this application. The resistance of shaded cells is very high for most panels. It can be measured quite easily: just connect a panel (covered or at night) to a 12v battery. The discharge current will give you some idea of the likely protection offered by a blocking diode if one panel is in deep shade. The discharge current for most solar panels is very small.

The major advantage of multiple SC is correct tracking of the power point of each panel. Installing blocking diodes to a single SC does not help acieve this aim.

[missourisailor]

Originally Posted by noelex 77

This is annoying. I think the best solution is to disable the temperature compensation and alter the charging parameters manually..

On Victron SC you can change charging profiles and disable temp.. But on other popular brands, you can not.

Originally Posted by noelex 77

Blocking diodes achieve very little in this application. .

Yeah, I don't understand your comments.
I realize that a "shaded panel" offers high resistance path to other current sources, but I'm getting the impression that you are stating to hook them up in parallel and forgo the blocking diodes.
This goes against everything that I have experienced and read.
Am I missing something?

[john61ct]

Bypass diodes are for the shade issue, not blocking diodes, and used for serial'd panels not parallel.

Blocking diodes aren't usually needed these days, built into SCs.