What happens to solar power when it isn't sunny? A simple question with an amazing answer.

"How does solar energy work when there's no sun?" has been a question for pretty much about as long as solar energy has been a thing.

Of course people wouldn't want solar panels on their houses if installing them meant that, come sunset, the movie they were watching suddenly shut off, forcing them to read by candlelight like colonial settlers. Making solar power a viable option, even when the sun sets or disappears behind some clouds, was one of the first things scientists and engineers had to figure out.

When the first devices that could capture the sun's energy were invented, they weren't very efficient.

Much like touch screens or video chatting or Dorito-flavored taco shells, solar power is one of those perfect ideas that took a while to get just right. Believe it or not, the earliest solar devices were introduced in the 1800s.

In 1878, Augustin Mouchot invented a device that could freeze water using the concentrated power of the sun. It was a cool experiment but not exactly reasonable or viable options for large-scale energy production.

Mouchot won a gold medal at the Universal Exhibition in Paris for his invention, but his device was gigantic, and coal was quickly becoming the go-to for efficient energy, so it didn't catch on.

The other downside to his invention? The solar-powered water-freezer only worked on (you guessed it) sunny days. But, that was 1878. Things have changed a lot since then.

Over the last century, the efficiency and feasibility of solar power has dramatically increased, and it's getting better every day.

Just look at this fun, easy-to-read chart!

I know, I know, it's a lot to take in. Just know that it's showing you that since 1975, we've gotten better and better at efficiently converting the sun's rays into energy that can power our homes, businesses, and even a few cars and planes.

So how does solar energy keep providing power when the sun goes down?

The answer is pretty simple: storage.

Today's solar panels are designed to soak up more energy from the sun than we actually need and store it for later.

The way they do it is pretty amazing. Photons (aka light particles) hit the solar panel really hard — so hard that electrons (aka what electricity is made of) get knocked loose. Then the solar panel guides those loose electrons into a battery or superconductor that can store them. If an area has a reliable electricity grid, homeowners can just hook their solar panels right up to it. For them, nothing changes from their normal source of power except (usually) a smaller electricity bill.

A lot of people don't realize that going solar doesn't have to mean going "off grid," says Dan Whitson, solar manager for Green Audit USA in Long Island, N.Y.

"The grid is pretty reliable here, so battery options aren’t necessarily cost-effective on Long Island," Whitson explained over the phone. "But that’s something we have to explain to homeowners that, you know, you’re still going to be connected to the grid even though you’ve gone solar."

If there are solar panels on your roof, it's not like your PlayStation is plugged directly into them. The solar panels run into your regular power lines and help offset some of the energy cost, or they run into a box that will store the electricity, quite literally, for a rainy day.

Solar farms are power-plant-scale versions of this concept.

They can be built in the middle of a desert where the sun is incredibly powerful and cloudy days are rare. The panels can even pivot automatically to follow the sun's path across the sky.

After the panels soak up as much energy as they can, the energy is transported to nearby cities. There's a solar farm in Austin, Texas, that produces enough power for 5,000 homes and offsets over 1 billion pounds of carbon dioxide emissions.

Oh and, yes, solar panels can still collect energy on cloudy days. They're just not as efficient about it.

That's because clouds don't block all the sunlight, just some of it. If you walk outside on a cloudy day and can still see, that's because there's still sunlight, even if it's a bit more muted than usual.

That's where storage and the grid come in. Energy companies rely on the grid to offset any dips in production they might experience on a cloudy day.

"All of the reputable solar production calculators out there take in 20 to 30 years of weather data based on region," Whitson said. "So they can predict how much sun you’re going to get throughout the course of a year. Most projections are taking into consideration that it’s not going to be sunny every day."

Also, as previously mentioned, efficiency is one of the key things scientists are constantly trying to improve about solar panels.

"How does solar energy work when there's no sun?" is a simple question that cuts right to the core of a pretty huge idea.

It's the type of question that scientists, engineers, researchers, and experts around the world have to ask every single day in order to get better at what they're doing.

It's the type of question that brought solar energy from an obscure experiment to a feasible source of electricity that powers millions of homes around the world.