The expected doubling of global energy demand by 2050 and its impact on supply, security, environment and climate challenge our traditional patterns of energy production, distribution and use. New routes are needed for the efficient conversion of energy from chemical fuel, sunlight, and heat to electricity or hydrogen as an energy carrier and finally to end uses like transportation, lighting, communication and information processing. Opportunities for efficient new energy conversion routes based on nanoscale materials will be presented, with emphasis on the sustainable energy technologies they enable.