FILE PHOTO - People visit an Apple store in Istanbul, Turkey August 15, 2018. REUTERS/Murad Sezer

(Reuters) - Apple Inc said on Thursday it has nearly doubled the number of suppliers using only clean energy for production work, including two that assemble and make the processor chips for the iPhone.

Apple last year said it meets all of its needs with renewable energy such as solar farms that power data centers. But a large part of its carbon footprint comes from its supply chain, and since 2015 Apple has worked directly with those companies to use clean energy for Apple production.

Forty-four companies are now in the program, Apple said on Thursday, including Hon Hai Precision Industry Co Ltd, whose Foxconn unit makes iPhones, and Taiwan Semiconductor Manufacturing Co Ltd, which supplies the A-series chips that power all of Apple’s mobile devices. Apple had previously disclosed 23 suppliers in the program.

The company defines clean energy as coming from wind, solar or bio-gas fuel cells, as well as what it calls “low-impact” hydroelectric projects like a site in Oregon that captures energy from water in irrigation canals to power one of its data centers.

Apple did not specify where the new suppliers in the program would get the clean energy. It encourages suppliers to build their own renewable energy projects, such as when iPad assembler Compal last year built rooftop solar installations on its factories in China.

When those options are not available, Apple says it aims to have suppliers sign power-purchase agreements with new renewable energy projects and using purchases of renewable energy credits only when there are no other options.

In an interview, Lisa Jackson, Apple’s vice president of environment, policy and social initiatives, said the company is also on track to pass its goal of adding 4 gigawatts of renewable energy to the grids of its supply chain by 2020 and has a “sight line” to “well over” 5 gigawatts.

Jackson declined to say whether Apple would drop suppliers such as Foxconn and TSMC - whose capabilities few others in the global electronics supply chain can match - if they fail to meet their commitments to the program.

“It took a while for them to come on board, and so we believe that now that they have, they’re fully committed to doing it,” Jackson said. “And obviously if they fall down on the job, we’ll be right there on their chase. I can’t tell you what will happen, but I hope it never does.”