XW battery methodology

Eric Ernst · May 2009

Hello, my first post, although I've been lurking for a while.

I am close to finalizing a Zantrex XW with battery back up system. Here is a question I'm not clear on about the XW.

I believe that the XW inverter and charge controller will keep the batteries topped off and ready for an outage, but will not use them during hours of darkness unless the grid goes down. Is that correct?

It is important because I don't think I need to buy batteries that are as expensive (good for continuous deep cycles) if the XW only uses them when there is a grid outage.

Thanks for any info you have.

E

mike95490 · May 2009

Re: XW battery methodology

Mostly, yes. You could get by with a small string of batteries (go 48V, that's 4 ea, 12V deep cycle batteries. 100AH @ 48V, 50% discharge gives 2.4KWh) You will only use them a couple times a year, when grid is down, but you will NOT have much capacity. Just enough to run a couple lights, radio and fridge for couple hours.
This is just a very rough summary.

Brock · May 2009

Re: XW battery methodology

What Mike said, but what you’re talking about will work and 100 amp battery is about the smallest I would go, the inverter can really hit the batteries hard starting a load and if you go with a smaller batteries the inverter might shut down due to low voltage.

The big advantage with this setup is you can sell back to the grid if you’re not using the power and if the power is out and it's sunny you can use all the power your panels can generate. In a situation like that you might want to shut off the fridge overnight and turn it on when the sun is out again.

The other advantage is with a smaller battery bank you will have less standby losses with the battery bank.

BB. · May 2009

Re: XW battery methodology

From another thread, Solar Guppy recommended a minimum of 400 AH @ 48 volts per inverter minimum:

Solar Guppy wrote: »

The XW-6048 is a great inverter and does every possible configuration for your RE. Gridtie, off-grid, true generator support ect.

Your ONLY choice for this inverter is 48V, and you will need at least 400ah PER INVERTER of batterys ... so your looking at close to 10K for the batterys using agms.

You will also need 4 charge controllers and your panels will have to have multiple home runs more than if you just used a straight high voltage GridTie inverter. The Maximum of any available mppt charger is never to exceed 150Volts, so typically this would be 2 possible 3 solar panels per string ( if each 24V ), then combined for the charge controller.

If you go all the new XW stuff, its all highly integrated, very clean installation and all the componets talk to each other so things like system watts or watts used, state of charger comes bulit into the package with a slick graphical remote system monitor.

The only other options would be Outback, but that would require 4 inverters stacked and they don't do split phase seemlessly like the XW's can. The Old Xantrex SW series really is no longer an option as its been discontiued after about 14 years of being in the market.

I have a single XW-6048, 440ah 48V agms with a pair of charge controllers, so its half of what your thinking ... it powers the AC and the solar can recharge enough that I can go forever without the grid as long as I get good sunshine each day ( only overnight ability ) ... to do more would require even more batteries!

For battery types, I would suggest AGM, they have a MUCH smaller float charge and no gassing. I had Deep Cycle Lead Acids before, a total pain to keep track of and I would never use them again over AGMs. For your bascially whole house UPS, the batteries will basically float all the time and AGMS are really only the logical choice for this large of a system

Oh, re-read your post, If you use ANY inverter with backup abilities, they REQUIRE a battery bank and seperate charge controllers .. for the XW-6048, the inverter can surge to 12kWh as loads demand, the smallest battery bank that can handle a 200amp discharge that load would created would be ~400 ah. Even if the XW is set to sell mode ( GridTie ) you need the battery bank as thats the buffer between the charge controllers which would get overwhlemed with AC ripple on two small a battery bank

XW battery methodology

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