4. United States
Through the Department of Energy, the United States is a leader in funding solar power research and development.
It also is one of only two countries in the world that has existing large scale concentrating solar power, says Yasmina Abdelilah, a solar energy analyst with the International Energy Agency.
The warm sunny climate in the southwestern United States provides a favorable location for concentrating solar power, which uses heat to power electric generation.
But thus far only 1 percent of all renewable energy in the United States, itself only about 7 percent of total consumption, is solar.
Solar power has grown primarily from state support. California, the leading state, has a limited form of feed-in tariff, as well as a 20 percent renewable purchase requirement.
There has been federal action, for example, to expand tax credits for solar hot water installation.
But the federal government has not adopted a national renewable purchase requirement, currently something that is under consideration in Congress, or feed-in tariffs, which policymakers deem to be unworkable in the United States due to the way electricity is regulated.