It's not the only big company transforming a broad swath of businesses. Wal-Mart is also driving the green economy. The company now requires suppliers - numbering more than 100,000 companies - to submit data about their environmental footprints. That has created a business opportunity for London-based Intertek, which found 50 new clients in the past six months as a result. "Wal-Mart suppliers are scrambling not only to adhere to new rules, but to proactively use the environmental data to design new products and services," Khan said. In many cases, he added, Intertek's new clients are not just looking to meet Wal-Mart's requirements. They want to reengineer their entire business for sustainability. Even start-ups are finding growth opportunities in a sober economic environment. Energy efficiency was a boom industry in 2009, with more than $1 billion invested in energy efficiency start-ups, according to Cleanedge.