Mppt Vs PWM solar chargers - Worth it?

[redbarron55]

I have just finished upgrading my 16 ft Scamp solar system from an intermittent flexible 100 Watt panel with a cheap Chinese PWM charge controller. Actually two different controllers as I though that the first was the the problem with the system.
With the failure of the system when I needed it the most on a long trip along with the need for more power for emergency communications equipment I decided to upgrade.
I installed three rigid 100 watt Grape Solar panels with the second Cheap Chinese controller and was fairly happy with the paralleled panels and charging.
As luck would have it I saw an ad in Craigslist for a 40 Amp Evever MPPT charge controller with the Blueltooth adapter and remote display.
So I wondered how well it would work in real life with those 3 100 watt solar panels wired in series.
Well today it was cloudy and the other system would basically put out Zip - Nada, (well maybe .5 amp, maybe) but this system showed about 2 amps at 55 volts and 8 Amps at 13.8.
WOO Woo!
So the MPPT lets the solar panels operate at their most efficient point for the conditions and the power is translated to the most efficient point for charging the battery.
Basically it is probably a better investment than a fourth panel.
Now to see what it does in full sun!

[gordon2]

Originally Posted by redbarron55

...
So the MPPT lets the solar panels operate at their most efficient point for the conditions and the power is translated to the most efficient point for charging the battery.
Basically it is probably a better investment than a fourth panel.
Now to see what it does in full sun!

Interesting but not quite a controlled experiment. I have to wonder what other variables affected the results.

I am sticking with a PWM controller for my very modest set up. That is based in no small part of the information from Bogart Engineering, see FAQ C-1 reposted below:

C1. The debate rages: which controller is best PWM (Pulse Width Modulation) or MPPT (Maximum Power Point Tracking). Why did you choose PWM technology instead of MPPT for your SC-2030 Solar Charger?
A very good question! They BOTH have good and bad. Plenty of hype has been written already. Here's my (Ralph's) view:

The "good" for PWM: It is simpler and lower cost technology. Under some common circumstances–it can actually deliver more amps to the battery. That could be when:

(1)days are moderate or warm, with few clouds.

(2) batteries are charging at over 13 volts, (in a 12 battery system) which they almost always are when actually CHARGING.

(3) Panel voltage is properly matched to the battery voltage, for example "12V" panels are being used with a 12V system.

PWM is actually more "power efficient" than MPPT–which means less total power loss in the controller itself. So heat sinks in the design can be smaller (and less expensive). Missing in most analysis of MPPT is that there is always a conversion loss with MPPT, which tends to be higher the greater the voltage difference between battery and panels. That's why PWM can actually beat MPPT under circumstances described above.

Some places that analyze MPPT assume that panels with 30V open circuit voltage are being used in a 12V system. Any good MPPT system will easily provide better performance in that case. They also may assume batteries are charging at 12 or even 11 volts, which is unrealistic. Lead acid batteries are typically below 13 volts only when discharging, or perhaps charging with very little charging current–meaning the actual potential gain in amps is not great.

The benefit for MPPT becomes apparent if you use panels not voltage matched for the battery. If they are not, MPPT will utilize more of the potential energy of the panels. For example, if you use 24 volt panels to charge a 12 volt battery system you must use MPPT, otherwise you would be using your panels very inefficiently. If you are trying to use PWM in that case, you are misusing the PWM technology.

Another potential benefit with MPPT is that if distance between panels and batteries is far, smaller wire can be utilized by running panels at higher voltage to the batteries. Running at twice the voltage reduces wire size to 1/4, which for a long run can be a significant saving in copper wire.

If temperatures are low enough, the slightly less power efficiency of MPPT will be compensated by the higher panel voltages, which will result in a little more battery current. But in actual measurements we made using a commonly sold MPPT solar controller, this would occur at temperatures less than 55 F degrees (in full sun, when charging at more than 13 volts), where there is a slight advantage to MPPT in my location (Boulder Creek, near the California coast). As temperature drops below that (in full sun) MPPT will get some advantage, such as could occur at high elevations in Colorado in the winter. Potentially this would be maximum about a 2.5% improvement in amps output for every 10 degrees F lower in temperature (or 4.6% per 10 degrees C colder. I'm using data from Kyocera KD-140 panels.)

There can be theoretically optimal situations (that I don't personally experience where I live) where MPPT could give some advantage: that is when solar current is present, but the batteries are quite low in charge–but because loads are high and even greater than the solar current the batteries are still discharging despite the solar current. Under these conditions the voltage COULD be at 12.5 volts, or even lower. Again, using data from Kyocera panels, ("Normal Operating Conditions") there is a theoretical maximum gain over PWM of 20% current assuming NO MPPT conversion loss and no voltage drop in the wires to the panels, at 20C (68F). With PWM, the voltage drop in the wires in this case would not affect the charging current. Now if in addition you lower the temperature to below freezing at 28 degrees F (while sun is shining) you might actually get up to a THEORETICAL nearly 30% gain while the batteries are discharging.

The only REALLY BAD part of MPPT, is all the hype surrounding it–for example one manufacturer advertises "UP TO 30% OR MORE" power harvested from you panels. If you are using solar panels properly matched to the batteries, 30% ain't gonna happen unless it's EXTREMELY cold. And your batteries have to be abnormally low in charging voltage–which tends not to happen when it's cold (unless you assume the battery is still discharging while solar is happening). Virtually all the analyses I've seen touting MPPT on the Internet ignore the conversion loss, assume really cold temperatures, assume unreasonably low charging voltages, assume no voltage drop in the wires from panels to batteries, use STC conditions for the panels (that the marketing types prefer) rather than more realistic NOCT conditions, and in some cases assume panels not voltage matched to the batteries.

The other thing that is misleading about MPPT, is that some manufacturers make meters that show both the solar current and the battery current. In almost all cases for a well designed MPPT type the battery current will be greater. The engineers making these know better, but it is implied (by marketing types?) that if you were NOT using MPPT you would be charging your batteries with only the SOLAR current that you read on their meters. That's not true, because the PWM BATTERY current should always be higher than the MPPT SOLAR current. It is the nature of the MPPT that maximum power occurs when the current is lower than the maximum, so they must operate there to get the maximum power. So to properly compare the two you need to compare MPPT with an actual PWM controller in the same circumstances.

Finally, the reason we went to PWM is that I was anticipating that panel prices were going to drop (which they certainly have over the last 5-10 years!) and that the small advantage of MPPT (under conditions where the correct panels are used for the batteries) would not justify their additional cost and complexity. So my thinking, for more total benefit per $, put your money in an extra panel rather than a more expensive and complex technology.

[redbarron55]

With the efficiency of the Epever at about 95% there is not much lost there and perhaps the PWM is more efficient as far as losses within the controller, but instead tosses away the excess power that could be generated.
The real difference is the efficiency and effectiveness under poor conditions.
With the three panels rated at 18 volt and 5 amps out (more or less) so the issue of wiring the panels in series made the hookup simpler than paralleling them (for me anyway). I had made a pair of paralleling cables which hit the floor as the panels in series just plug into one another and into the feed to the controller.
Just looking at the output the afternoon of installation overcast and under the trees there was output to the battery where with the other controller there was never any.
Very unscientific but charge current where there was none is not bad at all.
I am hoping that the system will power the camper with it's radio systems under emergency conditions and reduce the need for running the generator when gasoline is in short supply.
By the way I have read the information from Bogart and talked with them extensively some time ago and they have a good system. I especially like their power tracking system.
My system does not use the power output of the Epever controller, but rather the controller charges the battery and from there it goes through the PD 4045 power distribution system. I will be adding a second 105 Ah 12 volt battery until I get around to replacing the two 12 volt parallel with two Golf Cart 6 volt batteries.
For the price I paid for the Epever I would be hard to beat at $130.00 complete with the Bluetooth and remote monitor.

[Jim Bennett]

There is a lot more to the debate, but simply put to me by a local solar store is that regardless of type of controller the input voltage will be the same. The PMW uses up to the charge voltage required and dumps the rest while the MPPT converts all the power to a useful voltage, increasing the charge voltage a bit. In my case, I have sets of panels in series at 36V paralleled together, something a PMW controller can't even handle. The main purpose of higher input voltage from the panels is lower current and less line loss and being able to use a smaller conductor for the same wattage, though this factor in a short run like in a trailer is near moot.

If you have plenty of charge potential from your panels, a much more inexpensive PMW charge controller is likely going to work just fine. If your batteries are charged up by the end of the day, that is really all that matters.

[redbarron55]

OK, but today is sunny (for the first time since I installed the new controller and with the winter angle on the flat panels I am getting 56 volts at 2.6 amps in and 13.8 at 12.4 amps out to the battery.
171 watts to the battery and 178 in.
for 96% efficiency.
PLus I happened to have blown a 15 amp fuse to the battery when I just went out to look at the currents etc.
To each his own, but this is the best my setup has worked.
That 180 watts is not bad for the horizontal panels this time of year out of 300 watts (Name plate for the Grape GS Star 100W panels that cost $94 each) 5.56 amp and 18 volt mppt. That is 60% of max rating with the sun angle today.

[CarlD]

The conversion efficiency of the PWM and MPPT controller should be very similar because they are both Pulse Width Modulator controllers. The difference is the PWM controller only cares about the battery voltage where the MPPT controller cares about the battery voltage and the solar panel voltage. Some additional efficiency may be sacrificed in the control circuitry of the MPPT as it has more to do. As stated if the solar Voc is about 18 volts the PWM control should be fine. The left side of the power curve has a much shallower slope then the right side of the power curve. In other words if Voc is to low you are operating to the right of the peak power point and the efficiency drops very quickly. So make sure your Voc (open circuit voltage) is at least 18 volts. Note that the Voc drops a little under 1 volt per 10 degrees C increase which is why a PWM controller loses efficiency with temperature. The MPPT operating at a higher voltage easily compensates for this.



I am planning a MPPT with 36 volt 200 watt panel.

[redbarron55]

Not quite. The MPPT actually converts the dc from the panels to an AC signal with an inverter and changes the voltage (and current) to that required for charging the battery.
The conversion is quite different between the two.
There are some controllers that claim to be MPPT, but lack the circuitry to actually do the job.
This is why the watts from the panels are efficiently translated from a higher voltage to the voltage required for the battery.
The MPPT logic determines the Maximum power point by sweeping through the range determining the peak power point (as it constantly changes).
PWM controls by switching the power on and off to get the average valued desired and the power when switched off is basically "lost". More power longer time the circuit is turned on, shorter less.
PWM cannot increase the voltage from the panels to charge the battery, but the MPPT can as the DC to DC converter can increase or decrease the voltage.
PWM is like taking the light switch and flipping it on and off real fast to dim the lights where the MPPT is like an inverter generator where the the gas motor changes speed and creates varying voltage (ac) and frequency but is changed to DC and controlled to produce the desired 120 VAC 60 HZ.
In this case DC is made from that AC and varied as required for the battery.
If you have am MPPT controller without the inductor(s) for the inverter you have a PWM unit and not MPPT.

[CarlD]

The point I was trying to make is that both technologies utilize switchmode power converters. Both topologies can be very efficient. A PWM type solar controller will be very efficient if the solar panel voltage is sized correctly and there is no advantage to MPPT except maybe at high temperatures, which cause panel voltage to drop, and low light levels, which does the same. A PWM type will turn full on if the battery needs bulk charge and reduce output by modulating the panel voltage as determined by the battery voltage.


You talk about the power from the panel being "lost". This will happen when the battery is nearing full charge. You have to do this to avoid damaging the battery. The power is indeed lost, but it is really that your panel output is more power than the battery can absorb.


One other point, MPPT controllers for battery charging utilize some variation of DC-DC boost/buck, SEPIC, CUK, type converter, to raise or lower the panel voltage as required. There is no AC intermediate stage. However, a grid connected system would utilize an inverter, similar in principle to a sinewave output inverter generator, to create an AC voltage.



By the way your efficiency number are very encouraging. Please provide more data.

[Jon Vermilye]

Originally Posted by CarlD

The point I was trying to make is that both technologies utilize switchmode power converters. Both topologies can be very efficient. A PWM type solar controller will be very efficient if the solar panel voltage is sized correctly and there is no advantage to MPPT except maybe at high temperatures, which cause panel voltage to drop, and low light levels, which does the same. A PWM type will turn full on if the battery needs bulk charge and reduce output by modulating the panel voltage as determined by the battery voltage.


You talk about the power from the panel being "lost". This will happen when the battery is nearing full charge. You have to do this to avoid damaging the battery. The power is indeed lost, but it is really that your panel output is more power than the battery can absorb.


One other point, MPPT controllers for battery charging utilize some variation of DC-DC boost/buck, SEPIC, CUK, type converter, to raise or lower the panel voltage as required. There is no AC intermediate stage. However, a grid connected system would utilize an inverter, similar in principle to a sinewave output inverter generator, to create an AC voltage.



By the way your efficiency number are very encouraging. Please provide more data.

This is an important concept to grasp. The demonstrations that MPPT controller sales persons make usually start with the batteries at 50% or lower.

If you are the type that draws down your batteries to 50% or so per night, the advantages of a MPPT controller become more apparent. Your controller will go into the boost mode and supply lots of current to the batteries to bring them up to around 80% full charge.

On the other hand, most properly sized solar systems tend to keep the batteries at 80% or better for the average user. At 80%, your controller will never go into the boost mode, just the absorption, which limits the current to prevent battery off gassing and overheating. The difference between a MPPT & a PWM controller is less important doing the final 20% of battery charging. In both cases you don't need (or want) the maximum amperage from a properly sized set of panels.

[redbarron55]

All I know is that the MPPT charges the batteries faster and in lower light conditions.
Where the Cheap Chinese PWM unit barely puts out anything under those conditions with the panels paralleled the MPPT will charge with the panels in series.
By the way the DC to DC conversion is AC just not 60 cycle like you think of with AC mains.
The higher frequency allows smaller inductors and transformers to do the job.
The "Inverter" works like all of the other inverters in that the voltage can be changed with high efficiency compared to older technology.
As to the advantage of MPPT at low light extremes of temps etc. This is where I want the advantage anyway.
Who cares when you have long days and bright sun? A few percentage points of efficiency under good conditions are of little concern.
I hope to be able to power the communications equipment during the day and hopefully through the night in response to emergencies (Hurricanes etc. here in Florida.)
As an aside Craigslist has an Eaton 12-110-1800 B4G inverter and I am considering installing this for brief power for microwave etc.
I have an inverter generator that I could use, but during the emergency period where the communications is needed gasoline is hard to come by and there is only so much that you can carry with you on the way in.

[Gompka]

I think this also depends on your setup, I know most people with a small rv like scamp are using a single solar briefcase or a single panel. I use a single 100w panel and a renogy pwm controller, for 1 panel there is not really any benefit to an mptt controller, especially since the renogy is a good quality pwm that can be had for $30.

[redbarron55]

Here is a good reason for MPPT.
Three times .9 = 2.7 amps.
When PWM is used probably less.
58 watts in 58 watts out.
Probably not exactly right but very good.
A PWM controller would not do that.

[Dan-NS27]

Originally Posted by Gompka

I think this also depends on your setup, I know most people with a small rv like scamp are using a single solar briefcase or a single panel. I use a single 100w panel and a renogy pwm controller, for 1 panel there is not really any benefit to an mptt controller, especially since the renogy is a good quality pwm that can be had for $30.

I'm not sure about PWM, but I have read plenty about the benefits of MPPT.
I have a Renogy 100W panel (and soon a second) and a Renogy MPPT controller. I look at the status often and do like that the MPPT does put in a little more amps than the panel is producing. So if I look at the panel putting out 1.2A, the controller is putting 1.43 into the battery. It does quite well at putting as much power as it can into the batteries.

[Dan-NS27]

Originally Posted by redbarron55

Here is a good reason for MPPT.
Three times .9 = 2.7 amps.
When PWM is used probably less.
58 watts in 58 watts out.
Probably not exactly right but very good.
A PWM controller would not do that.Attachment 126480

I think having a higher panel voltage sure helps in your setup. If it were my setup, I'd have 20V .9A then it'd be putting in about 1.2A into the battery (assuming the batteries were close to being charged anyway).

[redbarron55]

Originally Posted by Dan-NS27

I'm not sure about PWM, but I have read plenty about the benefits of MPPT.
I have a Renogy 100W panel (and soon a second) and a Renogy MPPT controller. I look at the status often and do like that the MPPT does put in a little more amps than the panel is producing. So if I look at the panel putting out 1.2A, the controller is putting 1.43 into the battery. It does quite well at putting as much power as it can into the batteries.

That is 4.3 not 1.43 amps, a big difference
My base figures show that the input watts are translated to the out put watts at the different voltage level.
If the three panels were paralleled than the best case would be 3 X the 1.2 amps and probably less since they would be at 14 volts instead of their peak power point of over 18 at the panel.
The PWM would at best provide 3.6 amps to the battery where the MPPT is providing 4.3 or .7 amps more (Best and improbable case) for about 20% more charge current. (probably more)

[gordon2]

Originally Posted by Dan-NS27

... and do like that the MPPT does put in a little more amps than the panel is producing. So if I look at the panel putting out 1.2A, the controller is putting 1.43 into the battery. It does quite well at putting as much power as it can into the batteries.

If you like that, then get a controller than puts out six volts.. you will then see over 2.8 amps to the battery!

Of course then your battery will not get charged but the amp reading will be impressive.

Based on your numbers you are getting 21.6 watts from the panel (assuming 18 volts (Vmp) and sending 19.6 to battery (assuming 13.7 charge voltage). So you lose two watts. Will a PWM controller do any better or worse? That depends but just for the record, when the PWM controller drops the voltage, the amps also increase.. just like the MPPT controller.

[redbarron55]

The voltage at the input is 63 and 1.2 amps and the output is 14 and 4.3 amps.
The power is very close to the same and the panels are working at MPP.
A PWM will not do that.

[CarlD]

JD


It is interesting that your battery voltage is 14 volts and your panels are at 63.4 volts. I assume you have lead acid batteries. This is an indication that the panels are operating at a high Voc and the MPPT controller has ramped the output current down because the batteries are nearing full charge. If this is the case I would expect a properly matched PWM controller would have similar performance to a MPPT. It would be an interesting test to load the batteries under various solar energy densities and check the performance instead of just trying to charge the battery. Another area where a MPPT would outperform a PWM low light, high temperature, batteries under load.


Thinking about it, a LFP battery would probably benefit more from a MPPT controller than a lead acid because they can accept high current right up to full charge.



What was the energy density on the panels when the measurements were made? Clear, cloudy, panel angle?

[gordon2]

Originally Posted by redbarron55

...
Probably not exactly right but very good.
A PWM controller would not do that....

Originally Posted by redbarron55

....
The power is very close to the same and the panels are working at MPP.
A PWM will not do that.

But we are not allowed to talk about religion here.. and this is beginning to sound like religious devotion.

But bottom line is you have a good system that is doing very well for you with the multiple panels in series. Others get by fine with a good quality PWM controller because we don't have the space, money, interest or need for more than one or two 100 watt panels, or the need to raise the voltage for longer wire runs. The cost / benefit equation comes into play also. If I needed more power and had the space I think I might go the same route that you did. If I were looking to get more than 300 watts in a system at my home, I would surly use MPPT.

[Glenn Baglo]

Originally Posted by gordon2

But we are not allowed to talk about religion here.. and this is beginning to sound like religious devotion.

It was discussions like this that caused me to cut solar from my build list. Just too much trouble, I thought

Couple years ago, I added two 40-watt solar panels that came with controllers ( only need to use one controller ). No idea what kind of controllers these are.

I run the wires the panels came with to a hub, which runs to the controller, which alligator clips to the battery terminals. Now, even that is starting to sound complicated.
Anyway, these panels charge my batteries without me knowing anything about how many amps, watts or gigabits are doing what.

I try to have less power coming out than is going in to my batteries.