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best use of PWM with Renogy 100W panels
#1
I was thinking about how common 100W Renogy panels are (both mono and poly) and how to extract maximum power from them with PWM controllers.

Short version

  1. The Renogy 100W polycrystalline panel  is a better fit for PWM controllers because power is generated at lower voltages.
  2. raising float from 13.2v to 13.8v on either panel will increase power output by 4.5%
  3. setting float voltage to absorption voltage per sternwake will increase power output from either panel between 6-12%
  4. PWM starts to meet MPPT output on poly when ambient temps >97F

Longer version

Here are the ones I am talking about:

[Image: 100D__54543.1503503640.1280.1280__38558....00.750.png]
[/url][Image: RNG-100P-7__71447.1454451631.500.750.png]
[url=http://img.mousetrap.net/misc/RNG-100P-7__71447.1454451631.500.750.jpg]
Here is some math on their lab output at various setpoints:

[Image: Renogy100wpower.jpg]

In actual ambient temperatures the poly panel Vmp falls to 14.8v at 103.1F degrees.  The mono panel Vmp falls to 14.8v at 136F. 

I used the temperature coefficient of VoC to calculate the panel temperature required to drop each panels' Vmp to 14.8v.  Then I used this calculator to map panel temps to ambient temps. 

Raising float from 13.2v to 14.6v for AGM yields 10.6% more power.
Raising float from 13.8v to 14.6v for AGM yields 5.8% more power.

Raising float from 13.2v to 14.8v for AGM yields 12.1% more power.
Raising float from 13.8v to 14.8v for AGM yields 7.25% more power.



Related:  PWM vs. PPT power breakeven point

In the worst case for ppt (nominal 12v panels, high ambient temps and Vabs 14.8v ), a 95% efficient PPT controller would outperform PWM on poly until 96.53F ambient and mono until 127.4F ambient.   At those temps PPT would still continue to outperform PWM in Bulk and normal Float (ie Vfloat < Vabs).  Cost/benefit is not considered here, only power output.
frater/jason in Rains county, TX
blog | Promaster van | offtopic answers
"I would unite with anybody to do right; and with nobody to do wrong" F. Douglass
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#2
I agree, Polys have lower voltage and higher amps than Monos and the excess voltage of the mono is going to be shed just like the rest of the excess voltage so you are just left with less amperage. In most cases the difference is small but it can add up with a array.
Sparky created, (Sparkles on some Saturday nights)  Max the Wonder puppy approved

2011 Ameri-lite 25 ft bunkhouse with 750w of solar and a 675 Ah bank
2003 Ford Expedition with 435w of tilting solar.
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#3
Higher voltage panels do have the advantage of providing a larger window of productive voltage in sub-optimal solar conditions.

I'm thinking a two panel in series (24v) with an mppt like the Victron is the way to go.
-Douglas Tooley

My Blog
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#4
The thread is on PWM.

Two "nominal 12V panels in series would be ~36-44V. The Victron 75/15 would be even better with three.
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#5
A couple of weeks ago I started tilting my single PWM controlled 100 watt panel.  Since whatever breeze there is now cools both sides the panel temperature is lower.  The calculator linked could account for 50% increase in incident irradiation.  A new NOCT magic number might be the fix for the 2 sided cooling problem.  Maybe it would be easier to put the panel flat again and not bother with the math.
You cannot bring about prosperity by discouraging thrift. 1 of Ten Cannots, Rev. William John Henry Boetcker, 1916.
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#6
Tilting helps a lot, obviously more so in winter, especially farther from the equator.
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#7
(10-21-2017, 09:28 AM)DLTooley Wrote: Higher voltage panels do have the advantage of providing a larger window of productive voltage in sub-optimal solar conditions.


True, even if only marginally useful.  I say this because:
  • insolation doesn't affect voltage much until it gets really bad (like 20% at daybreak)
  • but amps drop off drastically as insolation decreases
  • so by the time voltage is meaningfully affected amps have already cratered
  • even if we can get volts back up into the charging range (by using higher voltage panels or serial connections), there isn't much power (volts x amps) to harvest.  (e.g. 30v at daybreak x 0.5A is still only 15W)
  • buying higher voltage panels for a PWM controller (the type of controller this thread is about) would sacrifice real power under normal circumstances to gain tiny amounts of power during infrequent low-insolation events. I don't think that's a good tradeoff.
[Image: PV-arrays-with-different-insolations-a-V...output.png]

I personally use higher voltage panels with MPPT, so I take your point.  With MPPT the higher voltage is never (?) a problem.

Now heat does drive down panel voltage significantly which is why I included those breakeven points earlier.
frater/jason in Rains county, TX
blog | Promaster van | offtopic answers
"I would unite with anybody to do right; and with nobody to do wrong" F. Douglass
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The following 1 user says Thank You to frater secessus for this post:
DLTooley (11-01-2017)
#8
A tilted and tracking panel will provide up to twice the power as a flat mounted panel.
Sparky created, (Sparkles on some Saturday nights)  Max the Wonder puppy approved

2011 Ameri-lite 25 ft bunkhouse with 750w of solar and a 675 Ah bank
2003 Ford Expedition with 435w of tilting solar.
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#9
Thanks. I was assuming amps were constant and varying voltages were the measure of relative energy. I have a volt meter on my panel. I’ve just obtained a ammeter and have been focusing on loads. A 2x3 array of 100 watt panels on a Victron would be safely within it’s limits. (66 volts @ ~11 amps???)
-Douglas Tooley

My Blog
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#10
problem is no one is making a cheap PWM with user presets. With the victrons and tracer clones it's just as well to get the MPPT and get a little extra from it.
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The following 1 user says Thank You to bardo for this post:
DLTooley (11-10-2017)


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