As we continue to grow as an organisation, sustainability remains an important issue that we are deeply committed to. With Earth Day coming up this Sunday, I wanted to take this opportunity to discuss the progress we've made thus far around our growing use of renewable energy and our commitment to moving towards a more sustainable future.
It's no secret that data centres can consume extreme amounts of energy to meet the needs of their customers. With the increasing demand for real-time data, AI, machine learning, and the continual migration out of server closets to purpose-built data centres, power consumption is continually on the rise. Digital Realty recognizes the importance of addressing our customers' growing demand for resource-efficient, sustainably constructed, and renewable-powered data centres, so we're continually investigating new ways to improve in these areas whilst maintaining our commitments to uptime, performance and scalability for customers whilst creating value for our shareholders.
A recent example of our efforts toward this initiative was teaming up with the San Francisco Public Utilities Commission (SFPUC) to enable the switch to greenhouse gas-free power for our 365 Main Street data centre, a project that makes us one of The SFPUC's largest clean energy customers. The SFPUC’s Hetch Hetchy Power System represents some of the cleanest energy available in California and this switch will substantially reduce the city’s greenhouse gas emissions – by 24 million pounds of CO2 annually – equivalent to the electricity use of 1,600 homes for an entire year.
In 2015, Digital Realty introduced the Clean Start℠ Programme to help clients discover just how easy it is to transition to clean energy. That same year, we issued the data centre industry's first-ever green bond. We allocated nearly $500 million of bond proceeds to sustainably-certified green building projects around the world. Since that time, Digital Realty has significantly expanded its renewable energy sourcing. More than 85% of our EMEA portfolio sources renewable energy, and in the United States we have executed three utility-scale power purchase agreements to source renewable energy from new wind and solar farms proximate to our data centres. These contracts allow us to address 100 percent of our U.S. colocation and interconnection energy usage with renewable energy. The environmental benefits from these PPAs are comparable to taking 58,000 cars off the road, or avoiding approximately 515,000 metric tonnes of carbon dioxide emissions per year.
Digital Realty has one of the largest portfolio of green building certifications in the data centre industry, with completed projects. This effort traces its roots back to our first LEED certification back in 2007. We also continue to actively pursue energy and water savings initiatives across our portfolio. We joined the US Department of Energy’s better Buildings Challenge 3 years ago, and by 2017 we had achieved (and exceeded) our 20% energy savings commitment.
While we've made great progress, we recognise that sustainability is an on-going journey, not a destination. Data centres are the backbone of today's digital economy and Digital Realty seeks to take a leading role to create a sustainable digital infrastructure. We recognise that the steps we take toward sustainability today will impact the whole of the data centre industry in the future. Our efforts are one piece of the puzzle as we work with our customers, suppliers, and employees scale up their own renewable energy and sustainability initiatives. By taking a holistic approach to our sustainability actions we are able to deliver highly efficient data centre solutions that meet the needs of an increasingly connected world.