New solar energy technology investigated
- By Kathleen Hickey
- May 14, 2008
A new molecular mechanism identified in plants could aid the government in creating and using solar energy to lower costs and improve energy resources in remote locations.
Researchers from Lawrence Berkeley National Laboratory have discovered a molecular dimmer switch that helps control the flow of solar energy moving through the plant, which protects the plant from absorbing too much sunlight and sustaining oxidation damage ' sort of a plant version of sunburn.
The discovery holds important implications for the design of artificial photosynthesis systems. Systems using today's artificial solar energy technology can suffer overload damage if they absorb too much solar energy.
Through photosynthesis, green plants harvest energy from sunlight and convert it to chemical energy at a transfer efficiency rate of approximately 97 percent. The highest rate for solar energy conversion to electrical energy using a man-made device today is less than 30 percent. Further study of photosynthesis could lead to higher energy conversion rates.
The dimmer switch is pigment-binding protein CP29, which operates as a valve that permits or blocks the release of excess solar energy during photosynthesis. CP29 is one of the so-called minor light-harvesting proteins in green plants. In addition, researchers have proposed that the valve can be controlled by raising or lowering ambient pH levels.
'This is really the first detailed picture ever obtained of the molecular mechanism behind the regulation of light-harvesting energy,' said Graham Fleming, a physical chemist at the laboratory and the University of California at Berkeley who is one of the leaders of the study.
'We believe we will soon be in position to build a complete model of the flow of energy through the photosynthetic light-harvesting system that will include how the flow is controlled. This model could then be applied to the engineering of artificial versions of photosynthesis,' he said.
In 2005, Fleming and his research group identified zeaxanthin, a member of the carotenoid family of pigment molecules, as the safety outlet in the photo-protection of green plants. A plant's light-harvesting system consists of two protein complexes, Photosystem I and Photosystem II. Fleming and his group found that intense exposure to light triggers the formation of zeaxanthin molecules in Photosystem II. These molecules interact with chlorophyll molecules to dissipate excess energy. However, researchers did not know until now how the interaction was regulated.
By using near-infrared absorption spectroscopy, researchers were able to determine that three minor light-harvesting proteins, C29, CP26 and CP24, were responsible for reducing solar-energy absorption, Fleming said.
'The next step is to examine the energy-quenching mechanism in the rest of the Photosystem II complex to see how it is used to regulate the flow of energy throughout the light-harvesting system,' Fleming said.
The program is in the fundamental research stage with no discussion of potential applications at this time, said Lynne Yarris, spokeswoman for the project. However, the developmental research could change how the government fills its energy needs.
Support for the research came from the Energy Department's Office of Basic Energy Sciences through its Chemical Sciences, Geosciences and Biosciences Division.
Kathleen Hickey is a freelance writer for GCN.