Inverters

I engineer small solar systems which use solar panels, DC charge controllers, a battery bank and an inverter. I'm fairly well versed on systems this size. Recently I joined a new group who are building medium and large size systems. I have had to study and get up to date on how large systems work. I have found hundreds of sources for inverters and frankly it gets confusing when you try to chose one over the other. I learned that grid tie inverters can operate using high voltages (400-500VDC) from the solar array and without a battery bank. They power your load and, if permitted, feed excess power back into the grid. If the grid should fail the grid tie inverter shuts down. To prevent this from happening you need another inverter with a battery bank to make a mini-grid. This fools the grid tie inverter into thinking the grid is still present even when it isn't. I live and work in the Dominican Republic where grid power is terrible. It's not unusual to have 3 or 4 power failures every day. We are planning to build systems up to 100KW so this problem is serious. The first system we built used 63 220Watt solar panels, 3 OutBack FM80 charge controllers, 4 OutBack FX3048T inverters set up for 120/240VAC and 48 Surrette 2v 1776AH wet type batteries. Based on what I have learned from the web and what is available it seems that if we get into systems much bigger than this the DC portion will get very cumbersome and may become the limiting factor. The next site will have twice as many panels. The client wants to run air conditioners during the day time. I suggested a grid tie inverter with a second inverter to form the mini-grid. But what concerns me is what do you do when you get into huge solar systems like say 1 megawatt or more. If you want to run it off grid what kind of an inverter do you need and can you avoid using the mini-grid with batteries. For daytime operation the mini-grid is required as the brain and will start a generator on cloudy days and at night. What kind of inverters are used on say a 25Megawatt system?