mppt vs pwm

[pianotuna]

Hi,

A nice little video comparing mppt vs pwm with the batteries in bulk mode.

mppt vs pwm

[MrWizard]

Shading
All panels parallel...output will be reduced only by the amount of the reduction of the panels that are shaded, this may or may not be the full output of these panels, depending on amount of shade etc...

Series is can of worms, two panels 17v at 4 amps in series produce 34v at 4 amps
The number of internal by pass diodes now play a major part in what happens
Panels with good by pass well drop output, from shade but still pass thru the amps from the sunny panel, do you might get 25v at 4 amps

Panels with poor low number of bypass diodes, might shut down most of the way and block the current, because there is no place for the amps from the sunny panel to pass thru aka around the shaded cells
Putting 3 or more panels in series requires no shading, or really good panel bypass diodes configuration

Series parallel attempts to give you the higher voltage and MPPT gains, yet limits the series to Paris of panels and puts the PAIRS in parallel so shading a panel doesn't kill the all the output
Shading one panel in one pair only reduces the output of one pair, not all the panels

[NinerBikes]

Wait until people start getting attached to their LiFePo batteries!

[jrnymn7]

I'm a little curious as to why comparing mppt to pwm often results in being accused of having some "aversion" to watts... what's up with that??? No one is denying mppt takes wattage and turns it into amps at a given voltage. We're just trying to get past the marketing hype, and get to the real facts. If that offends some people, I suggest they take a step back, and ask themselves why they are so emotionally attached to their mppt controllers? I mean, seriously?

[12thgenusa]

Thanks, PT.

[pianotuna]

Hi,

Here is a direct link to the page that 12thgenius is suggesting:

mppt vs pwm

It shows an average benefit from MPPT of about 18% over a seven day test. None of the test days were even close to perfect. However, they were also not hot days which may favor the MPPT side of the test.

[12thgenusa]

KJINTF wrote:
Agreed a fair fight is difficult to setup

The fight becomes a completely different game with LFP batteries
The guy over at http://www.marinehowto.com/ did a PWM Vs MPPT test
Results a clear 20% gain from MPPT
Suggested reading material

For those of you that haven't looked at this here is a clicky. Click "tree view" then scroll down to the one titled MPPT vs PWM Controllers.

He uses identical panels tested simultaneously with different controllers. It was fairly lousy weather in May in Maine.

He also has some interesting comments about cheap (Chinese) controllers.

Here's a copy of the test results. For those of you who are "watts averse", notice that the results are in amps.:)

[jrnymn7]

pianotuna wrote:
Hi jrnymn,

Since all the controllers I've seen just look at battery voltage they switch out of bulk faster than one might expect. Often I see the Blue Sky change from float to bulk when clouds pass by.

Now that IS bizarre. hmmm.

[jrnymn7]

I thought BFL might appreciate this:

DIY Solar Tracker

[time2roll]

My MS MPPT 60 will hold absorption as long as you like.
Actually you can have three different likes depending on morning start voltage.

[pianotuna]

Hi jrnymn,

Since all the controllers I've seen just look at battery voltage they switch out of bulk faster than one might expect. Often I see the Blue Sky change from float to bulk when clouds pass by.

[jrnymn7]

BFL13 wrote:
Could be just confusion over recharge amount vs time.

MPPT may be on for most of the recharge by looking at 50-95% vs 95-100% but it may be only on for a shorter part of the whole day, leaving much of the day with the controller "in PWM" doing Float where you can get all that "free" extra solar load running done.

Yes, exactly. I'm not looking at what time of day the bank is at full, just how much of the charge time is at the (allegedly) higher mppt rate.

But that is a good point... the sooner the better, so one can run loads without interfering with charging.

[Salvo]

I bet there's a big difference in temperature between front and back. How hot do you think the surface of a black car gets in the summer. I bet you can get a pretty good burn.

JiminDenver wrote:


A thermometer lived on the back of a panel for over a year starting with below freezing test and running through out the summer. I never saw those panel temps and it gets plenty hot here. That's why I asked what conditions you were in to see it.

[BFL13]

Could be just confusion over recharge amount vs time.

MPPT may be on for most of the recharge by looking at 50-95% vs 95-100% but it may be only on for a shorter part of the whole day, leaving much of the day with the controller "in PWM" doing Float where you can get all that "free" extra solar load running done.

[JiminDenver]

What I'm saying is there isn't a huge difference in the amps available in MPPT vs those in PWM on my set up, if the battery could take more, it would.

[jrnymn7]

Thanks BFL, yes, that is exactly what I'm getting at.

But when someone says mppt ONLY works during bulk, it seems to imply that mppt is only working during a small portion of the charge, (or maybe half, or whatever), when in fact, it is likely operational throughout a huge portion of the charge.

For example, on a 50-100% charge, mppt could very well be in operation for as much as 90+% of the time. This could be significant, if the array is small in relation to the bank; which I imagine is usually the case.