Advise on a new 2200W RV Solar System

[proesner]

Am I missing anything critical. I have some questions outlines next to components that came up as I was researching. Thanks!

 

[12VoltInstalls]

I probably would Class-T at the battery and not downline of the busbars.

 

[chrisski]

-70 amps into a into a 24 volt system. That’s probably fine if that’s what you want. Not sure of the panel total wattage. For my RV, there’s times in the summer where it can get close to full input on the roof mounted panels. Battery charge rate might want have you throttle back.

-I don’t like some of the hardware pictured. I don’t know if that’s the actual hardware you are using and even if it is the specs could be different than the piece I looked at.
—The busbars appear to be a type f brass busbars I chose not to use,
—The switch might only be rated to 125 amps at 24 volts and does not have a UL rating. Could get more than 125 amps at inverter low voltage cutoff and max loads.

 

[pvgirl]

You will want more then a 20a circuit breaker on the output of 35 amp charge controller. A 50amp breaker would be best with wiring to match.

 

[proesner]

-70 amps into a into a 24 volt system. That’s probably fine if that’s what you want. Not sure of the panel total wattage. For my RV, there’s times in the summer where it can get close to full input on the roof mounted panels. Battery charge rate might want have you throttle back.

-I don’t like some of the hardware pictured. I don’t know if that’s the actual hardware you are using and even if it is the specs could be different than the piece I looked at.
—The busbars appear to be a type f brass busbars I chose not to use,
—The switch might only be rated to 125 amps at 24 volts and does not have a UL rating. Could get more than 125 amps at inverter low voltage cutoff and max loads.

Thanks for the reply. 70amps of solar amperage into the 24vollt system? Do you arrive at that number because of the twin solar controllers? It's my understanding that the 35 designation on the controller is the max amperage rating that is allowed to go through it, not the actual rating. Only about 13amp will go through it per solar string.

I was on the fence about the $20-$30 busbars. I'm not sure what else are my options.

The switch? The master cut off switch you see in red? If you are talking about that, the one I have selected/pictured is rated for 300amp.

 

[proesner]

You will want more then a 20a circuit breaker on the output of 35 amp charge controller. A 50amp breaker would be best with wiring to match.

The 20A is based on the short circuit current * the circuit denominator, of the string of panels tied to that breaker. 13.41A (short circuit rating of panels on that string) * 1.5~(circuit breaker denominator) = 20.1A. Breaker chosen is 20A. The solar wiring will be 10AWG at about 50ft per side.

 

[chrisski]

Thanks for the reply. 70amps of solar amperage into the 24vollt system? Do you arrive at that number because of the twin solar controllers?

Yes.

Each controller puts out a max of 35 amps for a total of 70 amps x 24 volts = 1680 watts charging.

Do you mean 13 amps per SCC charging the battery? If so that could max out the SCC.

One good thing about the Victron 150/35 is the 48 volt option. The same two SCCs would max out around 3300 watts charging.

I was on the fence about the $20-$30 busbars. I'm not sure what else are my options

If those are the busbars I think, I have a pair sitting on the shelf unused. There is no cheap option for copper bar. I used Blue Sea.

The switch? The master cut off switch you see in red? If you are talking about that, the one I have selected/pictured is rated for 300amp.

is that 300 amps at 48 volts? The switch I am thinking of had a misleading 250 amp rating until you searched other ads and read the fine print.

I buy my parts rated for the highest volts the system will see. For my 24 volt lithium batteries, that would be at least a rating of 30 volts, but it they were lead acid with equalization, that could be 33 volts.

 

[Tomthumb62]

I was on the fence about the $20-$30 busbars. I'm not sure what else are my options.

The brass bus bars are fine if you don’t intend to run more than say 125A through them. They say they’re rated for 250A but I’ve read many times that they get way too warm at 250A continuous, so they’re likely over rated. Yes pure copper is always better for less resistance but it’s expensive and overkill if you’re not running many amps through them. My “250A” bus bars don’t see more than 50A on a regular basis. Max my system could do is about 120A total in and out but it will probably never see that.

If you do want pure copper bus bars, look to spend about $60-80 each for 300A bars. Victron and Blue Seas have nice ones. I believe the Blue Seas ones you have to buy the protective covers separately, I think those are about $30 each. If you need 600A ones, I think Victron has those too, I think also 1000A ones but those are some serious cash. Haven’t read your whole thread but I think you’re considering 48v, so in that case your amps will be much lower. My system is 12v but my power needs are pretty small: basic rv dc loads like lights, water pump, 1000w inverter powers apartment sized fridge (70w running), usb ports for charging things and a couple dc fans.

You can also DIY your own bus bars but you’ll need to make some covers, too. Maybe someone has a 3d printer file if you have access to one.

 

[12VoltInstalls]

my understanding that the 35 designation on the controller is the max amperage rating that is allowed to go through it, not the actual rating. Only about 13amp will go through it per solar string

But you should wire it, imho, to handle the potential output of whatever device. Maybe user a ‘lower’ fuse if that strikes your sensibilities, but wire it safely: at or exceeding the output potential of the device.

 

[pvgirl]

The 20A is based on the short circuit current * the circuit denominator, of the string of panels tied to that breaker. 13.41A (short circuit rating of panels on that string) * 1.5~(circuit breaker denominator) = 20.1A. Breaker chosen is 20A. The solar wiring will be 10AWG at about 50ft per side.

That would be fine for breakers on the solar input side of the charge controller, but your diagram shows the breakers on the output side of the charge controller which each can output 35amps, so the protection for that circuit would need to be sized for that current. (35amps * 1.25 = 44amps, next breaker size up is 50amps)

The charge controller will be reducing the voltage of the solar string to the voltage needed to charge the batteries, which due to the relationship of watts, amps, and volts, will lead to more amps on the output of the charge controller then is going in, for the same power(watts) as volts goes down amps will go up.

 

[proesner]

But you should wire it, imho, to handle the potential output of whatever device. Maybe user a ‘lower’ fuse if that strikes your sensibilities, but wire it safely: at or exceeding the output potential of the device.

So you're potentially saying a should fuse the solar circuit for 40A, not 20A, based on the total Amperage of the Solar Controller, not the planned Amperage of the Solar String?

 

[12VoltInstalls]

So you're potentially saying a should fuse the solar circuit for 40A, not 20A, based on the total Amperage of the Solar Controller, not the planned Amperage of the Solar String?

I might do that, I usually fuse stuff based on the load but I always consider it good practice to wire things for the current potential of the device I’m connecting.
So cable it to handle the SCC output, and fuse it ‘safer.’ That’s not a requirement, but has been my habit forever. If something can do only 20A I want the fuse or breaker close enough to cut off current if by some bizarre circumstance it sees 25A

 

[proesner]

That would be fine for breakers on the solar input side of the charge controller, but your diagram shows the breakers on the output side of the charge controller which each can output 35amps, so the protection for that circuit would need to be sized for that current. (35amps * 1.25 = 44amps, next breaker size up is 50amps)

The charge controller will be reducing the voltage of the solar string to the voltage needed to charge the batteries, which due to the relationship of watts, amps, and volts, will lead to more amps on the output of the charge controller then is going in, for the same power(watts) as volts goes down amps will go up.

I think I'm hearing what you're saying. If I missed this, this was a big mistake on my part.

Let's say the we have 100V and 15A coming in from one string of panels, and it hits the Solar Controller. It has to convert the 100V to 24V (to support the batter bank / inverter ratings), and then "ups" the Amperage to compensate for the lower V rating and continue the true amount solar power coming in.

This Amperage would be 100V/24V = 4.1; 15A * 4.1 = 61.5A going through the cables after the Solar Controller if I wanted to keep the 100% of power coming in from the roof. However, the 35A rating on the solar controller will basically cut that power in half. That will be a huge downside.

This is where a 48V system would come in handy.

 

[pvgirl]

I think I'm hearing what you're saying. If I missed this, this was a big mistake on my part.

Let's say the we have 100V and 15A coming in from one string of panels, and it hits the Solar Controller. It has to convert the 100V to 24V (to support the batter bank / inverter ratings), and then "ups" the Amperage to compensate for the lower V rating and continue the true amount solar power coming in.

This Amperage would be 100V/24V = 4.1; 15A * 4.1 = 61.5A going through the cables after the Solar Controller if I wanted to keep the 100% of power coming in from the roof. However, the 35A rating on the solar controller will basically cut that power in half. That will be a huge downside.

This is where a 48V system would come in handy.

Yup.

In your case, input to the charge controller will be at max power:
87.6 volts, 12.6 amps, which is 1,104 watts

That same number of watts will come out of the charge controller, less efficiency losses. Best case that would be 1104watts * 98%(max efficiency from datasheet), which is 1082 watts output. At 24 volts that will be 45 amps, or at 48 volts 23 amps. Your currently selected charge controller will limit the output to 35 amps no matter the battery voltage, so that will determine breaker and wiring sizing. But this minimal over sizing is within victrons specs, and will only limit output power during the very limited time the panels are putting out their max power, most of the time they will be putting out less and this limit will not be an issue.

 

[pvgirl]

You also should consider adding a second or third battery or a different battery design, as the maximum output of the battery you selected is only 100amps, and a 3000va inverter can pull more then that on a 24volt system. 3000va / 90% efficiency(estimate) * 22volts (minimum battery voltage) = 152 amps max continuous from the 24 volt battery bank. A 300amp fuse is the recommend value by victron for this inverter.

 

[proesner]

You also should consider adding a second or third battery or a different battery design, as the maximum output of the battery you selected is only 100amps, and a 3000va inverter can pull more then that on a 24volt system. 3000va / 90% efficiency(estimate) * 22volts (minimum battery voltage) = 152 amps max continuous from the 24 volt battery bank. A 300amp fuse is the recommend value by victron for this inverter.

This is some amazing advise. I'm going to readjust my setup. Thank you so much!

 

[proesner]

Good morning everyone... I've done some more research, made detailed considerations (attached PDF diagram) based on that research and most of the comments left on this thread.