Currently state of the art in data centers is to use the least amount of energy for a low PUE number removing heat from the data center.

What if the heat could be used to generate electricity? A dream? Yes.

Here is one attempt to turn heat into electricity.

Turning Waste Heat Into Power

ScienceDaily (Oct. 3, 2010) — What do a car engine, a power plant, a factory and a solar panel have in common? They all generate heat -- a lot of which is wasted.

University of Arizona physicists have discovered a new way of harvesting waste heat and turning it into electrical power.

Using a theoretical model of a so-called molecular thermoelectric device, the technology holds great promise for making cars, power plants, factories and solar panels more efficient, to name a few possible applications. In addition, more efficient thermoelectric materials would make ozone-depleting chlorofluorocarbons, or CFCs, obsolete.

A "forest" of molecules holds the promise of turning waste heat into electricity. UA physicists discovered that because of quantum effects, electron waves traveling along the backbone of each molecule interfere with each other, leading to the buildup of a voltage between the hot and cold electrodes (the golden structures on the bottom and top). (Credit: Justin Bergfield, University of Arizona)

The article doesn't discuss data centers. But does discuss photovoltaic and cars excess heat.

"Solar panels get very hot and their efficiency goes down," Stafford said. "You could harvest some of that heat and use it to generate additional electricity while simultaneously cooling the panel and making its own photovoltaic process more efficient."

"With a very efficient thermoelectric device based on our design, you could power about 200 100-Watt light bulbs using the waste heat of an automobile," he said. "Put another way, one could increase the car's efficiency by well over 25 percent, which would be ideal for a hybrid since it already uses an electrical motor."