Morningstar says Go Big, You can't Hurt Me!

[DannyB1954]

You can run 24 volt from solar panels and have a controller that will charge 12 volt batteries. I think half the people are talking about that, the other half talking about grouping the batteries for 24 volts. The former would give better charging on overcast days and the voltage loss would be less using the same wires, the latter would make finding lighting and appliances much more difficult. It would also eliminate the possibility of using the vehicle's alternator to charge the house batteries.

 

[BradKW]

You can run 24 volt from solar panels and have a controller that will charge 12 volt batteries. I think half the people are talking about that, the other half talking about grouping the batteries for 24 volts. The former would give better charging on overcast days and the voltage loss would be less using the same wires, the latter would make finding lighting and appliances much more difficult. It would also eliminate the possibility of using the vehicle's alternator to charge the house batteries.

hmm...no, I think everyone talking about the same thing here. I'll actually have 325 watts running to the controller...not certain how many volts that will actually be tho.

I've been doing searches and turns out 24v mobile appliances aren't rare at all...for reasons I don't understand, many refrigerators are rated to run on Either 12v or 24v. Cheap, solid state step downs only loose 10% and should be fine for low usage stuff like LEDs and chargers...

 

[highdesertranger]

the 10% is huge especially when you start throwing in multiple 10%'s. highdesertranger

 

[BradKW]

I feel pretty good about decision to go 24v...with my system basically on edge of what would be considered grid-tie-size, things I've read elsewhere make me feel 24v is the safer choice given some of the components I'll be powering.

But it definitely has some drawbacks. While my 12v needs are small in comparison, I'd rather not loose any efficiency if possible. So what if I got a single 12v battery as a 2nd bank and split the power feed from one 325w panel into a PWM? Seems like a simple and logical solution, but I've never seen something like that...which probably means there's a good reason not to do it?

 

[AngryVanMan]

Hmm, not something I've considered, two controllers on one array or one panel.  For one thing, if either of the controllers or both is a MPPT, the power tracking algorithm is going to go bonkers every time the apparent load on the solar array changes from the other controller...  And with two MPPT's, as they each try to move the panel voltage around to get to peak watts, they are probably going to get very, very confused by each other.  This would be unpredictable at best.

PWM is also problematic, because each controller is operating a different battery voltage.  When the lower voltage PWM is "on" and sending juice to the battery, the solar array voltage effectively gets pulled down to the battery voltage.  This way, the higher voltage controller would never see an opportunity to draw power from the array, as it would be sitting at <24V anytime the 12V controller is using power.

Unless I've missed something, I don't think you can do this, unless you dedicate a separate panel to the 12V system by itself.

 

[sushidog]

You are correct. If almost all of your power usage will be at 12 volts, converting from 24 volts wouldn't be worth the 10% loss. However if most of your power usage will be at 110v ac or as in my case, 48v native DC then there will only be 10% loss on the 12v items, such as the DC power board of your fridge or the 12v slides. It depends entirely on how you will use the power you make and store.

Chip

 

[akrvbob]

If I understand you right you are going to have two complete, separate systems. If that's what you mean I think it's a great idea. I'm a big believer in redundancy--if one controller fails you still have power. But I would get a pair of golf carts for the 325 watt panel that you are keeping as 12 volt.
Bob