For backup power, I am now a fuel cell bigot by Doug MohneyViews...

For backup power, I am now a fuel cell bigot by Doug Mohney
Views and Opinions on Green IT (Nov 1 2012)

As Hurricane Sandy dissipates across the northeastern United States, thousands of backup generators along its path are noisily burning diesel, putting particulate matter into the storm-cleaned air. If you want to be green and keep the servers on come heck or high water, the only solution that makes sense to me is a natural gas fuel cell.
I've been an advocate of on-site/co- generated power for a while, but various renewable options have drawbacks. Solar cells sound great, but unless there's a lot of land, roof space, or parking lot, most data centers will not be able to generate sufficient power from solar to run the whole facility. A hurricane with several days of rain will only serve to damp power generation -- in desert states such as Utah, Arizona, and Nevada, this isn't a problem -- just when the rest of the grid is unable to provide backup. There's also the not-pleasant through of having hurricane-force winds hurdling debris across or through solar panels -- ouch!
Wind turbines sound like a good idea too, but you again run into needing lots of real estate, plus height, noise, and radar/air traffic control issues once you start migrating from rural to suburban areas. Certainly during a large storm there's lots of wind energy to power your data center, but there's also the potential of having too much wind damaging or destroying equipment. Adding in the need to be able to buffer/bank power when the winds die down and wind is a non-starter.
If you can get on-site solar and wind power for your data center, by all means do so, but just keep in mind that you have to have a backup plan when Mother Nature decides to shuffle the cards.
So we're back to diesel generators and their four flaws: mechanical reliability, fuel, noise, and particulate emissions. Diesel generators have a lot of moving parts, so they need regular maintenance and testing. Even with rigorous preventive routines, the devices have a bad habit of not starting when you most need them.
Once started, diesel generators need a regular supply of fuel trucked in and in a power outage you're suddenly competing with everyone else who wants regular fuel deliveries. Shortages and blocked roads can easily add up to more headaches. Noise and particulate emissions -- smog, basically -- go hand in hand. Nobody wants to listen to the sudden drone of a generator or suck in all the gunk it is putting into the air.
Fuel cells are much more reliable than generators. There are fewer part and those parts don't make a racket. The typical output of a fuel cell will be practically no particulate emissions, some CO2 and water vapor, so it's quieter, cleaner, and simpler to operator. You also don't have to deal with a big real estate footprint as compared to solar or wind.
What's not to like? Using the Bloom Energy Server as an example, the equipment is expensive and you need easy access to natural gas. If your area or building isn't already setup for natural gas, there's piping and figures and trenching to be done, so it's a non-trivial capital project. But if you already have the pipes, then life is good because the odds of "losing" gas are much lower than traditional power. Pipelines tend to be more rugged and buried against incidents from the weather or utility-pole seeking vehicles. So long you keep an eye out for wayward back hoes digging around your pipes, natural gas is about reliable as you can get in a modern society.
Fuel cell equipment expense is the big headache. Bloom Energy and other manufacturers are working on bringing costs down and gas-based utilities are starting to team with Bloom for localized energy generation. With natural gas prices expected to be low and stable, utilities see gas fuel cells as a way to improve the environment and their bottom line.