best use of PWM with Renogy 100W panels

[frater secessus]

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:


http://img.mousetrap.net/misc/100D__54543.1503503640.1280.1280__38558.1503694532.500.750.jpg
http://img.mousetrap.net/misc/100D__54543.1503503640.1280.1280__38558.1503694532.500.750.jpghttp://img.mousetrap.net/misc/RNG-100P-7__71447.1454451631.500.750.jpg
Here is some math on their lab output at various setpoints:

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.

 

[jimindenver]

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.

 

[DLTooley]

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.

 

[John61CT]

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.

 

[Trebor English]

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.

 

[John61CT]

Tilting helps a lot, obviously more so in winter, especially farther from the equator.

 

[frater secessus]

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.

[img=150x104]https://www.researchgate.net/public...urves-and-b-output-power-and-output.png[/img]

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.

 

[jimindenver]

A tilted and tracking panel will provide up to twice the power as a flat mounted panel.

 

[DLTooley]

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???)

 

[jonsun]

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.

 

[Weight]

PWM questions. Use large wires between the panel and controller. Use large wires between the controller and battery bank. I have Renogy panels 10 awg extended with 8 awg to the junction box. Then 4 awg to the controller. I went up one size from the awg found on wire tables. Same with the battery side. I have 4 awg to a buss bar and then 2 awg to the batteries. Lowering voltage drop is a proven method to increase charging current. I don't recommend cheap controllers. Morning Star are quality.

 

[frater secessus]

I made an pasting error in the first post.  The increased setpoints secttion should read:

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

 

[Weight]

Flooded batteries don't like high float voltage. Check your electrolyte level often.

 

[John61CT]

Remember, there is no current after insolation stops.

I believe these are workarounds for controllers that don't have sophisticated Hold Absorb algorithms, and therefore suffer chronically from premature infloatulation?

In other words, never getting the bank to 100%.

And only for banks being actively drawn down when the sun isn't shining.

If the bank is just sitting in maintenance mode then likely best to reduce both Absorb and Float to lower 13.x voltage

 

[jonsun]

giving winter is coming on the high float voltage shouldn't do much excess gassing. There's just no time for it. in the spring slowly bring it down.

 

[frater secessus]

My point was that with a PWM controller holding higher voltages allows the panel to generate more power, as it is closer to Vmp. This was items #2 and #3 in the original post.

 

[John61CT]

Increased power output is fine, but it does need the qualification to make sure the resulting input at the bank does not greatly exceed its mfg specs.

Especially for chemistries other than lead FLA, many very expensive bank types can get seriously damaged by overvoltage for even short periods of time.

 

[frater secessus]

I was not interested in batteries at all with this microtopic, only how how panels, PWM controllers, and adjusted setpoints affect power production.

#3 bullet point in the first post linked to Sternwake's discussion of elevated Vfloat setpoints for deep-cycled banks.