Two years after Greenpeace slammed Apple for using "dirty energy" to power its cloud data, the environmental group has praised the company for its usage of renewable energy in maintaining its datacenters, calling it "the most innovative and most aggressive" firm in Silicon Valley in terms of using clean power.

Apple's datacenters scored 100 percent in Greenpeace's clean energy index, with none of their energy coming from coal, nuclear, or natural gas sources. The company was awarded "A" ranks in energy transparency, deployment and advocacy, and commitment, scoring a "B" rank in its energy efficiency. Facebook also scored three As and a B, but had a lower clean energy index of 49 percent, while Microsoft received Cs across the board and a 29 percent clean-energy index. Apple scored Ds and Fs in the same categories in the 2012 report — the same ranks Amazon received this year — but disputed the ranking at the time.

None of the energy used by Apple's datacenters comes from coal, nuclear, or natural gas

Apple committed to powering its datacenters with renewable energy in 2012. The company built a 20-megawatt solar array and 5-megawatt fuel cell system at its huge facility in Maiden, North Carolina. The installation provides 60 percent of the datacenter's power, while the rest is generated by local, renewable sources. Other centers in California and Oregon are powered by wind energy, while its newest location in Nevada is to be powered by geothermal plants and solar arrays. In May of 2013, Apple announced 75 percent of the energy used across its entire operation came from renewable sources.

Greenpeace praised Apple, saying it had the "inside track among the IT sector's leaders in building a green Internet," but still criticized the company for not feeding its findings back to the wider tech industry. "Sharing more detail about Apple's energy efficient designs would help the IT sector to learn from, and improve upon, Apple's best efficiency practices."