PWM vs MPPTon a 400 watt system.

[Rednecktek]

We aren't taking about a driveway light here.

You mean like either of my threads?

Back to somewhere near the OP, with my napkin math above it would seem that since a 100w panel through a PWM would only get you 70w/panel at best, then right about 300w would seem to be the point where MPPT really starts to shine as you're paying $300 for the panels, but only getting $200 worth of theoretical output. That's $100 closer to a MPPT and at that rate it would seem, again napkin mathing here, that at 400w you're starting to level out the curve on dollar per watt as you're spending $400 in panels for about 2.8 panels worth of power. I'm sure with enough sleep I could calculate out the bell curve on that, but jet lag sucks.

 

[brb58]

You mean like either of my threads?

Back to somewhere near the OP, with my napkin math above it would seem that since a 100w panel through a PWM would only get you 70w/panel at best, then right about 300w would seem to be the point where MPPT really starts to shine as you're paying $300 for the panels, but only getting $200 worth of theoretical output. That's $100 closer to a MPPT and at that rate it would seem, again napkin mathing here, that at 400w you're starting to level out the curve on dollar per watt as you're spending $400 in panels for about 2.8 panels worth of power. I'm sure with enough sleep I could calculate out the bell curve on that, but jet lag sucks.

You leave out the mounting of additional panels, the wiring of additional panels and the area of additional panels. The OP is mounting panels on an RV where space is a premium and location is a premium since you often can't use all the area on an RV roof due to shading.

In addition, you can also wire the panels in series if you so desire and you will get a little more benefit in low light conditions.

 

[12VoltInstalls]

scofficacy

neologism

 

[brb58]

neologism

You found something you are good at!

 

[sunshine]

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?

For 12v systems using low voltage panels you can use either, mppt or pwm,. Generally there is no 'sweet spot' as the system just replicates in parallel... What works for 200w gets copied for the 2nd, 3rd. 4th.....100. However, probably by the 5th it's time to get an All in One MPPT and hook your panels in series.
My 'sweet spot' is determined by my wallet....$15 pwms or $150 mppts.... I have 20 180w/200w panels (av price $5) converted = 40 X 12v Panels(av price $2.50 plus 10minutes labor). Obviously it will be pwm. I get 30amp PowrMr pwm from aliexpress for $14, replace the heatsink on the back and rate them as 10amps.
The other determining factor is tests carried out by others showing no marked difference between pwm & mppt in low voltage systems.

 

[Rednecktek]

You found something you are good at!

I don't know, I read somewhere he's pretty good in a kitchen. Of course that could just be baseless internet fake news.

 

[brb58]

The other determining factor is tests carried out by others showing no marked difference between pwm & mppt in low voltage systems.

LOL 30% improvement is not a marked difference?

 

[Rednecktek]

I have 20 180w/200w panels (av price $5) converted = 40 X 12v Panels(av price $2.50 plus 10minutes labor). Obviously it will be pwm.

Now see, that's confusing to me. If you leave 30w per panel inaccessible on a 100w panel, then after your 40 panels that's 1200w of solar power you're unable to utilize because you're on PWM. Why wouldn't you drop $100 and get a cheapie PowMr MPPT at the least? That's like leaving $1200 worth of 100w panels sitting in the shed and not plugged in to save $100 to me.

The other determining factor is tests carried out by others showing no marked difference between pwm & mppt in low voltage systems.

Now that I would love to see the work on. The only things I've ever seen that try to compare the 2 systems have always involved a single 100w panel, but I've never seen anyone do a scaling experiment where they start adding more and more panels to both types of controllers and graphing the output curves. If you have links to stuff like that I would really be interested in seeing it, it sounds amazing.

 

[Rednecktek]

LOL 30% improvement is not a marked difference?

And this is where my interest comes in. @Will Prowse did a video many years ago comparing the outputs of a panel through multiple PWM and MPPT controllers and was surprised at how even they were. What I find to be the flaw in his testing methodology is that he only used a single 100w panel per controller and there was no scaling involved to see where the losses and inefficiencies were as you bring more and more panels into a system.

 

[12VoltInstalls]

no marked difference between pwm & mppt in low voltage systems.

Low voltage colloquially or low voltage electrically? In other words I want to qualify ’low voltage’ in that context.

My 'sweet spot' is determined by my wallet

That is one valid factor that another poster isn’t willing to consider

Obviously it will be pwm.

If that’s working for you great.
If it were me I’d just get an mppt lol

the system just replicates in parallel...

buuuuuut… anything over what? say 15-16V-ish? doesn’t get used.
I’d totally do that with the panels unaltered and an mppt. Just my opinion.

read somewhere he's pretty good in a kitchen.

‘Creeping on me?
Or do you actually know somebody that knows me?

 

[brb58]

And this is where my interest comes in. @Will Prowse did a video many years ago comparing the outputs of a panel through multiple PWM and MPPT controllers and was surprised at how even they were. What I find to be the flaw in his testing methodology is that ne only used a single 100w panel per controller and there was no scaling involved to see where the losses and inefficiencies were as you bring more and more panels into a system.

Would actually be interesting if he could post the voltage coming in from the panel instead of just telling us the wattage produced. If the voltage was low enough because of time of year or time of day, of course the wattage would be similar.

This is why some of what he says has to be taken with a Costco sized grain of salt at times.

I can look at my solar controller and I can see the voltage and current coming in from the PV panel and the corresponding voltage current supplied to the battery. Quick math shows it to be 98% efficient most of the time. I would also know how much current there would be based on the PV current if I was using a PWM controller.

 

[sunshine]

If that’s working for you great.
If it were me I’d just get an mppt lol

Actually I have a few battery charging modules, hw-632 $5 from China, that I'm going to try out on some panels instead of a CC.

 

[Rednecktek]

‘Creeping on me?
Or do you actually know somebody that knows me?

I read it on MyFace I think... there may have been a cat involved.

 

[sunshine]

I've never seen anyone do a scaling experiment where they start adding more and more panels to both types of controllers and graphing the output curves. If you have links to stuff like that I would really be interested in seeing it, it sounds amazing.

Theoretically there isn't any difference with scaling both pv and load together. It is linear although the mppts may default to standard when more than one is in //.
The pv MPPT graphs do show the general principles and just consider the pv as a battery with the v on any point on the graph to simplify things. My multimeter confirms those principles whenever I make changes but testing can only be relative because of changing light and loads.

Direct to water heating threads and why only doubling the pv over theoretical values for any given load will give useful values explains some of the issues with solar.....look for posts by efficientPV.