BEIJING, Aug. 8 -- Sprawling across the vast suburbs of the Maiden, North Carolina, a massive solar farm is powering some of the most popular online services in the world, including iTunes and the App Store.

The largest private solar field in the United States, owned by Apple to support its local data center, comprises two 20-megawatt solar arrays, each covering 100 acres, and a few sheep that graze between the lines of panels.

It is part of Apple's efforts to reduce its carbon footprint by using renewable energy and driving energy efficiency in its products.

All of Apple's four data centers have used 100 percent renewable energy since March last year, and the one in Maiden, one of four opened in 2010, was designed from the ground up for energy efficiency, said Lisa Jackson, vice president for environmental initiatives at Apple.

The former administrator of the U.S. Environmental Protection Agency expressed the hope that Chinese companies, especially those in its supply chain, apply at least some of the ideas from the Maiden data center.

"On any given day, between 60 and 100 percent of the renewable energy it uses is generated onsite through the two solar arrays and another 10-megawatt biogas fuel cell installation, and we purchase any remaining power we need from entirely clean sources," Jackson told Xinhua.

On top of all the iTunes, apps, movies and TV shows downloaded via Apple products, the Maiden data center also deals with billions of messages and notifications, hundreds of millions of photos and millions of video chats every day.

"In each one of those transactions, no matter downloading a song from iTunes or interacting with Siri to ask a question, our customers do not contribute at all to any climate change or pollution," she said.

She pointed out that about 70 percent of Apple's overall carbon footprint now takes place in the manufacturing sector, and a significant part of its manufacturing happens in China.

"We shall not only work with the leading companies of our supply chain to improve energy efficiency, but also initiate things more innovative," she explained, "China has huge solar, wind and hydroelectric markets and our goal is to work with the government to expand clean energy use."

According to Apple's 2013 Environmental Responsibility Report, 167 million kilowatt hours of renewable energy are generated onsite in Maiden annually, enough to power the equivalent of 13,837 local homes a year.

A third solar array, with a capacity of 17.5 megawatts, is planned to keep pace with its growing computing and traffic capabilities.

"It needs fairly low maintenance, as the intelligent arms can trigger the solar panels to move to the correct positions under different weather conditions, and the sheep help us control the grass," she said.

The data center building, with a white roof designed to maximally reflect sunlight, is a model of energy efficiency.

It uses outside air and a chilled water storage system, in which water can be reused 35 times, to cool the servers and computers. As a result, air conditioners are turned off more than 75 percent of the time.

"The cleanest energy is the energy you never have to use. Even when it is renewable energy, we prefer not use it whenever possible," Jackson said.

Apple had been fiercely criticized by China's NGOs for pollution its suppliers caused, putting its environmental performance under media scrutiny.

In August 2011, a report jointly released by environmental organizations, spearheaded by the Beijing-based Institute of Public Environmental Affairs (IPE), found Meiko Electronics (Wuhan) Co., Ltd. had been discharging waste water containing concentrations of heavy metals, polluting the Yangtze River and a nearby lake.

Apple has worked hard to repair the damage. It launched the Clean Water Program in 2011 to help suppliers reduce water usage, promote water recycling and prevent water pollution.

Targeting water-intensive suppliers, including those producing printed circuit boards, enclosures and cover glass, the program chose 13 sites, which collectively consumed more than 41 million cubic meters of water annually, as pilot facilities last year.

"We start with a complete map of the facility's use of hazardous chemicals and wastewater process, carry out in-depth evaluations and sample water up to the discharge point," Jackson said, "Then we offer the supplier specific remediation actions depending on improvement needs."

"We find that it's often lack of understanding and ability to implement environmental requirements that leads to problems," she said.

Apple also initiated an 18-month program to train professionals in environmental health and safety.

In 2013, more than 240 factory personnel from over 60 supplier facilities covering 270,000 workers were enrolled in this program, which offers 25 courses in subjects like hazard risk identification and assessment, fire safety, industrial hygiene, water management and air pollution control.

"Apple has a supplier code of conduct. But if you just hand them the rules and walk away, you cannot expect full compliance. Instead, you have to train and audit. Even if a facility passes the audit, it still has room to improve."

The IT giant also disclosed some of its major suppliers, which it previously declined to make public. It has a total of 349 suppliers in China.

Apple's attempts have won positive feedback from China's NGOs. In mid-July, Apple was ranked first in a report jointly released by IPE and Natural Resources Defense Council (NRDC) in terms of enterprises' environmental information transparency.

"That doesn't happen by accident. We work really closely with IPE. They inform us of violations or concerns, and then we come to fix the problems. Again, we will share our solution data with IPE," Jackson said.

Apple sold a record 35.2 million iPhones globally in the third quarter of the 2014 fiscal year, up 13 percent over last year. It also sold 15.3 million iPads and 4.4 million Macs.