Computers are essential in research and industry, but they are also significant contributors to the worldwide power consumption. The LOEWE-CSC supercomputer addresses this problem by setting new standards in environmental compatibility as well as energy and cooling efficiency for high-performance and general-purpose computing. Designing a pervasively energy efficient compute center requires improvements in multiple fields. The hosting low-loss compute-center operates at a cooling overhead below 8% of the computer power. General purpose graphics processing units provide more compute performance per watt than standard processors. A balanced hardware configuration ensures that most of the compute power is available to the user when he employs optimized applications. Clever algorithms enable the user to fully exploit the computational potential and avoids to waste power when the processors idles, which is often a cause of inefficient programming. The LOEWE-CSC operated at 740MFlops/W during a Linpack benchmark run, by using commodity servers and ranked place 8 in the Green500 list of November 2010. These innovations provide a fundamental step towards cost-effective, environment-friendly exascale computing and IT operation.