PWM VS MPPT TROPICS

[s/v Jedi]

Originally Posted by noelex 77

Firstly thanks sailinglegend for doing those measurements.

I assume you are quoting the amps into the batteries after the voltage conversion from the MPPT.
I think Jedi assumes you are quoting the amps from the panel, upstream of the MPPT controller. Perhaps if you could clarify it would help.

I must admit I find the numbers surprising. I expected a much smaller difference.
I wonder if there is a fault with the bypass diodes in your panels (they do sometimes blow), or some other fault of experimental design.

Finally could everyone on this thread please remember we are taking about solar panels. There is no need for personal comments.

Ah the current from controller to batteries... but the voltage is certainly from the panels and not the battery voltage or they would be cooked at 30V+. These kind of measurements only work when voltage and current are measured at the same spot.

I'm still thinking this is a flame bait post because nobody with a degree in this science would post that or not know how to do the math, but I'll just let it go as "it's just the Internet" and it doesn't really matter if people learn something from these threads, or are fooled instead. It's all part of "the fun"

cheers,
Nick.

[neelie]

I'm still swimming in glue here.

Its fair to assume the the voltage out of the controller for both the P & S cases will be approximately the same. Thus the number watts being supplied to the battery in the 1/3 shade scenario with the P case, is 15 times the S. This does seem extreme.


Standing by for an explanation from anyone. What have I got wrong?

[sailinglegend]

Originally Posted by s/v Jedi

Okay then, I see that you added an extra column then. What is that extra column? [/B]......
On electrics you need some basic understanding: the power output is voltage times current. ...

s/v Jedi there is a danger that you are ruining this thread because you haven't read it properly. You are prolific poster with 27 in the last 24 hours, and 48 on just one day last week. I have read some useful stuff from you, and thanked you for it, but this post is getting silly. This is a serious engineering forum, not a fun forum. I shall be reporting you to the moderator because you are trying to make me look a fool.

There is no extra column. I listed the array voltages just to see what would happen to them when shaded, and clearly stated the charging current, which of course is the battery charging current - but adding "battery" would make the columns too wide. My Morningstar software doesn't measure the array current, which would go down by half in series with no shade. Anybody should be able to see from my table that with no shade the charging currents are the same, so that must have been the battery charging current.

I never mentioned anything about power output. It is clear from the table that all we are really interested in is the charging current. In both Parallel and Series this is almost identical - higher in parallel because of the curved deck - which I also stated in my first post.

As you say I only have 136 watts of solar, so why on earth did you think my figures in series showed 160 watts output - in February in the Med at 1130 hrs.

The results do seem to be extreme, but not unexpected. I repeated them with shading on both panels, with my crew, so that there could be no mistake. I do urge others to join this debate by doing tests themselves. I tried four different types of shading - in each case the results were the same. We can't choose what kind of shading we get - it comes at us from everywhere.

[Fuss]

Originally Posted by sailinglegend

s/v Jedi there is a danger that you are ruining this thread because you haven't read it properly. You are prolific poster with 27 in the last 24 hours, and 48 on just one day last week. I have read some useful stuff from you, and thanked you for it, but this post is getting silly. This is a serious engineering forum, not a fun forum. I shall be reporting you to the moderator because you are trying to make me look a fool.
.

Sailing legend.... It's a forum and unfortunately we all have to put up with some posters who do not know what they are talking about, post not from personal experience, post confusing stuff to appear more intelligent etc etc.

If you did some research you would see that Jedi has been here along time, posted mostly very well researched articles and advice and does so only from personal experience.

I hope he is not censored due to your complaint as this forum would be much poorer for it.

Below is your post to him yesterday telling him to get a life after he explained why he thought the number of repairs and mods required of your FP generator were not inline with a quality product.
He asked a very good question .... How can you recommend a genset that had 2 catastrophic failures.

Please don't waste time with posts that add nothing, or are you just trying to get your post-count up. So far you have averaged nearly 4 posts EVERY day for the last 4 years. 48 posts just yesterday - get a life!

This is an Engineering and Systems forum where we try and help each other with feedback of our experiences, not just offer opinions. If you want idle chit-chat then please find another forum..

[goboatingnow]

Lads ,Lads please lets look at the data

SERIES:.............No Shade-3/3 shade-2/3 shade-1/3 shade-Hand/arm
Charge current....4.85........0.11.........0.16.........0 .16.........1.66
ARRAY VOLTS.....32.88.......32.88.......32.88.......32.8 8........32.88

PARALLEL:..........No Shade-3/3 shade-2/3 shade-1/3 shade-Hand/arm
Charge current....4.95........2.45.........2.53.........2 .58.........3.4
ARRAY VOLTS.....15.33.......15.33.......15.33.......15.3 3........15.33

since we dont have charge voltage , or array current we cant compute watts, but then again its irrelevant.

What is clear is the series configuration exhibits significant sensitivity to shade, BUT then that is consistent with the lack of ( or not enough ) bypass diodes.

[sailorchic34]

For a system with only 1 bypass diode per panel the results from sailinglegend would be correct. OR if the panels had 8 diodes per panel but one or more went into thermal runaway and failed that that too would show the outputs as indicated.

The thing about diodes is they are almost never tested to see if they still function. Just because a panel came with 8 diodes per panel does not mean that they still function. Actually SL's test would be a good one to use for those with series wired panels. If your panels are in series and output drops low, its probably good to check and/or replace your diodes.

Maybe SL can pop the cover off a J box and check the diodes with a VO meter for function.

It would be nice if others would check their systems in series and parallel configuration. Well those with a MPPT controller anyway. Maybe Jedi can do a shade test on his panels just in series and let us know the results...

OK I'm going sailing... See Ya'll later....

[s/v Jedi]

Originally Posted by Fuss

Sailing legend.... It's a forum and unfortunately we all have to put up with some posters who do not know what they are talking about, post not from personal experience, post confusing stuff to appear more intelligent etc etc.

If you did some research you would see that Jedi has been here along time, posted mostly very well researched articles and advice and does so only from personal experience.

I hope he is not censored due to your complaint as this forum would be much poorer for it.

Below is your post to him yesterday telling him to get a life after he explained why he thought the number of repairs and mods required of your FP generator were not inline with a quality product.
He asked a very good question .... How can you recommend a genset that had 2 catastrophic failures.

Oh gods, it's that guy from the Fisher Panda. Yes then clearly he is stalking me to get his "revanche" for me showing his logic was flawed. Ah well, I'll put him in my ever growing ignore list with all the other Bleeps.

I won't even respond to his findings anymore as I doubt he did any measurements; he just made the whole thing up to counter me here LOL.

[btrayfors]

If it's not a hoax, it's certainly a flawed test. Or, the results are.

Consider the question of what is called "Array Voltage". One presumes that this is PV....the voltage actually coming from the solar panel(s) under various degrees of shading, from none to 100% shading. Are we to believe that the PV never dropped under any shading conditions, either in the series or the parallel configurations?

Simply not credible, on its face.

And, if by "array voltage" he means the OC voltage of the array, that's not really relevant across the shading table. He should, instead, have noted the "array voltage" once, then posted the actual PV during each shading condition.

PV x Amps = input Watts to the controller

Output voltage x output Amps = output Watts to the batteries

Output watts / input watts x 100 = percent efficiency at that state

Bill

[goboatingnow]

Originally Posted by btrayfors

If it's not a hoax, it's certainly a flawed test. Or, the results are.

Consider the question of what is called "Array Voltage". One presumes that this is PV....the voltage actually coming from the solar panel(s) under various degrees of shading, from none to 100% shading. Are we to believe that the PV never dropped under any shading conditions, either in the series or the parallel configurations?

Simply not credible, on its face.

And, if by "array voltage" he means the OC voltage of the array, that's not really relevant across the shading table. He should, instead, have noted the "array voltage" once, then posted the actual PV during each shading condition.

PV x Amps = input Watts to the controller

Output voltage x output Amps = output Watts to the batteries

Output watts / input watts x 100 = percent efficiency at that state

Bill

Well pv are current sources rather then voltage sources so the panel voltage isn't that important anyway.

Dave

[btrayfors]

Originally Posted by goboatingnow

Well pv are current sources rather then voltage sources so the panel voltage isn't that important anyway.

Dave

Now what, pray tell, does that mean?

Of course panel voltages are important. You need a high enough panel voltage for the MPPT controller to do its job and provide a high enough voltage for battery charging.

And, panel voltage is one of two very important components of total energy (watts), i.e.,

VOLTS X AMPS = WATTS

Bill

[goboatingnow]

Originally Posted by btrayfors

Now what, pray tell, does that mean?

Of course panel voltages are important. You need a high enough panel voltage for the MPPT controller to do its job and provide a high enough voltage for battery charging.

And, panel voltage is one of two very important components of total energy (watts), i.e.,

VOLTS X AMPS = WATTS

Bill

A PV panel is a current source hence the defining characteristic is its output current. The voltage can be any where from 0 to max while the current is at a defined point

Whether or not your are connected to a mppt controller or a battery is nor relevant in determine shading. All that is relevant is there is some form of current sink. So amp comparisons serve fine for the purposes for this comparison.

Dave

[btrayfors]

Originally Posted by goboatingnow

A PV panel is a current source hence the defining characteristic is its output current. The voltage can be any where from 0 to max while the current is at a defined point

Whether or not your are connected to a mppt controller or a battery is nor relevant in determine shading. All that is relevant is there is some form of current sink. So amp comparisons serve fine for the purposes for this comparison.

Dave

Dave,

With respect, that's utter nonsense.

What's important is the amount of energy (power or watts) produced by a solar panel which gets converted into energy (power or watts) to charge the battery.

As noted above, and as any basic understanding of Ohms Law will reveal, energy (power or watts) = volts x amps.

With any given panel, as the output voltage (PV) drops due to reduced light falling on the panel -- so, too, does the amperage output drop. Ergo, the total energy (power or watts) produced by the panel drops, inevitably reducing the amount of energy (power or watts) available to charge the batteries.

Amps alone do not charge a battery. They must be accompanied by a voltage high enough to overcome the internal resistance of the battery and, preferably, high enough to feed the battery all the amps it will accept for its present state-of-charge.

Example: to properly charge a flooded lead-acid battery during the absorption phase, you must have at least 14.6 volts DC.

Bill

[goboatingnow]

Originally Posted by btrayfors

Dave,

With respect, that's utter nonsense.

What's important is the amount of energy (power) produced by a solar panel which gets converted into energy (power) to charge the battery.

As noted above, and as any basic understanding of Ohms Law will reveal, energy (power) = volts x amps.

With any given panel, as the output voltage (PV) drops due to reduced light falling on the panel -- so, too, does the amperage output drop. Ergo, the total energy (power) produced by the panel drops, inevitably reducing the amount of energy (power) available to charge the batteries.

Amps alone do not charge a battery. They must be accompanied by a voltage high enough to overcome the internal resistance of the battery and, preferably, high enough to feed the battery all the amps it will accept for its current state-of-charge.

Bill

You have a Fundamental mis understanding of PV cells. You are treating them like voltage sources. Of course at any point in time you have a VI relationship. But lower light reduces current.

Forget about battery charging for a minute. Technically once you don't have absolute zero volts the panel,if it was a perfect current source would produce the same watt output as of it had full open circuit potential. Hence the voltage persay is not relevant to defining output.

Of course its not a perfect current source. That's another story.

[btrayfors]

Originally Posted by goboatingnow

You have a Fundamental mis understanding of PV cells. You are treating them like voltage sources. Of course at any point in time you have a VI relationship. But lower light reduces current. ......

There...you said it! Yes, lower light reduces current. It also reduces voltage. Ergo, it reduces power output from the panel. Less power output from the panel = less power available to charge batteries (and that's what we're talking about here -- charging batteries -- not the finer points of theoretical electrical engineering).

Not sure who's got a "Fundamental mis understanding of PV cells" :-)

Bill

[goboatingnow]

Originally Posted by btrayfors

There...you said it! Yes, lower light reduces current. It also reduces voltage. Ergo, it reduces power output from the panel. Less power output from the panel = less power available to charge batteries (and that's what we're talking about here -- charging batteries -- not the finer points of theoretical electrical engineering).

Not sure who's got a "Fundamental mis understanding of PV cells" :-)

Bill

Have a read of current sources ,, you'll see what I mean , ohms law always applies, but The defining characteristic of a PV panel is its a current source, whereas a battery is primarily a voltage source.

What the poster was contrasting was the performance of series versus parallel panel, he on fact gave us little information on what the battery charging was doing

How the battery is charged from a current source is merely a function of the design of the DC DC converter.

Dave