Power Consumption is a Hurdle for Exascale Computing
If history is any guide, about 10 years after the existence of exascale supercomputers, the technology will find its way into PCs. But if current trends hold true, an exascale computer are likely to consume vast amounts of power. The formidable challenge would be to create an exascale computing system that consumes much less power. If engineers can use new technology to create an exascale system utilizing relatively little power, the same technology can also be used to dramatically lower the power consumption of lower performance systems, to the point where giga-scale systems consuming mere milliwatts of power can be used in small toys and mega-scale systems that consume very few microwatts could be used in heart monitors.
Scaling down supply voltage can defitely increase energy efficiency but this can have a side effect—leakage power does not scale back as much as total power consumption, therefor that leakage power becomes a higher percentage of total consumption. More on exascale computing can be found here.