It's impossible to say which arm of the federal government has done the most to advance clean energy. The Department of Energy has played an invaluable role in incubating technologies and bringing costs down. The White House has driven change through executive actions like the Clean Power Plan. And the State Department negotiated the Paris agreement to curb global warming through greenhouse gas emissions reductions.

The military has stepped up its promotion of renewables too -- particularly the Navy.

Last week, the Navy inaugurated the 150-megawatt AC (210-megawatt DC) Mesquite 3 solar farm in Arizona, which will power about one-third of the electrical load at 14 California naval bases. It's the largest-ever federal procurement of solar power. And that's just the latest update on the way to installing 1 gigawatt of clean energy capacity by 2020.

In an era when simply acknowledging manmade climate change triggers political battles in Washington or the presidential debate stage, the Navy has quietly adopted the use of clean energy as a way to do its job better. Naval bases have a higher than average likelihood of being located next to the ocean, so sea level rise and changing climate patterns pose a direct strategic threat. But, even setting aside the long-term ramifications of decarbonization, the Navy has identified several immediate operational benefits to clean energy: greater resilience to grid disruptions, insulation from energy price shocks, cheaper overall energy and a nimbler footprint on deployment.

Following the success of initial demonstrations, the Navy's energy planners have gotten more and more creative. Now the initial directive to add clean generation has expanded to include energy storage, like a second-life program for the stockpile of used submarine batteries. Microgrids are underway as well. The lessons learned through these projects -- like how to corral third-party financing while facing constrained federal budgets -- could apply to subsequent procurements throughout the federal government.

Power and presence

John Kliem, a retired captain who runs the 1-gigawatt mission out of the Navy's renewable energy office, outlines the history of the Navy seeking out increasingly better sources of energy to propel the fleet around the world.

"We started out with sailing ships," Kliem said. "Pretty soon someone came along and said, 'You know, sometimes there's not wind; we could move better if we were to switch to coal.' So we put all these coaling stations all over the world so we could sail our ships on coal. That's how we got a lot of our bases."

It gave the Navy fleets more power and reliability. And then they switched again.

"Pretty soon we switched to fuel oil, and I'm sure there were people saying, 'Why did you do that? Coal comes out of the ground! Now you have to process something to get fuel!'" Kliem continued.

Next came nuclear fission. That technology greatly enhanced the time a vessel could spend at sea without refueling, and trickled down to civilian nuclear power in the decades that followed. More recently, the Navy has experimented with biofuels, partially powering a Great Green Fleet on fossil fuel alternatives. 

Now comes the era of renewable electricity.

The Secretary of the Navy in 2009 declared the goal of powering half the Navy's onshore energy needs with renewable energy by 2020. That meant procuring 1 gigawatt by the end of 2015, to ensure the capacity is up and running on time. The Navy established REPO in 2014 to carry that out, and now 1.1 gigawatts have been built or procured.

"The Secretary of the Navy set that 1-gigawatt renewable goal to diversify our power portfolio and integrate renewable energy, so that we're not reliant on a single source," Kliem said. "There was an economic aspect of it, because renewable energy is cheaper than brown power. It's not going to escalate; it's not going to be as volatile."

Image credit: Department of Navy Renewable Energy Program Office

Buy or host

When deploying renewable generation, the Navy must determine whether to host it onsite

Given the funding structure of the military, the Navy is not in the business of investing lots of capital in any particular project. That's better suited for private capital with enough tax equity to make use of the federal Investment Tax Credit. Instead, the Navy has identified ways to access clean power without putting money down.

One way is to pay to acquire it from an offsite location. The Navy has the legal power to enter into long-term power-purchase agreements. In this way, it functions much like MGM Resorts International, or Google, or Wal-Mart.

Another option is to leverage something the Navy has a lot of -- land. In these agreements, the Navy offers access to some of its 3.5 million acres for generating renewable energy that goes into the broader grid. In exchange, it receives the fair market value of the land in the form of infrastructure upgrades.

Such a deal recently closed for Naval Air Station Lemoore in California. Recurrent Energy will lease 930 acres of former agricultural land on the base to build 167 megawatts of solar PV. That power goes into the local grid, so it's not behind the meter on the base. But, as part of the deal, Lemoore will receive a gas- or biofuel-powered backup generator and other electrical infrastructure improvements. That leaves the home of the F-35C Joint Strike Fighter better prepared to power itself in the event of grid failure.

Lastly, the Navy may choose to work with a third-party developer to erect clean energy resources on a base for use onsite. Some of these are in the works, but they have not been announced publicly.

Second life for submarines

As it has procured hundreds of megawatts of renewables, the Navy learned something unexpected.

"We always knew we were going to get cost savings and diversification of portfolio," Kliem said. "We discovered we could write an RFP for more than renewable energy -- we could get batteries to support the grid."

Energy storage does not count toward the 1-gigawatt goal of renewable generation. But, said Kliem, the more his office looked into its value for energy security, the better it looked. That's when they started getting creative.

Batteries aren't new to the Navy. They play a vital emergency backup role on the fleet's nuclear submarines, for instance. After seeing use on the subs, these lead-acid batteries end up in Naval Support Activity Crane in Indiana, where they undergo charge and discharge testing to determine if they can go back in a submarine or need to be recycled. 

Once lead-acid batteries come off a submarine, they could still prove useful for stationary energy storage on base. (Image credit: U.S. Navy)

By 2019, Kliem said, there will be 44 megawatt-hours of energy storage from used submarine batteries sitting at the base. It's not a huge jump from charging and discharging them for diagnostic purposes to charging and discharging them for local power and broader grid services.

REPO currently is figuring out if this could work, and reaching out to partners in the Navy and the power sector. The goal is to compile the used batteries into a stationary storage unit to provide uninterrupted power supply or power quality in a microgrid on the base, and then create a utility energy service contract. It's still early in the planning phase, however.

Second-life battery applications are an embryonic but growing field for the electric-vehicle industry. The initial challenge is to sync up batteries that have undergone different levels of wear and tear, and get them to function together with enough reliability to sell the service. Like with EVs, this submarine effort will pay off if the initial engineering challenge unlocks a vast supply of cheap energy storage that would otherwise go to waste.

Microgrid expectations

The Navy is looking at more conventional battery applications, too, like power quality for sensitive operations. Naval bases host long-term, continuous scientific studies and missile testing, two cases where even a momentary loss of power can jeopardize the success of the study. Storage can also function as uninterrupted power supply for a base served by a microgrid, providing backup until load-following generators come online.

Diesel backup generators can do that much more cheaply, but they're far from ideal.

"There are so many things with the diesel that could go wrong," Kliem said. "If you don't religiously do your preventative maintenance, change the oil, make sure everything is lubed, make sure your fuel hasn't may not start."

These kinds of battery applications are concentrated in California for the time being, since it boasts quite a few naval bases and offers the strongest incentives for energy storage. The Navy recently closed an RFI for storage projects at Naval Base San Diego, Naval Base Coronado, Marine Corps Base Pendleton and Naval Weapons Station Seal Beach detachment Norco. That request drew a significant number of responses, and the Navy is evaluating them before sending out the RFP.

Last week, the Navy and the California Energy Commission revealed that UniEnergy Technologies will supply a solar-plus-storage microgrid at Naval Base Ventura County. The 6-megawatt solar array and 4.5-megawatt/18-megawatt-hour vanadium flow battery will serve a third-party offtaker most of the time, but in the event of a blackout, the base gets access to the microgrid to maintain critical operations. That project typifies the REPO approach to hosting distributed energy projects to access their benefits without the upfront costs.

Along the way to the 1-gigawatt goal, Kliem said, the Navy's efforts have avoided the release of 22 million tons of carbon dioxide and have generated $1 billion of economic stimulus to local communities. Really, though, those represent "a happy second-order effect."

"The real story is, we're a more capable warfighter because we have a diversified energy portfolio and these resiliency projects that we got as a result of this power portfolio diversification," Kliem said.