Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!netnews.upenn.edu!pender!jliu
From: jliu@pender (.)
Newsgroups: sci.electronics
Subject: Re: LASER cutters
Summary: solar cell efficiency!!!
Keywords: laser,solar cell,efficiency
Message-ID: <21202@netnews.upenn.edu>
Date: 3 Mar 90 05:22:23 GMT
References: <44900003@uxa.cso.uiuc.edu> <2232@rodan.acs.syr.edu> <532@sierra.stanford.edu> <21050@netnews.upenn.edu> <1990Mar1.183939.1108@utzoo.uucp>
Sender: news@netnews.upenn.edu
Reply-To: jliu@pender (.)
Distribution: sci.electronics
Organization: University of Pennsylvania
Lines: 34

In article <1990Mar1.183939.1108@utzoo.uucp> (Henry Spencer) writes:
>
>Remember that the best readily-available solar cells are only about 15%
>efficient, and that there are limits to how much light they can take
>without overheating and failing.  Not workable, I'm afraid.


The efficiency of a solar cell is a function of how much incident
electromagnetic energy IN ALL FREQUENCIES is converted into electrical 
energy. In normal operation, any incident frequency with energy above the
work function of the solar cell will excite photoelectrons. When they
say a solar cell is 15% efficient, that does not mean that it converts only
15% of the energy in all frequencies to electrical power. Rather, the
solar cell may have near perfect efficiency in the visible spectrum, but
be much less efficient at lower frequencies. The 15% efficiency is the 
net efficiency over the entire spectrum of sunlight, which includes visible,
uv, etc..

It is possible to fabricate solar cells which respond optimally at certain
frequencies. Since a laser is inherently a monochromatic or quasi-
monochromatic device, the solar cells can easily be tuned to the laser
frequency.

As for the other consideration, heat can be generated in solar cells by
either a resistivity in the wires imbedded in the cell or by the creation
of phonons (vibrational modes in the silicon crystal lattice). These 
characteristics, too, can be overcome by careful design, since only the
range of frequencies of the laser light need be considered.

--------------------------------------------------------------------------
John C. Liu			|	"To be a student is to be
Univ. of Pennsylvania		|	 morally handicapped."
Philadelphia, PA 19104		|                       - JCL
--------------------------------------------------------------------------