Solar - more cells = better?

[john61ct]

Originally Posted by CatNewBee

shaded panels just deliver less Amps, while the exposed panel run full throttle

" just " ?

With multiple panels to one SC, one panel getting partially shaded even just a little, will *very significantly* reduce overall output to the bank.

Especially with MPPT, with constantly changing conditions as we commonly see on boats, you can watch the algorithm wildly fluctuating, changing panel voltage seeking the MPP.

Yes, with PWM panels, built-in diodes can help somewhat reduce the overall impact from partial shading, but each additional one reduces output 100% of the time.

The best solution for partial shading so far has been gear using the new embedded "MPPT on a chip" ICs from Maxim. This allows each cell string within a panel to get its own optimized MPP.

Unfortunately market implementations aren't readily available at the retail level.

Jinko "Eagle MX" is one line, others mentioned on Maxim's site are Trinapeak, and "ET COM"? Also Zerun SunLoam "turnkey junction-box solution" incorporates the Maxim chips, but then you're back to whole-panel MPP.

[CatNewBee]

I am happy with my solar...

[hpeer]

So I’ve got two 315W (nominal, 250W practical) LG panels, each run through its own controller. When connected they just go to the batteries, when the battery reaches 14.4 the controllers disconnect, let the voltage fall a bit the reconnect. It’s a bit more complicated but it works fine. Because I leave the boat unattended in the yard, safety is a big point and this is a very safe system, very hard to see how it could start a fire. The actual charge current just runs through a 60A mercury wetted contactor, electronics control the contactor.

I’ve been considering MPPT controllers but am undecided. On the one hand I have both solar and wind generation, keeps the batteries (12vdc, 4 GC, series/parallel)
Up pretty well.

Now I understand that I’m loosing some power due compared to an MPPT controller. On the other hand I have enough charge capacity.

I’m (retroactively) justifying my panel/controller combination on the grounds that while I’m not getting full charge amperage, I’m getting enough to float the batteries. I’m thinking the big panels do give me more power than a “12v panel” in sub optimal conditions such as early morning and during overcast periods. And when the sun is good then I have enough, I’d just be wasting the balance anyway.

Now if i could come up with good use for the divert load, or I had a bigger bank and more load then an MPPT would make more sense.

So how much of this is rationalization and baloney and how much is common sense?

[sailorboy1]

Originally Posted by hpeer

On the other hand I have enough charge capacity.

Well what more really do you want? You can always make systems "beter", but is it worth it if you gain little to nothing and just make it complicated?

My vote is just leave it alone if it's meeting you needs.

[hellosailor]

Hpeer, you can look it it either way. Let's say that your panels need 8 hours on a clear day to put a "days worth" of power into your battery bank. Ooops, thunderclouds cam in at 2PM and now, you're going ot lose 20% of your "days worth" of charging.

With an MPPT controller giving you some 10-15% additional power (over what a simple PWM controller would give you, which is still a boost over a plain pure DC charge cut-off) you'd be able to get a full charge before the clouds came in. It is not just about getting more--it is about getting it faster.

And, because PWM charging of any sort (MPPT controllers are all just "smarter" PWM controllers) do not cause the same amount of boiling and gas bubbling on the battery plates, you'll need to buy less distilled water and spend less time topping them up.

But on the other hand, if what you have is sufficient for your needs, then by all means keep it and don't buy "more" until you need it. MPPT controllers should keep getting more flexible and cheaper as the solar market keeps growing, anyway.

[noelex 77]

Originally Posted by hpeer

Now I understand that I’m loosing some power due compared to an MPPT controller.

What voltage are the panels?
I assume from your description they are high voltage panels. If you have a 12v system and do not use the voltage conversion inherent in MPPT controllers, you are going to be throwing away power, probably lots of power.

The loss can be easily estimated once the panel voltage and battery voltage is known.

It also sounds like you are using a regulator with an “on/off” or sometimes called “bang bang” charging regime. This is different from PWM battery charging algorithms.

“On/off” charging algorithms are very wasteful and even worse, given your application, never really charge the battery correctly. Even if you have loads of extra charging capacity, this may be affecting battery life.

MPPT controllers can be a little flakey and unreliable so I can understand you seeking an alternative product, but given the drawbacks this does not sound like a great solution. Further details would help.

[hpeer]

60 cell panels
Pmax 230
Vmpp 30
Imp 7.58
Voc 37.6
Jax 8.08

Flexcharge NC25A

[noelex 77]

Originally Posted by hellosailor

With an MPPT controller giving you some 10-15% additional power (over what a simple PWM controller would give you

This is true with “12v” panels with 12v battery bank, but there are not many (or even any?) “12v” panels available in this sort of large size (315w). With higher voltage panels the loss will be much greater.

[noelex 77]

Originally Posted by hpeer

60 cell panels
Pmax 230
Vmpp 30
Imp 7.58
Voc 37.6
Jax 8.08

Thanks for the details.

If you have a 12v battery bank using a non MPPT controller with those panels you will be loosing roughly about 40% of the available power output due to mismatch between the solar panel and battery voltage.

[john61ct]

Yes once VoC is past say 22V, go to MPPT or you're throwing money away.

[hpeer]

Originally Posted by noelex 77

Thanks for the details.

If you have a 12v battery bank using a non MPPT controller with those panels you will be loosing roughly about 40% of the available power output due to mismatch between the solar panel and battery voltage.

Thanks for that.

Question, I assume that’s true for a clear day with good sun. What about on an over cast day? So am I getting 40% of whatever is available or 40% of max?

[motion30]

Originally Posted by hpeer

So I’ve got two 315W (nominal, 250W practical) LG panels, each run through its own controller. When connected they just go to the batteries, when the battery reaches 14.4 the controllers disconnect, let the voltage fall a bit the reconnect. It’s a bit more complicated but it works fine. Because I leave the boat unattended in the yard, safety is a big point and this is a very safe system, very hard to see how it could start a fire. The actual charge current just runs through a 60A mercury wetted contactor, electronics control the contactor.

I’ve been considering MPPT controllers but am undecided. On the one hand I have both solar and wind generation, keeps the batteries (12vdc, 4 GC, series/parallel)
Up pretty well.

Now I understand that I’m loosing some power due compared to an MPPT controller. On the other hand I have enough charge capacity.

I’m (retroactively) justifying my panel/controller combination on the grounds that while I’m not getting full charge amperage, I’m getting enough to float the batteries. I’m thinking the big panels do give me more power than a “12v panel” in sub optimal conditions such as early morning and during overcast periods. And when the sun is good then I have enough, I’d just be wasting the balance anyway.

Now if i could come up with good use for the divert load, or I had a bigger bank and more load then an MPPT would make more sense.

So how much of this is rationalization and baloney and how much is common sense?

Do you have a hot water heater? Seems that would be a good place for the divert load

[motion30]

I recently bought a new Outback 80 amp controller off the web for $443

[john61ct]

Originally Posted by hpeer

Thanks for that.



Question, I assume that’s true for a clear day with good sun. What about on an over cast day? So am I getting 40% of whatever is available or 40% of max?

Hard numbers are impossible.

Always lower than you think until you get used to reading the data on your phone.

[hpeer]

Wrote a long reply restating the question and answered it myself. Current out put is limited to 8 amps at whatever voltage up to Vmpp. That’s at full radiance. Reduced radiance reduces amperage available, but voltage remains the same.

So yeah, I basically get nothing from 1/2 my panels. No mitigating circumstances.

MPPT would raise voltage coming from panels while still provinding 8 amps, more power. Got it.