The dispute over how dirty Apple's data centers are continues: In the wake of Greenpeace's latest report criticizing IT giants [PDF] for relying on dirty energy for their data centers, Apple struck back at Greenpeace, arguing the advocacy group vastly overestimated the energy used by its North Carolina data center.

Apple denied accusations from Greenpeace that it relies on dirty, coal energy to power its massive data centers, which house its cloud services, arguing that it has already made significant strides in energy efficiency and citing its plans to build a solar-powered site at the North Carolina facility. Apple, of course, is not alone in Greenpeace's crosshairs: The group also targeted Microsoft and Amazon for using dirty energy to fuel their data centers, saying they haven't yet gotten the clean-energy message.

Although Greenpeace's campaign has again raised the question of just how green -- or dirty -- big tech companies' clouds are, we got to wondering just what it takes to actually green the cloud. It turns out that a number of simple, inexpensive steps to data center energy efficiency are available to those willing to take a second look.

Is it difficult to build a greener cloud?

Building a greener cloud is not as difficult as one might think. According to Paul Baier, Vice President of Sustainability Consulting for Groom Energy (and a senior contributor to GreenBiz.com), services like Slicehost (now a part of Rackspace) and Amazon Web Services make it easy for IT professionals to purchase the computing power they need, when they need it, which in turn avoids low utilization rates that waste energy.

Simple design choices to help companies get started

In addition to being a leader in green cloud services, Google has also been a leading sharer of best practices for data center operations and improving energy efficiency. According to Google, a $25,000 investment in parts to improve its airflow management in the data centers has saved the company $65,000 annually in energy costs. These best practices look at a number of factors that can significantly improve data center efficiency, including:

• Analyze air flow to the data center in order to make design choices
• Install low-cost materials such as meat locker curtains or sheet metal doors to separate the cold aisles from the hot
• Seal the rack space (similar to weatherizing your house)
• Use free cooling options, or ambient temperatures around the data centers to provide cooling (i.e. sea water cooling or evaporative cooling) instead of chillers
• Measure PUE (Power Usage Effectiveness) as often as possible by integrating it into the building management system
• Adjust the thermostat in the data center to a higher temperature

These steps can be a useful starting point for streamlining data center operations, no matter what their size.

How a data center's location comes into play

Data centers are generally not difficult to move, but they are dependent on the electricity rates and sources in the local area where they are situated. More opportunities can come from optimizing existing data centers, Baier says.

"The most important element is ensuring senior management focus on energy efficiency and sustainability for the data center and not solely reliability," Baier said in a statement. "For decades, data centers were optimized for reliability with little to no attention paid to energy efficiency. One important reality is that CIOs and data center managers focus on reliability and uptime and usually not energy efficiency. Poor reliability gets data center managers fired, but poor energy efficiency does not."

Regardless of where a data center is located, by looking at best practices and focusing on energy efficiency as a priority rather than just reliability, are the first steps in making a difference toward reducing the growing energy footprint that data centers are responsible for.