Best source of carbon-free energy is efficiency

Ars Technica covers the aforementioned McKinsey report, along with another report released by the National Academies of Science which concludes that conservation efforts could largely obviate the need for new power plants, and discusses possible reasons for the lack of uptake of more efficient technologies:

One aspect of the problem was described well by the International Energy Agency. For many efficient systems, the consumer-level payoff is relatively small, and comes gradually over many years--even for those systems that require a large, up-front investment. On the national level, however, the cumulative impact is enormous. The trick is crafting policies that make the national incentive for efficiency apparent to individual consumers.