I think remember in a conversation that the XW6048 should have a 400ah battery bank, yet the manual says a minimum 100ah battery bank.

(I found it, the 8/19/08 Solar Guppy Post: "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 ..."

What I was wondering is if the Xantrex manual is similar to the Microsoft expectations about running Windows XP with 512K of memory. Maybe it can be done, but in reality it doesn't work. Can the "technical reasons" please be explained? Is the 440ah to keep the system running longer, or will a smaller ah bank not work as well even when in Gridtie?

So does the battery bank have to be so big because all the power from the array first goes into the batteries and then back out to the grid? Or are the batteries really in equilibrium and not being charged or discharged, just conducting the output power from the array (somewhat like water flowing over ice)?

Will a small battery bank be so "overworked" by the chargers? Or will you thus loose a large portion of the array generated electricity because the minimum battery bank can't take it fast enough? And does such a minimum arrangement significantly shorten the life of the batteries?

A 100ah battery pack can only take about a 30 amp/hr maximum charge ... that's only ~1800 watt/hr , so off grid it would only work for the very small arrays and loads

Load wise, if you start pulling more that the C30 rate, the batterys are less efficient so for example with the 6kw XW-6048 you pull 4kw, you would get less than an hour before your batterys are flat dead with a 100ah battery pack

For Gridtie, the batteys are used to smooth out the varible solar to a more constant sell rate. If the bank is to small the inverter can oscillate on selling power level and the charge controllers can't do mppt since the load are varing so much ( also AC ripple on the DC batteys can cause the mppt to stop tracking )

A 440ah battery pack is not large by any means ... That's ~20KW of storage at 100% depth of discharge, so more like 15Kw usable or less than 2.5 hours if the inverter is running near full load

Xantrex Engineering has told me 400ah+ is the minimum, not sure why the manual has less, but a 100ah battery pack is near useless from a backup prospective. If your running Gridtie all the time ( don't need storage ) you should be running the GT inverters not the XW's

Typical off-grid system go for 3 days of backup ... so 2,000+ ah battery packs would be considered normal for this class of inverter

that 100ah minimal battery bank certainly would not be considered a good thing to use. in addition to sg's comments on it and looking at it from the built-in charger point of view of 100a into a 100ah b bank is a 100% rate of charge. few batteries advertise that they can take this amp for amp-hour on a normal basis. maybe under emergency circumstances this could be a minimum.

Thank you neil and solar guppy.