Panel voltage vs battery voltage.

[Sunking]

Thank you for your time! I am sure I will have other questions in the future! Learning... sometimes it's painful, sometimes it's expensive and sometimes... both!

You are welcome. Glad we finally got through to you. Yes solar is expensive, very expensive and extremely limited. FWIW don't feel left alone. 95% of everyone that comes here made the same mistake of buying something then comes here to find out why it does not work. It is expensive doing it right the first time, but a lot less expensive than doing it right the second time around or have to give up and take your losses. Education is not cheap.

[GlockG20]

Yes better than you have now.

Thank you for your time! I am sure I will have other questions in the future! Learning... sometimes it's painful, sometimes it's expensive and sometimes... both!

[Sunking]

So now that I understand how to improve the system performance as well as how the controllers work, I have a BlueSky MPPT charge controller sitting in storage. What if I took the 3 Renesola panels and put them in series on the Outback MPPT controller and then put the 2 Talesun panels on the BlueSky controller in series as well. I am looking for a single Talesun 250W panel now and of course the $$$ to get it. Would this work for an interim solution?

Yes better than you have now.

[Bucho]

I do not see any reason why not. He could configure 2 x 3 or 3 x 2.

Cool, I thought the Amperage would get too high for the charge controller, glad to hear I was wrong.

[GlockG20_10MM]

In the interim...

So now that I understand how to improve the system performance as well as how the controllers work, I have a BlueSky MPPT charge controller sitting in storage. What if I took the 3 Renesola panels and put them in series on the Outback MPPT controller and then put the 2 Talesun panels on the BlueSky controller in series as well. I am looking for a single Talesun 250W panel now and of course the $$$ to get it. Would this work for an interim solution?

[Sunking]

Can he just throw a 6th panel on his current charge controller and configure things so the system would work, I didn't think it was an option?

I do not see any reason why not. He could configure 2 x 3 or 3 x 2.

[Bucho]

He would still incur the cost of another controller and misc hardware and wiring. When for about the same cost or less just could buy the 6th panel to make things right...

Can he just throw a 6th panel on his current charge controller and configure things so the system would work, I didn't think it was an option?

You would still be left with a panel voltage that is too low where he is at now right?

Hopefully not, I agree with you that he needs a 6th panel.

The voltage would never get to a high enough state to match the output of the other string with a higher source voltage. About the only time it would ever be useful and functional is when the system drops down to Float voltage of 27.2 volts. Kind of like a 5 foot tall basketball player in a field of 7 foot players. The poor guy will never be part of the game and never see the ball 5 feet above his head of reach.

Interesting, I'd been wondering how that would work.

[GlockG20_10MM]

Which is why it's bad that your voltage isn't high enough.


Your MPPT charge controller converts the extra voltage into amperage. It's not perfectly efficient either way but there's probably a chart of it's efficiency at 24v and 48v somewhere you can look at.

The area highlighted answered my question and clears a ton of things up for me. THIS is the answer I was needing, now the rest is starting to sink in. THANK YOU!

[Sunking]

did you mean parallel?

Yeah my bad.

[sdold]

So lets say with his 5 panels in series he is required to have a fuse on each panel circuit going to a combiner, A fuse on the output combine, and rather large #8 to 6 AWG wire to handle 42 amps. That adds up to some serious cash.

did you mean parallel?

[Sunking]

I thought AMPS were what I need to charge the batteries and voltage was the driver to get the AMPS there" it is not clear because change voltage only reduces resistance lost in the wire.

Then you do not understand fundamentals. Yes amps is what you are after on the output side of the controller. On the input you want amps as low as possible. Here is one thing you do not understand. Power is a product of voltage and current. Example all these statements are true.

100 watts = 1 volt x 100 amps
100 watts = 10 volts x 10 amps
100 watts = 100 volts x 1 amp

A MPPT controller is a power converter much like a transformer of 95% and higher efficiency. So if I go in at 100 watts, I come out with 95 to 97 watts. MPPT Output Current = Watts / Battery voltage. So using an extreme example If I input 100 volts @ 1 amp(100 watts) on the out put I have 100 watts / 12 volts = 8.3 amps.

So with MPPT you want to run as high of a voltage as possible. Not only is it more efficient, but saves some serious cash.

So lets say with his 5 panels in series he is required to have a fuse on each panel circuit going to a combiner, A fuse on the output combine, and rather large #8 to 6 AWG wire to handle 42 amps. That adds up to some serious cash.

But if he had say a Midnite Solar Classic 200 he can wire all five panels in series operating at a voltage 150 volts @ 8.35 amps, you eliminate all hardware, combiner and fuses, and use a very inexpensive #14 AWG wire. That is a lot less expensive, more efficient with lower line losses and fewer eggs in the basket to go wrong. On the output of the controller you get 1275 watts / 24 volts = 53 amps.

[bulldrummerbullies]

Ok, hello! Quickly I am not totally new to off-grid solar but the longer I am in it the more I realize I know so little. This particular question deals with input voltage specifically. Oh... and before anyone says throw more $$$ at it... I am on a limited budget so that is not a viable option right now. Have to make due with what I have.

Now that being said:
System:
- 5 panels 24VDC 1.24kW potential
- 1 Outback MPPT 60A charge controller (12/24/48)
- 1 Tripplight 24VDC - 120AC inverter / charger
- 8 US Batteries 24VDC @ 760AH capacity

Everything is set up for 24VDC, but I saw somewhere that you could set the panels up at a higher voltage and that would increase efficiency. I am not an elecrician so this is where I get hazy. Wouldn't my kW capacity drop?

I know that in order to do this I would have to get 1 more panel or drop one panel out of the system. I also understand from what I was able to gather from the Outback literature that I can run the panels at 48VDC and the charge controller would make the required voltage step down for the batteries.

So is this a more efficient way to run the panels? And if so... why? Thank you for learning me!

You have been getting great advice from everyone. You need more panels at less one so you can go parallel. Now let us get back to your question "So is this a more efficient way to run the panels" going to a higher voltage is more efficient if you want to run smaller wire size. Resistance is reduced that is all. You can reduce resistance by increasing you wire size. You are being mislead by the term efficient. Inverter salesman tell you your system is more efficient because you can use cheaper wire, over sizing your wire will also make your system more efficient because of reduced resistance. if you are talking to a wire sale man. not a inverter salesman.
your statement "Anyhow... this is where I am not clear, I thought AMPS were what I need to charge the batteries and voltage was the driver to get the AMPS there" it is not clear because change voltage only reduces resistance lost in the wire.

[Sunking]

I get that 4 of his panels wouldn't charge a 48v bank any better than what he's got now but if he leaves the bank at 24v that's irreverent right?

Correct

Would leaving the bank at 24v, configuring 4 panels for "48v" and putting the 5th (and hopefully more) on a second charge controller be a viable option?

You would still be left with a panel voltage that is too low where he is at now right? He would still incur the cost of another controller and misc hardware and wiring. When for about the same cost or less just could buy the 6th panel to make things right...

Just to nick pick a little he does not have 24 volt battery panels which is part of the problem. At a minimum one needs 36 mono cells per 12 volts of battery which is a Vmp of 17 to 18 volts per 12 volts of battery. Sounds like he has 60 cell panels with a Vmp of 30 volts which is too low for a 24 volt battery. This gets back to your question of using a separate controller for the lonely single panel. The voltage would never get to a high enough state to match the output of the other string with a higher source voltage. About the only time it would ever be useful and functional is when the system drops down to Float voltage of 27.2 volts. Kind of like a 5 foot tall basketball player in a field of 7 foot players. The poor guy will never be part of the game and never see the ball 5 feet above his head of reach.

[Bucho]

Stop and think about it.

The only way to use his panels at 48 volts is 3 in series, and in groups of 3 in series.

I get that 4 of his panels wouldn't charge a 48v bank any better than what he's got now but if he leaves the bank at 24v that's irreverent right?

With that in mind my question is:

Would leaving the bank at 24v, configuring 4 panels for "48v" and putting the 5th (and hopefully more) on a second charge controller be a viable option?

Hopefully it makes more sense with 48v in euphemism quotes.

[Sunking]

It's probably just a question of how much he's willing to spend before it gets obvious. Would leaving the bank at 24v, configuring 4 panels for 48v and putting the 5th (and hopefully more) on a second charge controller be a viable option?

Stop and think about it.

The only way to use his panels at 48 volts is 3 in series, and in groups of 3 in series. Only 3, 6, 9 and 12 work in a 48 volt configuration with his 30 volt panels. 5 is a Prime number and only can be configure 5 in parallel or 5 in series. 3 is the only prime number that works or in multiple of 3's.

At 24 volts he can only use on paper 7 panels, but 7 is a Prime number and does not work because he has to use at least 2 panel in series. That only leaves him an option of 2, 4, or 6 panels. 5 will not work worth a dang.