Dumb question

[GregN5XO]

I have what may be a dumb question, we built a weekend 1400 sq ft cabin at our remote ranch, as we retire this year we will spend 4 to 5 days a week up there every other week or so....We are 100% off grid solar. I have a MPPT charge controller rated at 60 watts and up to max of 150 volts. I have 16 200 watt 12 volt panels on the first string, these are wired in groups of 2 in series for 24 volt application {we see 40 volts no load} my 8 AGM batteries are wired in series for 24 volts and parallel for amperage.....with a 5000 watt inverter running the house.....Fridge, tv, lights, fans, microwave, etc. We have 3 solar Air Conditioner/Heat pumps in, but those are 100% powered by independent solar panels, charge controller and batteries for each AC system.

So now to my question.....I am currently mounting another 16 solar panels again 12 volt panels at 200 watts. This will tie into a second matching charge controller rated at max of 150 volts and 60 amps. Would it be more beneficial to wire my solar panels up in say groups of 4 in series for basically a 48 volt charging system {no load voltage would be between 74 to 80 volts} or would it be better to wire it the same way as the first one with no load volt around 40}.

I want to do what will create the most efficient and beneficial charge to the batteries as possible, while supporting the load. Which would be better and why?

My original design was just two charge controllers and 2 sets of 16 panels for 24 volt type system. But a friend has been saying the higher voltage will be better????

 

[chrisski]

Specs on the panels will help, like a picture from the label. A 12 volt panel probably has a voltage of between 17 and 30 volts, which is a huge difference. I think in groups of 4, voltage will be maxed out at 120 volts, and another panel could not be added, but without specs, its speculation. Also, cold temps come into play as temps go up.

The size of the AGM batteries would help. I thought 100 ah when I read this until I saw a 5000 watt inverter and I thought I hope they’re bigger.

If you tell the model of the SCC, someone may be familiar with it. I know VIctron, but not others.

 

[rcrracer]

Tangentially related: When the heat pump batteries are charged, their solar panels are not being used. Any way you can utilize those panels to charge other batteries?

 

[GregN5XO]

Tangentially related: When the heat pump batteries are charged, their solar panels are not being used. Any way you can utilize those panels to charge other batteries?

I have given thought to that, but right now it would not be practical. But I like the idea and would have to figure a switch over system.

 

[upnorthandpersonal]

So now to my question.....I am currently mounting another 16 solar panels again 12 volt panels at 200 watts. This will tie into a second matching charge controller rated at max of 150 volts and 60 amps. Would it be more beneficial to wire my solar panels up in say groups of 4 in series for basically a 48 volt charging system {no load voltage would be between 74 to 80 volts} or would it be better to wire it the same way as the first one with no load volt around 40}.

Going higher voltage means you will have lower losses in the wiring (and can use smaller wire). However, if your panels have shading, you'll use more energy when one of the panels is shaded.

By the way, your 16 panels at 200W have the potential of generating 3.2kW. That's 133A at the 24V side. You're well overpowering your 60A charge controller. Might want to split the array and add another charge controller, or get a larger one.

 

[GregN5XO]

Specs on the panels will help, like a picture from the label. A 12 volt panel probably has a voltage of between 17 and 30 volts, which is a huge difference. I think in groups of 4, voltage will be maxed out at 120 volts, and another panel could not be added, but without specs, its speculation. Also, cold temps come into play as temps go up.

The size of the AGM batteries would help. I thought 100 ah when I read this until I saw a 5000 watt inverter and I thought I hope they’re bigger.

If you tell the model of the SCC, someone may be familiar with it. I know VIctron, but not others.

I do not have access to the panels right now, but they are 200 watt, 12 volt and the specifications are: Open Circuit voltage 22.3v, optimal operating 18.6. The charge controllers are units I picked up several years ago when I started building the system.....I purchased solar parts each month as cash flow came in for the past 4 years as we built the cabin.......I have three of these charge controllers, with the plan to eventually after we start spending more retirement time up there....to add a ground mounted set of panels and the 3rd controller.....along with 4 more batteries.

The batteries are Renogy 12 volt 200 amp AGM batteries, currently 8 of them are in place wired for 24 volts, with plans to add 4 more.

 

[GregN5XO]

Going higher voltage means you will have lower losses in the wiring (and can use smaller wire). However, if your panels have shading, you'll use more energy when one of the panels is shaded.

By the way, your 16 panels at 200W have the potential of generating 3.2kW. That's 133A at the 24V side. You're well overpowering your 60A charge controller. Might want to split the array and add another charge controller, or get a larger one.

Thanks, I can split them with no problem....Just a matter of moving the cables from one bus bar to another.

Am I doing the math wrong or did you misunderstand what I was saying:

There are 16 panels per charge controller, they are 12 volt panels, wired in groups of 2 to basically provide 24 volts.....so the way I calculated my power was based on 8 panels {groups} at 200 watts each, which put my power in the 1200 watt range....? Am I wrong?

 

[upnorthandpersonal]

There are 16 panels per charge controller, they are 12 volt panels, wired in groups of 2 to basically provide 24 volts.....so the way I calculated my power was based on 8 panels {groups} at 200 watts each, which put my power in the 1200 watt range....? Am I wrong?

16 panels per charge controller = 16 x 200W = 3200W, no matter how you arrange them.

 

[12VoltInstalls]

I think in groups of 4, voltage will be maxed out at 120 volts, and another panel could not be added, but without specs, its speculation. Also, cold temps come into play as temps go up.

I think he mentioned ~40V 2S so maybe 6 in series for 120V nominal? But 16 doesn’t divide by six…

I’d definitely go with more in series. Your solar input amps are higher than necessary. You can get the same or more power at lower amps with that simple change. In your situation I’d also change up to a 48V battery bank. Between those two changes you can get more out of your system.
Mirror the new setup to the old.

BTW do post the panel labeled specs. If they’re what I guessed at and chrisski alluded to there maybe an advantage to adding a couple panels to maximize your input. That 150V limit needs to be respected.

 

[GregN5XO]

16 panels per charge controller = 16 x 200W = 3200W, no matter how you arrange them.

That does not make sense.....if I take 2 12 volt 200 watt panels and wire them in parallel then we will see 12 volts but 400 watts. if we wire those same panels in series that is 24 volts but the wattage will remain at the 200 level of the single panel.

 

[GregN5XO]

I think he mentioned ~40V 2S so maybe 6 in series for 120V nominal? But 16 doesn’t divide by six…

I’d definitely go with more in series. Your solar input amps are higher than necessary. You can get the same or more power at lower amps with that simple change. In your situation I’d also change up to a 48V battery bank. Between those two changes you can get more out of your system.
Mirror the new setup to the old.

BTW do post the panel labeled specs. If they’re what I guessed at and chrisski alluded to there maybe an advantage to adding a couple panels to maximize your input. That 150V limit needs to be respected.

I plan on eventually converting to a 48 volt inverter, but that is down the road.

 

[12VoltInstalls]

That does not make sense.....if I take 2 12 volt 200 watt panels and wire them in parallel then we will see 12 volts but 400 watts. if we wire those same panels in series that is 24 volts but the wattage will remain at the 200 level of the single panel.

W=V*A

So no matter how you calculate the watts, in the end the watts are the actual potential.
2 commodity 12V panels in series:
(12V*2)*5.6A=134.4W
2 commodity 12V panels in parallel:
12V*(5.6A*2)=134.4W

 

[upnorthandpersonal]

That does not make sense.....if I take 2 12 volt 200 watt panels and wire them in parallel then we will see 12 volts but 400 watts. if we wire those same panels in series that is 24 volts but the wattage will remain at the 200 level of the single panel.

Sorry, no. Same as with battery cells: you can wire them in parallel and series all you want, in the end the capacity is the sum of all the cell's individual capacity. All you do with series and parallel connections is change the voltage/current ratio. Power = Voltage x Current. All you do with putting the two panels in series is increasing the voltage for the same amount of current, while in parallel you increase the current but keep the voltage the same. In the end, the same 400W is produced.

 

[GregN5XO]

Sorry, no. Same as with battery cells: you can wire them in parallel and series all you want, in the end the capacity is the sum of all the cell's individual capacity. All you do with series and parallel connections is change the voltage/current ratio. Power = Voltage x Current. All you do with putting the two panels in series is increasing the voltage for the same amount of current, while in parallel you increase the current but keep the voltage the same. In the end, the same 400W is produced.

So you are saying....That my 8 - 12 volt 200 amp batteries wired in series and parallel are not producing 24 volts and 800 amps, but really generating 24 volts at 1600 amps. That goes against everything I've understood.......

When you parallel the batteries the amperage goes up, but the voltage remains the same. When you series the batteries, the voltage goes up but the amperage remains the same.

 

[GregN5XO]

Sorry, no. Same as with battery cells: you can wire them in parallel and series all you want, in the end the capacity is the sum of all the cell's individual capacity. All you do with series and parallel connections is change the voltage/current ratio. Power = Voltage x Current. All you do with putting the two panels in series is increasing the voltage for the same amount of current, while in parallel you increase the current but keep the voltage the same. In the end, the same 400W is produced.

Two or more 12-volt batteries wired in parallel—positive to positive, negative to negative—is still a 12-volt system. Two or more 12-volt batteries wired in series—the positive terminal of one battery connected to the negative terminal of a second battery—develops 24 volts, but amperage doesn't change.

 

[upnorthandpersonal]

When you parallel the batteries the amperage goes up, but the voltage remains the same. When you series the batteries, the voltage goes up but the amperage remains the same.

Yes, and thus the power remains the same in either case.

If you take 2 x 12V 100W panels and wire them in series, the voltage goes up and the current stays the same.
If you take 2 x 12V 100W panels and wire them in parallel, the voltage stays the same and the current goes up.

In the end, the power of both systems stays the same: 2 x 100W = 200W.

 

[upnorthandpersonal]

So you are saying....That my 8 - 12 volt 200 amp batteries wired in series and parallel are not producing 24 volts and 800 amps, but really generating 24 volts at 1600 amps. That goes against everything I've understood

Let's use proper terminology: a 200AmpHour (Ah battery), not amp. Big difference.

If I have two 12V 100Ah batteries and wire them in series, I have a 24V 100Ah battery.
If I have two 12V 100Ah batteries and wire them in parallel, I have a 12V 200Ah battery.

In either case, I have 2.4kWh of energy capacity in these batteries.

 

[12VoltInstalls]

you are saying....That my 8 - 12 volt 200 amp batteries wired in series and parallel are not producing 24 volts and 800 amps, but really generating 24 volts at 1600 amps. That goes against everything I've understood.

8 12V 200Ah batteries is 1600Ah nominal.
No matter how you arrange them the watts will be the same. Watts is actually what runs things all else being equal. So yes, at 24V those batteries are 800Ah nominal but have the same watt-hour potential.

 

[12VoltInstalls]

I love it when two people answer at the very same time with the same data and 100% different words

 

[circus]

Your MPPT 60 amp rating is amps going into the battery. 16panels x 200watts = 3200watts.. 3200watts = 133amps @ 24 volts going into the battery. Last time I checked 133 is a lot higher than 60. No matter how you wire the panels, the wattage stays the same.