Last night, Tesla announced it had created one of the world’s cheapest home batteries, the the Powerwall, to be paired with a home’s solar panel generators...

But before anything else, CEO Elon Musk talked about the main reason for creating his product: addressing climate change.

He called out people’s skepticism that the U.S. will never be able to achieve the levels of solar power necessary to bend the Keeling curve, which shows CO2 concentration levels in the atmosphere.

“A lot of people aren’t clear on how much surface area is needed to generate enough power to completely get the United States off fossil fuels,” he said. “Most people have no idea. They think it must be some huge amount of area, or maybe some space solar panels…But this is completely unnecessary. Actually very little land is needed to get rid of all fossil fuel electricity generation in the United States.”

Here’s the amount of land that would actually be needed to power the U.S. with solar and battery combinations, he said:

“It’s really not much,” Musk said. “Most if it will be on rooftops.”

One of the first groups to map this out was the Land Art Generator Initiative, which uses art to promote clean energy. In 2009, they calculated that we’d only only have to cover an area a bit bigger than California with solar panels to power the entire world with solar energy.

And just to power the United States? A few counties in Texas.

That represents about 160 million Powerwalls, Musk said.

“That may seem like an insane number,” but we have done things like this before, he said. It would take only a couple of years of replicating the rate of new cars and trucks that are swapped into the market each year, about 100 million.

As far as the business case for the batteries, Kimbal Musk, Elon’s brother and a Tesla board member, told CNN Money that they could save homeowners 25 percent on electricity bills by storing electricity when rates are usually low (like in the middle of the night), and powering on when rates are high (like when people are eating dinner), although GreenTech Media’s Jeff St. John writes that this relies on a host of green-friendly tax and regulatory incentives that may not be there down the line.

Of course, Tesla and its sister company SolarCity are making sure they are. Right now they cost $3,500 for the high-capacity version and $3,000 for the low. And there will also be much larger versions for utilities.

And then there’s the fact that the U.S. keeps pumping out enormous quantities of oil and gas, which will continue to prevent fossil fuel-based energy prices from reaching the kinds of alarming levels that would start making people seriously consider solar.

But if you care more about the price on the planet, this announcement represents a huge step.

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