A 40-foot trailer loaded with 25 tons of liquid metals may be the solution to the renewable-energy industry’s biggest challenge: making sure electricity is available whenever it’s needed.

A Boston-area startup founded by MIT researchers is working to turn this new concept into a commercially viable product, liquid-metal batteries that will store power for less than $500 a kilowatt-hour. That’s less than a third the cost of some current battery technologies.

The technology promises an alternative to the massive pumped-water systems that make up 95 percent of U.S. energy-storage capacity. At that price, developers will be able to build wind and solar projects that can deliver power to the grid anytime, making renewable energy as reliable as natural gas and coal without the greenhouse-gas emissions.

“If we can get liquid-metal batteries down to $500 a kilowatt-hour, we’ll change the world,” Donald Sadoway, chief scientific adviser at Cambridge, Massachusetts-based Ambri Inc., said in an interview.

Power storage will compensate for the intermittent nature of renewable energy. Batteries can store energy when the wind blows at night, and then send electricity to the grid the next day when it’s needed.

First Prototypes

Ambri won a $250,000 grant Feb. 5 from New York state to develop and test a prototype battery with Con Edison Inc. The company, backed by investors including billionaires Bill Gates and Vinod Khosla, plans to install its first two prototypes by early 2015 at a Massachusetts military base and a wind farm in Hawaii. It opened its first manufacturing facility in November and is planning a larger one next year.

Ambri is the first company to pursue liquid-metal storage and the technology has the potential to reshape the battery industry, said Brian Warshay, an energy smart technologies analyst at Bloomberg New Energy Finance in New York.

“There’s nothing out there quite like it,” Warshay said. “If they can get under $500 a kilowatt-hour, that would be a really good price point.”

Sadoway, who is also the John F. Elliott professor of materials chemistry at Massachusetts Institute of Technology, wouldn’t say what goes into liquid-metal batteries. They use materials that are “abundant” and easy to harvest from the earth, which is key to making them cost effective.

‘Dirt Cheap’

“To make it dirt-cheap you have to make it out of dirt,” he said. Earlier versions used molten magnesium and antimony, separated by a layer of salt, to store and release electricity. Those materials only worked at temperatures that were too high to sustain and didn’t produce enough voltage. Sadoway and his team tested more than 1,000 cells with dozens of alloys and salts to find one that’s commercially viable.

They will compete against lithium-ion batteries, the same technology used in laptop computers and electric cars, which are becoming more common for grid-storage. AES Corp., the largest operator of power-storage systems, said yesterday it’s now selling them to utilities and renewable-energy developers, for about $1,000 a kilowatt.

Lithium Ion

That technology is a better fit for cars and portable electronics than for large storage systems that feed the transmission grid, Sadoway said. “Lithium-ion plants are too expensive to build and it makes no sense to string a bunch of these tiny things together.”

Other companies are developing other storage technologies. Duke Energy Corp.’s Notrees wind farm in Texas has 36 megawatts of dry cell storage capacity, provided by Xtreme Power Inc., a Kyle, Texas-based battery maker that filed for bankruptcy protection in January.

International Business Machines Corp. is developing a lightweight lithium-air battery for electric vehicles. Toyota Motor Corp. (7203) and Bayerische Motoren Werke AG are also pursuing the technology.

Musk’s ‘Gigafactory’

Collecting and storing energy from the grid costs about $1,500 a kilowatt-hour using current types of battery technologies, according to New Energy Finance. Improving the designs may reduce that to $575 by 2020. The average U.S. home used 903 kilowatt-hours a month in 2012, according the the U.S. Energy Department.

Billionaire Elon Musk announced last month plans to lead development of a $5 billion “gigafactory” to produce lithium-ion batteries for his Tesla Motors Inc. electric cars and solar projects by 2020. He expects to drive down costs by about 30 percent, which New Energy Finance said would translates to about $500 a kilowatt-hour.

Pumped Hydro

Sadoway expects Ambri’s liquid-metal batteries to be competitive with pumped-hydropower systems. The most common form of storage involves pushing water to an uphill reservoir when electricity demand is low, and releasing it to run hydropower generators when more energy is required. Some facilities exceed a gigawatt, but they can only be built in areas with suitable topography.

There’s about 23.4 gigawatts of pumped-hydro capacity in operation in the U.S., compared to about 304 megawatts of battery storage, according to the U.S. Energy Department.

Ambri batteries, which can be delivered on a truck, will be an alternative to pumped-hydro systems, which require a hill, a nearby hydropower plant and plenty of water to run it, Sadoway said. “Ours won’t have any geographical constraint.”