A smart ‘switch’ in photosynthesis holds lessons for solar technology

Photosynthesis can teach scientists a lot about solar technologies. Shutterstock

Photosynthetic organisms like plants are the ultimate natural solar panels. They are extremely efficient at converting sunlight into stored energy. Researchers working on “bio-inspired” solar innovations – drawing from the natural world to create new technologies – find this extremely interesting.

They’re keen to understand exactly how the photosynthetic machinery works to harvest light under different conditions, such as cloudiness or rapidly changing shade conditions. Once they’ve figured out the process, scientists will be better able to mimic nature’s clever solutions for cleaner energy production.

It is remarkable to think that the amount of energy from the sun which falls in one hour on the earth can power all human activity for an entire year. It’s clear, then, that solar energy – a free resource – is a very attractive option for everyday use.

There is a great deal to learn from natural photosynthesis, a complex process during which solar energy is stored in energy-rich molecular compounds. This is the most compact form of energy storage.

With colleagues from France, The Netherlands and Japan we have recently published research that takes our understanding of light harvesting a step further.

We wanted to find out how photosynthetic organisms such as plants and cyanobacteria cope with rapidly fluctuating sunlight intensities. We studied individual light-harvesting protein complexes and discovered that they have a remarkable ability. Light, which is normally effectively harvested, is also used by these photosynthetic “nano- antennae” to finely control how much of it should be harvested.

This mechanism is immediately switched on when the light intensity suddenly increases. It serves to protect the photosynthetic machinery – and ultimately the whole organism – from damage before other proteins or mechanisms come to the rescue.

Our discovery is extremely exciting and has important implications. It points to one remarkable “design feature” of these natural light-harvesting units: that they are self-regulating systems. And, very surprisingly, this self-regulation is done using only light, which is the cheapest way of performing this task.

No energy or time has to be invested by the system to get accessory molecules or proteins to perform the job of regulation. So one could imagine mimicking these nano-antennae in solar technology – designing solar cells that use a similar self-regulation capability. It would be a very cost-effective approach.

All of this is important because the world’s global energy demand is soaring due to population and economic growth. In the short term, this demand may be met by fossil energy resources such as coal. But finding solutions to stabilise the carbon dioxide emissions from these resources may be an even greater challenge. For this reason the International Energy Agency is strongly promoting renewable energy resources with a low carbon footprint.

Devising such sustainable, environmentally friendly energy resources is one of the greatest global challenges of our age.

The magic of photosynthesis

Our world has been predominantly shaped by photosynthesis. It’s a complex process finely operating at the border of life and death. Photosynthesis delivers energy to the ecosystem. In doing so, it sustains life. But it can also cause lethal effects whenever an organism is exposed to excessive sunlight. For instance, the damaging effects of intense sunlight are a common issue for crop plants around the world and for photosynthetic microorganisms that produce oxygen.

Successful photosynthesis depends equally on two things: the efficient harvesting of solar energy and precise regulation of energy flow and dissipation.

To understand this regulation process, we studied protein complexes in cyanobacteria. This was done using a single-molecule spectroscopy setup in Amsterdam, co-developed by Dr. Tjaart Krüger.

The great news is that in future, this sort of research can be conducted on the African continent. Since starting his own research group at South Africa’s University of Pretoria early in 2013, Dr. Krüger has obtained a grant from the National Nanotechnology Equipment Programme. This has been used to design and build a unique single-molecule spectroscopy system at the institution.

This cutting-edge experimental setup is the first of its kind on the continent. It is sensitive enough to measure individual photons that are emitted from individual molecules. The facility enables researchers to obtain incredibly detailed information about interactions and energy transfer processes inside living cells. We can examine one molecule at a time. This hasn’t been possible before at such a detailed level.

The setup is currently mainly used to understand the primary processes of photosynthesis in a large range of organisms. These processes are then extracted into design principles that may be used to draw the blueprints of next-generation solar cell devices.

Real world applications

Our discovery, and others that may follow using the system we’ve built in Pretoria, will hopefully one day be applied in daily life.

Imagine having solar panels on your roof that ensure a constant amount of electricity – regardless of how brightly the sun shines, how cloudy it is or where the sun is (which may be very different between morning and late afternoon, summer or winter). In other words, the electrical current produced by your solar cells is independent of the environmental conditions out there. When the house owner wishes to have a certain amount of kWh, this is what the smart solar cells will deliver.

One could also create light sensors that not only respond to the smallest unit of light – a photon – to perform their designed function, but operate in a system so intelligently designed that it knows when there is too much light. This same system would be able to control the level of light by harmlessly dissipating all excess light.

Increasing our understanding of how light interacts with natural or synthetic nanoscaled systems holds a fascinating potential for the development of technologies that are currently beyond our imagination.

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