President Obama has found his new Energy Secretary. This morning, Obama nominated Ernest Moniz, an MIT nuclear physicist, to head the Department of Energy.

Moniz steps in to replace Steven Chu, another physicist who led the DOE during a boom time for government clean energy investments. Moniz will take the reins at the department during another transition -- a shift to austerity and tighter budgets. He could also take over at the DOE just as the sequestration hits federal agencies.

Some in the cleantech industry were hoping for a business leader to take over at the department. But Obama decided on someone who already understands the ins and outs of how the organization works.

"There were a lot of people hoping to see a businessperson over an academic," said Rob Day, a partner with Black Coral Capital. "But they also have to realize that the DOE is much bigger than the Office of Renewable Energy. An Energy Secretary needs to cross bridges and understand politics."

Moniz has extensive experience in government. From 1997 to 2001, he was the Under Secretary of Energy at the DOE. Before that, Moniz served for two years at the Office of Science and Technology Policy in the office of the president. And he's also a member of President Obama's Council of Advisors on Science and Technology.

With the DOE going through major changes now that stimulus programs have run their course, Moniz will need to figure out how to direct limited funds to clean energy programs that are still a priority for the Obama administration.

"Chu was running things under a time of growing budgets. We're now entering a time of shrinking budgets. Moniz has a lot of government experience inside the executive branch to manage that," said Joe Romm, a Senior Fellow at the Center for American Progress. (Full disclosure: Joe Romm was my boss and editor when I worked at Climate Progress, which was published by the Center for American Progress Action Fund.)

Romm, also a physicist and MIT alum, was a student of Moniz's in 1981. They also worked together when Romm was acting assistant secretary at the Department of Energy in the 1990s under the Clinton administration. He also believes that Moniz was a better choice than a businessperson would have been.

"Being a businessperson is overrated in a cabinet job. Running the department is a real challenge. You have to manage physics labs, weapons labs, the nuclear portfolio, conventional energy, and renewable energy programs. And there are a lot of people you have to answer to: Congress, the public, the media, and a president who can tell you what to do. You're not as much of an executive."

Moniz is seen as a safe pick. But he's also taking a lot of heat from environmental groups that have slammed him because of his support of natural gas.

"At a time when the last thing we should be doing is undermining our progress against climate change, Moniz is the wrong choice to head one of the most important agencies in the fight for a sustainable energy future," wrote Elijah Zarlin, campaign manager for the progressive activism group CREDO Action, in a petition email to stop Moniz's nomination.

However, Moniz has made it clear that he believes gas is only a medium-term fix for addressing climate change: "Gas has to be a bridge to somewhere. And that somewhere is the carbon-free options. So we need to work hard on having a bridge to somewhere and to having that span be as short as possible," he said at a 2012 Bloomberg conference.

Environmentalists also criticize Moniz's role as the director of MIT's Energy Initiative, an interdisciplinary research program on renewables, efficiency, and fossil fuels. Because the initiative has taken money from oil and gas companies for research, environmental groups worry that Moniz is too close to the fossil fuel industry.

Others in the business world are worried about another academic leading the DOE. Writing on this site recently, solar expert Jigar Shah said he thinks Moniz will put too much emphasis on R&D and not enough on critical tools for deployment.

"I know some have concerns," said Rob Day. "But he's been working with them on new energy technologies to reduce carbon intensity and address climate change. He's proven his understanding of cutting-edge technologies, renewables and efficiency. I think the ability to work with such a range of players is an asset going into the department."

Joe Romm, one of the strongest voices on natural gas within the climate advocacy community, said he didn't fully agree with the environmental groups on their assessment.

"Sure, he's not an opponent of fracking, but I saw no evidence that Steven Chu was opposed to fracking either," said Romm. "An energy secretary doesn't have the freedom to just rein in fracking -- it really comes from the EPA more than any place. Plus, he understands global warming and the value of clean energy technologies. Anyone who understands that is a good choice."

Moniz must be confirmed by the Senate before he can take over at the Energy Department.

From the 2012 Bloomberg New Energy Finance Summit (skip to 20:20 to hear Moniz's remarks on fracking and natural gas):