From reading here, I now see that the SW5548 inverter is being phased out, and Solar Guppy recommends avoiding that one. For the XW model the choices are 4548 or 6048. For a 4560W system, would the XW 6048 work better, or would the XW 4548 be OK even though the system technically exceeds it by 60W?

And are SW and XW inverters GT inverters? I can't keep all the letters straight. Do all of them work with a battery backup if the grid power is off?

Thanks for the help.

The XW can be used as battery backed-up grid tie.
The GT is grid tie only, no battery possible
Ive got no idea about SW

Regarding the sizeing, have you gone to Xantrex's page, and played with the inverter/arrray size tool ? Enter your areas temperature ranges. Nameplate ratings are rarely met from solar panels. The XW will "throttle back" to protect itself in case of over power. It also depends on your battery voltage, the limit is in AMPS, not watts.
Your 4,560W array is likely to output only 3,876w on a good day, and at 48V, is nearly 80 amps, if I've done my math right.

For the minimal price difference, I would recommend the XW-6048 over the XW-4548, this are battery based inverters that can also sell back to the grid

The GT inverters are batterLESS inverters that directy sell all PV energy back into the grid, but without a grid, they remain offline.

For just gridtie, a GT5.0 ( 5kW ) would be a good match for your array. If your going to have a hybrid system, you need the XW-6048, batteries and a pair of XW-60-150 solar charge controllers, which is the link from the solar panels to the batteries an XW system requires

Thanks for the help.

Would it be acceptable to use two Outback MX-60 instead of the two XW-60-150? What is the downside to doing this? Or is it best to have all the same brand (Xantrex)?

MX-60 are now discontinued in favor of the new flexmax units

The XW-60-150 is more robust unit, has dynamic mppt tracking, its a passively cooled unit ( no fans like Outback products ) and would allow full networked ( Xanbus ) so the chargers can talk with the inverters, using off the shelf cat 5 cables.

Xantrex is the only manufacture that meets all required Saftey ( array GFI ) emissions ( FCC Class B ) for its entire GT and XW line of products

OK, this may be a newbie question, but why do I need two XW-60-150 charge controllers with one XW-6048?

Your charge controllers are seperate from the inverter, so it will depend on the Wattage of the solar array, which I read was 4,560W

Each controller ( MX or XW ) is limited to 60 amps and when selling back top the grid the battery voltage would be ~ 51 volts DC. So 51 * 60 is ~3,000 watts, which is way below the array wattage, that is why for you installation you would require two charge controllers

Do you know of any place that currently has the XW6048 in stock that sells them at a fair price? Louis at Sun Electronics said he doesn't have any more in stock. But for that one item I would purchase everything through him right away. Now, if I can't get the good inverter I'm not sure what to do or where to go.

Also, is there supposed to be state tax on this inverter purchase? It was my understanding that solar components were sales tax exempt. Do you have to fill out a form then and get the tax back from the state?

Also, how "minimal" would the price difference have to be to pick the XW-6048 over the XW-4548? And will the 4548 wear out quicker than the 6048 if it is running at 90% or 95% of its rating, rather than the 6048 at about 75%?

Did Louis say when they might have more in stock? , I'd suggest just ordering thru Sunelec as I doubt many places actually stock the XW parts but order as THEY get orders

You can check out http://www.beyondoilsolar.com/xantrex-xwinverter.htm, I have ordered before thru them, but nothing is "stocked", like most internet shops, they are just order process places and then have products dropped shipped from the one or two RE distributors in the US

Price difference is about 600-700 dollars, not enough to warrant going with a smaller unit and yes, running a unit near it maximum power day after day is going to limit its life.

On the Tax exempt status, its you pay then apply for a rebate, its not 100% clear to me that a battery based inverter is considered tax exempt, I would send an email to Jim.Tatum@dep.state.fl.us, he was a contact that answered all the Florida rebate questions when I had my system done last year.

This is the sales tax rebate form
http://www.dep.state.fl.us/energy/energ ... _11_07.pdf

Of course, nobody can know exactly how much the lifespan is decreased, but I wonder if it is really worth the price premium of just over 20%. Even if the lifespan was decreased 20%, which seems to be a lot, things would come out even.

And, I wonder where this decrease starts to occur. In running, there is the Lactate Threshold. If you want to finish a marathon, you must run under that threshold. You can run far under the threshold and finish much slower, you can run just at the threshold and finish in your best possible time, but if you run over that threshold you will "hit the wall" before you see the finish line.

I can't see an inverter lasting twice as long at 66% (for the XW6048) than at 90% capacity (for the XW4548). I can see the lifespan being drastically reduced if you're at 100% or even over for much of the time. But too, I thought the inverter had a program built in for protection from such things.

In general, lowering an electronics product by 10 degrees doubles its life. Will an XW-4548 last as long as a XW-6048 in your application? no one can say for sure. Running the XW4548 at 90% will run hotter than a XW6048 will run at 70%, The larger unit has more FET's and larger transformer

I assumed with a 4500+ watt solar array that debating a cost increase of 700 dollars was a very small part of the overall cost of the installed system. Further, since you selecting an XW inverter with battery backup, you intend to run house loads if power is lost. a 6Kw inverter can be much more handy that the 4500 watt in this case and if the time comes you do use this configuration, when a load can't be added running on battery's your going to lick yourself for "saving" 700 dollars

This is all my view and I understand everyone else has there way of seeing things

I didn't know about the 10 degrees to double the lifespan. That really is gigantic.

Also, I do agree with going with the larger XW6048, but they are apparently not available to purchase at this time.

That's the guideline we use for spacecraft electronics too. (within reason)

Hot/Cold thermal cycles are a big factor too, heating parts up, and cooling them down, causes cracked solder joints, broken wires etc.

By the way, the 10 degrees is "10 Degrees Centigrade" not Fahrenheit (would be 18 degrees Fahrenheit). And the corollary is that you drop the temperature by 10 degrees Centigrade/Celsius, you will extend the life by 2x.

The other "killer" is thermal cycling... It is better to avoid cycling temperatures too, both min/max temperatures and temperature cycling (keep things between cool and warm vs cool and "hot" cycling, and try to reduce the numbers of thermal cycling). I used to evaluate disk and tape drives in another life and found (really confirmed) that thermal cycling and fast ramping (within product ratings) of environmental temperatures would kill any product that was not properly designed and assembled.

-Bill

OK, I've been wondering about this for days.

How do you know that the battery voltage would be ~ 51 volts DC? Is that because the battery bank should be 48V for maximum efficiency? And what if you use only 24 V? Are there benefits? From the Xantrex XW Calculator, it seems that 24 V would give me more options for the solar panels.

Well, maybe now after writing the questions I have partially figured it out. Is it 48V because that allows each XW-60-150 to deliver the maximum watts back to the grid? So if it was 24V you could only deliver half as many watts, and would need two inverters instead of one? But the charge controller could handle as much as 150V? But you really can't have a battery pack over 48V for safety reasons?

Thanks for the help.