Solar Voodoo ? 24v Panels in a 12v System ?

[twistedtree]

Originally Posted by noelex 77

There is very little real world information on MPPT gains and losses on boats, so your results are interesting.
A couple of questions
How did you measure the difference?
What was the average gain?
What sort of conditions gave the most gain or loss?
Thanks

My experience is on my house, not boats, but I'm not seeing why a boat should be any different in terms of the MPPT effect. Granted, on a boat the panels are always horizontal where on a house they can be faced south and tilted seasonally. That will impact the overall effectiveness of the panels, but I think at any give time the benefit of MPPT should still be there. Is there some other effect I'm not thinking of?

As for measuring, it wasn't super scientific - just a matter of watching the ammeter while the batteries are charging. At first I had a Trace C-40 PWM charger and on a sunny day would see 13-14A charge current. I later switched to an Outback MPPT charger and my charge current jumped up to around 17A. It's fair to say that's the maximum gain. It's not the average that you will get over a full charge cycle or over a full day. If you are just maintaining float charge, for example, you won't get any gain at all.

Max boost comes when the battery voltage is the lowest, so in practice that's when you are in the early part of bulk charging.

As for average gain, I can't give you a precise number because I didn't have any data logging with the PWM charger. I did with the MPPT but I'm trying to remember data that's now close to 4 years old. What I do remember is that my batteries started getting fully charged on a regular basis where they were not before. That was huge.

The real motivation for moving to MPPT, and I'd say it definitely delivered on it, was:

1) I had very limited solar resource (panels) and wanted to get the most out of them. I think this will be key on a boat since space for panels is typically very limited. Getting the most out of that space seems key. Power per square foot is probably the number to optimize on a boat. On land, it matters but power per $ usually trumps it.

2) At the time, the power gain from the MPPT cost less than adding another panel. Panels are about half the cost now, maybe even less, so this won't be as compelling now as it was back then. Also, the more panels you have, the more gain you get per $ spent on an MPPT charger. The charger is a fixed cost, but the gain depends on the number of panels you are MPPTing (pardon my butchery of english). On a boat with only two panels, adding a third panel will give you 50% more power - more than an MPPT charger will derive from the two existing panels. But on a boat you are much more likely to run into #1 above as the compelling reason.

Anyway, I'm planning to add panels to my boat over the winter, and wouldn't consider anything but an MPPT charger. I'll fit as many panels as is practical, then want to get the max utilization out of them. That means MPPT.

[noelex 77]

Originally Posted by twistedtree

My experience is on my house, not boats, but I'm not seeing why a boat should be any different in terms of the MPPT effect. Granted, on a boat the panels are always horizontal where on a house they can be faced south and tilted seasonally. That will impact the overall effectiveness of the panels, but I think at any give time the benefit of MPPT should still be there. Is there some other effect I'm not thinking of?
.

Thanks for clarifying.
Home installations are different. The panels are subject to nearly identical conditions meaning multiple panels have the same power point. Shadowing is much less common and when it does occur it will usually effect all panels equally.
The lack of a similar power point for all panels on a boat makes optimizing the output difficult. Even expensive MPPT regulators locking on to an incorrect PP are not uncommon.
The wire losses can also be substantially lower in a MPPT domestic installation similar savings are not possible on a boat.

In domestic installations the average gains from MPPT are reported to be about 10-15%. The effect on a typical yacht installation from MPPT will be less, but there does not seem to be any reliable data to back up the real gains or losses.

[twistedtree]

Originally Posted by noelex 77

Thanks for clarifying.
Home installations are different. The panels are subject to nearly identical conditions meaning multiple panels have the same power point. Shadowing is much less common and when it does occur it will usually effect all panels equally.
The lack of a similar power point for all panels on a boat makes optimizing the output difficult. Even expensive MPPT regulators locking on to an incorrect PP are not uncommon.
The wire losses can also be substantially lower in a MPPT domestic installation similar savings are not possible on a boat.

In domestic installations the average gains from MPPT are reported to be about 10-15%. The effect on a typical yacht installation from MPPT will be less, but there does not seem to be any reliable data to back up the real gains or losses.

Why do the panel conditions vary so much more on a boat? In my experience with land systems, an array almost never experiences uniform shading - it's almost always partial.

If the panel location on your boat causes shading as the boat pitches and rolls then you've got a problem either way, and I agree most MPPTs won't lock on well. I imagine on many boats this is inevitable, but if it is inevitable, I'd seriously reconsider panels in the first place.

What else impacts panel shading on a boat?

[noelex 77]

Originally Posted by twistedtree

Why do the panel conditions vary so much more on a boat? In my experience with land systems, an array almost never experiences uniform shading - it's almost always partial.

If the panel location on your boat causes shading as the boat pitches and rolls then you've got a problem either way, and I agree most MPPTs won't lock on well. I imagine on many boats this is inevitable, but if it is inevitable, I'd seriously reconsider panels in the first place.

What else impacts panel shading on a boat?

Unfortunately for many boats, particularly yachts, the solar panels have to compete with the mast standing and running rigging as well as wind generators aerials etc
Often when the output of some of the panels is reduced by shade from these structures other panels will still be producing there full output
In this way solar can still provide lots of power. On my boat , as on many similar cruising yachts, solar panels provide virtually all our electricity.

[twistedtree]

Originally Posted by noelex 77

Unfortunately for many boats, particularly yachts, the solar panels have to compete with the mast standing and running rigging as well as wind generators aerials etc
Often when the output of some of the panels is reduced by shade from these structures other panels will still be producing there full output
In this way solar can still provide lots of power. On my boat , as on many similar cruising yachts, solar panels provide virtually all our electricity.

Makes sense. I guess this is where per-string or per-panel chargers would help, though cost-effectiveness would be questionable.

So in this case would you argue that matching panel voltage to battery voltage is the way to go? Hence panels in parallel, not in series? And a PWM charger?

[noelex 77]

Originally Posted by twistedtree

Makes sense. I guess this is where per-string or per-panel chargers would help, though cost-effectiveness would be questionable.

I agree. I think the ideal for a yacht would be an individual MPPT regulator (or just converter, with a central regulator) would be ideal. There have been some cheap MPPT regulators with ultra high efficiency circuitry developed by the solar car electronic people, unfortunately there don’t seem any in current production that are suitable.

Originally Posted by twistedtree

So in this case would you argue that matching panel voltage to battery voltage is the way to go? Hence panels in parallel, not in series? And a PWM charger?

I think good quality MPPT regulation probably still offers a small overall advantage, but it would nice to have some objective evidence to be sure, In boat installations there is often not room for any more solar panels so even a small gain can be worthwhile,although its rare to find a boat where similar money spent on power reduction, or alternative means of generation, would not be a lot more effective.
There have been many long threads on series or parallel connection. I believe the theory supports parallel connection or limited series connection (where panels are likely to experience the same conditions), but others disagree. Once again some controlled tests would be invaluable

[daddle]

I recently added an MPPT. If I had room I would have added more panels. But I don't have easy room for more panels so the MPPT adds about the same for comparable cost. The MPPT does about what they claim. Generally better, never worse, starts earlier in the day...

[osirissail]

Besides MPPT controllers being fairly new they are quite complicated when it comes to "sizing" the one needed for your solar array. How to Size a MPPT Solar Charge Controller - AltE

And, as best as I can determine from the various solar equipment websites, they vary from twice to 4 or more times more expensive than PWM charge controllers. All that for "up to 30%" more input to your batteries? Then again solar is hardly cost effective in and of itself. Only in applications where other battery charging systems (alternators, shore power chargers, etc.) are not always available does it make sense.

[coldar1]

I have an existing array of 3 X 12V X 250W REC solar panel. Each pos lead goes to an individual circuit breaker switch then to a common pos feed to my Outback FlexMax 80 MPPT. The Neg leads go to a common bus and then to the MPPT. In good sunshine, I regularly see 13.8V @ +40 Amps going to the 3 X Rolls AGM batteries. Question: I can buy a 24V X 255W solar panel of the same dimensions as my existing panels, but I'm unsure if I can mix a 24V panel with the 3 X 12V panels. Any comments or guidance would be appreciated.

[OceanSeaSpray]

Originally Posted by coldar1

I have an existing array of 3 X 12V X 250W REC solar panel. Each pos lead goes to an individual circuit breaker switch then to a common pos feed to my Outback FlexMax 80 MPPT. The Neg leads go to a common bus and then to the MPPT. In good sunshine, I regularly see 13.8V @ +40 Amps going to the 3 X Rolls AGM batteries. Question: I can buy a 24V X 255W solar panel of the same dimensions as my existing panels, but I'm unsure if I can mix a 24V panel with the 3 X 12V panels. Any comments or guidance would be appreciated.

The short answer is no.

The Vmp of each "feed" at the tie-in point would need to be about the same, so you would need to check whether you can match the new 255W panel Vmp by placing two 250W REC panels in series, and you would still end up losing a REC panel you can't use...

It is a can of worms and not a very good idea. If your REC panels are 36-cell units, you need to stick with 36-cell units to expand the system in parallel. Somehow coming up with some combination where you only have panels of the same current rating in series and only have parallel "series strings" that result in the same Vmp at the controller input would be technically ok, but a hassle practically.

If you don't do that, your high voltage panel will be operating completely inefficiently, pushing current through the bypass diodes of the REC panels and you would be lucky to get half of its rated power.

[zboss]

Originally Posted by noelex 77

I agree. I think the ideal for a yacht would be an individual MPPT regulator (or just converter, with a central regulator) would be ideal. There have been some cheap MPPT regulators with ultra high efficiency circuitry developed by the solar car electronic people, unfortunately there don’t seem any in current production that are suitable.

I use a Genasun for each of my 4 panels. Highly efficient and relatively inexpensive but you give up some features.

https://genasun.com/products-store/m...e-controllers/

I think I paid $130 each.

[nimblemotors]

Originally Posted by noelex 77

I think the ideal for a yacht would be an individual MPPT regulator (or just converter, with a central regulator) would be ideal. There have been some cheap MPPT regulators with ultra high efficiency circuitry developed by the solar car electronic people, unfortunately there don’t seem any in current production that are suitable.

Yep, I've got a new 'microMPPT' controller that connect to each panel and generates the same voltage output from all panels so they can be in parallel,
and reported to be 98% efficient.
I've been surprised they have not been available, but shading is normally not such a big deal in most fixed solar installations where they just remove anything that causes shade. Not so for a sailboat!

[socaldmax]

Originally Posted by OceanSeaSpray

The short answer is no.

The Vmp of each "feed" at the tie-in point would need to be about the same, so you would need to check whether you can match the new 255W panel Vmp by placing two 250W REC panels in series, and you would still end up losing a REC panel you can't use...

It is a can of worms and not a very good idea. If your REC panels are 36-cell units, you need to stick with 36-cell units to expand the system in parallel. Somehow coming up with some combination where you only have panels of the same current rating in series and only have parallel "series strings" that result in the same Vmp at the controller input would be technically ok, but a hassle practically.

If you don't do that, your high voltage panel will be operating completely inefficiently, pushing current through the bypass diodes of the REC panels and you would be lucky to get half of its rated power.

This is correct.

However, you could add the panel, and connect it to it's own cheap MPPT controller. If you have the room and would still like to get another 15-17 amps, that's what I would do.

Check out the Eco-worthy.com website, they sell a $102 controller I'm very impressed with. I have no affiliation, but I've installed 5 of these so far and we're all impressed with the construction, output and flexibility of these things, especially for the price.

You can set absorption and float voltages in .1v increments, it can control a separate load based on multiple parameters, etc. It also displays panel output in watts, battery V, charging current in amps and cumulative total output.

[goboatingnow]

Gains from MPPT is a very mixed bag. for example if you have a series of parallel panels where through heating etc Vmp is close to the required battery charging voltage , then Mppt will do nothing for you

If on the other hand you have a situation where the Vmp is significantly different then a Mppt process can avail of the non linear VI curve of a PV to maximise power transfer

It should be pointed out that Mppt is going useful if you system needs enough power so that the panel is operating close to max obtainable capacity for the given level of illumination

I think people are mixing up voltage conversion and maximum power point tracking

dave

[socaldmax]

Based on what?