Solar Cell Performance improved x40

[The Grim Squeaker]

MIT opens new 'window' on solar energy
Cost effective devices expected on market soon

July 10, 2008

Imagine windows that not only provide a clear view and illuminate rooms, but also use sunlight to efficiently help power the building they are part of. MIT engineers report a new approach to harnessing the sun's energy that could allow just that.

The work, to be reported in the July 11 issue of Science, involves the creation of a novel "solar concentrator." "Light is collected over a large area [like a window] and gathered, or concentrated, at the edges," explains Marc A. Baldo, leader of the work and the Esther and Harold E. Edgerton Career Development Associate Professor of Electrical Engineering.

As a result, rather than covering a roof with expensive solar cells (the semiconductor devices that transform sunlight into electricity), the cells only need to be around the edges of a flat glass panel. In addition, the focused light increases the electrical power obtained from each solar cell "by a factor of over 40," Baldo says.

Because the system is simple to manufacture, the team believes that it could be implemented within three years--even added onto existing solar-panel systems to increase their efficiency by 50 percent for minimal additional cost. That, in turn, would substantially reduce the cost of solar electricity.

Fact sheet: MIT's solar concentrators

In addition to Baldo, the researchers involved are Michael Currie, Jon Mapel, and Timothy Heidel, all graduate students in the Department of Electrical Engineering and Computer Science, and Shalom Goffri, a postdoctoral associate in MIT's Research Laboratory of Electronics.

"Professor Baldo's project utilizes innovative design to achieve superior solar conversion without optical tracking," says Dr. Aravinda Kini, program manager in the Office of Basic Energy Sciences in the U.S. Department of Energy's Office of Science, a sponsor of the work. "This accomplishment demonstrates the critical importance of innovative basic research in bringing about revolutionary advances in solar energy utilization in a cost-effective manner."

Solar concentrators in use today "track the sun to generate high optical intensities, often by using large mobile mirrors that are expensive to deploy and maintain," Baldo and colleagues write in Science. Further, "solar cells at the focal point of the mirrors must be cooled, and the entire assembly wastes space around the perimeter to avoid shadowing neighboring concentrators."

The MIT solar concentrator involves a mixture of two or more dyes that is essentially painted onto a pane of glass or plastic. The dyes work together to absorb light across a range of wavelengths, which is then re-emitted at a different wavelength and transported across the pane to waiting solar cells at the edges.

In the 1970s, similar solar concentrators were developed by impregnating dyes in plastic. But the idea was abandoned because, among other things, not enough of the collected light could reach the edges of the concentrator. Much of it was lost en route.

The MIT engineers, experts in optical techniques developed for lasers and organic light-emitting diodes, realized that perhaps those same advances could be applied to solar concentrators. The result? A mixture of dyes in specific ratios, applied only to the surface of the glass, that allows some level of control over light absorption and emission. "We made it so the light can travel a much longer distance," Mapel says. "We were able to substantially reduce light transport losses, resulting in a tenfold increase in the amount of power converted by the solar cells."

This work was also supported by the National Science Foundation. Baldo is also affiliated with MIT's Research Laboratory of Electronics, Microsystems Technology Laboratories, and Institute for Soldier Nanotechnologies.

Mapel, Currie and Goffri are starting a company, Covalent Solar, to develop and commercialize the new technology. Earlier this year Covalent Solar won two prizes in the MIT $100K Entrepreneurship Competition. The company placed first in the Energy category ($20,000) and won the Audience Judging Award ($10,000), voted on by all who attended the awards.

fact sheet

Dang, it works on old panels as well?
That settles it, i'm waiting a bit more before convincing my parents to buy solar panels. It's good to see how solar power is blazing ahead over the past 3-5 years, let alone the next 3-4, but I REALLY wish it was 5 years ahead in that schedule, before material costs begin to climb and even getting a panel might prove tricky.

[Chardok]

couple questionsfor the scientifically or at least specific-subject illiterate:

#1: are there any actual figures for power generation? (Compared to current models)

#2: Is this theoretical or is it a done deal? ( I fail at extrapolation, perhaps...)

#3: does it use exotic materials (like lithium deuteride molecular photonic depleted americium hydride - found in concentrations of one part per quadrillion and even then only in new nebulae more than 7 trillion light years across and impossible to manufacture on earth)

[Sikon]

This is the same basic principle as using a reflector such as a parabolic metal trough to concentrate sunlight onto solar cells. When a solar cell receives more intense sunlight, it produces more power, so a lesser area of solar cells are needed for a given amount of power. Solar cells are very expensive per unit area, a few hundred dollars or more per square meter for those of decent efficiency, so such can be worthwhile if the rest of the reflector costs much less than the solar cells themselves per square meter.

Fundamentally, this is the same basic idea as what someone can do with a solar cell and a bunch of aluminum foil but more elegant, thin, and particularly suited to use without a setup rotating to track the sun.

In this case, there's no curved reflector as such but a special panel that acts a little like a light duct channeling light which is concentrated at the edges. As a result, a relatively small area of solar cells can receive increased sunlight intensity. Luminescent solar concentrators similar to this were worked on in the 1970s, but these researchers say that their new system has more stable dyes and better performance.

If a very high intensity of concentrated light is obtained on the solar cells, cooling issues can arise, but whether or not active cooling is needed depends on a lot of details, such as the concentration factor in a commercialized version of this.

#2: Is this theoretical or is it a done deal? ( I fail at extrapolation, perhaps...)

The principle certainly technically works. However, whether or not this appears and succeeds as a commercial product versus the competition is harder to tell without more data. One will see in a few years.

With inefficiencies in light transmission (especially for past LSCs), such would tend to have a greater total area than a regular solar array of the same power output, but the area of very-expensive solar cells themselves needed would be much less. As a result, the total cost might be substantially less, possibly, depending on what their total expenses work out to be in production if they successfully commercialize the product.

#3: does it use exotic materials (like lithium deuteride molecular photonic depleted americium hydride - found in concentrations of one part per quadrillion and even then only in new nebulae more than 7 trillion light years across and impossible to manufacture on earth)

Not exotic materials as such.

Its implementation may involve a little gallium consumption, etc. like a lot of other solar cell arrays (and a lot of semiconductor-based electronics in general). Actually, a benefit of a solar concentrator system is that the area and mass of actual solar cell material needed can be much less per unit of power produced.