In February, Moniz was nominated by President Barack Obama to fill the vacancy left by departing energy secretary Stephen Chu.
Moniz was previously under secretary for energy in Bill Clinton' administration in the 1990s. Most recently, he headed the Massachusetts Institute of Technology's (MIT) Energy Initiative focusing on developing independent sources of energy.
The appointment has been viewed positively. Fred Krupp of environmental advocacy group Environmental Defense Fund said: ""I look forward to working with Dr. Moniz on accelerating the transition to a clean energy economy by developing a smart ‘green’ electric grid, promoting energy efficiency and renewable energy and furthering other critical energy projects."
However, some critics have lambasted what is seen as Moniz's emphasis on natural gas as the predominant source of US electricity generation until 2050.
It is also unclear whether Moniz will steer the Department of Energy towards more recognition of how easily and cheaply wind can be integrated into the grid.
In March, Bill Snape, senior counsel at environmental group the Centre for Biological Diversity, noted that Moniz does support renewables and understands there must be an energy revolution because of climate change. But he said it is "disturbing that [Moniz] is arguably leading the charge for natural gas – it is not a clean energy source".
Speaking about the nomination, Obama said: "He is a physicist by training, but he also served as under secretary of energy under President Clinton. Since then, he's directed MIT's Energy Initiative, which brings together prominent thinkers and energy companies to develop the technologies that can lead us to more energy independence and also to new jobs.
"Most importantly, Ernie knows that we can produce more energy and grow our economy while still taking care of our air, our water and our climate."