Advertisement

Blog

Cheap Solar Absorbs Entire Spectrum

The biggest problem with photovoltaic (PV) panels may have been solved by researchers at the Massachusetts Institute of Technology (MIT). Today, the most efficient solar panels use expensive multi-junctions, each of which capture a different part of the solar spectrum, but not all of it.

MIT's solution is to put an intervening material between the sun and a normal infrared PV panel. This designer material absorbs the entire solar spectrum, reflects light outside the solar spectrum, and glows infrared (heat) with the total power absorbed from the sun. MIT calls it solar thermophtovoltaics (STPVs).

Scanning Electron Micrograph (SEM, scale bar is 200 nanaometers) of tungsten sputtered on the Al2O3 dielectric shells, allowing for a wide variety of materials to be used.
(Image: MIT)

Scanning Electron Micrograph (SEM, scale bar is 200 nanaometers) of tungsten sputtered on the Al2O3 dielectric shells, allowing for a wide variety of materials to be used.

(Image: MIT)

Jeff Chou, a post-doctoral researcher at MIT, working with professors Nick Fang, Evelyn Wang, and Sang-Gook Kim, told EE Times:

To increase the efficiency in solar thermophotovoltaic (STPV) systems they require a material that only absorbs across the solar spectrum and reflects light outside of the solar spectrum. The reason is to minimize thermal radiation losses in the infrared. When this is achieved, the solar energy can be efficiently stored as heat with minimal losses. STPV systems also require a selective emitter that radiates thermal energy to a photovoltaic. In order to maximize efficiency, only radiated energy above the bandgap of the photovoltaic should be emitted, and thus a selective emitter is also required. The material we developed with 2D metallic dielectric photonic crystals is potentially capable of serving as both the selective absorber and selective emitter functions to boost the overall efficiency of STPV systems.

A metallic dielectric photonic crystal with solar broadband, omni-directional, and tunable selective absorption with high temperature stable properties is fabricated on a 6' silicon wafer.
(Image: MIT)

A metallic dielectric photonic crystal with solar broadband, omni-directional, and tunable selective absorption with high temperature stable properties is fabricated on a 6″ silicon wafer.

(Image: MIT)

The team's material should technically be called a planar photonic crystal, since it is not actually a 2D monolayer, but is studded with rings the width of which determine the spectrum of light they absorb. The researchers, however, insist on calling it a 2D material because planar dimensions, not it thickness, determines its advantageous properties.

“We call it a 2D photonic crystal, because it is periodic in two dimensions (x and y). Thus the name 2D is what is commonly used in the photonics community for such materials,” Chou told EE Times. “So the 2D I mention is in regards to the periodicity and is not in reference to an actual atomically flat 2D material.”

Regardless of definitions, the planar periodic photonic crystal can be tuned across the entire spectrum of solar energy, and naturally reflects any wavelengths outside that spectrum. To boot the material is able withstand temperatures over 1,000 degree Celsius (1,832 degrees Fahrenheit), making it ideal for solar concentrators, plus is able to absorb nearly equally well at angles up to 70 degrees so that expensive mechanical tracking systems do not have to be included.

“Along with a wide spectral property, an ideal, practical solar absorber should be tuneable, absorb at wide angles, be stable at high temperatures, and be mass manufacturable for low cost reasons. The absorber we developed is the only one that has all of these properties, making it an ideal absorber,” Chou told EE Times.

Previous versions of the prototype in an earlier project did not fill the cavities with dielectric, but were left open to the air. This still allowed the material to be tuned to the sun's frequency spectrum, but not trap the thermal energy there which led to inefficiencies. Earlier versions also required small metallic substrates, but the current fabrication method can be run on any standard CMOS line of any size — even 12-inch wafers.

The researchers plan to experiment with using different metals than the relatively expensive ruthenium used today, which they believe is feasible since the chemical properties of ruthenium do not come into play with the process. Chou is also working with Kim on applications and expects commercialization of the technique to take five years.

To read the rest of this article, visit EBN sister site EETimes.

8 comments on “Cheap Solar Absorbs Entire Spectrum

  1. Daniel
    October 9, 2014

    “The researchers plan to experiment with using different metals than the relatively expensive ruthenium used today, which they believe is feasible since the chemical properties of ruthenium do not come into play with the process. Chou is also working with Kim on applications and expects commercialization of the technique to take five years.”

    Collin, whether it can increase the efficiency of PV. As of now the efficiency is 30-40% and more research has to happen in that side to increase the efficiency.

  2. SP
    October 9, 2014

    Solar has tremendous potential and more reserach has to be done in this area. FUture has much brighter prospects for solar. This is not yet fully tapped or implemented.

  3. prabhakar_deosthali
    October 10, 2014

    Truely Solar energy has a tremendous potential for reasearch.

    Just a digression from the technology field to  Medical use of solar energy –  There is a person in India who has survived for 411 days drinking only hot water and taking solar energy through his retinas for survival. This 411 days fast was done under medical supervision and doctors are trying to put forth theories how such absorption of solar energy is possible by humans through their eyes. Even NASA got interested in this person's experiment and supposedly has carried out some reasearch to see how such technology can be used for astronauts living on space stations for longer periods

    I think this a very good subject for reasearch by doctors as well as the technologists and somebody who can find how solar enegry can find its way to human body energy system can surely win a Nobel prize and such discovery can help eliminate the famine in many underdeveloped countries

  4. Daniel
    October 10, 2014

    “Solar has tremendous potential and more reserach has to be done in this area. FUture has much brighter prospects for solar. This is not yet fully tapped or implemented.”

    SP, yes you are right. As of now only less than 2% of the world's total energy requirements are meeting through solar energy. We cannot rely on hyderal and atomic energy for a long time; the only reliable source is solar energy.

  5. Daniel
    October 10, 2014

    “There is a person in India who has survived for 411 days drinking only hot water and taking solar energy through his retinas for survival. This 411 days fast was done under medical supervision and doctors are trying to put forth theories how such absorption of solar energy is possible by humans through their eyes.”

    Prabhakar, thanks for sharing this interesting story, Great.  After 411th days what happened to that person.

  6. prabhakar_deosthali
    October 11, 2014

    @Jacob,

     

    This person is still active and practicing his Solar energy technique. This 411 day fast he did in yesr 2000. During the fasting period, he was doing all regular activities and was never confined to bed except for the routine medical check ups by the doctors. he lost only 16 kg wt in the intial fasting days and thereafter his BP, blood sugar and all the basic parameters remained normal. he even climbed a hill along with his fellow disciples sometime after 200 days of fasting.  Doctors had kept a strict vigilance on him during the whole fasting period to ascertain that he did not take any sort of food or liquid in any form during the fasting except hot water .

    He opened a Solar healing center in USA . Currently he is based in Calicat, India.

     

  7. Eldredge
    October 12, 2014

    To boot the material is able withstand temperatures over 1,000 degree Celsius (1,832 degrees Fahrenheit), making it ideal for solar concentrators, plus is able to absorb nearly equally well at angles up to 70 degrees so that expensive mechanical tracking systems do not have to be included.


    These are two significant advantages for this material, which also help to reduce the cost of solar energy technology. It will be interesting to see if this can be exploited to benefit the solar energy industry.

  8. Daniel
    October 13, 2014

    “This person is still active and practicing his Solar energy technique. This 411 day fast he did in yesr 2000. During the fasting period, he was doing all regular activities and was never confined to bed except for the routine medical check ups by the doctors. he lost only 16 kg wt in the intial fasting days and thereafter his BP, blood sugar and all the basic parameters remained normal.”

    Prabhakar, good then I think it can be developed as an alternate branch of medicine, for curing or treatment of such diseases.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.