As effective as solar panels are, one of their major downsides is that they only produce power during the day, so excess energy needs to be stored for use overnight. But now, engineers from the University of California, Los Angeles (UCLA) have developed a prototype device that works almost the opposite way, harvesting energy from the cold night sky to passively power an LED.

The device works on the thermoelectric principle, where an electric current is created through the temperature difference between two surfaces. This idea could ultimately end up making for thermoelectric exhaust pipes that help charge a vehicle’s battery, camp cooking gear that tops up phones, and clothes that use body heat to power wearable electronics.

In this case, the thermoelectric device also made use of another odd phenomenon called radiative cooling. This process is often seen in surfaces that face the sky – at night, they can become colder than the surrounding air because they radiate heat straight into space, since the atmosphere doesn't block infrared energy. Past experiments with radiative cooling have shown promise as a way to cool buildings without needing to use energy.