Do Solar Panels Work at Night?

It seems like an obvious flaw: How can solar panels work when the sun isn’t shining? What do people with solar-powered homes do after sunset — just sit in the dark and twiddle their thumbs until dawn? Considering that sunlight is free and offers a 5-billion-year supply of energy, solar power is a seemingly ideal way to power your home — if it works at night, that is.

The bad news for night owls: Solar power does need energy from the sun to work. The good news? There are ways to take advantage of our star even when it’s on the other side of the planet. 

Researchers are constantly refining and innovating new ways to make solar power work at night. Some have even dared to ask: “What about moonlight?”

How Do Solar Panels Work?

Solar panels generate electricity through the photovoltaic effect. Particles of sunlight called photons strike semiconductor material — usually silicon — and knock its electrons loose, creating an electric current. 

If ketchup is the energy we need and a glass bottle is the solar panel containing it, the photons in sunlight act as our hands, smacking the bottle to let the ketchup loose. With no sunlight hitting a solar panel, that ketchup isn’t going anywhere. A solar panel alone also can’t store any electricity it produces, so any solar power not being used in the moment goes to waste. 

This has led some people to wonder about moonlight. After all, moonlight is just reflected sunlight — the same photons used to generate electricity in a solar panel during the day. So could moonlight keep a solar panel running overnight? 

Technically, yes — but only barely. Conventional solar panels can produce a tiny amount of electricity under a bright full moon, but moonlight is roughly 400,000 times weaker than direct sunlight. Instead of you smacking the ketchup bottle, you’re asking a newborn baby to paw at it with its tiny hands instead. The resulting power is far too small to run a home or meaningfully charge a battery. 

Not to mention, the moon isn’t even fully shining most of the time. Some nights it’s not there at all. Even conventional solar panels wouldn’t be much use if the sun called in sick multiple times per month. That said, there are still ways to utilize solar panels after the sun has set.

Saving for a Rainy Day

Today’s solar systems rely on something much more practical: energy storage. During the day, solar farms — vast arrays of panels fulfilling the job of a traditional power plant — often generate more electricity that what’s immediately needed by the areas they serve. Rather than that extra energy go to waste, it can be stored in batteries for later use. 

When the sun goes down, the system simply begins drawing from that stored electricity instead. Large battery farms perform the same job for entire communities as the solar panels they’re paired with, releasing surplus energy during the evening or on cloudy days. (Keeping with the ketchup analogy, you can think of these batteries as the little packets you keep in the fridge.)

Making all of this work is part of developing a “smart grid” — a modern electrical network that constantly monitors electricity supply and demand. Instead of simply sending power in one direction from a power plant to customers, the smart grid can route electricity in both directions between homes, businesses, batteries, and renewable energy sources in real time. 

If one neighborhood generates more solar power than it needs during the day, that energy can be stored or sent elsewhere to be used when it’s needed, even if that’s hours later.

Some homes are even becoming tiny power plants of their own. Solar technology has advanced to the point where it’s practical and affordable enough for many homeowners to utilize it, and even store their own daytime electricity for use after sunset. 

You can even put excess energy back into the grid and charge your utility company rather than the other way around. Even portable solar panels are commercially available that can be laid out in your yard or, for apartment dwellers, put on your balcony.

The Night Shift

Scientists and startups are exploring other ways to generate electricity after dark — and not from moonlight or starlight. One experimental technology developed by researchers at Stanford University takes advantage of radiative cooling — the natural process by which Earth releases heat into the cold of space. 

Modified solar panels equipped with thermoelectric generators can still work at night, converting a tiny portion of this escaping heat into enough electricity to keep small sensors and LEDs running.

Engineers have even proposed using satellites equipped with giant mirrors to reflect sunlight from space, directing it toward solar farms after dusk. The idea remains experimental, though, and has raised concerns among astronomers about light pollution and the night sky.

For now using solar power at night isn’t about adding more sunlight — it’s making better use of the sunlight we’ve already captured. As batteries become cheaper, grids become smarter, and new technologies continue to mature, solar energy will keep shining long after the sun disappears below the horizon.