Nuclear power is the single largest source of clean energy in the United States, but how can the value of “clean” be measured? Two recent reports by researchers at the Massachusetts Institute of Technology and Pacific Northwest National Laboratory, respectively, measured the clean energy benefits of nuclear energy in different ways: the benefits to human health from the air pollution avoided and the future economic value of avoided carbon emissions.

Are you an energy genius? It’s hard to tell whether or not Americans are really aware of the energy that controls our lives, so the following quiz should be revealing. Click through the multiple-choice options below to reveal the answers.

Scoring: Zero to five correct answers out of the 23 questions means you may need to read up on energy so you’re not at the mercy of others. A score of 6 to 10 correct answers is a good passing grade. Answer 11 to 15 correctly, and you’re really energy literate. Getting 16 to 19 correct means you should be advising Congress. Twenty or more right answers suggests you’re Spock reincarnated.

Around the world, national and local policymakers and business leaders are making bold and ambitious commitments to clean energy goals. In the United States, one in three Americans now lives in a city or state that has committed to or has achieved 100 percent clean electricity, according to the Luskin Center for Innovation at the University of California–Los Angeles.

Over the past three years, some of the country's biggest utilities have been committing to weaning themselves off carbon-emitting generation by 2050, reported a September 16 story from Green Tech Media (GTM).

Here's a look at the five largest U.S. utilities by market capitalization that have set net-zero targets so far: