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Old 03-24-2016, 09:46 AM   #21
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When choosing a controller, it suppose depends on your needs, and everyone will have their own opinions.

I chose MPPT over PWM because:

It has up to a 30% more charge efficiency over PWM.

It can handle higher voltage inputs (smaller wire and allowed me to run panels in series not parallel).

Flexibility.

Since I was already putting quite an investment in my solar system, I didn't want to cheap out on the controller.

Cheers!

James
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Old 03-24-2016, 10:10 AM   #22
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Here is a name brand Renogy MPPT controller that can fit a lot more SOLAR budgets. LESS than half the price of the others.

Don
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SOLAR - MPPT Renogy Charge Controller.jpg  
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Old 03-24-2016, 10:40 AM   #23
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Here is a name brand Renogy MPPT controller that can fit a lot more SOLAR budgets. LESS than half the price of the others.

Don
Don, based on my configuration ( 2 100w panels in parrellel. ) would you covert to a MPPT controller?
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Old 03-24-2016, 10:42 AM   #24
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I already know that, thanks. The battery is 4 weeks old and I'm adding the same manufacturer.
Perfect. That will be a nice package
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Old 03-24-2016, 10:47 AM   #25
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Originally Posted by jgerhard View Post
When choosing a controller, it suppose depends on your needs, and everyone will have their own opinions.

I chose MPPT over PWM because:

It has up to a 30% more charge efficiency over PWM.

It can handle higher voltage inputs (smaller wire and allowed me to run panels in series not parallel).

Flexibility.

Since I was already putting quite an investment in my solar system, I didn't want to cheap out on the controller.

Cheers!

James
If Renogy actually have data to backup the 30% more efficiency I would love to see it. If that is true it is only under a very specific voltage, temperature (very cold), time of day scenario. This 30% does not last all day.

MPPT controllers also lose efficiency in the voltage step down. Renogy actually (credit to them) provide this in their manual.

For your four 100watt panels connected in series you are around 70 volts and the controller is stepping this down to 12 volts nominal. Renogy show an max efficiency of 92%. So you are loosing 8% of your power to heat in your controller.

The low cost MPPT controllers, like what Mustang linked above, are also not adjustable so you are not charging your battery as efficiently as possible. Each battery manufacturer lists what charging specs work best for their battery to get the most efficient charging and longest life out of it.


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Old 03-24-2016, 10:50 AM   #26
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Don, based on my configuration ( 2 100w panels in parrellel. ) would you covert to a MPPT controller?
You would get a larger benefit from adding an extra panel over an MPPT controller.
You may realize some gains if you have small wiring and are experiencing large voltage losses. You would have to wire your panels in series to up the voltage and reduce amps which the MPPT controller could take advantage of.

For example. Lets use the SC2030 PWM controller I have for $129 usd and the Renogy MPPT shown above for $209 and lets use four 100 watt panels.

Connected in series for 72 volts and 5.3 amps for the MPPT controller. Volts*amps=watts = 382W
Connected in parallel for 18 volts and 21.2 amps for the PWM controller. =382W

Let’s assume that the batteries are discharged and will accept all the amps we can provide and that both systems were wired properly and voltage losses are equivalent.

It is a cold morning and the panels are producing their optimal output voltage of 18 volts. From the manual we know that the max efficiency is 92% so we are getting….
382*.92=351 watts to the batteries at 14.6 volts (bulk charge) = 24amps going into the batteries.

Same cold morning for PWM…..
21amps getting to the controller but the controller has to clip the output to 14.8 volts (voltage adjusted to match charge specs)
14.8*21.2amps= 313 watts going to the batteries.
82% efficient

So……Cold panels and dead batteries and MPPT has an 10% advantage. Pretty good.

What about after the panels warm up from the sun and it starts to get hot out. Now the voltage output is 15 volts from each panel
20C above standard conditions (25C) and panel efficiency drops ~8%. Voltage is reduced to 16.5 volts per panel

MPPT is 66.2 volts * 5.3 = 351 watts
PWM is 16.5 volts * 21.2 = 350 watts

MPPT efficiency loss of 8% and we are now at 323 Watts and 22amps.
PWM efficiency is now better (around 10%) and we get the same 313 watts and 21 amps.

So equivalent at this point. No benefit with MPPT.

If your batteries are not depleted and can’t accept the 20+ amps the panels can provide then you are wasting energy with either system.
Let me know if you see any holes in my logic or math.

Cheers
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Old 03-24-2016, 10:52 AM   #27
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After reading the last several posts, I'm guessing that if you wanted to minimize the total weight of a solar system, you'd set it up with higher voltage panels and an MPPT controller - with cost being no object, that is. Would that be correct?
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Old 03-24-2016, 12:24 PM   #28
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Well, I'm not having any trouble with keeping my array recharged every day. My consumption is well managed, and the Colorado sunshine seams to be doing its job......

Interesting stuff though.....
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Old 03-24-2016, 01:58 PM   #29
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After reading the last several posts, I'm guessing that if you wanted to minimize the total weight of a solar system, you'd set it up with higher voltage panels and an MPPT controller - with cost being no object, that is. Would that be correct?
I just had a quick look and....

100W 18 volt panel is 17.2 lbs
260W 36 volt panel is 40lbs

The pounds per watt is pretty close. The high voltage panels are typically for residential use and are pretty big.
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Old 03-24-2016, 02:00 PM   #30
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PWM vs MPPT. Here is a video that helps show the difference. It is a 40 watt panel, but even at only 40 watts you see the benefits... now add another 200 watts to the input/output the difference looks even better.
Don
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