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Old 04-03-2018, 11:44   #1
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MPPT vs PWM cotrollers?

I see most budget solar offers include MPPT controllers, higher priced ones sometimes PWM. How much is the advantage PWM has over MPPT?

I saw claims, but those are obviously from vendors, wanting to sell their stuff at 2x the price. In case the +30% claims are real, this of course worth but for another 5% I wouldn't bother investing more $$ in decaying electronics.

I expect running ~3-400Wp worth of panels to charge a 300Ah lead-acid bank.
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Old 04-03-2018, 11:59   #2
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Re: MPPT vs PWM cotrollers?

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I see most budget solar offers include MPPT controllers, higher priced ones sometimes PWM. How much is the advantage PWM has over MPPT?
As I understand it, it's the other way around i.e. MPPT controllers offer better efficiency than PWM controllers, and usually they cost more.

Before making a similar decision myself a couple of years ago I did a search of the forum and found some excellent threads on the topic.
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Old 04-03-2018, 12:25   #3
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Re: MPPT vs PWM cotrollers?

The other part you jeed to think about is which panels. If they are larger panels (cheap $/watt) that are going to need to operate at high voltage you need aMppt controller to step it down.

In the nd installing no solar is a pita and a lot no term investment, use the good stuff right at the start!
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Old 04-03-2018, 12:32   #4
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Re: MPPT vs PWM cotrollers?

MPPT is the premium controller. In the RV world it's cheaper to add another solar panel than spending the money on MPPT. With a sailboat the space for solar has more limitation so MPPT is the way to go.
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Old 04-03-2018, 12:43   #5
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Re: MPPT vs PWM cotrollers?

My understanding and my research found that MPPT was generally superior to PWM. This left me wondering why anyone buys PWM. The price difference for the small controllers I was looking at was small, approaching insignificant.
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Old 04-03-2018, 12:50   #6
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Re: MPPT vs PWM cotrollers?

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The other part you need to think about is which panels. If they are larger panels (cheap $/watt) that are going to need to operate at high voltage you need aMppt controller to step it down.
Looking at the real estate (33' mono), I see 100-200Wp panels viable. Maybe I have space for a nice 330W panel but I suspect I could place <200W panels smarter and more exposed to the sun. However, peak power is not my concern, goal is a well balanced performance during the day. The system has to perform fair in cloudy days and mornings/afternoons - in real life I'd profit more from 6A vs 5A in a cloudy day than from 30A vs 25A at noon.


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In the nd installing no solar is a pita and a lot no term investment, use the good stuff right at the start!
Kind of expected to ditch the whole thing in 4-5years when panel efficiency reaches 50%

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With a sailboat the space for solar has more limitation so MPPT is the way to go.
That was my line of thinking too. Of course, 5-10% effective Ah doesn't matter, but above 15% I definitely consider sacrificing some $$.

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My understanding and my research found that MPPT was generally superior to PWM. This left me wondering why anyone buys PWM. The price difference for the small controllers I was looking at was small, approaching insignificant.
True, so far I was mostly looking at full panel+controller+etc sets, but Ebay&Amazon are full of MPPT controllers 40A<200$, this one apparently getting nice reviews. Maybe worth If I pick the parts myself...
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Old 04-03-2018, 13:38   #7
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Re: MPPT vs PWM cotrollers?

Yes you have it backwards.

Quality recent featureful controllers are MPPT, Victron 75/15 is under $100

If you think that's expensive, go with PWM, but probably sacrificing 20% or so of power output.

Also stick to panel Vmp rated not too much higher than the charge setpoint you want, say 22V max for 12V, but you'll get more watts from 18-19V instead.
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Old 04-03-2018, 13:48   #8
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Re: MPPT vs PWM cotrollers?

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Yes you have it backwards.

Quality recent featureful controllers are MPPT, Victron 75/15 is under $100.If you think that's expensive, go with PWM, but probably sacrificing 20% or so of power output.
By no means . Just the local solar stores near me showcased 500€+ units, which made me thinking. BTW, 30A with some reserve would be my guess for 300W panel. In partial shading situations though maybe I should be thinking about 2-3 controllers, thus the Victron comes in the picture?


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Also stick to panel Vmp rated not too much higher than the charge setpoint you want, say 22V max for 12V, but you'll get more watts from 18-19V instead.
^^
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Old 04-03-2018, 14:01   #9
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Re: MPPT vs PWM cotrollers?

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By no means . Just the local solar stores near me showcased 500+ units, which made me thinking. BTW, 30A with some reserve would be my guess for 300W panel.

^^
Think more like 18A on a really good day with no shading for 300W

The victron bluesolar mentioned are great
https://www.victronenergy.com/solar-...llers/mppt7510

I made a mistake and got 75/10 instead of 75/15 but it's a rare moment that the current gets near 10A from 2 x 100w panels with angle & shading. 10A is max output, not input.

With a wifi or Bluetooth dongle you can set up and see a months worth of data on a tablet or laptop.
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Old 04-03-2018, 14:20   #10
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Re: MPPT vs PWM cotrollers?

I lost a PWM controller once and replaced it with an MPPT. This was on nominal 12 volt panels where the maximum power voltage was around 17v in full sun and even less in partial sun. It was a very rare occasion when I saw more amps going into the batteries than coming out of the panels. I have replaced my panels and controllers with panel with an MPP voltage in the 36 volt range and this is where MPPT makes sense. If I didn't have an MPPT controller the batteries would drag the panel voltage way below their maximum power point. Even on cloudy days I am getting some battery charging. If the panels you get are nominal 12 voolt panels, I doubt the output difference is worth the cost.
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Old 04-03-2018, 14:23   #11
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Re: MPPT vs PWM cotrollers?

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Think more like 18A on a really good day with no shading for 300W

The victron bluesolar mentioned are great
https://www.victronenergy.com/solar-...llers/mppt7510

I made a mistake and got 75/10 instead of 75/15 but it's a rare moment that the current gets near 10A from 2 x 100w panels with angle & shading. 10A is max output, not input.

With a wifi or Bluetooth dongle you can set up and see a months worth of data on a tablet or laptop.
Sounds good! The 15A is really appealing for <100$. However, I am thinking if I want to upscale in the future, the 30A model is ~230$ now.

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replaced my panels and controllers with panel with an MPP voltage in the 36 volt range and this is where MPPT makes sense...If the panels you get are nominal 12 volt panels, I doubt the output difference is worth the cost.
Thanks Bill! I am in the fortunate situation of having nothing at the moment, thus I can select all elements I want. Will stay away from 12V panels, and won't wire them in parallel then...
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Old 04-03-2018, 14:31   #12
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Re: MPPT vs PWM cotrollers?

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Sounds good! The 15A is really appealing for <100$. However, I am thinking if I want to upscale in the future, the 30A model is ~230$ now.
Worth considering more than one controller for more panels so if one set is shaded the effect is less overall.
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Old 04-03-2018, 14:36   #13
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Re: MPPT vs PWM cotrollers?

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Worth considering more than one controller for more panels so if one set is shaded the effect is less overall.
Deal settled then
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Old 04-03-2018, 16:27   #14
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Re: MPPT vs PWM cotrollers?

Best shade handling comes from one MPPT controller per panel.

Best of course if the panels are selected to maximize SC output.

So Victron 75/15 would be a bit overpanelled with 300W, but not from a safety POV, just wasting a bit of output in peak conditions.

Upside is much higher average output in normal suboptimal ones, get the bnk to Full earlier in the day with a morning kickstart.

But more mainstream would be 220-250W max, or going to the next model up for the 300W panel, which unfortunately is also a big step up in price.
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Old 04-03-2018, 16:47   #15
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Re: MPPT vs PWM cotrollers?

Panel prices are rather odd, ~300Wp panels are usually cheaper than 100-150 ones per Watt.

Interesting point about the suboptimal conditions: I only see max efficiency on the Victron site, how much does it decrease when the input goes down to 10-20% of the peak power?

Depends how it finally adds up, one large panel might end up under the boom - there are my "suboptimal conditions" (nonideal angle+some shade). But I can definitely fit a 300W panel there without messing up the foredeck. Then the possible future upgrade is also clear: 3x100W smaller panels elsewhere hooked up on a second 75/15.
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