Due to rising energy costs, energy-efficient data centers have gained increasingly more attention in research and practice. Optimizations targeting energy efficiency are usually performed on an isolated level, either by producing more efficient hardware, by reducing the number of nodes simultaneously active in a data center, or by applying dynamic voltage and frequency scaling (DVFS). Energy consumption is, however, highly application dependent. We therefore argue that, for best energy efficiency, it is necessary to combine different measures both at the programming and at the runtime level. As there is a tradeoff between execution time and power consumption, we vary both independently to get insights on how they affect the total energy consumption. We choose frequency scaling for lowering the power consumption and heterogeneous processing units for reducing the execution time. While these options showed to be effective already in the literature, the lack of energy-efficient software in practice suggests missing incentives for energy-efficient programming. In fact, programming heterogeneous applications is a challenging task, due to different memory models of the underlying processors and the requirement of using different programming languages for the same tasks. We propose to use the actor model as a basis for efficient and simple programming, and extend it to run seamlessly on either a CPU or a GPU. In a second step, we automatically balance the load between the existing processing units. With heterogeneous actors we are able to save 40–80 % of energy in comparison to CPU-only applications, additionally increasing programmability.