Grid-tie inverter are great in terms of cost and efficiency. But when the grid goes down, the mega power PV plant sits idle. Since the probability of grid failure is so low, it doesn't justify a backup system. That doesn't mean the need is not there.

I got two large 3KVA and 2KVA APC UPSs for computers. My project is to feed the UPSs with a large 48V battery bank and charge the bank with two C40 charge controllers tie to the DC side of the ST2500s.

Since the C40 operates ~55V battery voltage, it should not affect ST's MMP higher voltage operation. Does anyone have a comment on this setup?

Hi,

Your ARE going to cause MAJOR problems if you are trying to charge your batteries from the same array the ST/XR is tracking off of. This flat out wont work , no if or buts about it.

I understand your concerns about a grid-failure and having 6Kw of solar panels doing nothing , your ups thing could work for critial loads but you would have to switch on the charging only if the inverter are offline. You could grid charge the batterys to keep them topped off but anything you are attempting is real for another cl*** of inveters , that being the SW series , the new outback or the AE MM-5000 style.

Hi Thomas,

I am doing what I think you want to do. I have a STXR on a 2000W array on the house. In the garage, I have a SW2512 and a large 4000AH battery bank. The bank is float charged with an old 40W Hoxan panel and a small charge controller. The AC input comes from a branch breaker in the main panel and the output goes back to a sub panel in the house with all af my important loads. The SW is in the standby mode just passing grid power thru to the sub panel and waiting for a power outage.

The combined output of the array goes to 2 mechanically interlocked CD breakers. One of the breakers goes to the DC input of the STXR and the other breaker feeds an underground cable to the garage where it is connected to a 48V in, 12V out MPPT charge controller for the 12V battery bank.

Sometime within the first few days of a power outage I have to go into the basement to throw the breakers to transfer the array to the garage to charge the batteries. I plan to eventually replace the interlocked breakers with a Kilovac latching relay and a delayed controller to automate the process. As it is set up now, the array can not be connected to both systems at the same time so there are no MPPT interaction issues.