What is the future for photovoltaics?

[Chaos' lil bro Order]

Yes, I was wondering if anyone was, perhaps familiar with the industry of photovoltaic cells and how that industry is maturing. In particular, how efficient are the best cells available today. I would guess its measured in something like Watts/Surface Area, or some statistic like that.

Another question I had was about how the cells capture EM energy. Do they collect a wide band of the EM spectrum, like say Gamma to Radio EM, or is it collecting mainly in say the visible 400-750nm spectrum, or mabye just a single wavelength?

Thank you in advance for good answers.

 

[Barny]

Hi, I'm sure you'll be able to get some better informed answers then what I'm about to say, however it might be enough to point you in the right direction for your own research. Anyway as far as I'm aware...

Currently the most common photovoltaic cells are Silicon in 3 forms - Amorophous, Multi-Crystaline and Mono-Crystaline. These have efficiencies ranging from 5% to 25% (worst case to best case) depending on the system, Mono crystaline being the most efficient, amorphous the least. The average for commercial use is about 18%.

A photovoltaic cell can generate electricity out of any photons with energy greater then the band gap. However I think that if a photon has energy greater then the band gap energy of the material, then this energy is generally lost as heat. If you google this paper , Shockley and Queisser, Journal of Applied Physics, March 1961, Volume 32, Issue 3. It has a good discussion of this subject, and a derivation of a maximum efficiency.

Most research is now focussing on developing Multi-junction Cells, as well as new compounds and organic dyes with photovoltaic properties. Multi-Junction cells have the advantage of making wider use of the EM spectrum.

I found this book really good. Clean Electricity from Photovoltaics, Mary Archer. ISBN 1-86094-161-3,

Hope that's some help.

 

[Chaos' lil bro Order]

Excellent reply Barny, just what I wanted. Thanks buddy, I shall enjoy reading your links.

 

[Barny]

No problem!

 

[Redbelly98]

Silicon converts light up to about 1100 nm. It also converts down into the near-u.v., not sure of the exact cutoff wavelength there.

Solar radiation is roughly 1000 W/m^2, and Barny's efficiencies jive with what I've heard (around 15% for typical commercial devices, over 20% for "high-end" photovoltaics).

BTW, over 40% efficiency were achieved in the lab in Dec. 2006, but I've yet to hear of commercially available cells using the new technology.

I can't post URL's since I haven't made 15 posts here yet, but if you Google "Solar Cell Breaks the 40% Efficiency Barrier" (include the quotes) you'll get a link to an article about it.

The article also mentions 30% was achieved as early as 1994. These devices must be quite expensive, as they are used in satellites but you never hear of them being available to homeowners.