Renogy Solar System

[jgerhard]

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

[Mustang65]

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

[Jmooney]

Originally Posted by Mustang65

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?

[Jmooney]

Originally Posted by jgerhard

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

[Subaru297]

Originally Posted by jgerhard

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.


Cheers

[Subaru297]

Originally Posted by Jmooney

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
20°C above standard conditions (25°C) 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

[SmokerBill]

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?

[Jmooney]

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.....

[Subaru297]

Originally Posted by SmokerBill

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.

[Mustang65]

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

video

[Subaru297]

Originally Posted by Mustang65

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

Interesting. Do you know why the input power changes when switching between PWM and MPPT?
The panel output should be the panel output no matter what is hooked downstream of it shouldn't it? Or do you think of the panel like a battery and the PWM controller is putting a larger draw on it thereby reducing the voltage?

That test certainly shows in MPPT's favor by 20-30% under those conditions. (Stressed battery)

Found this too....
http://www.schams-solar.de/download/...n-mppt-pwm.pdf

Shows that MPPT has a big advantage (40%) under shaded conditions. Testing procedures aren't exactly clear though. Showed 8% advantage to MPPT under most other conditions.

[Mustang65]

Originally Posted by Jmooney

Don, based on my configuration ( 2 100w panels in parrellel. ) would you covert to a MPPT controller?

I would look at it from your current usage/charging performance. If the PWM is meeting all your current needs, I would see no reason for upgrading to an MPPT controller. If you do a lot of dry-camping in the early spring or late summer fall (angle of sun), then it would help you. If you plan on adding more loads and longer dry-camping outings I would say go for it. If you do decide to upgrade to MPPT, temporarily wire them both in and switch between them at first to see what the actual benefits are. Then you can give us the actual numbers.

Oh, you asked if I would convert... I would probably say yes because I would pick up the 25% of loss from each panel.
Don

[Mustang65]

Originally Posted by Subaru297

Interesting. Do you know why the input power changes when switching between PWM and MPPT?
The panel output should be the panel output no matter what is hooked downstream of it shouldn't it? Or do you think of the panel like a battery and the PWM controller is putting a larger draw on it thereby reducing the voltage?

I would lean more to the internal resistance of the PWM and the MPPT controllers on the input side that is altering the panel output.

I have been monitoring my 250 watt panel output and granted there will be some loss due to panel temperature, but by the time the panels heat up the batteries are already in FLOAT mode, so there is no effect on the charging.

It will be interesting this summer (when we spend the summer in Hiawassee GA) as I am going to connect the Arduino to both the panel output and the MPPT output to monitor the voltages, amps, panel temp along with the suns power (insolation) in real time. Should have some interesting output to report back on.

Don

[Subaru297]

Just found this after posting my question above. I have never read it explained like this before but it would explain the input power diferential and the 20-30% power boost seen when the batteries are discharged a fair amount.

MPPT vs PWM Charge Controllers
MPPT (Maximum Power Point Tracking) charge controllers are designed to harvest the maximum amount of power from the solar array. It is generally accepted that even the most basic MPPT controllers will provide an additional 10‐15% of charging capability compared to a standard PWM regulator. In addition this efficiency, there are several other important differences and advantages between PWM & MPPT technologies.pwm controller

PWM Charging

Traditional solar regulators featuring PWM (Pulse Width Modulation) charging operate by making a connection directly from the solar array to the battery bank. During bulk charging when there is a continuous connection from the array to the battery bank, the array output voltage is ‘pulled down’ to the battery voltage. The battery voltage adjusts slightly up depending on the amount of current provided by the array and the size and characteristics of the battery.

The Vmp (maximum power voltage) is the voltage where the product of the output current and output voltage (amps * volts) is greatest and output power (watts = amps * volts) is maximized. Module wattage ratings (e.g. 100W, 205W) are based on Pmp (maximum power) at Vmp under standard test conditions (STC). Using a nominal 12V system as an example, the battery voltage will normally be somewhere between 10 – 15 VDC. However, 12V nominal solar modules commonly have a Vmp(STC) of about 17V. When the array (having Vmp of 17V) is connected to the batteries for charging, the batteries pull down the output voltage of the array. Thus, the array is not operating at its most efficient voltage of 17V, but rather at somewhere between 10 and 15V.

Because these traditional controllers rarely operate at the Vmp of the solar array, potential energy is being wasted that could otherwise be used to better charge the battery bank and maintain power for system loads. The greater the difference between battery voltage and the Vmp of the array, the more energy is wasted by a PWM controller during bulk charging.

MPPT Charging

MPPT controllers are designed to quickly and accurately determine the Vmp (maximum power voltage) of the solar array. MPPT controllers ‘sweep’ the solar input to determine the voltage at which the array is producing
the maximum amount of power. The controller harvests power from the array at this Vmp voltage and converts it down to battery voltage, boosting

Copied from here...
MPPT vs PWM Charge Controllers

Good discussion by the way. I have learned something new and understand MPPT a bit better in the process. I still feel the need to give a little love to the lowely PWM controllers though....

Cheers

[Mustang65]

Originally Posted by Subaru297

I still feel the need to give a little love to the lowely PWM controllers though....

Cheers

Don't get me wrong.. as I say if the PWM controller is doing what you need it to, then there is nothing wrong with using one. I have always been one to try and extract every bit of power that is made available.. and that is my driving force.

Don

[Subaru297]

And I'm a cheapskate so that is my driving force!

I am not toying with the idea of switching out my PWM controller at all. Just trying to present pro's and con's to other people reading here that are trying to make the decision. My SC-2030 and TM-2030 are paired and do exactly what I need them to do.
In reality this is almost a pointless argument anyway. If I was riding the cusp of getting my batteries charged each day and almost running them down each night then I would certainly gain from the 10-15% boost I would get from MPPT. As is I think I am charged shortly after mid day so any power after that is essentially wasted so I would just be wasting more with MPPT.

Another good read...
Frequently Answered Questions - Bogart Engineering

Click on the MPPT vs PWM question.

Here is another attractive low cost MPPT controller and it is built and designed in USA!
http://www.roguepowertech.com/produc...pt/mpt2024.htm

Looks like it has interesting logging capabilities built in too.


Cheers