Solar Panel Voc-MPPT?

ken white wrote:

red31 wrote:

ken white wrote:

The PWM Controller makes the solar panel assume the battery voltage under normal operating conditions,

What makes the panel match batt voltage without a controller, ie directly connected?

The panel has an operating space where it acts as a constant current device - its internal impedance varies linearly with supplied voltage.

An ideal constant current device can assume any voltage across it.

The panel also has an operating space where the resistance changes non-linearly with voltage, and this starts to occur at the voltage point when the panel current starts to diminish quickly for a given irradiance.

Maximum panel power occurs on the non-linear resistance part of the I-V curve and that's where the MPPT controller operates.

A battery also has an internal impedance that is dynamic and is a function of its internal charge level and the physical condition of its plates.

If we were only interested in maximum power transfer, it would occur when the controller acts as an impedance matching device and matches these two internal impedances.

x2! Ken you hit the nail on the head in clearly and consisely describing solar panel operation. They are highly non liniear devices, as are Lead Acid batteries. Optimizing performance of a solar panel a charging device for a battery is non trival.

BFL13 wrote:
Should be interesting tests!

When orienting, I don't have to run back and forth. The DMM has alligator clips so I can watch the dial while moving the panel--can do it with two hands, don't need more thanks to the clips.

Problem is if Isc is over 10amps--blows fuse in meter. When I had the two 100s at 6.2a each, I had to check just one, not both in parallel.

Once I then connect back up, now I have to run to the Trimetric to see what it says compared with the Isc I just saw at the panel.

Only have to do that once in a while. Once set up and you see you get rated Isc when you should, you can assume the lower amps you get at other times will be the most you could be getting just then.

Now I am wondering if I could just double the Isc and keep using the same marker. My panel Isc is 8.3. 230w/13.5 = 17 so that's going to be my expected amps? Twice 8.3 is 16.6

So ignoring the variable battery voltage, I might just say if I am not getting twice whatever Isc is , then something is wrong? Say I got 5a for Isc, then I should see 10a on the Trimetric? If not, then something is wrong?

What is a "DMM"? Some kind of meter? Sorry, acronyms are too vague at times. How did you get alligator clips for your DMM?

“Annual income twenty pounds, annual expenditure nineteen six, result happiness. Annual income twenty pounds, annual expenditure twenty pound ought and six, result misery.” Dickens.

86 watts is larger than 85 ;)

I predict a Psychic loss.

"An increase (Profit) or decrease (loss) in the acting man's satisfaction or happiness. Psychic profits and losses are sensible, subjective, mental and purely personal. They can be neither measured nor weighed. They can only be felt or sensed. The psychic profit or loss derived from any action can be compared with that of another solely in terms of more or less."

red31 wrote:

ken white wrote:

The PWM Controller makes the solar panel assume the battery voltage under normal operating conditions,

What makes the panel match batt voltage without a controller, ie directly connected?

The panel has an operating space where it acts as a constant current device - its internal impedance varies linearly with supplied voltage.

An ideal constant current device can assume any voltage across it.

The panel also has an operating space where the resistance changes non-linearly with voltage, and this starts to occur at the voltage point when the panel current starts to diminish quickly for a given irradiance.

Maximum panel power occurs on the non-linear resistance part of the I-V curve and that's where the MPPT controller operates.

A battery also has an internal impedance that is dynamic and is a function of its internal charge level and the physical condition of its plates.

If we were only interested in maximum power transfer, it would occur when the controller acts as an impedance matching device and matches these two internal impedances.

Salvo wrote:
Check this out. Some real data.

https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/25291818/srt/pa/pging/1/page/2.cfm

MPPT gains over pwm are in the 8% region when battery is held between 12.0 and 12.4V. What do you think the gain becomes when battery is at 13.0V?

---------deleted some--

Sal

That is my big question. I know I keep getting the amps with PWM, but I don't know if I will with MPPT if say Voc is low but Isc is still ok. (or other factors that come into play with MPPT using power instead of amps, allowing voltage to now matter)

I agree it is not possible to define one answer for many different situations, so I will just have to find out what I get in my own situation.

Also I keep seeing MPPT guys using Imp with their comparisons with PWM, which makes PWM look worse than it is. ( you get the higher amp Isc, not Imp with PWM)

Kind of a tortoise and hare situation with MPPT being the hare?

ken white wrote:

The PWM Controller makes the solar panel assume the battery voltage under normal operating conditions,

What makes the panel match batt voltage without a controller, ie directly connected?

Salvo wrote:
MPPT gains over pwm are in the 8% region when battery is held between 12.0 and 12.4V. What do you think the gain becomes when battery is at 13.0V?

I have solar for well over 6 years. Battery surface charge plays a major role in charging.

Sal

Gain of what?

A good charge controller will taper off the current/charge into the battery when the battery voltage increases above various SOC percentages - this operation reduces gassing and internal battery temperatures, and thereby increases battery life.

Bulk, Float, and Equalize charges all perform quite differently and are a function of charge control algorithms that vary with manufacturer, design topology, and model.

This means no blanket assertion, based on a specific test, under non-controlled conditions will give quantitative absolute results, but rather will give limited, qualitative type results.

Check this out. Some real data.

https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/25291818/srt/pa/pging/1/page/2.cfm

MPPT gains over pwm are in the 8% region when battery is held between 12.0 and 12.4V. What do you think the gain becomes when battery is at 13.0V?

I have solar for well over 6 years. Battery surface charge plays a major role in charging.

Sal

BFL13 wrote:
"Amps only tell one part of the system performance"

But it is the only part that matters to me! A is in AH. It is not VH or WH, it is AH. :)

LOL...

Then you won't be able to actually quantify system performance. :)

Just a quick question, how does the utility company bill you?

KiloWatt-Hours are a unit of energy consumption.

Just something to ponder.