PV Gap

Darrell Said:

A 5 square metre array of silicon solar cells has an efficiency of 21%. Averaged over the course of a day (24?

We Answered:

250 watts per square meter over 5 square meters give 250*5, or 1250 watts of insolation. Since the efficiency is 21%, 1250*.21 or 262.5 watts average are collected. A watt is a joule per second. A day has 24 hours, each with 60 minute, each with 60 seconds, so 24*60*60, 86,400 seconds. 262.5 joules per second for 86,400 seconds mean 22,680,000 joules, or 22.68MJ.

Minnie Said:

How can i cut silicon solar cells?

We Answered:

the term is cleaving. You want to cleave the wafer along a crystal axis. The easiest way to do this is get a very hard clean flat surface. put the wafer/cell/device on this surface. get a very very sharp fine point metal tool. push the very point of the tool down on the very edge of the wafer. Do not saw or shake, just push. Increase presure without shaking your hands and the wafer will crack along a crystal axis. It might not crack along the axis you want and might destroy your device but you will at least know the direction of the axis after youve done it. The key is to push straight down on the very edge of the wafer without vibrating your tool.

Good luck.

Leah Said:

What is the best current efficiency of silicon solar cells?

We Answered:

http://www.gizmag.com/go/6563/picture/29…

The 40% is not Si, but it is multi-junction, to capture a broader frequency spectrum of sunlight. The picture in the link is hard to read, but I believe there is Ge and GaAs as well as other materials. Also, this is a concentrator type cell, achieved by SpectroLab in Dec 2006.

For Si single crystal, I believe the highest efficiency is in the 22% range, by Sanyo.

http://www.renewableenergyaccess.com/rea…

Emma Said:

Solar Cells...?

We Answered:

Don't know the proper formula to calculate what the least amount of Silicon monoxide needed to produce the least amount of reflection.

But to the second part of the question. The more light that is being reflected, the less light there is being absorbed by the solar cell. The less light there is being absorbed by the solar cell, the less light there is being transformed into energy of another type by said solar cell.

In other words, the more light that is being reflected, the less efficient the solar cell will be, in regards to producing electricity.

Sarah Said:

What are the advantages of nanocrystalline solar cells when compared to silicon-based solar cells?

We Answered:

Well the nanocrystalline (monocrystalline and polycristalline) are basically more efficient then the silicon based photovoltaic cell. Silicon-based solar cell are one generation older than the crystalline bassed.
I am not sure but I think crystalline cells last longer(up to 40 years) than silicon ones

Ian Said:

Theoretical Maximum Efficiency of Silicon Solar Cells is 29%-Why?

We Answered:

There is a limit to how much "band width" can be engineered into a photovoltaic cell. This is a "single junction cell." This is overcome by having multijunction cells each of which is sensitive to a different range of bandwidths: http://spie.org/x35978.xml?ArticleID=x35… Multi junction cells with efficiencies over 41% have been created in the lab.

Margaret Said:

How can you explain the relationship between silicon and solar cells in a simple way?

We Answered:

Solar Cells are photodiodes.

Photodiodes are semiconductor junctions. Junctions have a postive and negative side separated by a "depletion" region. When photons of light are absorbed by the photodiode in the depletion region, electrical charge carriers are created which contribute to an electric current. These tend to be swept toward one side or the other depending on their charges.

Silicon is a semiconductor. If a photodiode is constructed out of silicon it would be like a solar cell.