In 2016, engineers from Eindhoven University of Technology created a “mini-factory” that uses sunlight to create a sustainable and cheap production of medicine. Now they have improved this mini-factory to keep production at the same level even if it is a cloudy day or nighttime. This boosts the average yield of the device by about 20 percent because of a feedback system that costs less than 50 euros. The feedback system automatically slows down or speeds up production, removing any barriers for green reactors that operate on sunlight.

Even with the naked eye the amount of light captured by the 'mini-factories' is visible, lit up bright red. The 'veins' through the leaves are the thin channels through which liquid can be pumped. The start products enter the one channel, light causes the reactions and the end product comes out via the other channels. (Source: Bart van Overbeeke)

The 2016 development of the artificial leaf was one of the first to make chemical reactions using sunlight. Chemists had wanted to develop this for years, but they were unable to harness enough sunlight for the technology to be successful. The key to the success of the artificial leaf is due to newly created materials to seal in a specific part of the sunlight inside. The other discovery that made it possible was to apply thin channels to the materials that pump and expose the liquids to the sunlight so the chemical reactions will take place and the end product flows out of the ends of the channels.

While this development was huge, it still had its problems. One of the biggest problems with applying the leaf on a large scale was the erraticism of sunlight. If it was a cloudy day, the sunlight varies in intensity and composition.

"If there is too much light, you get unwanted by-products and if there is too little light, the reactions do not take place or do so too slowly," Noël explained. "Ideally, the system should automatically adapt to the amount of incoming sunlight."

The feedback system that the team created solves this problem. The system is made of a light sensor to measure the light reaching the channels, a microcontroller to translate pump speed and pumps drives to push the fluid through the channels. The system costs less than 50 euros.

The system was tested under artificial light in the lab and outdoors in natural sunlight on the roof of buildings on the TU/e campus. The system was able to keep production stable for an hour between 86 percent and 93 percent, at 90 percent yield. Without the feedback system, the looping varied between 55 percent and 97 percent.

When teamed up with the system, the artificial leaf creates a cheap and sustainable reactor. This is one step closer to being able to produce chemical products on a large scale wherever and whenever, as long as there is sunlight.

“It is inevitable that energy prices will rise. And with a source of energy like the sun that is free and available, these kinds of technological solutions can make the difference,” said Noël.

The paper on the new system developed was published in Green Chemistry.