A team of scientists has devised a new way to more accurately compare how efficiently plants and photovoltaic, or solar, cells convert sunlight into energy, which could ultimately help researchers improve plant photosynthesis, a critical first link to enhancing the global supply of food, feed, fiber, and bioenergy. Image: USDA
Scientists now have a way to more accurately compare how efficiently plants
and photovoltaic, or solar, cells convert sunlight into energy, thanks to
findings by a research consortium that included a U.S. Department of
Agriculture (USDA) scientist.
The study, published in Science,
could help researchers improve plant photosynthesis, a critical first link in
the global supply chain for food, feed, fiber, and bioenergy production.
Comparing plant and photovoltaic systems is a challenge. Although both
processes harvest energy from sunlight, they use that energy in different ways.
Plants convert the sun’s energy into chemical energy, whereas solar cells produce
electricity. The scientists, including Agricultural Research Service (ARS)
research leader Donald Ort in the agency’s Global Change and Photosynthesis
Research Unit in Urbana, Ill., identified specific designs that hold
excellent promise for improving efficiency.
ARS is the USDA’s chief intramural scientific research agency.
The first step was to facilitate a direct comparison of the two systems. The
researchers set a uniform basis for the comparison and examined the major
factors that define the efficiencies of both processes, first considering current
technology, then looking forward to possible strategies for improvements.
In all cases, the research team considered the efficiency of harvesting the
entire solar spectrum as a basis for comparison. Additionally, the researchers
compared plants to solar cell arrays that also store energy in chemical bonds.
Calculations were applied to a solar cell array that was coupled to an
electrolyzer that used electricity from the array to split water into hydrogen
and oxygen. The free energy needed to split water is essentially the same as
that needed for photosynthesis or a solar cell, so the comparison provided a
level playing field.
Using this type of calculation, the annual averaged efficiency of
solar-cell-driven electrolysis is about 10%. Solar energy conversion
efficiencies for crop plants are about 1%, which illustrates the significant
potential to improve the efficiency of the natural system, according to Ort.
While, in the context of the team’s efficiency analysis, solar cells have a clear
advantage compared to photosynthesis, there is a need to apply both in the
service of sustainable energy conversion for the future.
This energy-efficiency analysis between plant photosynthesis and solar cells
will lay the groundwork for improving the efficiency of plant photosynthesis in
agriculture for improved yield.