Question:
Einstein's photo electric equation K=hv-eV gives the maximum
kinetic energy of electrons emitted from a metal if incident em radiation of
frequency v exceeds the potential barrier eV. For a given frequency above the
emission threshold, the number of electrons emitted increases with the
intensity of the light source. Since electric current is the rate of electron
flow in a conductor, and power = current times voltage drop, then would not
more intense light increase the power of photo-voltaic cells? Would the use
of concentrators such as Fresnell lenses and parabolic mirrors be a cost-
effective method of increasing the power of photo-cells?
Replies:
You are quite right. Concentrators will certainly increase the
power from the photo-cells. But cost effectiveness is rather more
complicated. How does the cost of the concentrator compare to the cost of
additional photo-cells? Does the concentrator need to track the source (sun)?
This would be an additional cost. Some concentrators are unfocused and do not
require close tracking. Another concern is whether the increased intensity at
the photo- cell might overheat the device. All of these concerns affect the
cost-effectiveness.
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