In 2002, Tendris founded Oxxio, the first and largest 100% green energy supplier in the Netherlands. Oxxio, was successfully exited in 2005 to UK-based energy and utility company Centrica.

Tendris first company, Durion was the first green energy company to make sustainable power available at significant savings to the Netherlands' general population. In addition to Durion’s environmentally friendly impact was its consumer-driving cost efficiency: Durion's green energy was available at a reduction of 10%-15% less than "traditional" energy prices.

Working with a host of strategic partners, Tendris put green energy on the grid with record speed, and then followed up with a successful grassroots marketing campaign. Consumers signed up in droves, eager to make a meaningful environmental contribution as well as accumulate household savings. Today, 10% of the entire Dutch market is green thanks to Oxxio.