April 29, 2004


Material grabs more sun (Kimberly Patch, April 21/28, 2004, Technology Research News)

One way to make solar cells more efficient is to find a material that will capture energy from a large portion of the spectrum of sunlight -- from infrared to visible light to ultraviolet.

Energy transfers from photons to a photovoltaic material when the material absorbs lightwaves that contain the same amount of energy as its bandgap. A bandgap is the energy required to push an electron from a material's valence band to the conduction band where electrons are free to flow.

The trouble is, most photovoltaic materials absorb a relatively narrow range of light energy. The most efficient silicon solar cells capture about 25 percent of the sun's energy. Multijunction solar cells combine several materials to capture multiple bands of photonic energy. Today's most efficient combination -- germanium, gallium arsenide and gallium indium phosphide -- boosts efficiency to 36 percent, but is relatively difficult to make and therefore expensive.

Researchers from Lawrence Berkeley National Laboratory, the University of California, and the Massachusetts Institute of Technology have engineered a single material that contains three bandgaps. The material is capable of capturing more than 50 percent of the sun's energy, said Wladek Walukiewicz, a senior staff scientist at the Lawrence Berkeley National Laboratory.

The material could lead to relatively inexpensive, highly-efficient solar cells.

Posted by Orrin Judd at April 29, 2004 8:46 AM

Applied material science is probably the most important and least valued area for research right now.

Posted by: David Cohen at April 29, 2004 9:07 AM

I'm skeptical, if only because I remember when GaAs was the big thing (for virtually every purpose), and they've been saying that a substance like this was "just around the corner" since my father worked on his Ph.D. thesis on this very subject four decades ago.

Posted by: Chris at April 29, 2004 9:26 AM

Don't forget - 1100 watts per square meter. Solar cells are neat, but that is their limit.

Posted by: jim hamlen at April 29, 2004 9:50 AM

Jim, on a sunny day, probably on the equator.

Posted by: Uncle Bill at April 29, 2004 10:19 AM


Indeed. Solar (and still less wind and hydro) isn't the long-term answer - just not enough possible power. About the only plausible non-fossil-fuel options are nuclear (especially if any of the latest round of cold-fusion anomolies pan out), space-based solar (which would require lift systems that would have enormous military value), or um, hard to say what else - geothermal?

Posted by: mike earl at April 29, 2004 10:22 AM

Geothermal is mining. All the best places, with the highest temperatures, have been fully exploited and are already returning reduced yields as they age. And don't forget the environmental impacts-- if you flash the fluid to steam, you get precipitates with high quantities of sulfur, arsenic, antimony, nickle, lead and other metals. You have to dispose of this like any other ~toxic waste~, as well as manage the scaling in your pipes from this stuff, too.

Surface boiling spring systems support unique microclimates and ecosystems. These are usually destroyed during a powerplants startup testing, because the boiling springs they depend on are extremely fragile. I'm not interested in the biology, but I can tell you that the slime at Steamboat Springs and Beowawe , former geyser fields in Nevada, looked nothing like any of the places in Yellowstone, and most of them there. Think of boiling springs as Amazon Basins in a half acre.

It's been discovered that these "extremophiles" contain all sorts of useful stuff. This has resulted in Yellowstone (and a few other preserves) being the only area that are left to be exploited and where there is some guarantee that such ecosystems will be available for the future. (There's nothing wrong with harvesting slime from National Parks if you also have no problem with harvesting other natural resources, from animals to minerals to plantlife, within such preserves.)

So just like any other energy source, geothermal has its tradeoffs and is no more free than the petroleum it's supposed to replace.

Posted by: Raoul Ortega at April 29, 2004 12:57 PM

Another irony The irony is that in eco-socialist places like VT, it's nearly as hard to get a community to accept a wind/solar farm as it would be a gas or coal fired power plant.

In other words, these types of renewable energy
projects on a scale required to do anything
substantial still don't solve the aesthetic
issues which is a large part of the NIMBY

What people say they want only matters if they are
willing to say it with dollars.

Posted by: J.H. at April 29, 2004 3:25 PM