Google says that modern off-the-shelf motherboards can run off of 12VDC inputs only. And that's apparently what they're doing in-house from the white paper.
While I welcome the neat knowledge that I can use only 12VDC PSs, I'm still puzzled because I figured that Google would skip the extra AC to DC conversion, and that their power distribution would like something like:
GRID -> AC/DC CONVERSION -> BATTERY ARRAY -> (DC/DC DOWN CONVERSION)? -> SERVERinstead of the apparent:
GRID -> TRANSFER SWITCH -> UPS (AC->DC->AC) -> POWER SUPPLY (AC->DC) -> SERVER GENERATOR -^Using 12VDC only power supplies, they have to match the PS to the server (granted they probably buy servers in lots of 10,000). While using DC-only distribution in-house means snaking a wire extension out a spare PCI slot.