The Phoenix metro area has about 66,000 homes running off of solar energy, but what keeps them running during a solar eclipse?

Earlier this year, APS installed two battery storage units. Think of them as buildings that host hundreds of powerful batteries.

The two buildings act as shock absorbers for solar energy. During nighttime, or on a cloudy day, the batteries kick in and push out power.

Before APS installed these batteries, solar homes would rely on power from the city's power grid.

The two current buildings can't provide enough power for all the solar homes yet, so they help create power that gets distributed into the power grid and in turn, powers homes across the Valley.

However, what these batteries can do that current power sources, such as coal and gas power, cannot is they can save and store unused solar energy, something that APS is looking to expand on in the future.

"The important thing about solar (energy), is that it is only produced when the sun is up," said Scott Bordenkricher, director of innovation at APS. "So we need to be able to have resources that can take that energy when it's produced, but maybe not needed, and store it for time when it is needed: In the evening, at night, or during an eclipse. That is going to be critical for the growth of solar."