For decades, solar panels have been a symbol of clean energy — but they’ve always had one major limitation: they only work when the sun is shining. That could soon change. Researchers at Stanford University have developed a new way for solar panels to generate electricity even at night — by tapping into a natural phenomenon known as Earth’s radiative cooling.

 

This breakthrough could reshape the future of renewable energy, making solar power more reliable around the clock.

 

 

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How Solar Panels Can Work After Sunset

 

Traditional solar panels convert sunlight into electricity through photovoltaic cells. When the sun goes down, they stop producing power. To keep the lights on at night, solar farms and homes usually rely on batteries or the electrical grid.

 

But Stanford’s team, led by Professor Shanhui Fan from the Department of Electrical Engineering, found another way. Their approach doesn’t use sunlight at all. Instead, it takes advantage of the heat difference between the Earth and outer space.

 

Here’s how it works:

 

At night, any surface facing the clear sky naturally loses heat by radiating infrared energy into the coldness of space.

 

As a result, the surface becomes slightly cooler than the surrounding air.

 

The Stanford researchers connected a thermoelectric generator (TEG) to a standard solar panel. This small device converts temperature differences into electricity.

 

The result: even in total darkness, the system can produce power by harnessing the flow of heat from the warmer air to the cooler panel surface.

 

 

 

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Results From the Experiment

 

The team tested their prototype on a rooftop in Stanford, California, under clear night skies. Their setup was able to produce around 50 milliwatts of electricity per square meter (50 mW/m²) of solar panel area.

 

That might not sound like much compared to the hundreds of watts per square meter that panels generate during the day, but it’s enough to power low-energy devices like sensors, LED lights, or small electronics — and more importantly, it proves that solar installations don’t have to go completely dark at night.

 

According to the researchers, this technique can be further improved. With optimized materials and better thermoelectric generators, the nighttime output could increase significantly in the future.

 

 

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Why This Breakthrough Matters

 

Solar energy is one of the fastest-growing sources of clean power worldwide, but its intermittency — the fact that it stops at night or on cloudy days — is a big challenge. Most solar systems today depend on large, expensive batteries to store daytime energy for nighttime use.

 

Stanford’s discovery offers a new piece of the puzzle. While it won’t replace batteries or grid power anytime soon, it could:

 

Extend the working hours of solar installations, improving their overall efficiency.

 

Provide continuous power for remote or off-grid sensors where replacing batteries is difficult.

 

Reduce the cost and complexity of some small-scale solar systems.

 

 

“Photovoltaic panels are optimized for daytime, but we often forget there’s a lot of useful physics at night too,” said Professor Fan. “Our work shows we can capture some of that energy instead of wasting it.”

 

 

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The Road Ahead

 

The research is still in its early stages. To become commercially viable, engineers will need to boost power output, make the technology cost-effective, and integrate it seamlessly with existing solar panels.

 

But the potential is exciting. As renewable energy plays an ever-bigger role in powering our world, innovations like this could help us move closer to 24-hour clean energy — not just when the sun shines, but long after it sets.

 

For now, Stanford’s nighttime solar panels are a reminder that nature’s energy isn’t limited to daylight. Even the Earth’s own heat, radiating quietly into the cold of space, can be turned into electricity with the right technology — a small but powerful step toward a more sustainable future.