Solar Cells - Please Enlighten Me

[Benno85 (Ben)]

Hi everyone,

Ok, on the back of the just-listed thread regarding India's proposed commitment to solar energy, I've got a question that I'd like to throw out there....

Do the PV (photovoltaic) cells that are used in solar panels react to a specific part of the spectrum? Ie, is the current technology limited to only the "visible light" spectrum?

Thoughts much appreciated

Benno

[renormalised (Carl)]

PV cells mainly react to visible light, and since most of the light from the Sun falls in and around 560nm, then that is the light they're most sensitive to. But generally, it's just the visible light they react to. UV photons tend to knock electrons completely out of the PNP layers of the silicon cells, so their efficiency in this section of the spectrum is rather low. IR even less so, as it hasn't the energy required to create a potential difference across the layers, so no current flows.

There are new solar cell technologies being developed that can react to those areas of the spectrum outside the visible, such as near IR and UV, but they're not commercial viable as far as I know, yet.

[Benno85 (Ben)]

That's great Carl, exactly what I was looking for.

My thoughts were leading towards whether or not current solar technology is utilising to full effect the entire spectrum and not just visible light (ie, can a sloar cell still be a viable source of power when there is cloud cover).

[renormalised (Carl)]

On overcast days, so long as it's not too dark, a solar cell will react and create some charge, but naturally enough the darker it is the less it will produce until it reaches a threshold level where the cells stop operating. I can't remember exactly what level of illumination is needed to produce current flow, but let's just say if the level of light drops down to late afternoon type of light levels, you're not going to get much charge.

[xelasnave]

I have noticed that on an overcast day you can get 7 volts from a 12 vlt panel and I have thought to have a series of 6 volt batteries to pick up power when there is little Sun.
It would seem most reasonable that other regions of the EM spectrum could be harvested... interesting
alex

[OneOfOne (Trevor)]

I remember reading something a number of years ago about research into multiple layer cells where each layer is made of different materials and so is sensitive to different wavelengths. The light not utilised in one layer passes through to the next one, this would allow a much greater energy efficiency and cheaper production as you only have to put the protective materials (glass etc) around one cell to cover all of them, if you get what I mean. Haven't heard anything about it though.

[mswhin63 (Malcolm)]

Below is a link to some research on different material that could be used for solar power. Although not fully developed yet it shows promise.

http://www.abc.net.au/catalyst/stories/2550612.htm