I have a grid tie system (Xantrex GT3.0) so my PV is connected for high voltage - about 300V max. I also have a battery bank (48V) and another inverter to use when the grid is down. Problem: I can't find a charge controller with a 300V input so I can charge the batteries from the PV array. I may design my own (buck type switching down converter with microprocessor control) but would like to know if anything is available. I would think others would have this same need but have never seen anything in print.....yet.

It is a well know need in the inner circles of designers for a HV charge controller.

There are many technical challenges a few that come to mind are switching losses due to FET performance, the killer is current, all the HV gridtie boxes are in the mid teens in amps as they only down convert to ~200V worst case, for battery charging RE style for a 48V battery bank is 40-60 amps. Spend an evening and look at the available FET's, then do the calc's for swicthing losses, a real eye opener. Then there is the fun mired of NEC/UL requirements with higher voltages, things like componet and circuit clearances.

There will be products like your suggesting in the future, just none you can buy today