Both sunshine and artificial light energy can be used to charge the RPT-02 SOL wireless headphones, which sportswear brand Adidas and speaker brand Zound Industries have designed for exercise enthusiasts.

Called RPT-02 SOL, the headphones feature a headband that incorporates a solar cell fabric called Powerfoyle, which transforms sunlight and indoor light into electricity.

"Built in part from recycled plastics and powered by light, the adidas RPT-02 SOL are self-charging sport headphones designed to endure the everyday challenges of an active lifestyle," said Adidas.

Although natural sunlight provides the best level of power for the headphones, household lamps and lights also power the photovoltaic material.

Unlike lots of other photovoltaic materials on the market, which only harvest energy from direct sunlight, Powerfoyle is also able to garner energy on cloudy days from invisible UV rays that pass through clouds.

Adidas said that the headphones can play music for up to 80 hours on a full charge.

"How much the unit will charge is directly equivalent to the amount of light that it is exposed to," said Zound Industries product manager Anders Olsson. "The more LUX, the more the unit charges."

"This means that direct light from the sun is always stronger than any indoor or artificial light, so the best charge will always be on a sunny day outside," Olsson told Dezeen.

"The whole point is that the unit charges a little bit all the time if there is some kind of light, even when not powered on or used."

Designed by Swedish solar technology manufacturer Exeger, Powerfoyle is comprised of a stack of 100-atom-thick photovoltaic sheets that have been printed onto a plastic sheet.

Powerfoyle was modelled on the way that plants transform light energy into chemical energy during photosynthesis. When the nanolayers of material are exposed to light, they generate electricity which powers the headphones.

Wearers can identify where the strongest light is coming from through a light indicator on the side of the headband. The Adidas Headphone app also allows users to track their charge and battery status in real-time.

The latest addition to Adidas' headphones range claims to be sweat and splash-proof. The design features a washable headband and ear cushions, with the Adidas logo embossed on the side of the headband.

"We worked with the ergonomics to ensure that they stay in place while doing sports activities – still comfortable enough to wear in an everyday scenario," Olsson explained.

"The product is also IPX4 rated so it will withstand sweat and light rain."

The headphones are made with 51 per cent plastic, 87 per cent of which is made from post-consumer recycled PC-ABS and recycled nylon.

The main other materials are electronic components such as PCB, Battery, switches and LEDs as well as metal parts inside the headband, wiring and foam inside the ear cushions.

The RPT-02 SOL headphones are due to go on sale on 23 August.

Recent solar-powered products featured on Dezeen include a blanket made from conductive yarn developed by Central Saint Martins design graduate Mireille Steinhage. Design and physics researchers at Finland's Aalto University also designed clothing with concealed solar panels, making the technology invisible to the naked eye.

The images are courtesy of Adidas.