More solar energy efficiency thanks to quantum physics and biochemistry
The energy efficiency of a system, even if referred to very different systems, is the capability of the system to exploit the energy it receives to satisfy a need: the lower the consumption needed to reach the desired result, the better the energy efficiency of the system.
The energy efficiency of a system can be measured with a number from 0 to 1, where 0 is a system that uses energy without producing a result, and 1 is the optimal efficiency, where each part of energy released produces a result. These extreme limits are purely theoretical.
With all data available, it is possible to calculate the degree of energy efficiency, from systems that are easy to measure, like engines, to more complex systems where indicators and statistics are needed to assess the level of energy performance with good approximation.
Measurement of the energy efficiency of a system is recommended since it enables the identification of all types of waste and energy losses that can become a resource to be used in economic, environmental and social terms, as well as to reduce costs.
Solar energy is associated with solar radiation and is the primary source of energy on Earth since it is used by all living organisms. Moreover, almost all energy sources available to man derive, more or less directly, from it, including fossil fuels, wind energy, sea wave energy, hydroelectric energy, biomass energy.
Man has always tried to use different techniques to try and make use of solar energy, and in the modern era, being aware of the scarcity of fossil fuels and of the state of the environment and climate, the study of solar energy is one of the activities research and innovation are increasingly addressing.
Now solar devices and sensors can become even more efficient thanks to the combination of quantum physics and biochemistry according to the results of the study “Enhanced energy transport in genetically engineered excitonic networks” conducted by Eni under the framework agreement between Eni-CNR and the partnership Eni-MIT signed in 2008. The study was published in the journal Nature Materials and focuses on technological innovation in the field of solar energy.
The study was conducted by an international and interdisciplinary team of researchers of the Department of Physics and Astronomy and the European Laboratory for Non-Linear Spectroscopy (LENS) in Florence and the Department of Chemistry of the University of Perugia, the National Institute of Optics of the National Research Council (INO-CNR), the “Quantum Science and Technology in Arcetri” (QSTAR) research centre, the Massachusetts Institute of Technology (MIT) and the Eni research centre Donegani in Novara.
Natural photosynthesis takes place through a process in which light is captured by a protein “receiving antenna” and then transmitted by a chain of pigments linked to it, called chromophores, to the “power station”, where it is converted into biologically usable energy.
To achieve optimum efficiency of transport mimicking natural systems, the research team used artificial photosynthetic antennas developed in the laboratories of MIT, composed of genetically engineered viral structures, in order to control the distance between the two types of chromophores, donors (light absorbers) and acceptors (light emitting diodes) anchored at specific points of the structure.
An “interaction force” is established between the two chromophores that is based on distance and it is responsible for the efficient transport of excitation energy with an efficiency close to 100%, as compared to a level of efficiency that in natural photosynthesis is lower than 1%, greatly exceeding the efficiency guaranteed by the best solar cells.
The researchers explain this phenomenon with the principles of quantum physics: when the exciton (the energy unit) is created on different chromophores simultaneously, it tries to find the optimal route to the reaction centre through various paths in parallel. The molecular movements active at room temperature make the processes faster, enabling an efficiency improvement in the field of photovoltaic energy.
“After a seminar held by MIT at our facility – they explained at the Eni Donegani Research Centre – we realized that such “antenna systems” could be used, with some adjustments, to achieve high-efficiency solar devices, by mimicry of the energy transport process occurring in natural photosynthesis”. Eni then decided to support a new project together with MIT aimed at the study of the possible occurrence of quantum transport in these systems, also involving INO CNR and LENS from the University of Florence.
As Paolo De Natale, Director of INO-CNR, explained, “To analyze energy transport in antenna systems we conducted an experiment in which they are stimulated through extremely fast laser pulses that are first absorbed by donor molecules and then re-emitted by acceptors, thus allowing the measurement of transport efficiency.
For the genetically engineered structures, we measured an exciton propagation twice as fast as compared to the same antennas based on non-engineered virus and, consequently, propagation distances greater than 67%.”