Friday, December 30, 2016

Future of emerging PV Technologies

The solar resource is huge although its energy density is rather low. However, it is not so
low as to lose any hope of massive utilization but it is not high enough to make it easy.
Obviously, the proper strategy for recovering a dispersed resource is to do it with
high efficiency at a low cost per area. But the standard PV-effect, as described in this
chapter, only delivers to the external circuit with high efficiency those charge carriers
generated by the few photons with energy close to the band gap. The excess energy of
photons whose energy is greater than the band gap is typically wasted as heat. Even
worse, all of the energy of the photons whose energy is below the band gap is wasted
since they are not absorbed and therefore generate no charge carriers.

Thus, the maximum efficiency that can be
obtained under the best conditions from a single junction solar cell is in the range of 40%.
The best efficiency so far obtained for single-junction solar cells is 27.6%, with GaAs
research-type cells [75] under concentrated sunlight of 255 suns, that is, of 255 times the
unconcentrated standard power density (i.e. at 255 kW/m2). Typical commercial silicon
cell efficiency is ∼15% measured at standard conditions (input optical power density of
1 kW/m2, 25◦C and standard terrestrial solar spectrum).

One way of extracting more power from the sun is to use stacks of cells of semiconductors
having different band gaps. Higher band gap semiconductors are located on
top of the stack allowing photons of energy less than their band gap to pass through,
where they can be absorbed by inner cells of lower band gap
Read More




Return to top of page
Powered ByBlogger | Design by PARMAN | Blogger Template by UKK As-Siraaj