17 November 2015

Six dramatic advances in solar energy

Harvesting, collecting, and deriving usable energy from the Sun and other sustainable sources for people around our planet has made important leaps forward of late. Whether it is summer or winter in your part of the world, that’s excellent news for our future energy needs.

The dual nature of light, recently demonstrated
in an image from the Carbone group at École
Polytechnique Fédérale de Lausanne, and featured
as Figure 1 in a review paper in the Journal of Photonics
for Energy
: "Energy-space photography of light
confined on a nanowire simultaneously shows both
spatial interference and energy quantization."
An open-access article in the Journal of Photonics for Energy co-authored by nine international experts* details some of those advances. Here’s a short list from their review of the state of the art, titled "The role of photonics in energy."

1. Making cheaper and more efficient solar cells

Today’s solar cells are based on inorganic semiconductors -– particularly silicon, the second most abundant material in the Earth’s crust. However, silicon solar cells, although relatively expensive to manufacture, are not the most efficient at converting solar energy into electrical energy.

Solar cells based on other semiconductors are more efficient at conversion but also cost more to make.

A new generation of solar cells in development promises the advantages of low-cost materials, high-throughput manufacturing methods, and low-energy expenditure. These very new emerging cells are still less efficient than more established inorganic solar cells, but they have been improved dramatically over the last few years. Particularly promising are technologies using organic-inorganic hybrid materials such as perovskites.

2. Limiting lost light

Researchers are also working on methods of trapping light within a solar cell more effectively, to limit the amount of energy lost due to reflection off the silicon crystals or layers of protective glass. Existing antireflective coatings have performance limitations, often minimizing the reflection for only a select region of the solar spectrum, and are also dependent on the angle of incidence.

One possible solution is adding nanostructured surfaces (e.g., micro- or nanopillars or nanowires) to minimize reflection.

3. Directing and driving

An alternative to converting sunlight into electricity is harvesting the thermal energy of sunlight directly. Sunlight can be focused onto long pipes coated with an optically absorbing material and filled with a high-thermal-capacity fluid, which is used to drive a turbine. Coatings such as carbon-nanotube and metallic-nanowire arrays with high absorption capabilities are helping toward the goal of creating nearly perfect absorbers.

4. Storing it for later

Research is also being done on storing solar fuels as an energy source, via water-splitting, a process which occurs naturally during photosynthesis. Splitting separates water into its oxygen and hydrogen elements, and can be induced in a photochemical reaction. The induced process of sunlight-driven water splitting is as yet not efficient. But with that solved, the hydrogen produced could be stored in fuel cells and later used for local electricity generation, for example as a transportation fuel for electric vehicles.

5. Following the Sun

Optical and photonic sensors are widely used to make existing technologies that harvest energy and produce power more effective. Tracking systems adjust the positioning of solar collectors to ensure a continued optimum angle relative to the Sun (perpendicular to solar radiation). Sun trackers have the potential to increase the energy collected by solar energy systems by 10% to 100%, depending on factors including the time of the year and geographical position.

6. … or the wind

Wind farms utilize light detection and ranging (LIDAR) technology, which determines wind speed by measuring the Doppler shift of light backscattered by aerosols in the atmosphere. The accurate measurements of wind speeds and turbulence make it possible to more effectively survey potential wind farm sites, optimize their design, and make dynamic adjustments to their operation.

Want to know more? Read the two-part synopsis of the review article in the SPIE Newsroom:

*The paper is authored by Zakya Kafafi, the journal’s editor-in-chief, and Nelson Tansu of Lehigh University; Raúl Martín-Palma of the Universidad Autónoma de Madrid; Ana Nogueira of the University of Campinas; Deirdre O’Carroll of Rutgers University; Jeremy Pietron of the U.S. Naval Research Laboratory; Ifor Samuel of the University of St Andrews; Franky So of North Carolina State University; and Loucas Tsakalakos of General Electric–Global Research Center.


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