Nature has offered a lot to scientists, offering the inspiration to produce major breakthroughs in various fields thanks to the study and understanding of organisms found in nature. From medicinal breakthroughs based on jungle flora to attempts to replicate the human knee, this long illustrious relationship shows no sign of ending and this article would like to highlight two relatively recent entries to the progress made by researchers studying nature, namely, quantum biology and the production of the artificial leaf, in the advancement of the solar energy industry.
Photosynthesis as a drive for energy
A solar cell, in its most basic form, is a device that generates electricity by capturing and converting sunlight that strikes the device; one could argue that the device and the process is nothing more than an attempt to mimic nature, from a process that is considered to be the essential source for the continuation of life: photosynthesis.
Photosynthesis is an astonishingly efficient process found in chlorophyll-containing plants (and certain single-cell organisms termed prokaryotes) that converts incoming insolation to chemical energy; a typical leaf has an efficiency rate of 95% whereas current solar cell efficiency rates barely touch 40%. Photosynthesis is a process where, in the presence of sunlight, carbon dioxide and water are converted into organic compounds (sugars) and oxygen, with the oxygen then being released into the earth’s atmosphere. To put it in a different way so as to highlight the importance of this chemical process, light from the sun catalyzes a reaction that produces oxygen (caused by the splitting of water) that ultimately sustains life on earth.
The parallel with solar energy technology (photovolataic cells) centers on the ability to convert sunlight into electricity. An additional - perhaps unintended - bonus for researchers from the understanding of the process of photosynthesis features the splitting of water: energy cannot be stored in the true sense of the word but creative solutions do exist for the storage of energy, and splitting water into the constituent molecules of hydrogen and oxygen is one of the creative ways in which to achieve energy storage. As the energy derived from renewable sources is intermittent, fully utilizing energy sources to power cities and towns will require the development of energy storage solutions. By pursuing the development of an efficient solar cell, first through better understanding quantum effects in a biological process and second through a constituent reaction of photosynthesis, a more efficient solar cell and a creative energy solution might just have been found.
A general picture of quantum science
The chemical process of photosynthesis is well understood: carbon dioxide and water, through a series of oxidative and reductive chemical processes catalyzed by sunlight, splits water to release oxygen with the hydrogen molecules combining with the carbon dioxide to form carbohydrates at an amazingly efficient rate. The conversion process in solar cells is equally well understood but the solar cells are not nearly as efficient as compared to their counterparts in nature. To understand how to improve the efficiency of solar cells, one must first try to understand how nature does it so well. This is where quantum science comes into play. Quantum science is an area of science, rife with oddities, that explores how the worlds of physics, chemistry, mathematics and computing are affected by quantum effects on a sub-atomic level (a quantum effect, in its broadest sense, is a mathematical expression of the result of the interaction between waves and particles and the interaction between matter and energy). To understand how nature converts light energy into chemical energy so very well, an understanding of quantum biology is required.
Quantum biology as a route to more efficient solar cells
Quantum biology aims to explain how processes in nature take place. Using quantum mechanics (a set of scientific principles that govern the interactions between matter and energy), and more specifically the oddities found in quantum mechanics, researchers at the University of California, Berkeley, in 2007 were able to construct an experiment using ultra-fast femtosecond lasers and photosynthetic bacteria to gain insights into how photons travel in such photosynthetic organisms. What they discovered was quite fascinating and extraordinary: the process of photosynthesis directs or ‘channels’ photons from sunlight to the reactive centers where the series of oxidative and reductive events take place. Along the way, quantum effects take place and the thread of thought is that these quantum effects are responsible for the very efficient process. In conventional silicon-based solar cells, photons from sunlight initiate a process where an electron is ejected (with the ejected electron continuing to eventually exit the device and generate electricity). This ejected electron travels along a single pathway.
The femtosecond laser experiment at the University of California, Berkeley, followed the process of light striking photosynthetic bacteria and noted that instead of a single pathway, the photon/energy was able to simultaneously take multiple pathways and then “determine” on the shortest, most energy-efficient pathway. When the most efficient pathway was chosen, the other pathways would collapse and all the energy would be retroactively focused on the selected pathway. As mentioned earlier, oddities exist in quantum mechanics and one such oddity is the ability for particles/photons to exist in two or more states at the same time; this quantum coherence allows for photons to take multiple pathways at the same time and also to go back in time and focus all the energy on the pathway deemed most efficient at energy conversion. Therefore, quantum coherence plays a part in allowing for the near-100% efficiency found in photosynthetic organisms.
Implications of quantum coherence for solar cells
By understanding the results of the femtosecond laser experiment and by understanding how nature has designed a near-perfect ‘solar cell’, the solar industry will be changed in a considerable way. The two bugbears of the solar energy industry are cost and efficiency. The understanding of quantum effects in biological systems allow for the possibility of a near-perfect solar cell, one with an efficiency of nearly 100%. Solar cell producers and manufacturers will greatly benefit, as, through economies of scale, the solar cell will also become cost-effective. Thus, a near-perfect and cost-effective solar cell is truly within sight, accelerating the rollout of this technology and changing the face of this industry.
The artificial leaf as a creative way to store energy
The production of an artificial leaf, one that artificially mimics the process of photosynthesis, is one of the most recent solutions to the issue of energy storage. By splitting water molecules into hydrogen and oxygen, energy can be stored and used in a fuel cell to generate electricity as needed. The concept of an artificial leaf is not new, with attempts to create one going back ten years. Back then, the artificial leaf used very expensive raw materials and had degradation issues; the efficiency rate was poor and the artificial leaf had a lifecycle of one day. The advancements made over the last decade have allowed for the production of an artificial leaf that could transform the solar industry. Professor David Nocera, at Massachusetts Institute of Technology (MIT) in America, recently unveiled at a meeting of the American Chemical Society a prototype of an artificial leaf developed by his team that was ten times more efficient at photosynthesis than a photosynthetic leaf.
For this artificial leaf created by Professor Nocera’s team, the raw material used was silicon, the relatively inexpensive and abundant natural resource used in solar cells, and the catalysts were cobalt and phosphorus, materials that are also relatively abundant and inexpensive. Furthermore, the artificial leaf created by Professor Nocera was very stable whilst generating electricity, with tests conducted by the group showing no sign of activity degradation even after 45 hours of use.
The attractive feature of this artificial leaf from Professor Nocera is the simplicity; instead of a cell that consumed very expensive raw materials and suffered from stability issues as in previous attempts, the artificial leaf makes use of readily available materials. The abundant and inexpensive raw materials, coupled with a high degree of stability, allow for the possibility of a roll out for developing countries and even for off-grid scenarios, making this invention a truly remarkable one for the sole application of powering a home.
The device, no bigger than an ordinary playing card (for example, like one used for playing card games), is placed in a gallon (3.78 liters) of water and exposed to sunlight. Making use of the catalysts specifically selected by his group, the device mimics one of the processes associated with photosynthesis: the splitting of water molecules to produce oxygen and hydrogen. In this alternative solar cell, when exposed to sunlight in a water medium, the catalysts would bubble out oxygen molecules leaving behind a hydrogen-rich water environment; this is a first-generation device that illustrates the potential of water splitting to one day generate electricity. The expectation is for the next generation device to include a side-by-side container where the catalyst would bubble out the hydrogen molecules to one container with an adjacent container storing the bubbled-out oxygen molecules, collectively making-up the integral components of a fuel cell, ready to be recombined to provide electricity as and when needed.
Implications of the artificial leaf for industry
In research circles, the ultimate aim of energy research is in creating a device to store energy. The artificial leaf shows great promise in achieving this aim. By producing hydrogen and oxygen gases and storing them in a fuel cell, the artificial leaf will be able to provide electricity in difficult environments/terrains or at times when there is no sunlight. Further development of this remarkable artificial leaf will benefit material suppliers (silicon, and the material used for current and future catalysts) and fuel cell manufacturers. If this technology is adopted, and the signs are that such an adoption is very likely, then fuel cells will be required to store the separated gases to power the fuel cell when electricity is needed, thus benefiting fuel cell manufacturers.
The evolvement of solar energy technology based on nature
One of the challenges faced by the solar industry is the relatively low rate of efficiency found in current solar cell technology. An understanding of quantum biology will allow for solar cell components to be refined to accommodate photons from sunlight selecting the most energy-efficient route, thus immensely increasing the efficiency rate. Such a result will allow for near-perfect solar cells, eliminating the issue of efficiency and further reducing on the cost of the solar cell.
Another challenge faced by the solar industry is the cost of manufacturing the solar cell, as the cells are usually made from rare and expensive raw materials. With the widespread adoption of the artificial leaf, the solar industry will benefit by the reduced manufacturing costs through using cheaper and more-abundant raw materials. In particular, the artificial leaf will be of substantial relevance to countries that are in the Sunbelt region (countries located at a latitude of +/- 35 degrees of the equator), as these countries have a very high level of insolation.
Different approaches have been taken in order to enhance solar cell technology. For example, utilizing different materials to reduce costs and to increase the rate of efficiency has facilitated this advancement in solar cell technology, from first-generation to fourth-generation. In order to accelerate the process of producing more efficient and cost-effective solar cells, exploiting quantum biology and the artificial leaf will further bring forward this advancement in the solar industry.