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Old 30-01-2013, 14:19   #1
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PWM VS MPPT TROPICS

I am refitting my new to me Cape North 43. I have a civil engineering degree but lord help me if I can figure the electrical stuff...all the acronyms .

Here's a link to the "new" Blue Sky PWM controller I'm thinking of buying. I had to dig through the catalogue to see that it was PWM and not MPPT.

http://www.blueskyenergyinc.com/uplo...Data-Sheet.pdf

There's some exhaustive info here on CF on MPPT vs PWM and a lot of acronimonimiis (acronyms) that us dirt engineers need more schooling on.

Question: My boat will be in the tropics 7.5N. With high ambient temperature and higher panel temperature and I see the MPPT as not having much of an advantage over the PWM at high panel temp. Is this correct?

I understand that MPPT is better at lower panel output voltages?

But with higher temps there is panel output voltage loss?

Am I correct that the PWM will not be a poor decision for the tropics as far as efficiency?

I have a good alternator on the engine but want to be close to being efficient. Hope I'm not beating a dead horse. This shouldn't be a question of my total daily load or total panel watts.

Question is: is the PWM closer to or better efficiency than the MPPT in the tropics? Lotsa sun and lotsa heat.

Thanks & Peace

Brian
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Old 30-01-2013, 18:55   #2
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Re: PWM VS MPPT TROPICS

I currently run PWM controllers both at home and on the boat, both in the tropics (currently about 16N and 10N respectively). Works just fine, certainly not a bad decision.

MPPT will likely give you a bit more efficiency, but exactly how much in higher temp venues is a matter of much debate (just search the threads here to see this debate).
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Old 30-01-2013, 19:13   #3
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Re: PWM VS MPPT TROPICS

Solar panel prices have dropped and MPPT controller prices have stayed about the same. If you have the room, install another or a bigger panel and use a PWM controller. But it won't take much more panels to make up the difference, about 10-15% max.

David
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Old 30-01-2013, 19:14   #4
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Re: PWM VS MPPT TROPICS

I'd say it depends on how much elect. you need and how much space you have for panels. Sooner or later most people will wish they had more production especially if you don't want to run the engine.

My feeling is that unless the boat is really large sooner or later you are going to run out of real-estate to put panels so then the only thing left is to make those you have more efficient. We choose MPPT for both boats for that reason. Even if it only adds 5% more efficiency that is 5% more than you did have. I'm hoping ours are giving us 10% more efficiency but can't prove that. We are space limited on the small boat to 200 watts and really out of room with 480 on the larger boat. 200 works fine for us on the smaller boat and we might actually need less on the larger boat with a more efficient fridge, but I'll bet sooner or later we will find a use for all of it.

Link to the solar on the Mac....

Macgregor 26S Outside Mods page 33

Link to the solar on the Endeavour...

Endeavour 37 Electrical Mods Index

If you amortize the cost difference between PWM and MPPT over a few years it isn't that much more to go with the better controller. If you add in the expense of fuel and wear and tear running an engine for charging it is even less. I haven't seen too many people post that they put too much solar capacity on their boat ,

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Old 30-01-2013, 23:12   #5
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Re: PWM VS MPPT TROPICS

Quote:
Originally Posted by BriRich View Post
I have a civil engineering degree but lord help me if I can figure the electrical stuff...all the acronyms .

Question: My boat will be in the tropics 7.5N. With high ambient temperature and higher panel temperature and I see the MPPT as not having much of an advantage over the PWM at high panel temp. Is this correct?

I understand that MPPT is better at lower panel output voltages?

But with higher temps there is panel output voltage loss?

Am I correct that the PWM will not be a poor decision for the tropics as far as efficiency?

This shouldn't be a question of my total daily load or total panel watts.

Question is: is the PWM closer to or better efficiency than the MPPT in the tropics? Lotsa sun and lotsa heat.
Brian
At higher panel voltages, MPPT has an efficiency advantage.
At low panel temps, MPPT has an efficiency advantage.
In cloudy conditions or when there is shading across parts of the panel, MPPT has an advantage.

MPPT has a higher usage rate than PWM. That is the controller uses some power to do its thing, so for small total panel sizes that fixed amount that the controller uses is a bigger percentage of output. The reading I have been doing indicates that the break-even point is somewhere between 200-600w.

The gist of what I read is that in hot conditions, ie the tropics MPPT will have a minimal advantage.

If the panel output is under 200w, then PWM will have an advantage unless it is pretty cold and or there is lots of clouds or shading.

Sounds like a PWM would work about as well for you as a MPPT and will be cheaper.
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Old 31-01-2013, 00:12   #6
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Re: PWM VS MPPT TROPICS

We had the very worst, Chinese ebay junk, and we changed to the best, a Blue Sky MPPT and gained almost 20%.
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Old 31-01-2013, 00:41   #7
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Re: PWM VS MPPT TROPICS

I have a cheap controller and a Blue Seas MPPT on my yacht at 10 degrees North, in early morning and overcast cooler days the MPPT is better, mid day I would say the old controller is just as good if not better. My batteries are usually 80% charged so often one controller is on bulk and the other on float and visa versa. If you have panels which are not all identical 2 controllers is probably better than one I am told?
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Old 31-01-2013, 01:25   #8
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Re: PWM VS MPPT TROPICS

You are correct in assuming the advantage of MPPT is reduced at higher temperatures.
The normal cell temperature of the panels is quite high even in low air temperatures so the effect is not quite as great as might be imagined, but the average gain from MPPT appears to only be 5-10% so it does not take much loss before the difference becomes very small.
In tropical temperatures I would expect something like 5% gain from MPPT. If you can add more panels it is nearly always more cost effective to do this, even allowing for the mounting/wiring costs etc.
If you have reached your limit you need to decide if the small gain is worthwhile.

Other factors to consider:
The very efficient panels work on a higher voltage so you need a MPPT controller with these.
MPPT controllers are more complicated and therefore more likely to fail.
MPPT controller produce more radio (SSB) interference.
Large good quality controllers are mostly MPPT.


For non MPPT regulators look at the Plasmatronics range. Blue sky seem to have more than their fair share of failures.
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Old 31-01-2013, 03:52   #9
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Re: PWM VS MPPT TROPICS

I would suggest that you make your judgement between a PWM or MPPT controller based on whether you can modify the charge settings to suit your installation. Far more efficiency gains could be made by adjusting the regulator to match your battery bank and solar panel size. Without doing this all regulators will drop down to float too early and waste charging capacity.

See the following possible settings for a simple Morningstar Sunsaver MPPT controller that I have just bought and you begin to see how you could get your panels to stay in absorption mode longer without overcharging or over gassing your batteries. You need someone to make these adjustments who knows what they are doing.

Just some of the parameters that can be changed:

Absorption Voltage
The voltage at which the battery should come to full charge. For lead acid batteries, the Absorption voltage usually ranges from 14.0V (for gel type) to 15.0V (for L-16 battery types)

Float Voltage
The Float charge stage follows Absorption. After the battery has come to full charge in the Absorption stage, the SunSaver Duo will drop to the lower Float stage voltage. Gassing is reduced and the battery is maintained at full state of charge.

Float - Low Battery Threshold
When the battery has been discharged further than usual, it is common to allow a longer Absorption stage (before entering Float) on the next charging cycle. If the battery voltage drops below this threshold, the 'Time Before Float' duration is extended to the 'Time Before Float - Low Battery' duration for the next charging cycle. This extended duration allows the battery more time to recover from a deeper-than-normal discharge cycle.

Float - Cancel Threshold
When the battery has been discharged much further than usual, it is better for the battery to cancel the Float stage of the next charging cycle. If the battery voltage drops below this threshold, the Float stage is canceled for the next charging cycle. This allows the battery to remain in Absorption charging longer and to recover from the deep discharge it has experienced.

Time Before Float
Defines the length of time the controller is to remain in the Absorption stage before transition to the Float stage.

Time Before Float - Low Battery
Defines the length of time the controller is to remain in the Absorption stage before transitioning to the Float stage. This value will only be used if during the previous discharge cycle, the battery voltage dropped below the 'Float - Low Battery Threshold'.

Time Until Float Exit
Defines the length of time the controller will remain in Float after the battery voltage has dropped below the Float setpoint voltage due to insufficient solar charge or heavy system loads.
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Old 31-01-2013, 06:11   #10
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Re: PWM VS MPPT TROPICS

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Originally Posted by sailinglegend View Post
I would suggest that you make your judgement between a PWM or MPPT controller based on whether you can modify the charge settings to suit your installation. Far more efficiency gains could be made by adjusting the regulator to match your battery bank and solar panel size.
Well said
Adjustability of battery parameters makes a significant difference to charging efficiency and battery life.
Not all controllers do it the same as Morning star but look for one that enables to infinitely vary at least absorption voltage, absorption time, float voltage and return voltage.

However, this is not dependent on MPPT. There are very adjustable controllers that are not MPPT (just PWM) and MPPT regulators that are not properly adjustable.
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Old 31-01-2013, 07:23   #11
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Re: PWM VS MPPT TROPICS

One advantage that hasn't been mentioned: an MPPT controller will allow one to hook panels in series for higher output voltage, which can provide higher efficiency and use smaller gauge wires.

We get a 25% increase in daily AHr output with our panels in series vs. in parallel.

Mark
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Old 31-01-2013, 08:48   #12
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Re: PWM VS MPPT TROPICS

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One advantage that hasn't been mentioned: an MPPT controller will allow one to hook panels in series for higher output voltage, which can provide higher efficiency and use smaller gauge wires.

We get a 25% increase in daily AHr output with our panels in series vs. in parallel.

Mark
One also has the option of buying higher voltage panels that cost about $1.00 a watt vs. $1.45 a watt at the moment. We didn't, but that is an option.

I'm interested in your setup. How many panels? 12 volt or 24 volt (final voltage)? Total wattage? Controller?

I keep seeing the power to operate a MPPT coming up but the Blue Sky controllers we have (25 amp and 30/40 amp) both say

Quote:
0.35W Typical standby • 1.0W Typical charge on
That is not much and since they can boost the amperage and the PWM can't I'll stick with them. Our 25 amp Blue Sky controller sells for $180 to and a 20 amp Morningstar PWM is $80. So $100 difference about $20 more a year over a 5 years. Not much in my book .

To control the parameters with the Blue Sky you also have to add the IPN Pro-remote ($185) but it will also control multiple controllers if you have them on the network which could be good if you have shading on some panels. It also gives complete battery monitoring (volts, anps, amp/hrs, % of discharge, etc.). We don't use it but probably will add it to the Endeavour as I don't think the Link 2000 that came with it is totally working correctly.

Seems like the MPPT vs. PWM is kind of like which is best here in the states.....Ford or Chevy ,

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Old 31-01-2013, 11:17   #13
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Re: PWM VS MPPT TROPICS

Hi! This Joie, Brian's wife. I am an Electronics Engineer. He has delegated this task for me.We appreciate your posts, that's a wealth of knowledge for us!

Considering all the facts and figures stated on this blog, it is a borderline decision to get an MPPT controller for our boat. There are pros and cons about MPPT vs PWM controllers, it boils down to the facts that efficiency, interference, higher temp venues, panel sizes are all to be considered. So as the EE in the family and considering we do have a SSB (that needs some repair) we will go with the MPPT.

Thanks so much ! Cheers and kampai!

This is Brian...thank heavens my Wife knows about that stuff...I will learn. We value all the input. Many thanks. We're overseas but know how to ship stuff...where is a good source for an MPPT controller?

Thanks Gents and Ladies

Brian & Joie
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Old 31-01-2013, 11:28   #14
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Re: PWM VS MPPT TROPICS

Quote:
Originally Posted by BriRich View Post
Hi! This Joie, Brian's wife. I am an Electronics Engineer. He has delegated this task for me.
He is a very smart man
Quote:
Originally Posted by BriRich View Post
..where is a good source for an MPPT controller?
What sized solar panels?
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Old 31-01-2013, 12:09   #15
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Re: PWM VS MPPT TROPICS

Re: panel voltage, Panel voltage is rated at standard temperature, which is 68 degrees F (20 C). The temperature coefficient of the panel relates to voltage loss per degree rise above standard temperature. Roughly its about 1 volt loss for each 20 degrees f rise (11C rise).

This is part of the reason that 12V panels are rated for 17V's. So with the average panel temperature being oh 110-120 degrees F. or higher, your looking at an output voltage of 15V to 15.5V.

Also while various controllers use only a few watts or so, another loss is from heat. If you were to take the case off and feel the heat sinks (careful they could be hot) they would be warm to very warm or even hot. That heat is energy not getting to the battery. Oh its not much, maybe 10 watts or so, but its not factored in the controllers energy usage. That's for all types of controllers BTW not just Mppt

I'm not a big fan of mppt controllers, mainly because the cost of the unit could be better spent on one more panel which would provide more overall power.

One other thing, while you can put panels in series and use a Mppt controller, any shading on one panel would effect the output on all panels in series. In parallel you only loose 70-80% of the one panel. As someone who spends a whole lot of time at anchor, there will be parts of the day when one or more panels will be shaded...
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