The 51 volts comes from how the XW-6048 or FX-3048 ( outback ) sells to the grid with a battery based system. A Fully charged battery is 12.7V , so X4 = 50.8V . Anything above this then is going into the battery as excess charge ( with a fully charged battery bank )

The Charge Controllers will be current limited to what the inverter picks for a sell voltage, the more the chargers put into the battery, the more load the inverter apply s to the battery's. A voltage just above fully charged battery's means the excess charge is flowing into the grid, not the battery's.

To have the same wattage at 24V, you need 2X the amps so 2X the controllers. Also efficiency drops at the lower voltage as current losses are the Square of the current in electronics, so double the current and the losses increase by a factor of 4X. This is why high voltage gridtie units are so efficient, they are much lower currents and use the higher voltage to get the same wattage

Battery based systems are not over 48V ( nominal ) due to safety and regulatory concerns

As to why you don't want 150V into the charge controllers, since they are very high current units, there are other losses in these devices, one is called switching loses that increase as the voltage input increases and at 60 amps the loses really build up, which means more heat and lower efficiency in the conversion

Hope this helps!

YES, the replies have been very helpful. The problem is every time I learn a bit more I have more questions. I don't know why it has to be so complex.

OK, I understand the XW6048 is at 48V, selling to the grid. So therefore the battery pack MUST be 48V? I think so, but I'm not sure.

The charge controllers hook into the inverter, but I'm not sure how many controllers you can have on one inverter. I don't know if you also need a "distribution panel," which I don't know what that does.

Can the charge controller work on a different voltage than the inverter? I think it can, because they say the controller can even charge a battery pack with a higher voltage. But do you just set the voltage on the charge controller based on the PV panel setup you're plugging into it? And then the charge controller is set up to change the incoming voltage to 48dc outgoing since you've got an XW6048? And if you had an XW4024 the controller could and would be set up to change the outgoing voltage to 24dc? And if you had two charge controllers they could each work on a different incoming voltage depending on the PV panel setup for that controller, and each controller would change the outgoing voltage up or down to match the inverter it was hooked up to.

Somehow this must all make sense once you read the manuals and have the equipment, it is just so difficult to figure it out before so you know what equipment to get.

Thanks for the help.

Well it is complex and forums can help with some basic understanding, but your talking about a very lethal voltage/current/power setup and this is not a good first time project

I think what your missing is that the inverter / battery's have nothing to do with solar, its a device that takes energy from the battery's and makes 240 vac in the XW's case

Solar chargers take solar energy and charge battery's, the connection goto the battery's NOT the inverter and have there own breakers, combiners distribution panels ect

Now in what your considering, you will run this inverter so the excess charge into the battery ( can be from ANY source that is charging the battery's ) and have that sell back into you grid.

There is so much more than this basic understanding. You have NEC ( National Electric Codes ), this must be installed to these regulations and inspected by either polk-county building department or Bartow City building department in your case and they have an entire process to make sure you do it correctly. You have battery selection and sizing, all the required interconnects, breaker and or fusing, the wiring and sizing, conduit requirements. Choosing the preferred equipment is just a very small part of the process

If you should choose not to do the permitting process, you put at risk your home as it can't be sold ( permit for work will need to be shown at sale ) and if there is a claim on your home owner insurance, they will disallow any claim as you installed a power system without proper permits

I am happy you choose to visit and post at my forum and I and other can answer questions and help with learning about possible system choices, but don't fool yourself thinking we can provide an online course that will allow you to install a 6kw solar / hybrid / grid tie solar system. Unless you have the training or work with someone who does, you likely to have some dangerous results that can hurt you, your family our your property.

Yes, I agree completely. Even if I was crazy enough to try this at home, the state has saved me by requiring it to be installed by somebody who knows what they are doing.

However, sometimes those who "know what they're doing" only want to do it their way. That is why a forum such as this is so beneficial and appreciated. The answers are informative AND independent. Like the guy who was told to put the 3kw inverter on the 4.5kw system and nobody could figure out what was going wrong until this forum gave him the correct answers.

I am being told that it MUST be either 18 or 24 Sharp 224 panels, or the Xantrex XW6048 won't work properly and the warranty will be voided. That isn't what even the Xantrex website says. So it is very confusing.

From what I have learned here, the batteries are like a bathtub. The PV panels put energy (or water for this anology) in, going through the XW-60-150 charge controllers. It doesn't matter how much energy (water) is being supplied by each controller, they are independent. Then, when the inverter needs energy (water) for whatever reason, whether to power the house or sell to the grid, it is drawn from the battery bank (bathtub).

So the real question the becomes:

Why won't they let me have 22 Panels like I want, instead of either 18 or 24 panels, which I'm guessing is 6 or 8 strings of 3 PV panels hooked together?

The Xantrex website says it would be OK with 4 strings of 2 Sharp 224 PV panels for the controller, so if you have two controllers that would be 16 PV panels. Then, for the third controller there would be 3 strings of 2 Sharp 224 PV panels, that would be 6, for a total of 22 panels. I have also considered 3 strings of 3 Sharp 224 PV panels on two controllers, and 2 strings of 2 Sharp 224 PV panels on the third controller.

(A side story: When we were building the house we were told the warranty for the front door would be voided if we painted it the dark color we chose instead of white like the designer and builder wanted, because the door faced East! We said we didn't care, put it in writing and give us the color we chose. There was no further discussion, and AFAIK the door is still under the warranty.)

I don't know "who" is telling you 16 or 24 sharps, I don't even think sharps make sense, your much better off cost wise using Evergreen panels

The only install I know in this area is solarsource, they use beacon products, which I have explained to them are below the bottom of the barrel, they get a great deal on them, thats all they install or sell

It very simple, the panel increment is what ever it takes to have the solar panels output ( vmp ) be higher than the battery charging voltage. here in Florida you should chose either

( 5 ) 12V panels in series
( 4 ) 18V panels in series
( 3 ) 24V panels in series

for 48V batterys, you need at least 60 volts vmp, in the summer heat the panels will run about 70C

Use the Xantrex String calculator to verify the panel manufacture and exact panel and temperature range ( ambient ) min/max

Then you can put as many stings in parallel ( with fusing and combiners ) as the charge controller is rated for. When that is exceeded, just add more charge controllers

On the inverter / battery side you have two concerns. First is how long you expect to keep things powered off the battery's by themselves and second when running Gridtie only, the inverter still need a decent battery pack for technical reasons I'm not going into, but for an XW-6048, figure a MINIMUM of 440ah for a 5kw grid-tie operation ... which gives you about 10kwh of energy for when your running stand-alone down to 50% depth of discharge. We have here in Lakeland Battery US and I got my 220ah 6 Volt AGM's for about 5K ( 16 of them, 8 in series the the two strings in parrallel )

Here in Florida, I have yet to met an installer that has any technical depth in selecting manufactures or options for inverters , panels and battery's. They are so small ( volume ) they find a wholesaler to see a single brand of parts and that's all they do. You really can't expect much more, there just is no business to make this full time for them

YES, now that is making sense! The key is the battery charging voltage needed.

And now it is back to the question that I'm not sure that I'm getting an unbiased and correct answer to:

For the XW6048, with two XW-60-150 charge controllers, is it allowable for one charge controller to have three strings of three Sharp 224 watt panels, and the other charge controller to have four strings of three Sharp 224 watt panels? (And yes, I may be switching from Sharp 224 panels, but I didn't want to introduce more calculations for a different panel.) The voltage from each charge controller would then be the same, only the amps would be different. Why should that be a problem? Could the one controller "overpower" the other controller and somehow feed back to it? It doesn't seem possible, but I don't really know. Even when both controllers are hooked up to the same number of panels one group could be more than the other because of shadows, so it would be delivering differing amps. I guess an unequal charge controller setup is less than optimal, but why and by how much? And the inverter shouldn't care, it is just getting the energy from the battery pack?

Your correct, its makes no difference having different panels/wattage ect on each charger controller. All that has to be meet is the charge controllers voltage range is met ( and the vmp voltage is above the battery voltage at temperature )and the panels don't exceed the amps the controller is rated for.

If charger "A" has 500 watts and charger "B" has 1500 watts for an example that will work fine

Thanks for all the help Solar Guppy!

(I would have posted this earlier but my daughter and son have been sick for the past few days.)