How photosynthesis can help increase solar efficiency

One of the keenest areas of solar power research these days is into how nature turns the sun’s rays into energy for growth.

While MIT researchers have devised what they call an “artificial solar leaf” – essentially a silicon solar cell with different catalytic materials bonded to each side that allow it to split a water molecule into oxygen and hydrogen – a group of scientists from around the world says that by mimicking natural photosynthesis and using tiny molecular circuits, harvesting and transporting solar power could be made far more efficient.

This theory comes from Graham Fleming at UC Berkeley and the Lawrence Berkeley Laboratory; Gregory Scholes of the University of Toronto; Alexandra Olaya-Castro from London’s University College; and Rienk van Grondelle of the University of Amsterdam. Together they authored “Lessons from nature about solar light harvesting” in the journal Nature Chemistry.

The researchers began with the observation that in plants, antenna complexes capture sunlight and direct the energy to “reaction centers” that then carry out the chemistry necessary to make the energy useful. Berkeley’s Fleming emphasizes that while a number of hurdles need to be overcome to devise man-made systems based on this model, “a clear framework exists for the design and synthesis of an effective antenna unit for future artificial photosynthesis systems.”

London’s Olaya-Castro, meanwhile, notes that a key fact to consider is the extraordinary ability of leaves to separate out energy they can use from energy that might be counterproductive.

“On a bright sunny day, more than 100 million billion red and blue ‘coloured’ photons strike a leaf each second,” she said. “Under these conditions plants need to be able to both use the energy that is required for growth but also to get rid of excess energy that can be harmful. Transferring energy quickly and in a regulated manner are the two key features of natural light-harvesting systems.”

That’s why, says Toronto’s Scholes, the molecular circuitry they envision would have to be remarkably intricate – “10 times smaller than the thinnest electrical wire in computer processors.” According to Scholes, “these energy circuits could control, regulate, direct and amplify raw solar energy which has been captured by human-made pigments, thus preventing the loss of precious energy before it is utilized.”