Carbon neutral by 2020 — it's an ambitious goal, but Austin Energy is the nation's top seller of renewable energy among 850 utility-sponsored programs, which makes its goal to power the city solely on clean energy within reach. As the gateway to the scenic Texas Hill Country, acreage in Austin that's devoted to green space includes 206 parks, 12 preserves, 26 greenbelts and more than 50 miles of trails.