The Energy Dudget
""We have somewhere between 20 and 30 layers of semiconductor material,"
explains David Lillington, president of Spectrolab, Inc., . . . The resulting
efficiency nearly doubles that of standard silicon solar cells, which hover at
22 percent. That gain requires, however, the use of light-concentrating devices,
such as miniature plastic lenses and mirrors. The new solar cell achieved 40.7
percent efficiency under such concentrated light at the testing center at the
National Renewable Energy Laboratory in Colorado. One cell of just 0.26685
square centimeter (or roughly 0.04 square inch) pumped out 2.6 watts of
electricity when bathed at the maximum light concentration.""Even though
installed cells would require concentrators, the fact that fewer cells can
produce the same amount of power--and that similar cells are already widely
produced--means this system could potentially generate electricity in the range
of 8 to 10 cents per kilowatt-hour--roughly equal to consumer electricity prices
today." "the record-breaking solar cells are at least 12 months away from
full-scale manufacturing, Lillington says. "Before we put this new cell into
production it needs to go through a qualification process to make sure it can
withstand the rigors of the environment." Of course, its Martian peers have
lasted 28 months in that harsh, alien environment.
[NOTE: The Mars rovers
worked (and still are) much longer than predicted, with the rooftop collectors
-- surprise! -- getting a brush-off now and then by a passing dust storm. And
all this with a solar flux of about 600W/m^2 i.e. only 44% of Earth's.]
And
the triple-junction solar cell may not hold the efficiency record for long. "We
are also looking at four-, five-, even six-junction solar cells," Lillington
notes. "There are at least three or four different approaches to take the
efficiency into the 45 percent range."
Based on p.4 of the paper, quoting from
http://www.life.uiuc.edu/govindjee/paper/gov.html:
"One of the most efficient crop plants is sugar cane, which has been shown
to store UP TO 1% of the incident visible radiation over a perid of one year. .
. . . The annual conversion efficiency of corn, wheat, rice, potatoes and
soybeans TYPICALLY RANGES from 0.1-0.4% (Odum, 1971)"
The nearest, albeit for algae, was the following article:
"The
combination of algal and anaerobic waste treatment in a bioregenerative farm
system"
Gedaliah Shelef, Department of Environmental and Water Resources
Engineering, Technion - Israel Institute of Technology, Haifa, Israel
http://www.unu.edu/unupress/unupbooks/80434e/80434E0n.htm
SEE
TABLE 2. Summary of Algae Production Data Based on Technion Pilot Plant and
Field-Scale Pond Operation:
Average daily incident irradiance (total) 450
cal/cm²-day
Average daily incident photosynthetically available
irradiance 202 cal/cm² day
Photosynthetic light conversion efficiency
(based on total irradiance) 2.96%
Photosynthetic light conversion efficiency
(based on photo-
synthetically available irradiance) 6.59%