Talk:Solar cell

Archives
Jan. 2005 – Jan. 2006

Source Request

Hello I think the theory section really needs some good quality sources. Just a request. Neozero497 04:53, 9 November 2007 (UTC)

Major revision (intended...)

I made major changes in the introduction to account for the following:

- A solar cell (photovoltaic cell) is a current generator

- that converts irradiation (photons) into free charge carriers

--> which is basic physics solar cells rely on...

- The working principle of solar cells is based on the photovoltaic effect that made Albert Einstein a Nobel Prize winnar -->which is the basic info about the scientific origin

- Two processes within the photogeneration process of charge carriers (electrons and holes) within solar cells can be distinguished: --> which is adapted from the existent version, slightly adapted to, from my point of view, better english because of distinct listing (1st, 2nd).

- Solar cells have many applications.... --> than listing of historiy

- Recently...

- Solar cells are regarded as one of the key technologies towards a sustainable energy supply.

-->which accounts for the role PV is supposed to play in the energy game

Simple explanation

Article says: "3. An array of solar panels converts solar energy into a usable amount of direct current electricity". It's explaining that a solar panel converts solar energy into electricity by saying that step 3 is converting solar energy into electricity! Someone with knowledge on this subject should write a more precise explanation. -- ironcito 16:23, 16 February 2006 (UTC)

Article removed from Wikipedia:Good articles

This article was formerly listed as a good article, but was removed from the listing because the intro is poor at the moment, with the first sentence 'A solar cell, or photovoltaic cell, is a not specifically a "p-n junction"' suffering from poor grammar, and also failing to start by defining what a solar cell is - much more important than what it is not! Worldtraveller 00:13, 12 March 2006 (UTC)

Good. This article is certainly not "good" as it is. It looks like it has been edited by half a dozen people, none of whom read anything written by the others. There are redundant sections that need to be merged and cleaned up. Ugh. I started to work on it, but it's too much for me to tackle right now. I did clean up a bad edit from ten days ago, though. Large chunks of source were deleted, including most of the see also and references, and the categories and interlanguage links. Apparently nobody is watching this page. Several people edited the page after the bad edit, without noticing the damage (like the fact that the page had no introduction.) --Srleffler 04:59, 21 April 2006 (UTC)

p-n junction contra-definition removed

I have removed the following comment from the introduction: "A solar cell, or photovoltaic cell, is a not specifically a "p-n junction". This is in fact a specific example of a photovoltaic device characteristic of the first generation of solar cells, including Si wafer devices."

I agree that the introduction should define a solar cell, and not provide excess information as to what it is not.

That being said, there is a strong preference in the solar cell wiki to use the description of a functional Si wafer photovoltaic device as the definition of a solar cell. A silicon-based photovoltaic cell is a special case of solar cell and does not provide the general case that defines the function of a solar cell. It is quite true that the great majority of commercial devices in large-scale production are made based on the science of a p-n junction in doped silicon, but there are many more types of solar cell devices that convert photons to electricity (based upon incident sunlight), yet cannot be defined using the function of a p-n junction and a resulting mesoscopic electric field in a space charge region.

If the information for a silicon solar cell device is highly valued, it would seem to deserve to be spun off to a separate wiki page. One could enter the topics such as the semiconductive properties of solid silicon,the electron configurations of atomic silicon, and the many internal varieties of silicon solar cells (e.g. single crystal, multicrystalline, Si thin film, etc.). Topics that are very relevant to current industrial production of silicon solar cells, but have little to do with a great number of emergent solar cells. In this way I believe the currently bloated and kludgey solar cell wiki could be cleaned and improved in scientific content such that solar cell represented the science of the device in the way that the fuel cell wiki page does. --Nanomech 12:06, 15 March 2006 (UTC)

"renewable" fact should be factored into price per delivered kWh

The article:

"Using the present (2005) commercially available solar cells and system technology leads to system efficiencies between 5 and 15%. Electricity generation costs range from around 50 eurocents/kWh (0.60 US$/kWh) (middle of Europe) down to around 25 eurocents/kWh (0.30 US$/kWh) in regions of high solar irradiation. Since, in grid-connected applications, this electricity is generally fed into the grid on the customer's side of the meter, it can be compared to prevailing retail electric pricing, which varies from between 0.04 and 0.50 US$/kWh worldwide."

So, what, do solar panels break over time? (They might need to be cleaned off or something, and I guess you can count this human labor - land cost for the cell sitting there is of course approximately zero).

If they don't have a very short life span, then the figure for cost per kilowatt-hour delivered has to say something like "over the first year". [Since as the soloar panel sits there (let's say it cleans itself off with some of the renewable energy) the produced number of kilowatt-hours goes to infinity (over a thousand years) while the price is something you just paid once.]

What is the lifespan of a solar panel? If it is not long-term, please update article to reflect this, otherwise please give greater emphasis to renewable aspect of this form of power generation.

Thank you.

81.182.77.88 12:52, 20 March 2006 (UTC)

The life span is usually 20 to 25 or more years depending on the type. The cost analyses usually already amortize the cost of manufacture over the expected lifetime of the solar array. Note that "over the first year" is way off the mark. The manufacturing process is expensive in equipment, materials and energy. The payback time before even net energy is produced over that required for manufacture for the most common solar cells is currently 3 to 4 years. Once structural support, battery storage, inverters, installation costs, etc are considered, solar panels are just not economically justified without subsidies where conventional large scale grid based electric power generation is available.--Technicaltechy 09:03, 1 April 2006 (UTC)

Does the efficiency, open voltage, or short circuit current change over the lifetime of the solar cell? Maybe a graph or rough estimate to show this effect or a sentence that if there is no change over time would be nice. Wikitil 21:34, 28 June 2006 (UTC)

Say, does anyone know of any studies that take into account the actual LCA of manufacture, including the energy requirements of the workers involved in every stage of the production, who we must presume will be driving solar powered cars to work, and living in solar heated and cooled houses, and eating food grown with solar power, and sending their kids to solar powered schools, and taking vacations on solar powered planes... And that's everyone involved, from those mining the raw materials, to the person who calls you (on a solar powered telephone) to ask you how your installation went. I just can't see to find any studies that address that basic requirement of making solar power a self-renewing industry. Why is that? -- Rogerborg 14:33, 18 September 2006 (UTC)

Reference 4: http://www.csudh.edu/oliver/smt310-handouts/solarpan/pvpayback.htm

Could somebody with editing privileges take a look at reference 4 and correct the statements associated with it in the main article? TIA -- ShineOn 128.223.162.50 16:23, 5 February 2007 (UTC)

Merging Solar panel into Solar cell

Old comments on this moved from top of article

Should this be merged with solar panel? Rmhermen 17:10, Feb 28, 2004 (UTC)

• Definitely. I think the scientific/functional details should be under solar cell and the application and anecdotal information should be under solar panel. Another deficiency is that solar panel completely ignores those (also active solar panels whose purpose is to collect thermal energy only. -User:RatOmeter

I think the scientific/functional details should remain under photovoltaic cells because that is the proper term. Having worked as a technician making these cells I recognize that to the general public they are generally known as solar cells. However, if you think about it a photovoltaic cell becomes a solar cell when you put it out in sunlight, what if it is under indoor illumination then is it really producing solar power or photovoltaic power. It would be nice to have some discussion of amorphous cells, polycrystaline cells, single crystal cells, multi junction stacked cells, cells on glass substrates, cells on flexible plastic substrates, and the various materials, amorphous silicon, Cadmium sulfide/copper sulphide cells, zinc phosphide/copper sulfide, gallium arsenide etc...--Mmunroe 9 July 2005 07:16 (UTC)--mmunroe 06:45, 16 April 2006 (UTC)

New discussion

While there necessarily isn't a dispute yet, I have a feeling this may be the subject of debating. Simply put, solar panels are just a whole bunch of solar cells put together. All the information from the Solar Panel article can be easily assimilated into the Solar Cell article, with a neat section on panels. But if they're almost the same thing, why should they be different articles? —MESSEDROCKER (talk) 04:49, 2 April 2006 (UTC)

They shouldn't be merged, 'cos there's another whole type of solar panel - the type that heats a fluid directly. Photovoltaic panels are made of lots of solar cells, but these others aren't. Presently the Solar panel article is a bit sketchy on direct heat collection, but it's got to be discussed somewhere: some proportion of readers who navigate to 'Solar panel' will not have photovoltaics in mind at all. --Nigelj 09:59, 2 April 2006 (UTC)

So an idea is that the Solar Panel article should be divided into two; one half discussing the photovoltaic kinds of solar panels (which would link to this article) and one half discussion the kinds that directly draw h eat? —MESSEDROCKER (talk) 13:43, 2 April 2006 (UTC)

Encyclopedias are supposed to describe concepts, not words or phrases. Therefore, I think there should be one page for the concept of "device that converts radiation directly to electric current", and another for the concept of "device that traps solar radiation to heat a fluid". There could be some debate about the titles of these two articles, I admit. The first one could be "photovoltaics", and the second one could be "solar heating panel". "Solar cell" would redirect to "photovoltaics". "Solar panel", since it is ambiguous, would be a disambiguation page. What do you think? --Heron 14:50, 2 April 2006 (UTC)

I'm not too sure about renaming Solar Cell to something else, seeing as it unambiguously refers to photovoltaics. Other than that, sounds like a good plan. Let's see what the others think. —MESSEDROCKER (talk) 17:30, 2 April 2006 (UTC)

Taking Heron's suggestion as a start, the Solar panel disambiguation page would still be important as many visitors, thinking only of one use or the other would continue to use that term and head there. Having said that, I'm still not sure that the concepts of Solar cell and Photovoltaic panel are coincident. Solar cells are also used individually in low-power applications, for example to detect and measure light levels, or to power a watch or calculator. Photovoltaic panels are always concerned with efficient and cheap bulk power generation. I would vote for three articles ('Solar cell', 'Photovoltaic panel' and 'Solar heating panel') plus a disambig page called 'Solar panel' for the latter two. Existing information could be shufffled around to make all three cleanly, I think. --Nigelj 19:03, 2 April 2006 (UTC)

I'm happy with that. --Heron 20:04, 2 April 2006 (UTC)

Me too. Straw poll, anyone? (Sorry, I just like things getting accomplished quickly.) —MESSEDROCKER (talk) 20:38, 2 April 2006 (UTC)

As a scientific note of agreement with respect to the recent comment by Nigelj, a 'solar cell' is a single photovoltaic device that is used specifically to convert photons from the sun to an electric current (as opposed to light from a fluorescent lamp or laser). If you connect multiple solar cells together, you have an assembly that could logically be termed a 'panel'. Given the term 'solar heating panel' describes an analogous assembly of thermal cells, the term 'photovoltaic panel' or 'solar cell panel' sounds acceptable. I would definitely like to see the two concepts of cells and panels kept separate if possible, as the Solar cell wiki is already pretty heavy with excess content and biased with commercial plugs. Perhaps spring cleaning is in order for Solar cell? Nanomech 22:06, 2 April 2006 (UTC)

Indeed. Another thing we could do is when "Solar panel" becomes a disambiguation page, we could point out the difference between the three terms: "Photovoltaic panel", "Photovoltaic cell/Solar cell", and "Solar water heater". —MESSEDROCKER (talk) 22:53, 2 April 2006 (UTC)

I think the disambiguation idea might be the way to go. Solar panels can be thermal or PV based, serving very different needs. Cells and panels, as you say, should not be confused. Because Wikipedia articles are interlinked, I think merging too many topics on one page can be confusing, instead we could use linking features to allow readers to explore the various terms as they wish. My 2 cents. --aljo 19:17, 5 April 2006 (UTC)

I have slightly edited the "Interconnection and modules" subsection to begin this transition to differentiate "solar cell" from "solar panel". Nanomech 10:11, 9 April 2006 (UTC)

I don't think merging the two articles is a good idea. This topic is probably too big for one article. A better approach would be to divide the material so that solar cell discusses the technical details of photovoltaic cells and how they work, while solar panel discusses the application of solar technology to electricity and heat generation (this could include solar heating panels as well as photovoltaics). This provides a cleaner division of subject matter between two articles. --Srleffler 05:11, 21 April 2006 (UTC)

Well, the general consensus (at least within the discussion thus far) has been not to merge the two together, but have three articles: Photovoltaic panel (solar panel for electricity production), photovoltaic cell (very small-duty electricity production, or measuring light), and water heating panel (solar power to heat water). "Solar panel" would be made into a disambiguation page. While it was my original idea, it's not the idea anymore. —THIS IS MESSEDOCKER (TALK) 10:46, 22 April 2006 (UTC)

Solar Cell wiki needs to be edited and condensed

As a research scientist in photovoltaic materials (including silicon and non-p-n junction varieties) I would like to proprose a major change in the Solar Cell wiki page, condensing it to something representative of current research technologies (including silicon) and the science of the photovoltaic phenomenon. As I have commented earlier, there is a lot of repetition and unbecoming commercial advertisement that has made this wiki site undesireable compared to closed-source literature coverage on photovoltaics. Please, let's make a positive effort to improve the content and the organization of the wiki to make it top-notch. A good solar cell wiki improves the public relations for all of us in solar cell technologies. I have some suggestions that I would like to help implement.

Examples: Section 4: "Materials and Efficiency" -- the reference to "Materials" is repeated in Section 10 ("Current Research") and the reference to "Efficiency" is repeated in Section 7.1 ("Energy conversion efficiency").

I'm suggesting condensing text in the wiki that include the above-mentioned sections into two distinct sections to follow "Theory". These two new sections would be "Light Absorbing Materials" and "Energy Conversion Efficiency".

A "Light Absorbing Materials" section can deal with the numerous types of silicon offered today, the semiconductor thin-film assemblies like the CIGS system, the varieties of simple inorganic semiconductor absorbers that are being used in quatum dot and ETA-cell sensitized systems, the dyes that actually absorb the light in dye-sensitized cells, and the polymers that serve to absorb light in the organic polymer systems. This may contain the sprawl of silicon definitions across the wiki in the future too. While the majority of solar cells use silicon as a light absorbing material, the material itself should not serve as the definition of a solar cell.

Also, is there a better quality image of the NREL efficiency plot anywhere else? The image is low-resolution and pixelated.

An "Energy Conversion Efficiency" section would similarly contain some of the indirect adverstisements for one technology over another in the materials section. There is a significant amount of simple math for this estimation that could be included here too.

Section 6: "Theory" -- this is a fairly good section, but is unecessarily silicon-heavy. The section could be edited and simplified to reflect the science of a solar cell as a photovoltaic device and not only a "p-n junction'.

More input on the basic electrochemistry of the device would help to separate the three fundamental steps of 1) light absorption, 2) carrier generation, and 3) carrier separation. A subsection on the properties of a p-n junction is invaluable here, but this is just one way that a solar cell can function.

Section 10: "Current Research" -- this is a very messy section that appears to be essentially filled with personal and commercial plugs for specific varieties of solar cells--a very non-Wikipedian section. And I'm not confident how "current" some of the research is anymore. Not sure what to suggest for this one other than a careful inspection and slow revision.

All sections below "References"--more commercial plugs, but interspersed are a few informative links. Also requires a careful inspection, but I assume many of these links can go based on Wikipedian standards of quality.

I can only hope for the best, but I would truly like to be proud to tell people to look at the wikipedia link on "solar cells" for reliable information about photovoltaics. Thanks to all for considering my comments.Nanomech 11:13, 9 April 2006 (UTC)

If you've got the time and the energy, Nanomech, you seem very well placed to go straight ahead and make these changes yourself. WP:BB :-) --Nigelj 12:01, 9 April 2006 (UTC)

Nanomech, I agree. This article badly needs a major cleanup and reorganization. There is much redundant material here. If you have the time and energy, go for it! I agree with Anthony717's comment below, though: I don't think solar panel and solar cell should be merged. Rather, I would prefer to see one article that focuses on the technology and science of photovoltaics, and another that focuses on the application of solar technology to home energy generation (which could include solar heating as well as photovoltaics.)--Srleffler 05:15, 21 April 2006 (UTC)

Solar panel and solar cell ought not to be merged. Solar cell should focus on the technology. Solar panel should be kept as an introduction to people new to solar power. The Solar hot water article should also be kept, as solar hot water is an important industry and a very efficient technology. This wish to merge pages seems misguided. If anything, Wikipedia articles must be larger, and, when too large, be divided out into sub-articles.Anthony717 02:07, 14 April 2006 (UTC)

Solar Cell wiki Revision (April 2006)

As suggested earlier ("Solar Cell wiki needs to be edited and condensed"), and having received encouragement to do so, I have made significant revisions to the Solar cell wiki page. This is an effort to reduce text redundancy, subdue some non-wikipediean commercial plugs (both from industry and academia), and to remove overlap with the information presented also in the Solar panel wiki. However, even with the reorganisation and condensation, the wiki is still long (40kb). Hopefully we will all be able to edit it a bit more easily now. My goal is to help bring this page back to the state of a good wiki that reports the science and technology of solar cells. I have made my best attempt to arrange the sections in a logical fashion that will allow new additions for new technologies without making the page as cumbersome. Edit comments are below. Nanomech 10:30, 23 April 2006 (UTC)

Introduction

Some refinements have been made to the introduction based on the comments by the other editors in earlier discussions. There is a now clear distinction in two sentences between a photovoltaic cell and a solar cell, specifying a photovoltaic cell as a general description of a solar cell applied to solar and non-solar light. In keeping with the general concensus to distinguish solar cell from solar panel, I have also specified that a connected assembly of solar cells can be referred to as a solar panel. Redundant references to p-n junction and silicon p-n junction were edited out. Nanomech 20:35, 24 April 2006 (UTC)

The silicon solar cell image was moved down to the beginning of the second paragraph. The link was interferring with the Introduction statement that search engines report with search results. Nanomech 06:43, 26 April 2006 (UTC)

Wiki separation

It was discussed (and by "straw poll" recently agreed upon) to maintain separation between Solar cell and Solar panel. Hence the edits were performed with a page to page comparison between the two wikis. Again, I found text repetition (some verbatim) and removed as much of the overlap as possible, with directed links to Solar panel where necessary. For example, "Cost Analysis" was removed from Solar cell as it is in fact related to the cost analysis of silicon solar panels ("installed systems"), rather than being generally directed to the cost analysis of making a single solar cell.

Repetition

I have been carefully examining the various subsections of the wiki and have found numerous occasions were the text was repeated (paraphrased or verbatim) from another subsection. These repeats have now been condensed into one statement where necessary.

Theory subsection

All of the Silicon and semiconductor information in the "Background to classic solar cells" section is clearly explained in their respective wiki pages, and links have been defined for those two at the beginning of theory to supplement the reduction in that subsection. Most of the theory on Si and semiconductor physics represented here was overly-reductionist and scientifically inaccurate. This was removed and links to the silicon and semiconductor wikis are in the "Light Absorbing Materials" section.

I have also moved "Simple Explanation" into Theory as an introductory subsection termed "Simple Explanation". I have further specified two more subsections for consistency with the introduction that describe the two fundamental processes in a solar cell: "Photogeneration of Charge Carriers" and "Charge Carrier Separation".

(Sub)Section Condensation

Earlier, I suggested condensing text in the wiki that included the sections "Materials and Efficiency", "Energy conversion efficiency", and "Current Research" into two distinct sections to follow "Theory". These two new sections are now present as Light Absorbing Materials and Solar Cell Efficiency Factors. "Solar cells and energy payback" was also moved into the new "Solar Cell Efficiency Factors" section. "Current Research" remains, but has been reduced with an introduction including a ling to Timeline of solar cells that will hopefully avoid quick cut-and-pastes of recent news articles.

Applications and Implementations

"Interconnection and Modules" was moved into this section in the condensation process and the title was removed. A directed link to solar panel was also indicated here. This section was moved above theory as well.

Manufacture and Devices

This is a very well-written section that specifically pertains to multicrystalline silicon solar cell manufacture. It needs a more specific title as such. I would appreciate better suggestions than mine: Retitled "Silicon Solar Cell Device Manufacture".

External Links

A few NREL links were removed as they now point to lost web sites.

Photoelectric effect

Solar cells do not use the photoelectric effect. Solar cells are made of semiconductor material, the incoming light (photons) move electrons from the valence band across the band gap to the conduction band. The resulting electron-hole pairs are separated by the internal electrical field of the p-n-junction. In this way different charges on the two electrodes of the solar cell are created, which can be used to drive an current through a wire.

Corrected the recently modified introduction that sought to use the photoelectric effect in the solar cell definition. Nanomech 21:34, 18 April 2006 (UTC)

Agreed. Someone confused the photoelectric effect with the photovoltaic effect.--Srleffler 05:04, 21 April 2006 (UTC)

Doesn't the word photoelectric effect have the meaning of internal photoelectric effect, which also includes the PV effect? --- a reader, 21:03, 28 Apr 2006 (UTC)

The core explanation resides in the two-part requirement for the photovoltaic effect. The photoelectric effect can be viewed as a general case for the first requirement of the physical phenomenon termed the photovoltaic effect, in that the former refers to free electrons being ejected from their low energy state in a material in response to absorbed photons. The internal photoelectric effect has been used to refer to a special case regarding valence band electrons injected into the conduction band in a semiconductor. The photoelectric effect has no voice on what happens to the electrons following photoexcitation. In fact, many phenomena can follow this first step, including exciton recombination, chemical transfer of the charge carrier to a surface molecule, and trapping of carriers in defect sites. These phenomena tend to inhibit generation of electrical current due to charge separation and are considered performance reducing in photovoltaic cell research. That brings us to the second requirement of photovoltaics: the separation of charge carriers to generate electical current. Separation can be accomplished by drift or diffusion, but the charge carriers must make it to an ohmic contact and be monitored as electrical current to be considered photovoltaic. This commentary stands in contrast to the note above that "Solar cells do not use the photoelectric effect." Of course they use the photoelectric effect, but it's what happens next that separates the photovoltaic effect from the huge body of other phenomena surrounding photon-electron interactions. Nanomech 12:28, 29 April 2006 (UTC)

Conduction construction materials

I removed this from the Solar panel article:

When making solar cells for solar panels, Gallium arsenide is more efficient than crystalline silicon, but also more expensive.{{dubious}}

This article is the proper place for this incomplete information. Incomplete because those are not the only two technologies for converting solar energy into electricity. --Sunpower 09:33, 27 April 2006 (UTC)

Electrical output

I removed this from the Solar panel article:

When exposed to direct sunlight, a 6-centimeter diameter silicon cell can produce a current of about 0.5 ampere at 0.5 volt (equivalent to about 90 W/m² average, range is usually between 50-150 W/m², depending on sun brightness and solar cell efficiency).{{dubious}}

With new technology squares smaller than 6cm d. can produce about 1/2 volt. --Sunpower 09:38, 27 April 2006 (UTC)

Solar-concentrating photovoltaics

This section was removed. Although it might be misplaced here, and does need rewriting, it does look useful and should be perhaps moved to Solar power and linked from here. I'll just put it here in this box, for now, till I or someone else uses it. --Singkong2005 03:54, 5 June 2006 (UTC)

Solar-concentrating photovoltaics

- Ironically, despite the high cost of multijunction cells, they are used as part of one of the most cost-effective and promising technologies, known as solar-concentrating photovoltaics. In these systems, solar energy is concentrated several hundred times, which actually increases the cell efficiency, and reduces the semiconductor area needed per watt of power output. Many reputable sources are projecting that the cost of concentrating system will soon drop to US$3/Watt. - - For examples of concentrating systems under development, see the recent experimental "Sunflower", or the "SunCube".

It was removed because of the external links at the end being too commercial. You could add it back without the external links. Perhaps add the Wired one as a reference. Stephen B Streater 08:12, 5 June 2006 (UTC)

The modified contribution to S-C PVs was moved out of Light Absorbing Materials and into Current Research... for wiki consistency. The manner in which the post was added introduced an unsupported bias implying S-C PVs will change the face of PV technology. Solar concentrators have been around for many years, so while it is valid to mention them in this wiki, it should be acknowledged that they are not disruptive to the current technology or revolutionary. The linked Wired article appears to be more of a Public Relations plug for Bill Gross than the PV system itself. It is an example of a current application of S-C PVs, however. Modifications to the subsection were made for a clear statement, Wiki consistency, and to clarify the link to Wired (a silicon PV is used). Unsupported monetary claims were removed also. Nanomech 13:43, 8 June 2006 (UTC)

theory: photogeneration

I've changed the first part of this section "what happens when a photon hits silicium". It has several misconceptions:

1. a photon whose energy is below the bandgap value (Eg) CAN be absorbed, although no charge carriers are formed (phonon pairs are created instead, ie, heat).

2. A photon whose energy is above Eg CAN be absorbed, and are these photons that create the charge carriers fundamental to the photovoltaic process! The surplus energy is absorbed by phonons, ie, heat. In silicon, being an indirect bandgap semiconductor, phonon generation must occur at electron-hole photogeneration, and thus only photons well above Eg contribute to this process.

3. there is no such thing as "photon energy is within the bandgap energy of silicon"! the BG is a value (1.1eV in Si, if I'm not mistaken). The upper and lower values of this band refer to the electron energy potential, and are "unknown" to the photon.

4. reflection of light at the surface of a silicium slab occurs at every photon energy, although it can vary according to it.

For reference, I've found these absorption curves on google (although several sources carry this information, e.g. Kittel) http://www.ioffe.rssi.ru/SVA/NSM/Semicond/Si/optic.html .

85.138.235.25 00:44, 19 June 2006 (UTC)Joao

Split, & create Solar cell (physics)?

Re Solar power#Photovoltaic cells which includes particular applications of solar cells, such as "Concentrating Photovoltaic (CPV) systems". I wanted to move most of the material to the Solar cell article, but this article is quite long already, and technical about the electronic aspect; Solar panel doesn't seem suitable either, as it's not just about photovoltaic systems.

I suggest we split Solar cell, so that Solar cell (physics) focuses on the underlying physics, going into technical details. The Solar cell article would just give a basic explanation, with more focus on applications (such as the one mentioned), and achievements to date (e.g. highest % conversions achieved, leaving extended technical explanations to Solar cell (physics)). Good or no? --Singkong2005 ^{(t - c - WPID)} 11:41, 25 June 2006 (UTC)

I have a suggestion: I think we need a separate article on "Concentrating Photovoltaic (CPV) systems", similar to the section on Concentrated Solar Power (CSP) Plants in Solar thermal energy. I added the section on Concentrating Photovoltaic (CPV) systems in Solar power, just a few weeks ago. Pretty much cobbled it together from bits and pieces that I stole from other articles, but I did add a lot of external links that give a pretty good idea of what is out there. While looking into it I became pretty much convinced that Concentrating solar systems are going to dominate the Solar power plant scene, but I don't know yet whether it will be "Concentrating thermal" or "Concentrating photovoltaic". For that reason I believe that we need to expand our coverage of "Concentrating solar power" systems. There are two ways of doing is: We can either have a single article on "Concentrating solar power", with two sections in it: One on "Concentrating thermal", the other on "Concentrating photovoltaic". Or we could have two separate articles on those two subjects. JdH 00:05, 30 June 2006 (UTC)

Solar boat

please put it in a new section and anyone who lives or knows someting about this boat should add some more information. http://news.bbc.co.uk/2/hi/uk_news/england/london/5189318.stm Yousaf465 18:19, 18 July 2006 (UTC)

No, the concept has no direct relevance to this article topic. If the boat itself is notable, it should get its own page. Femto 10:49, 21 July 2006 (UTC)

I've added an 'External link' to this article on Electric boat --Nigelj 21:57, 21 July 2006 (UTC)

Manufacturers removed

Removed the whole section, Wikipedia is not a business directory. Here's the diff in case someone wants to create a proper list of solar cell manufacturers with internal links to existing articles. Femto 10:42, 21 July 2006 (UTC)

Re:[1] On the contrary, what's your justification to restore that list? See WP:EL, Wikipedia is not a collection of external links, especially not a directory of company websites. It's pretty clear the linklist is inappropriate. Femto 14:21, 25 July 2006 (UTC)

I concur. Only companies notable enough to have their own articles should appear, and they should have internal links. Stephen B Streater 08:57, 28 July 2006 (UTC)

The Wikipedia is supposed to be USEFUL. That means many things. To some, it means a theoretical discussion of photonics. To some, it means a list of manufacturers. There is no reason not to have both. Be comprehensive. Not elitist. Right now, I very much need to know who the major manufacturers are. Google hasn't helped here, I get tons of noise. Wikipedia COULD help if it were not for some misguided notions of what appropriateness is. -Steve Johnson — Preceding unsigned comment added by 168.150.253.55 (talk • contribs)

What ever happened to....

Does anyone know wtf ever happened to wide bandgap InGaN solar cell research that seemed to be all the rage about 4 years ago [2]? and why since then we've heard like .....nothing regarding them? are they dead? --Deglr6328 22:29, 2 September 2006 (UTC)

39% Efficiency Claim is unsupported (citation invalid)

The article reads: "GaAs multijunction devices are the most efficient solar cells to date, reaching as high as 39% efficiency [3]." However, the citation links to a company that advertises 28.3% efficiency cells. Someone should either supply a valid citation or remove the 39% claim (which I find unreasonably high).

next generation cells, [[3]],reg. Mion 07:14, 18 October 2006 (UTC)

I hate to beat a dead horse here, but 1) that's not the same link as the citation and 2) there is no 39% claim in it. All his charts end at around 30%. He does write " Efficiencies up to 0.63 may be realised with multi-gap devices, P. Würfel, Physica E1418 (2002)", but he appears to be refering to a theoretical result, not a physical device.

The key is the use of nanocrystals, [[4]] (2004), can you end your quote with "~~~~"? reg Mion 22:03, 22 October 2006 (UTC)

Nanocrystal solar cell, it needs some updates (its now 2006). reg .Mion 22:08, 22 October 2006 (UTC)

Sorry the type of cell you are talking about should be 37 ? [[5]]? Mion 22:25, 22 October 2006 (UTC)

Another cleaning is called for

To all PV scientists reading this wiki. Please go over the Solar Cell site and remove poor grammar, uncited claims, and corporate "plugs". There is some degeneration of the Solar Cell information with time and a maintainance check is now necessary. Thank you for your efforts and your help. Nanomech 06:32, 23 October 2006 (UTC)

Solar panel energy payback

I am not sure that the calculation of energy payback of solar cells are practical in the way that they never include the energy cost of extracting, concentrating, distributing all the materials used in the fabrication of solar cells, plus, no mention of the energy cost to build the machines that are used to fabricate the solar cells ... and the energy cost for the people to come and work to the manufacturing plant.

The references used in the articles mentioned in "Solar cells and energy payback" are using a lot of rule of thumb to assess a quick payback. Therefore I think this part should be either removed or implemented with a practical calculation as I illustrated above.

By the way, I wish that kind of practical calculation be done for every products made.

http://www.csudh.edu/oliver/smt310-handouts/solarpan/pvpayback.htm

is currently used to support the sentence:

"Whether solar cells generate positive net energy is disputed by some researchers who object that such analysis doesn't take into account waste, inefficiency, and related energy costs that would come with a real-world solar cell."

But the source actually says exactly the opposite. It says the that they definitely *do* generate positive net energy, and their analysis includes the cost of extracting, concentrating, and delivering solar grade silicon, contrary to the talk point above. Zilles 00:38, 23 May 2007 (UTC)

Since cells are not used in isolation, the pertinent calculation is that of the system (module, inverter, etc.) This article should focus on cells.--Oldboltonian 01:14, 17 June 2007 (UTC)

p-n junction description unclear

I believe the last sentence of this quote out of section "The p-n junction" may have things reversed, or is worded ambiguously. The electric field which is established points from the n-type to the p-type layer, and so a current can flow only in that direction, i.e. electrons may only pass from the p-type side to the n-type side, and holes may only pass from the n-type to the p-type side; whereas the following quote implies the opposite. Perhaps I misunderstand the wording of this sentence.

If a piece of p-type silicon is placed in intimate contact with a piece of n-type silicon, then a diffusion of electrons occurs from the region of high electron concentration (the n-type side of the junction) into the region of low electron concentration (p-type side of the junction) ... an electric field [...] is created by the imbalance of charge immediately either side of the junction which this diffusion creates. The electric field established across the p-n junction creates a diode that promotes current to flow in only one direction across the junction. Electrons may pass from the n-type side into the p-type side, and holes may pass from the p-type side to the n-type side.

References: http://science.howstuffworks.com/solar-cell1.htm http://www.dur.ac.uk/~dph0www5/solar.html http://solardat.uoregon.edu/download/Lessons/PVLessonPlan1SolarCells.pdf

Detritus 03:50, 5 December 2006 (UTC)

New 40% efficiency solar cells

Superefficient, Cost-Effective Solar Cell Breaks Conversion Records[6]

That article has a new graph that can be used to upgrade from the one currently in this article. Seen [here].

Solar cell converts 40.7% of sun into electricity By Stan Beer Friday, 08 December 2006 A subsidiary of Boeing, has set a new world record in converting sunlight into electricity with a new type of land-based solar cell. The new photovoltaic cells, which are currently being tested in the Australian desert, can convert 40.7% of the sun's energy into electricity, smashing the previous highest performance mark of 33%. [Link]

More on [Google News]

Just wanted to point that news out in case it hasn't already been brought up. --Steele the Wolf 22:59, 13 December 2006 (UTC)

Wanted to add an article on this subject : http://www.worldwatch.org/node/4803 --YoavD 12:41, 11 January 2007 (UTC)

solar fiber

I heard that information on solar fiber technology was moved from the solar power article to the solar cell article. But today the solar cell article doesn't even mention the word "fiber". Has something gone horribly wrong? --68.0.120.35 06:05, 6 January 2007 (UTC)

Question

Don't the solar cell works like a greenhouse?, but instead of heating generating electricy. Sow it will also be a problem with the global heating and the Greenhouse_effect? --25 january 2007 (GMT+1

Function of a solar cell

It traps heat and convert it in to electrcity

"Manufacturers" list

This list was added to the article a few minutes ago:

Manufacturers

Aleo Solar Amonix Advent Solar Arise Technologies Axitec BP Solar Canrom CEL (Solar) Centrosolar Concentrix Solar CSG Solar Cyrium Technologies Day4 Energy Daystar Technologies Denmark Solar Industry Deutsche Cell EDTEK Emcore Energy Photovoltaics ErSol E-Ton Solar Evergreen Solar First Solar Fitcraft Prod. Flexcell Free Energy Europe GE Solar

Global Photonic Energy Global Solar Gratings, Inc Guascor Hae Sung Solar Heliovolt Helios Technology Honda (Solar) Int. Auto. Sys. ICP Solar IMEC Solar Innovalight ISET Isofoton JuMao Photonics JSC "Kvazar" JX Crystals Kaneka Silicon PV Konarka Kyocera Solar Maharishi Solar Miasole Microsol Power Mitsubishi H.I. (Solar) Motech Industries Nanosolar Nanosys

Origin Energy Australia Pacific Solar Photovolt Photowatt PowerFilm Q-Cells REC Rose Street Labs RWE SCHOTT Solar Sanyo Solar Products Shanghai LiLei Elect. Sharp Solar Shell Solar Solar Systems Solterra Spectrolab Spheral Solar SRI Stellaris Corp Sun Power Suntech Power Sunways Sustainable Tech. Int. Tata BP Solar India United Solar Ovonic

Wikipedia generally avoids lists like this, so it has been removed. Thoughts? --Ckatz^chat_spy 18:34, 29 January 2007 (UTC)

For anyone trying to learn about this subject this is important information. I think we should leave it in the article and make sure the list is complete and up to date. Afterall Wikipedia is about maintaining and distributing high quality information. Frank van Mierlo 21:44, 29 January 2007 (UTC)

Information, yes, but not information for the sake of information. The article is about solar cells, and how they work - not a business directory of who is manufacturing them. You might wish to check out WP:NOT, specifically the section Wikipedia is not a directory. --Ckatz^chat_spy 22:24, 29 January 2007 (UTC)

Sure however I believe we also have break all rules in our charter. In this case it is a rapidly developing industry that has a real impact on our lives and this list helps readers to grasp what is going on. By the way I have no financial interest in any of these companies nor any other affiliation with them. I just genuinely believe this is good information. It is often in industry that the real progress is being made. Frank van Mierlo 22:42, 29 January 2007 (UTC)

PLASMON-ASSISTED SOLAR CELLS

Hi, I think you could add something about this new discovery that improves efficiency around 19-33%: http://newton.ex.ac.uk/aip/physnews.819.html#2

212.0.126.98 07:35, 16 April 2007 (UTC)

How plants do it: quantum computation

http://www.sciam.com/article.cfm?articleID=ED1D1446-E7F2-99DF-3CBF8B2F66C0C5D4&chanID=sa003 —The preceding unsigned comment was added by 212.0.126.98 (talk) 08:06, 16 April 2007 (UTC).

Euro usage - "Comparison of energy conversion efficiencies"

As Ireland's the only official Euro user with an English official language, I think it's appropriate to use US currency (or British currency) as the primary referent in almost any en.wiki page, and have thus altered it here. &^@@#%&!!!!! chauvinistic or experimentalist editors who force others to act as )&&$^(@ conservative pedants. ;) 69.243.168.118 13:37, 22 April 2007 (UTC) Formerly the IP-Address 24.22.227.53 (egh. I think I'm too tired to properly grammar check this paragraph)

p-n explanation correct?

From the article:

When the electrons diffuse across the p-n junction, they recombine with holes on the p-type side. The diffusion of carriers does not happen indefinitely however, because of an electric field which is created by the imbalance of charge immediately either side of the junction which this diffusion creates. The electric field established across the p-n junction creates a diode that promotes current to flow in only one direction across the junction. Electrons may pass from the n-type side into the p-type side, and holes may pass from the p-type side to the n-type side. [...] Ohmic metal-semiconductor contacts are made to both the n-type and p-type sides of the solar cell, and the electrodes connected to an external load. Electrons that are created on the n-type side, or have been "collected" by the junction and swept onto the n-type side, may travel through the wire

It seems to me as if this paragraph contains an internal contradiction. If we have a p-n junction, electrons will diffuse from n to p until the emerging electrical field stops them. Then the junction acts as a diode, allowing electrons to flow from n to p. But later it says that electrons created on the n side go through the wire rather than directly to p. Why would they do that? I would assume electrons freed on n simply go through the diode over to p. My conjecture is that the above sentence should read Electrons may pass from the p-type side into the n-type side. Is that correct? AxelBoldt 00:26, 28 April 2007 (UTC)

I think this comment above makes the same point. AxelBoldt 16:23, 29 April 2007 (UTC)

Meh.. The text isn't at all clear. This paragraph is actually talking about what happens when a p-n junction is initially formed and its free carrier concentration profile in equilibrium. The later text is referring to non-equilibrium conditions (photoexcitation, which produces additional electron-hole pairs). The p-n junction in thermodynamic equilibrium has a space charge (depletion) region which is devoid of free carriers due to the balancing of forces from diffusion and the built-in electric field caused by the charge separation at the junction.

Under photoexcitation, electron-hole pairs are generated by photon absorption. It's desired that these EHPs are generated in the depletion region or within a diffusion length (the average length a minority carrier travels before recombining) of the junction because it's the electric field of the junction that separates the EHPs (electrons to one side, holes to the other). If the EHPs are not separated, they contribute nothing to the net current. The build up of excess (separated) minority carriers on both sides of the junction is what leads to the photocurrent. When the excess carriers recombine with majority carriers, more majority carriers must flow in to keep the system in equilibrium. If the p-n junction is connected to an external circuit, these additional majority carriers largely come from the circuit; holes flowing into the p-side and electrons into the n-side (they also come from thermal generation, which doesn't contribute to external current and is a big part of the reason many sensitive long-wavelength detectors are operated at cryogenic temperatures). These equilibrium-restoring majority carrier current components are what you observe to be the external current caused by a solar cell under illumination.

I'll add this page to my watchlist and perhaps work on it when I get the chance. It needs some serious refactoring to clarify things. -- mattb 16:54, 29 April 2007 (UTC)

I'm still struggling here. If an electron is freed by light in the depletion region, shouldn't it be pulled towards the n side of the junction (which after all is positively charged in equilibrium)? So after your explanation I would expect these electrons to collect on the n side and eventually flow out through the wire (or equivalently combine with holes that flow from the wire into the n side). So my conjecture right now is that if I measure the voltage across an isolated p-n junction in equilibrium, then p is negatively charged with respect to n, but if I shine light on it, then n is negatively charged with respect to p. Is that correct? AxelBoldt 18:57, 30 April 2007 (UTC)

Sorry, I typed my explanation too fast and botched it. Your first statement is correct; I reversed the flow of majority carriers. Holes will flow into the n-side and electrons into the p-side, meaning that the photocurrent is actually in the reverse bias direction (a forward-biased pn junction injects holes to the n-side and electrons to the p-side). What's interesting is that when you hook this up to a load resistance, the photocurrent causes a voltage drop in the load which adds forward biases the pn junction, though the net current flow is still in the reverse bias direction.

Most of the excess carriers never themselves make it to the contacts before recombining, but it is this recombination that causes more majority carriers to flow in.

If you measure the voltage drop across a lone dark pn junction in equilibrium, there will be none. Charges will rearrange themselves to balance all the forces out again, and without energy input (in this case a battery or light), there will be no sustained current flow. The "built in" voltage of diodes can be observed under high forward bias. Under illumination, the pn junction will be reverse biased, and you will see close to the maximum voltage possible for that light level since there is little current flowing through your voltmeter. If you attach an ammeter you'll see close to the maximum external current that the cell can deliver at that light level. There's an optimal point of operation (load resistance) that balances the voltage and current to deliver the most power, and that's typically where systems try to operate solar cells.-- mattb 19:26, 30 April 2007 (UTC)

Possible factual error - could someone with a proper EE-background please check "Maximum-power point" ?

The article says:

---

The quickest way to determine the optimal load for a given constant light condition (i.e. a stable quiescent point) is to measure the Thevenin equivalent Voltage (i.e. open circuit), then using a potentiometer as a load, monitor the voltage across it as the pot is dialed. When the load voltage is exactly half of the Thevenin equivalent Voltage, disconnect the potentiometer and measure its resistance on an ohmmeter. By the maximum power theorem, the potentiometer resistance will be the optimal value of the load for maximum power transfer (due to the equal voltage division between internal Thevenin equivalent Resistance and the load).

---

I think this method is wrong for the Equivalent circuit of a solar cell. It only applies for a constant voltage source with a fixed output resistance Rs.

A Solar Cell is basically a constant current, not voltage, source. However, the parallel p-n-Junction of the photodiode clamps the open-circuit Voltage of the Cell at a point that is determined by its forward Voltage at the output current of the cell under the incident light. For an ideal p-n-junction, the forward current halves app. every 25mV. Therefore, increasing the load voltage by 25mV would lead to doubling the parasitic forward current through the p-n-junction.

If, for example, at some operating point the open-circuit voltage is 475mV at 1A forward current, and the output resistance is 0.1R, then increasing the current drawn from the cell from 0.0A to 0.875A would reduce the forward current through the p-n-junction from 1A to 0.125A, by a factor of 8. The Voltage across the p-n-Junction would then be 0.475V-(3*25mV) = 0.400V. Rs would drop another 87.5mV, so the terminal voltage would be 0.3125V. Power is 0.3125V * 0.875A = 273mW.

If we reduce the load resistor Rl any further, and even optimistically assume that p-n-current drops to 0, then we get half the open circuit voltage of 0.475V at Rl=0.233R, and only get an output power of 233 mW.

Therefore, the only way to determine the optimum load is to measure the actual output current I and Voltage V at the terminals as you dial the pot and then calculate the output power P=I*V at each point and maximise it. The optimum load is then Rl = V/I;

The problem here is that this optimum load point does not only vary with incident light, but also with temperature, which influences the p-n-forward voltage at app. -2mV/K.

Please note that I do not have actual experience working with solar cells, so maybe someone knowledgeable could check this.

If this is correct, then I would just remove the paragraph "The quickest way..".

It may be the "quickest", but it's not correct. The PV cell is neither constant current nor constant voltage, but more importantly, the current is not a linear function of the voltage, especially in the open-circuit condition. The open-circuit voltage is determined by the forward I-V curve of the diode, which is completely nonlinear. I had removed that paragraph a while back, with a comment to that effect, but I hadn't noticed the uncommented anonymous undo that followed and put it back. So, I just now took it out again. Whoever thinks there's something to it should comment here. Dicklyon 17:26, 2 June 2007 (UTC)

I'm currently futzing around with some solar cell stuff while not teaching. I don't know enough (yet) to say its right, but it doesn't seem 100% wrong, either. Likely it is some sort of approximation. I'll see what I can dig up, but my own work will be a priority, so don't hold your breath too long. At a glance, it doesn't upset me too much as far as approximations go. A Thevenin equivalent requires the network in question to be both linear and bilateral, but the rule can sometimes be bent a bit if you are describing it at some specific operating point (which the contentious bit seemed to imply). I don't know if it applies here, but like I said, I'll look into it. Until then, Dicklyon makes some good points. Burtonmackenzie 19:48, 6 June 2007 (UTC)

I'd be OK with it as an approximation, but still it should come with a source, if it is indeed a method in use. Here is a ref I used (#16 in Photovoltaics) that says manufacturers provide short circuit current, open circuit voltage, and peak power point; they wouldn't need all three of those if it were a linear circuit, so to me that implies that the method is not what's used. Dicklyon 02:47, 17 June 2007 (UTC)

Here's a PDF ref that discusses the use of a Thevenin equivalent model for a solar cell. But they get the voltage from the peak-power point, which gives a pretty good model anywhere near that point. Getting it from the open-circuit voltage would give a very different and not usefully accurate result, in my estimation. Dicklyon 02:52, 17 June 2007 (UTC)

And Here's a book that shows the kind of empirical expression actually used. It's not so simple. Dicklyon 03:09, 17 June 2007 (UTC)

This is the first time I've commented on a Wikipedia page, so apologies if I manage to screw up the formatting (or anything else for that matter). At any rate, Dicklyon is correct -- the Thevenin equivalent as described at the start of this entry is incorrect. The maximum power point voltage is typically somewhere in the neighborhood of 85-90% of the open-circuit voltage, and the maximum power point current is typically around 80-90% of the short-circuit current. Keep in mind that the equivalent circuit of a solar cell is a constant current source in parallel with an ideal diode and a shunt resistor, all of that in series with a series resistor. The relationship between output current and output voltage looks something like this:

$I=I_{L}-I_{0}\left\{\exp \left[{\frac {q(V+IR_{S})}{kT}}\right]-1\right\}-{\frac {V+IR_{S}}{R_{SH}}}$

where $I_{L}$ is the current from the current source (proportional to the intensity of the incident light), $I_{0}$ is the dark saturation current of the diode, $R_{S}$ is the series resistance, and $R_{SH}$ is the shunt resistance. $I$ and $V$ are the output current and voltage, and the other variables should be recognizable as the usual physical constants. The product of $I$ and $V$ is the power output of the cell, and the solution of the equation that maximizes that product yields the voltage and current at the maximum power point. There's a chart on this site labeled "Basic Solar Cell Current and Power Output" that shows what the resulting I-V and P-V (power-voltage) curves look like. There's also an interactive page at the University of Delaware that allows one to manipulate a simpler version of this model.

The book that Dicklyon referenced includes this equation, or at least one very similar. Other books that could be used as references include The Physics of Solar Cells, Crystalline Silicon Solar Cells, and a number of others.

--Squirmymcphee 02:38, 28 June 2007 (UTC)

Thanks for your comment of support and further info. Dicklyon 03:45, 28 June 2007 (UTC)

Could someone explain why solar cells are blue?

Is it the boron or a common opical coating or what?

Silicon has a high index of refraction, higher at short wavelengths than at long; so it has a significant reflection, esp. of shorter wavelengths. I'm not sure about coatings; there may be an SiO2 layer of a thickness that helps with anti-reflection, and if so that can also influence the color. Anyone know more? Dicklyon 07:21, 28 June 2007 (UTC)

This book says it's the residual reflection of the AR coating. Seems likely, since bare silicon is more reflective, a lighter blue-gray. Dicklyon 07:32, 28 June 2007 (UTC)

Bare silicon reflects about 35% of incident sunlight on average (weighted to reflect the spectral content of sunlight), so antireflection coatings are a necessity. The coatings are optimized to maximize the number of photons coupled through the coating and into the silicon. However, the index of refraction of silicon spikes in the UV/dark blue part of the solar spectrum, and no other materials match this spike. As a result, antireflection coatings on silicon solar cells reflect much more light in the UV/dark blue than they do in other parts of the spectrum, giving them the dark blue appearance. Sunlight is not particularly strong in that part of the spectrum, so in terms of solar cell performance it is not a big deal.

As for the coatings themselves, silicon dioxide is a poor choice because its index of refraction is very close to that of glass and the other encapsulation materials used in making a PV module -- once encapsulated, an SiO₂ antireflection coating would have little effect. The materials typically used for solar cell antireflection coatings have indices of refraction between about 1.9 and 2.4, solidly in the middle of the indices of refraction for silicon (about 3.8) and glass (about 1.5).

Silicon Solar Cells: Advanced Principles and Practice by Martin Green contains a pretty good short history of solar cell antireflection coating development. A quick summary, updated by me to reflect current trends: Early solar cells used silicon monoxide (SiO). However, SiO itself absorbs light, so it wasn't a terribly satisfactory coating. Several substitutes were found, the most popular being titanium dioxide (TiO₂), which became a sort de facto standard AR coating for the PV industry from the '70s through the end of the '90s. In recent years it has been supplanted by silicon nitride, whose index of refraction can be controlled by the ratio of silicon atoms to nitrogen atoms; for this reason, it is often abbreviated SiN_x. It is generally deposited using plasma-enhanced chemical vapor deposition (PECVD), which allows for easy control of the silicon/nitrogen ratio. These coatings have the added advantage that they can passivate the surfaces of the solar cell nearly as well as a high-quality silicon dioxide coating, and because of this it has become a key enabling technology in the drive to make crystalline silicon solar cells thinner.--Squirmymcphee 17:02, 28 June 2007 (UTC)

Business-side info

I had previously added some business information on solar cell manufacturers, as well as a link to a global directory of solar cell manufacturers (http://www.enf.cn/database/cells.html). The information was taken down by someone who hadn't actually reviewed the validity of the information but was deleting based on the fact that I posted up several links to ENF.

I will be reposting the information shortly, and would like to hear from any business-experts from the PV industry who feel the links do not add value to readers of the article.

Kit Temple 13:43, 2 July 2007 (UTC)

As I mentioned in my response to you on my talk page, the removal was not about the content, but about the fact that all your wikipedia contributions are external links to enf.cn, and that therefore you are presumed to be a spammer. If you want these links back, the best strategy is to propose them on the these talk pages, and let some other editor, not known as a spammer, decide if they are worth adding to the article. And please do tell us what relationship you have with the enf.cn site. Dicklyon 15:10, 2 July 2007 (UTC)

Hi Dicklyon. I did indeed take your advice and post messages on the talk pages.

I will be upfront and say that I have a direct relationship with the site in question, but have made strong efforts to include valuable information that is relevant to the pages as well as putting up some relevant links. The PV database in question has taken about 10 man-years of work to put together of the last two years (eg. many people working on it over the period) - it is also completely free of charge for companies to appear and for people to use (so people using the resource do not generate income). I have waited until the site is a clear best-in-class before adding the information to Wikipedia. I would like to add a clear note that the database has not generated net profit, and is done for the benefit of the industry (with other areas of the company supporting it).

In regards to waiting for others to repost - well since some of the pages are rarely visited, and the talk comment I have added has been the first talk comment ever added for those pages (eg. solar trackers), then it would be better to resubmit the info if few people throw up objections to it over the next few days. Most people submitting appear to be technically focused people (judging from the content added) - and I am looking to add business-focused information. Readers of Wikipedia are interested in both aspects.

I will try your suggested way first, but if there is complete silence from some of the more specialsied pages (such as solar trackers, dye cells etc.) because no people with a business focus ever bother to look at the discussion page, then I would like to resubmit the information/links and wait for people to spot it on the main page an initiate a discussion on the value.

If there is complete silence, that means you haven't convinced anyone. See WP:COI before re-posting links to your organization. Dicklyon 18:03, 2 July 2007 (UTC)

For the more visited pages, I will cross my fingers that some people who are familiar with the business aspects will spend the time to evaluate the quality of the content. Kit Temple 16:48, 2 July 2007 (UTC)

Maybe I misunderstand what it is you wish to add to the article, but based on what you're describing here it seems to me that the policies outlined in Wikipedia:What_Wikipedia_is_not suggest that for the most part it is not appropriate. Seems to me that general business-focused information -- such as the manufacturing cost of solar cells, the total volume shipped industry-wide, etc. -- is appropriate. The sort of thing that might appear on a news service or in a consultant's report -- Company A signed a silicon feedstock supply contract with Company B -- is not. A directory of manufacturers is pretty specifically prohibited by Wikipedia policy (see "Wikipedia is not a directory" in the aforementioned link).--Squirmymcphee 20:10, 3 July 2007 (UTC)

Hi Squirmy. I accept your point below that the brand article link below can be seen as Spam, the relevance to a Wiki article about brand strength from market research reports (in the case of the information with the link deleted for example) is beyond my experience so I won't comment on that. However, I have read the link you point to where it mentions "Wikipedia is not the yellow pages." The article seems to be strongly suggesting not to turn Wikipedia directly into a directory (eg. don't put long lists of companies within the article), it doesn't seem to be against linking to directories as a useful resource of information. If someone is looking into the subject of solar cells, isn't it useful to have a link to a complete unbiased list of which manufacturers make cells? Kit Temple 10:11, 7 July 2007 (UTC)

I personally don't see a problem with adding a link to the front page of your site to the External Links section. There is already one such link there, though, and given the number of PV directories on the internet I don't think it is practical or desirable to list every last one of them. On the plus side, your directory includes information on manufacturing volumes; on the negative side, it is a commercial web site that arguably uses outdated figures to entice interested parties to purchase more detailed and possibly more up-to-date information (2006 figures have been available from multiple sources for at least four months now, albeit not for free). I haven't been around Wikipedia long enough to know what to do here, so it's probably best to see if others have any opinions on the matter. --Squirmymcphee 21:42, 8 July 2007 (UTC)

Actually, the use of 'outdated figures' is not deliberate. Collecting new numbers takes a huge amount of work. We have recently finished collecting the latest numbers from China and there are now 215 panel manufacturers and 40 cell manufacturers - imagine the time it takes to call up every single one of those companies and talk to the appropriate directors! (because the information can't be found on their websites). Unfortunately if we update the Chinese numbers now to 2006, then we will wipe out the European 2005 numbers due to the database system having to show the same information, so it will have to wait another 6 weeks or so until we have finished collecting all the European numbers and can update both sets. Kit Temple 13:07, 11 July 2007 (UTC)

Content evaluation request

On the suggestion of one of the more experienced Wikipedians, I am submitting suggested comments/links here in the hope that other editors not linked to the ENF site will evaluate the relevance and resubmit it to the main page:

Solar cell brands and manufacturers

Because solar cells can be of varying quality, they can impact the quality of the solar panel (module). A survey by photovoltaic research company ENF among photovoltaic installation companies around the world found that 49% of them found the brand of the solar cell used in the panel to be important. The most commonly named cell brands that installation companies thought were high quality were Sharp, Q-Cells and BP Solar.

Links:

• Directory of Solar Cell Manufacturers
• Directory of Solar Cell Manufacturing Equipment Suppliers

This seems to be a pretty clear-cut case of spam to me. Aside from the fact that brand preferences don't belong in an encyclopedia entry, the link goes directly to an advertisement for a very expensive report.--Squirmymcphee 20:28, 3 July 2007 (UTC)

New Solar Cell Efficiency Record (July 2007)

DARPA's VHESC consortium led by Delaware has achieved 42.8%: | UD-led team sets solar cell record, joins DuPont on $100 million project. I don't think it's been independently verified yet, though.

Perhaps a table of efficiency records by date would be an interesting addition? — RJH (talk) 19:34, 1 August 2007 (UTC)

Efficiency	Date	Group
42.8%	July 2007	High Performance Solar Power Program
40.7%	December 2006	Boeing's Spectrolab, Inc.
32.3%	November 1999	National Renewable Energy Laboratory[7]
16.6%	April 1997	AstroPower, Inc.[8]
14.6%	1995	AstroPower, Inc.

There's already a chart published by NREL showing the record laboratory cell efficiencies on the main page. Obviously it doesn't include the very latest, but in time NREL will likely incorporate it. As for your table, the records attributed to Astropower are only records for the specific type of multicrystalline silicon they were using -- even in the mid- to late-'90s, there were commercially produced solar cells getting better efficiencies than those. And that is the crux of the matter when it comes to tabulating record efficiencies: What constitutes a "record"? If you comb the academic literature, you'll find people attaching long chains of qualifiers to their project so they can call it a record (e.g., "record high-efficiency for planar screen-printed solar cells using material X and processed using technique Y"). If such a table is to be included, I would suggest using the categories and figures published a few times a year in the academic journal Progress in Photovoltaics. Of course, that would require somebody with access to the journal to compile and maintain the table (I have access, but no time at the moment), and even though it keeps the number of categories to a minimum you'll still be talking about a lot of page area covered with tables. Considering the questionable value of laboratory efficiency records to anybody but scientists and academics, I think the existing NREL chart does the job just fine.--Squirmymcphee 14:37, 3 August 2007 (UTC)

Link Removal

The link that I removed was WP:LINKSPAM as the sole point of the linked to page was to sell a collection of journal articles. Admittedly, a tag of vandalism was a little harsh, but it looked like the link was added by a single purpose account, so ... Burzmali 13:32, 12 September 2007 (UTC)

Beware of Greek Scientists?

Hi,

I recently removed a section added by User:Prester John. I will attempt to explain my reasoning. The article that was referenced stated "[Solar panels] may be harming the environment more than convenional sources of energy, according to a study by scientists." The article only states that the scientists are based in Greece, not whom they are, where they published the work, nor any details therein. I removed this to stay in line with WP:VER; As in a scientific context, WP:VER recommends the use of scientific journals when making claims such as this one. (See : WP:VER#Science article in the popular press)

Regards User A1 01:16, 6 November 2007 (UTC)