DDR3 memories operate at lower voltages compared to DDR2 memories, which in turn operate at lower voltages compared to DDR memories. This means that DDR3 memories consume less power than DDR2 memories, which in turn consume less power than DDR memories.
Typically, DDR memories are fed with 2.5 V, DDR2 memories are fed with 1.8 V, and DDR3 memories are fed with 1.5 V (although modules requiring 1.6 V or 1.65 V are common, and chips requiring only 1.35 V may become common in the future). Some memory modules may require higher voltages than those listed. This happens especially with memories supporting the operation at clock rates higher than the official ones (i.e., memories targeted to overclocking).