An unexpected discovery could yield a full spectrum solar cell

Research News ^ | November 18, 2002 | Lawrence Berkeley National Laboratory

[MainFrame65]

BERKELEY, CA — Researchers in the Materials Sciences Division (MSD) of Lawrence Berkeley National Laboratory, working with crystal-growing teams at Cornell University and Japan's Ritsumeikan University, have learned that the band gap of the semiconductor indium nitride is not 2 electron volts (2 eV) as previously thought, but instead is a much lower 0.7 eV.

The serendipitous discovery means that a single system of alloys incorporating indium, gallium, and nitrogen can convert virtually the full spectrum of sunlight -- from the near infrared to the far ultraviolet -- to electrical current.

"It's as if nature designed this material on purpose to match the solar spectrum," says MSD's Wladek Walukiewicz, who led the collaborators in making the discovery.

What began as a basic research question points to a potential practical application of great value. For if solar cells can be made with this alloy, they promise to be rugged, relatively inexpensive -- and the most efficient ever created.

(See the link for charts and illustration) http://www.lbl.gov/Science-Articles/Archive/MSD-full-spectrum-solar-cell.html

[MainFrame65]

Two layers of indium gallium nitride, one tuned to a band gap of 1.7 eV and the other to 1.1 eV, could attain the theoretical 50 percent maximum efficiency for a two-layer multijunction cell. (Currently, no materials with these band gaps can be grown together.) Or a great many layers with only small differences in their band gaps could be stacked to approach the maximum theoretical efficiency of better than 70 percent.

[MainFrame65]

If you have not seen this, you might find it of interest.

[Willie Green]

Thanks for the ping!
Based on the shear magnitude of our energy consumption, it is still doubtful that solar will ever play a major role as a primary source of energy. Nevertheless, given the myriad applications where solar cells are already used, this potential improvement in technology and efficiency is still very significant.

[Robert A Cook PE]

Interesting.

Now watch the democrats immediately turn this into the "we don't any oil at all..... (Except for the greed of the Texas oil companies we would be free at last!)"

(Please open page 6969 of your "Give peace a chance" hymnal, and begin singing "Kumbuyacomebuya".)

[MainFrame65]

If it gets to 10% I would be surprised. Solar becomes a "continuous" source only when combined with sufficient energy storage to fill in ALL of the output gaps. But it makes a fine supplemental source, and its peak output corresponds to some peak usage profiles, but not others. It simply cannot work as a baseload source. For that we have to go back to the real continuous sources - hydro, coal and oil, gas, and nuclear.

As for this particular article, higher efficiency reduces collection area, but not the other disadvantages. Clouds will still reduce output significantly, if perhaps less than older cells. However, the ability to produce electricity from lower-energy photons will broaden the utility of these new cells, when (if?) they finally get them out the door.

[MainFrame65]

The same folks that think vehicle mileage is a function of legislation rather than engineering.

[B4Ranch]

ping

[Carry_Okie]

One must also look at solar cell efficiency as a system including both storage hysteresis and junction losses when converting it to AC.

It may eventually be a practical power source for remote locations where line losses and maintenance are expensive, but in many of those applications it would rightly have to compete with bio-mass cogeneration.

[MainFrame65]

No question. But this does represent a significant increase in electrical output from solar energy input. And if I understand it correctly, this is due not so much to efficiency of conversion but to the ability to convert a broader spectrum of light to usable electricity. This might also mean less sensitivity to haze, pollution, or cloud cover than current solar cells.

So depending on cost, when they are finally comercially available, these might make remote and portable power more useful, as well as more readily available.

However, solar simply does not work as baseload power due to its inherent unreliability. Continuous, reliable power from solar would require enough storage to exceed the longest outage anticipated, plus enough excess capacity to fill that storage in the shortest availability period anticipated.

We simply MUST get over our irrational attitude toward nuclear power, and build the capacity we need. And for the time when natural fossil fuels become scarce and expensive, we need the capacity to replace that energy as well.

[Carry_Okie]

Completely agreed.

The first step toward reestablishing nuclear is for Bush to rescind Carter's EO banning nuclear fuel reprocessing. The "waste storage problem" is largely the result of a fraud perpetrated by Greenpeace at the behest of the Ford Foundation.