A big drawback of solar power is that it doesn't work at night or on cloudy days. But researchers at MIT say they now have an inexpensive way to store solar energy when the sun isn't out.

Daniel Nocera, a chemistry professor at MIT, and Matthew Kanan, a postdoctoral fellow in Mr. Nocera's lab, have developed a catalyst made from cobalt and phosphate that can split water into oxygen and hydrogen gas. When used in conjunction with a photovoltaic solar panel, their system can use water to store the sun's energy.

A press release from MIT explains how it works:

    The key component in Nocera and Kanan's new process is a new catalyst that produces oxygen gas from water; another catalyst produces valuable hydrogen gas. The new catalyst consists of cobalt metal, phosphate and an electrode, placed in water. When electricity -- whether from a photovoltaic cell, a wind turbine or any other source -- runs through the electrode, the cobalt and phosphate form a thin film on the electrode, and oxygen gas is produced.

    Combined with another catalyst, such as platinum, that can produce hydrogen gas from water, the system can duplicate the water splitting reaction that occurs during photosynthesis.

At night, the hydrogen and oxygen can be recombined into a fuel cell to produce a carbon-free electric current that can power your home or charge an electric car.

Wired explains why this system represents a breakthrough:

    Solar energy currently makes less than one percent of the world's electricity. The main drawback of the technology, preventing wider adoption, is that solar systems only make power while the sun is shining. At night or on cloudy days, those in need of power must look elsewhere. So storage of electrical energy has been a long-sought after technological advance. Batteries work but they're too big and expensive. Fuels, fossil or renewable, are different: They act as their own storage, allowing for easy transport and usage. That's one reason that coal and oil have such a dominant hold on the world's energy market.

But how much water would it take to power a home? The Guardian suggests that it would be less than a gallon a day:

    Converting an Olympic swimming pool of water into hydrogen and oxygen per second would create 43 terawatts of power. "In the next 50 years, the world needs 16 terawatts. By the end of the century, we'll need around 30," said Nocera. "There's a heck of lot of energy stored in chemical bonds."

    For a home, Nocera said that it would be enough to split a few litres of water per day into hydrogen and oxygen. The water would be reformed when the gases were put through the fuel cell.

    There is much work to be done in converting Nocera's idea into a commercial product. At the moment, his catalyst can only accept small amounts of electrical current at once, meaning that it would be an inefficient way to quickly store large amounts of energy. But Nocera is certain that engineers will iron out the issues and produce commercial-scale products within a decade.

Nocera and Kanan are not the first to come up with a way of splitting water molecules to produce hydrogen and oxygen. The process, known as electrolysis, was discovered as early as 1800. But electrolysis has always required expensive machines using exotic metals or nanoparticles, and it has required the water to be pressurized and heated. Nocera and Kanan's process uses common elements to split room-temperature water.

"This is the nirvana of what we've been talking about for years," said Nocera in the press release. "Solar power has always been a limited, far-off solution. Now we can seriously think about solar power as unlimited and soon."

Scientists don't normally talk like this, and Nocera is not alone in his robust claims. The MIT press release quotes James Barber, a biochemist at Imperial College London who was not involved in this research.

"This is a major discovery with enormous implications for the future prosperity of humankind," he said. "The importance of their discovery cannot be overstated since it opens up the door for developing new technologies for energy production thus reducing our dependence for fossil fuels and addressing the global climate change problem."

(At this point, it's hard not to think of the story in the satirical Onion newspaper titled "Amazing New Hyperbolic Chamber Greatest Invention In The History Of Mankind Ever.")

This is the second time this month that MIT has made headlines with advances in solar technology. Two weeks ago researchers in the university's engineering school announced that they had developed an inexpensive mixture of organic solar concentrating dyes that can be painted on to windows.