A scientist from the Washington University in St. Louis wrote an article that was published in the May 13 issue of Science that compared the efficiency of photosynthesis and solar cells. According to Robert Blankenship, a member of DOE’s Council and Biochemical Sciences, it is a misconception made by most people that photosynthesis is more efficient in capturing the energy in sunlight.
The question was first discussed during a Department of Energy workshop in May 2009. It was attended by distinguished chemists, biologists, physicists, and solid state scientists. David M. Kramer, PhD, Hannah Professor of Biochemistry and Molecular Biology at Michigan State University and co-author of the article, said that the study of the efficiency of photosynthesis can show whether biofuels industry is viable.
According to the scientists, efficiency is subjective. It must first be defined in order to compare the effectiveness of plants and solar cells. Plants store the sun’s energy in little stored-fuel packages while photovoltaic solar cells just convert the sun’s energy to electrons.
To be fair with plants, the photovoltaic arrays used in the comparison would also store energy in chemical bonds. They connected a PV array to an electrolyzer that used electricity to split wter into oxygen and hydrogen. This energy used to split water is similar to what a plant utilizes to form carbohydrate.
With that setup, photovoltaic-based electrolysis has an efficiency of 10 percent. This is higher than the 1 percent solar energy conversion efficiency of crop plants. Some crop plants reportedly have efficiencies between two to four percent. Microalgae grown are observed to have a higher efficiency than normal plants.
Blankenship doesn’t want to dismiss plant crops just because of the result of their experiment. Efficiency is just one of the factors that can decide the viability of a technology. There are more important things to consider such as life cycle costs, valuation of the environment impacts of the end product, and the capital costs.
The experiment did manage to prove the misconceptions wrong and led the scientists to question why photosynthesis is inefficient. Then they could work on a solution to improve the efficiency of plants. To do so, scientists must find a solution to two problems. These are light saturation and RuBisCo, an enzyme that is required to pull carbon dioxide from air.
Solar cells are more effective in converting sunlight into energy but plants should not be counted out. Experts suggested replacing photosystems in plants so that they could be as efficient as present day solar panels.