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PWM vs MPPTon a 400 watt system.

Ya, so, well. I said that.

Are you having a rough day? Geeesh
It’s Christmas!

Anyway, I know how to do math.

In practice, the reality is that on one hand the minimal voltage over battery voltage of one or two panel systems sorta isn’t quite as effective as it is when giving mppt 100V, and on the other hand for 100- or 200W of panel on pwm does a really good job charging batteries. In fact, I recall Will did a video a few years back where the pwm units surprised him how much they were putting out.

Anyways- while my thumbs have nothing to do with it- 100 or 200, maybe 300W systems are just not as remarkably improved as 3S, 4S, 6S x several strings is. Further, i support the idea of facing panels two 90* separated compass directions. Parallel connection for two 100W panels. So 2S2P @400W total is the first higher-voltage rung. Not a stupid persons rule of thumb, an actual planned outcome.

I survived for several years on a pwm just fine. True- “there is no system too small” to use mppt. Nevertheless, pwm can work well for many 0.2kW systems.
You have no idea what you are talking about.

I have watched your posts in the past and just had to shake my head but I just can't let this slide by.
 
So a 300W system consisting of 3 100W 20V panels isn't worth doing MPPT for? You basically have to have 3 of those panels on PWM to get the same output of 2 of those with an MPPT.

If a 100W panel is 20Vmpp and 5A Impp, you will get 5A out with a PWM and 7.14A with an MPPT @ 14V charge. You don't think a 42% improvement is worth it? If you have 3 100W panels, that is 15A vs 21A.

As far as series vs parallel, assuming you have similar voltage drop between the panels and the controller by sizing the wires appropriately, you will get the exact same output. really the only reason you do series is to be able to use smaller wire and get a little more early morning late evening output.
Exactly!
 
You have no idea what you are talking about.
Okie dokie then.
Without knowing what I’m talking about I had a pwm with 200W of panel and an mppt with 200W. Because I don’t know what I’m talking about I guess I imagined the output was virtually the same. These were parallel panels. I didn’t bother with series for what should be obvious reasons but did go 2S2P once I stopped playing around.

I don’t need to defend myself. You are free to think and act on your own free will. Ya, there’s a lot I don’t know but what I do know, I know. However, just because your beak is tweaked doesn’t give you the right to be a jack wagon. You’re probably the type that thinks fla batteries got the memo and stopped working when lithium came out, too.

FWIW I ran a pwm with 200W of panels for 2-1/2+ years. As much as you don’t like to hear it- it worked quite well. But I did want a comparison and did one. Another panel would have made way more of a difference and cost 1/2 as much. It’s not denying math, it’s what happened in real life.

The ‘big jump’ happened at 2S2P and bidirectional facings.

Have a merry Christmas
 
If a 100W panel is 20Vmpp and 5A Impp, you will get 5A out with a PWM and 7.14A with an MPPT @ 14V charge. You don't think a 42% improvement is worth it? If you have 3 100W panels, that is 15A vs 21A.
Sorry for the analogy but a 42% faster car won't get you to a destination 42% quicker in normal traffic....most of the time they arrive together with all the speed limits. Even with MPPT, so beneficial with most installations, for 12v home systems with matching panels there isn't that great a difference.
You have based those figures on the common misconception that a PWM drops the panel voltage down to battery V when in fact it is the load causing the drop in V under constant light. At max light intensity and at the max Immp the panel will not differentiate between the two.

Only at a lower light intensity will there be a difference between mppt and pwm and this gets greater as the output decreases, thus reducing the overall difference. The apparent higher voltage of these Rich Panels compared to the usual, will also swing the results in favor of mppt but only slightly.

Edit for a better explanation....it is a 100 watt panel, apply only a resistive load that drops the V down to the 20Vmmp and at max sun this will be causing a current at the Immp of 5amps : vi=100watts .... watts in : watts out....100watts. Now put a CC in the circuit...pwm or mppt....both have 20v coming in because that is what the load dictates...both have 14.4v going out.....both have 5amps going in....and both have 7amps going out.100watts ignoring losses.
 
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You have based those figures on the common misconception that a PWM drops the panel voltage down to battery V when in fact it is the load causing the drop in V under constant light. At max light intensity and at the max Immp the panel will not differentiate between the two.

Only at a lower light intensity will there be a difference between mppt and pwm and this gets greater as the output decreases, thus reducing the overall difference. The apparent higher voltage of these Rich Panels compared to the usual, will also swing the results in favor of mppt but only slightly.
you are very confused. A PWM controller does exactly what the acronym means in that it pulses the PV input to control the voltage. If the light is low enough, it will have a 100% duty cycle. The maximum current that a PWM controller can deliver is the Impp.

On the other hand, the MPPT is basically a DC to DC converter so any voltage exceeding the charge voltage is preserved. A MPPT controller like a Victron is 98% efficient. A PWM can be efficient if the panel voltage is close to the charge voltage but that is hardly ever the case.
 
A PWM can be efficient if the panel voltage is close to the charge voltage but that is hardly ever the case.
I did point out that this is for 12v systems where the pwm is usually putting out 14.4v and did give credit to the mppt for the Rich Solars 2v higher voltage than the usual V of a 12v panel so the differences are there as you say when applying the PWM mode losses. Thanks for the correction.
However, wouldn't the panel be responding to the modulation of v caused by the pwm to offset some of the losses and this is the reason that direct comparison tests show little difference in normal use?
 
this is for 12v systems where the pwm is usually putting out 14.4v and did give credit to the mppt for the Rich Solars 2v higher voltage
I think I have enough stuff around that I could do another test run snd record it… if I still remember this in May when it’s not 15*F out.
I’ll need to buy a coupla accumulating 12V watt meters and rig some cables but I have a couple spare PWMs and MPPTs on hand to use. Maybe 12V water heater element for loads into a water tank? Or two water pumps? Or a couple 5A fans.
Basically a more sophisticated version of the experiment I did before, still side by side, concurrent time, identical conditions, and record the data.

What happens IRL is not always what happens on paper. I’m not arguing that mppt isn’t good or useful. I just want to replicate and document.
 
I did point out that this is for 12v systems where the pwm is usually putting out 14.4v and did give credit to the mppt for the Rich Solars 2v higher voltage than the usual V of a 12v panel so the differences are there as you say when applying the PWM mode losses. Thanks for the correction.
However, wouldn't the panel be responding to the modulation of v caused by the pwm to offset some of the losses and this is the reason that direct comparison tests show little difference in normal use?
It puts out 14.4V when it gets into absorb. It's not there during bulk so the wattage during bulk is even lower! An MPPT puts out as much wattage as the PV panel can put out.

The max current a PWM controller puts out is the Impp of the panel. Why is that so difficult for you to understand?
 
BTW...I am the CTO and CFO of a small company in San Jose that makes DC to DC converters. Before I arrived, One of our products was the back up power hardware for cellular base stations. We made our own charging circuits and they were MPPT. Not a chance in hell we would use a PWM design.
 
What happens IRL is not always what happens on paper. I’m not arguing that mppt isn’t good or useful. I just want to replicate and document.

Yeah, look at any of my driveway or shed lights threads and you'll see that reality and paper aren't eve in the same time zone.

@12VoltInstalls : I wish I had enough equipment and time shoreside to do an experiment like that. I think it would be amazing to see if there's a "sweet spot" where the cost of an MPPT controller makes it worth it over a PWM. I can tell from what pieces and playing I've done that a single 100w panel wouldn't make a lick of difference. What about 2 panels? 3 panels? At what point are you kneecapping yourself with a PWM and justifying the cost of a MPPT?

If you remember this when the sun comes back to visit, I'd love to see the results! :)
 
LOL...what does that even mean?
It means it’s working for him
I think it would be amazing to see if there's a "sweet spot" where the cost of an MPPT controller makes it worth it over a PWM
I was going to say there wasn’t a “sweet spot” but after a moment it occurred to me there may be some precise theoretical “sweet spot” but I don’t think finding it is actually relevant.
Why? It isn’t a question of one or the other being superior nor any magic in mppt. It’s more of a question of if pwm or when pwm becomes insufficient for your setup/needs where the difference that mppt makes sense in $$ and need.
In my case 200W sometimes and 400W usually would run a small 120V refrigerator on pwm. But I needed a bit more, bought an mppt and a few more panels, and discovered (maybe not surprisingly) that both facing series/parallel panels two directions and mppt with only 400W was a huge improvement- enough that I actually didn’t install the other panels until the days getting shorter in fall prompted me too.

IMHO finding ’the sweet spot’ could be done by testing I suppose, but EEs that code these things probably already know the answer. On paper.
But in practice it’s what works and when it isn’t enough you go for more which probably should include mppt.
 
Why? It isn’t a question of one or the other being superior nor any magic in mppt. It’s more of a question of if pwm or when pwm becomes insufficient for your setup/needs where the difference that mppt makes sense in $$ and need.
Right! So my napkin math says that (and this is napkin math) a bog standard 20v/5a 100w panel to a $30 PWM controller that maxes out at about 14v would max out your charging at 14v X 5a = 70w, so 70% efficient.

A decent brand MPPT controller costs about $200, but gets you 99% efficiency, so you're paying $170 more for the extra 29w of power, which would be about $5.86/watt.

Now, if you used a bog standard 30v/6.5a 200w panel to a $30 PWM you'll get 14v X 6.5a = 91a which would be 45% efficiency and you'd really NEED the MPPT to be worthwhile, so that $170 extra gains you another 109a which is only $0.64/watt.

At what point with the bog standard 20v/5a panels does it make it worth while to kick up to a MPPT? I'm not willing to pay almost $6 a watt for only 30w, but I'd pay $0.65 a watt for another 109!

2 bog standards in parallel would be 140w, but 2 in series with a MPPT would be 198w. That'd be about $2/watt roughly.

3 panels? 4 panels? See where I'm going with this? Besides using higher voltage panels where the PWM would seriously nerf you right out the gate, what does the cost per watt look like as you start stacking the 100w panels? What's the "Sweet Spot" or bell curve for that look like?
 
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what does the cost per watt look like as you start stacking the 100w panels? What's the "Sweet Spot" or bell curve for that look like?
Ya, you could do that scientifically but a lot of variables

On the other hand your napkin math is anecdotally pretty good common sense and imho that’s answered the question. :)

That’s why paralleled on pwm is important. Less lossy. But $/W once common sense makes you start thinking about that then probably that’s when mppt is the solution.

The dollars at the 200W range or even 400W range are not life-changing. Circumstances for some may make more panels / mppt initially unreachable. Nevertheless, it’s not that much more money on the grand scale of things. Big percentage difference, not much dollar difference at the 12-month view. .
 
These posts just proves to me that our schools are failing us.
You know, you don’t have to like or even use the practical “this works” approach for yourself. But your superior air and insulting demeanor is offensive and uncalled for. Some people don’t care if they leave 3.647 watts on the table or even give a flying rip about the math. Or even 100W on the table if what they do or did works.

Nobody’s saying mppt isn’t “better” but some like myself hold to the idea that if in practice it’s enough - it doesn’t matter.
LOL...what does that even mean?
It seems like you want be a jackwagon.
Maybe you don’t. No way to say. But…
These posts just proves to me that our schools are failing us.
No. This just proves you’re not reading the posts, a), and b) you are coming across as a controlling rigid personality with a black/white interpretation of life that isn’t tolerant of other people because you think they’re inferior so you just can’t help yourself but post stuff like that.
The max current a PWM controller puts out is the Impp of the panel. Why is that so difficult for you to understand?
Why is that so difficult for you to understand?”

We understand it but in our contexts we don’t care and most people are generally averse to people looking down their noses at them.
our products was the back up power hardware for cellular base stations.
Great.

Running driveway lights or small short-term loads (like my original system that only needed to power my shower and coffeemaker every day) can be done with more flexible criteria. And accept pwm.

With all your engineering background and sophisticated knowledge perhaps you could consider providing helpful input to folks with technical questions that they don’t have the knowledge to solve on their own rather than make fun of people whose practical approaches don’t meet your criteria for a scientifically developed spec sheet of performance carried to three decimal places. Some people with small systems can do fine with a $200 (now $260) “kit” that includes a pwm.

Whether that setup would work for you isn’t usually even relevant.

People do things for fun, or to meet a particular desire or need, a myriad of reasons, and sometimes they have a critical need where budget or fixed dollars are in play.

I suggest thinking about your approach to other people’s problems and whether your input is a blessing or benefit to the recipients of your posts. Mere facts or even substantiated opinions aren’t always beneficial when you consider the vast variety of circumstances people might be in, or what difficulties or challenges may have brought them to this day and situation.

I’m pretty docile in most circumstances but people who pop in to be a jerk for free to myself or anybody else get me fired up. It sounds like you have a lot of experience so you should have substantial information to benefit beginners and non-technical people trying to Diy whatever systems they are attempting to complete. You can choose basically only four routes in life: a leach/dependent, a blessing, a curse, or a bystander. Only one benefits society and some bystanders are medically or mentally impaired so they should get a pass.
 
This site is intended for people to get accurate information. Since you don't have accurate information, maybe you shouldn't post.

This thread is about PWM for a 400W system. We aren't taking about a driveway light here.
 
We aren't taking about a driveway light here
Actually I think the guy with the little departure we had mentioned driveway lighting. If you read the thread
look at any of my driveway or shed lights threads and you'll see that reality and paper aren't eve in the same time zone
This site is intended for people to get accurate information. Since you don't have accurate information, maybe you shouldn't post.
Since nearly every post you’ve made is in politically volatile “chit chat” and the few other thread posts have been demeaning others or myself, (and you have a preoccupation with pwm scofficacy) I’m surprised by your opinion. Accurate information doesn’t seem to be your forte.

This site is a diy help forum started by a guy along with a few others frustrated by alligator postings in another solar forum. Sortofa selfless action. When people are hungry you feed them. Thirsty, give them water. Not adequately clothed? You clothe them. Plus you reap what you sow!

Randomly dropping in to a self-help diy community and being acerbic over a difference of opinion or just being downright mean does nothing to help the community. It’s just divisive and unwelcome.

All one has and leaves behind in life is one’s legacy. So many things in life we are unable to make choices in; covid, SIDS, house fires, economic loss, cancer, a car accident. You can choose what you leave behind for a legacy; choose to spread life or choose to spread death.

Merry Christmas.
 
Since nearly every post you’ve made is in politically volatile “chit chat” and the few other thread posts have been demeaning others or myself, (and you have a preoccupation with pwm scofficacy) I’m surprised by your opinion. Accurate information doesn’t seem to be your forte.
Actually...he is very accurate. And what in the hell is scofficacy?
 
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