According to Fred Miller, Eaton's product line manager for data center solutions, "UPS and green don't really go together. These are not efficient beasts, they're power hogs."
Still, there are ways to make them more efficient, Miller says, including making filtering technology an option, so the UPS comes on only when needed, when it senses a problem. That can raise the efficiency of an online UPS from 86% to 95% or more. The savings, obviously, vary according to how much you're paying for electricity.
Filtering technology costs more, of course, and also affects the continuity of the power. For absolutely mission critical applications, filtering is not a good choice, Miller says, but it may be worth using in other applications. Many modern UPS, including ones from Eaton, offer this as an option.
Apart from pure efficiency, there are other ways for UPS to go green. Look for UPS that runs cooler, for example, so it requires less energy to cool. That can add up to signficant savings, as cooling is often the second highest data center expense.
Also, a green UPS that generates less heat may require less space on the rack. As the rise of virtualization technology leads to denser data centers and puts rack space at a premium, that can make a big difference.
Finally, there's the issue of hazardous materials in the UPS. Eaton claims to have removed 95% of the hazardous materials from its products. Frankly, I don't know how big a deal this is, especially if you keep your UPS for a long time, but in this case less is certainly more.