12v or 24v?

[bobdelso]

I bought 4, 300 watt split cell solar panels. They run at 33 volts, 9.2 amps. My goal is to run a 700watt air conditioner in an RV during the day and a few hours after night.

I bought them without realizing I would need such a large MPPT charge controller. It seems at 12v that I need at least a 150v and 100 amp charge charge controller which tends to run 400-600. I can also go with a 24v and could use a 50 amp charge controller. But then I need a 24v battery pack. I'm probably going to supplement the 1200 watts with a few 200 watt panels, but those will likely be on a seperate charge controller.

Option 1, 100amp charge controller, 12v 280ah diy lithium pack

Option 2, 50amp charge controller, 24v 2, 100ah diy lithium packs, or maybe 2, 280ah packs.

I think cost wise it makes the most sense to bite the bullet on an expensive charge controller and thick 12v wiring.

What would you do?

 

[Bluerso]

You could also use 2 charge controllers in the 12v setup with 2 panels on each controller. Or run the panels in 2s2p configuration then you could do a 100v charger.

Do you need to power 12v lights or appliances? If so you’ll need a way to do that in a 24v setup.

 

[bobdelso]

You could also use 2 charge controllers in the 12v setup with 2 panels on each controller. Or run the panels in 2s2p configuration then you could do a 100v charger.

Do you need to power 12v lights or appliances? If so you’ll need a way to do that in a 24v setup.

I won't need much for 12v. Water pump, lights and usb will be it. If I did 24v I would use a buck converter.

I'm not sure I fully understand solar charge controller ratings. Its usually voltage / charger output current right? So I could use 2, 100/50 chargers

 

[Northernchateau]

IMO go with 24 volts. (Two 12 volt Batteries in series.)
Lots of choises for charge controls, inverters, smaller wire, smaller fuses/circuit breakers.

As far as charge controllers, look for what input voltage they can handle, input amps, and input watts.

In your case with the 4 panels you have you can run them 2s2p.
2pr of in panels in series then feed them in parallel to the charge controller.
33 volts x 2 = 66 input volts @ 9.2 amps (that's your series connection)
9.2 amps x 2 = 18.4 amps from your parallel connection.
Look at a 20 amp Renogy Rover or Epever or a Victron Energy charge controller. Any of them will handle your panels and will run 12v or 24v.

 

[chrisski]

Recommend you come up with a Power requirement, like 12 kwh Per day, and run that through some sort of calculator for off grid to see if you get excess power, or "Power not captured." I have one in my signature block.

I say 12 kwh because the Air Conditioning will run non-stop in Arizona in my RV from May until October during daytime hours, and much longer at night for middle of the summer months. That gives 10 kwh power for the AC for 14 hours of run time, and 2 kwh for other use.

I have 1350 watts of power and expect to produce around 7.8 kwh tops and only in May and June, which lets me run a 700 watt AC for about 11 hours. All that power would go to AC and not recharging batteries. Its not until 3500 watts of panels that I get enough power saved up to run this AC all day long and most of the night (through the hotter months).

Next years project is getting a working AC in the RV and I'm trying to figure that out. My RV is just so poorly insulated, that when the AC is on, it never shuts off. Once it hits 90 outside, the AC is on non-stop and we have it set to 78. I'm sure most are no different. There's a few spots that will be easy for me to do something for insulation, like the skylights. I put my hand up to those when the AC is on and its pretty hot. If I could cut down on those enough to keep the cold air in, and my AZ shut off even a little, that would help a lot.

I went to somewhere with elevation by us to escape 110 degree days where temps at elevation were 90s in Late May, which is cool for our area. I turned the AC on at noon and shut it off at night. Those power requirements are a lot less and if the AC is run non-stop for only 6 hours a day, then at 1350 watts of panels I already have, I would be able to run your 700 watt AC off that and charge batteries.

 

[Sojourner1]

Recommend you come up with a Power requirement, like 12 kwh Per day, and run that through some sort of calculator for off grid to see if you get excess power, or "Power not captured." I have one in my signature block.

I say 12 kwh because the Air Conditioning will run non-stop in Arizona in my RV from May until October during daytime hours, and much longer at night for middle of the summer months. That gives 10 kwh power for the AC for 14 hours of run time, and 2 kwh for other use.

I have 1350 watts of power and expect to produce around 7.8 kwh tops and only in May and June, which lets me run a 700 watt AC for about 11 hours. All that power would go to AC and not recharging batteries. Its not until 3500 watts of panels that I get enough power saved up to run this AC all day long and most of the night (through the hotter months).

Next years project is getting a working AC in the RV and I'm trying to figure that out. My RV is just so poorly insulated, that when the AC is on, it never shuts off. Once it hits 90 outside, the AC is on non-stop and we have it set to 78. I'm sure most are no different. There's a few spots that will be easy for me to do something for insulation, like the skylights. I put my hand up to those when the AC is on and its pretty hot. If I could cut down on those enough to keep the cold air in, and my AZ shut off even a little, that would help a lot.

I went to somewhere with elevation by us to escape 110 degree days where temps at elevation were 90s in Late May, which is cool for our area. I turned the AC on at noon and shut it off at night. Those power requirements are a lot less and if the AC is run non-stop for only 6 hours a day, then at 1350 watts of panels I already have, I would be able to run your 700 watt AC off that and charge batteries.

Reflectix in the windows on the sunny side and those cushions that go in the roof vents with a piece of Reflectix there also helps alot with slowing the heat coming in if you don't do it already.

 

[chrisski]

The 14 x 14 were easy. The larger skylights is what I’m trying to figure out.

I will use the reflectix you mentioned, but I’m losing an argument with my wife when I do?

 

[Sojourner1]

My wife was against the Reflectix until we used it, now theres no hesitation to use it in the windows. The larger skylight use a cushion from a old couch or something cut down to size and a large pillow case or something with Reflectix cut to size. It makes a difference.

Even in the extreme cold it helps hold the heat inor cold out but you'll get condensation on the window that will need wiping off in the morning.

 

[chrisski]

What I notice loses heat a lot in the winter is the slide out floor. That is just 1” or 1/2” wood with no insulation. I’m sure a lot of heat comes in the RV from the summer.

 

[bobdelso]

IMO go with 24 volts. (Two 12 volt Batteries in series.)
Lots of choises for charge controls, inverters, smaller wire, smaller fuses/circuit breakers.

As far as charge controllers, look for what input voltage they can handle, input amps, and input watts.

In your case with the 4 panels you have you can run them 2s2p.
2pr of in panels in series then feed them in parallel to the charge controller.
33 volts x 2 = 66 input volts @ 9.2 amps (that's your series connection)
9.2 amps x 2 = 18.4 amps from your parallel connection.
Look at a 20 amp Renogy Rover or Epever or a Victron Energy charge controller. Any of them will handle your panels and will run 12v or 24v.

When I look at this data sheet is says I would need a 100/50 charger to have 1200(1400) watts of solar. Would a 20amp work?

 

[chrisski]

My guess is you want a 50 amp version.

A 20 amp controller at 24 volts would provide up to 720 watts of power and at 12 volts 360 watts of power. It will not push that much for very long though. It will start at a couple of watts at sunoise and then grow to 60%-90% of rated output when the sun is in the sky.

You need to push a bit more than 720 watts to power your air conditioner and charge the batteries.

Along with the charge controller comes panel placement. I did a poor job at planning my panels on my roof and pit 600 watt panels down to a 100/50. For the 12 volt build, that should push 36 amps tops, but I only see 20 - 25 tops. I added 350 more watts on the roof with a 100/30. I also have an additions 400 watts of portable panels panels through an additional 100/30. The best I’ve seen my 1350 watts of panels make is 1050 watts and 74 amps to a 12 volt battery bank.

With good planning, you would not have to use three SCCs like I did and could get 1420 watts of panels hooked up to the 100/50.

 

[Brassburnz]

IMO go with 24 volts. (Two 12 volt Batteries in series.)
Lots of choises for charge controls, inverters, smaller wire, smaller fuses/circuit breakers.

As far as charge controllers, look for what input voltage they can handle, input amps, and input watts.

In your case with the 4 panels you have you can run them 2s2p.
2pr of in panels in series then feed them in parallel to the charge controller.
33 volts x 2 = 66 input volts @ 9.2 amps (that's your series connection)
9.2 amps x 2 = 18.4 amps from your parallel connection.
Look at a 20 amp Renogy Rover or Epever or a Victron Energy charge controller. Any of them will handle your panels and will run 12v or 24v.

Here is the link to Midnite Solar Sizing tool from another thread. The tool is for a 30 amp SCC but it gives you a place to start. You'll need to get your numbers from the label on your panel. When you plug in 300 watts, 2S2P the result says excessive watts, but for a 50 amp SCC you would be OK. http://www.midnitesolar.com/sizingTool_kid/index.php

Go with 24v. I faced a similar dilemma of 12v vs. 24v. I have a 12/24v, 40 amp Renogy charge controller. I have four 180 watt panels. I can run them 2S2P safely with a 40 amp Renogy Rover SCC into a 24v battery bank. Although Renogy states the SCC automatically detects 12v or 24v, I had to use the app to set it manually. 24v, 2000/4000w PSW inverter. How long is the run from your batteries to the inverter? Check out the difference in cable prices.