Talk:Solar cell
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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.
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
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Article needs latitude application info...
The Wikipedia is, of course, updatable. A valuable section to add to this article on photovoltaic-energy generation would be something that - even in a very general way - addresses the issue of p.v. applications in various latitudes (or latitude zones).
The general info about cents/kwh is fine, but so unspecific as to give the reader little idea of where the technology sits at present. We get the idea that it has application in "desert" areas, but in the English-speaking world, few people live in this climatic zone.
Progress in the p.v. field must be pretty continual, so a more general idea of power generation and power storage issues for different latitudes could be further detailed as relevant advances emerge.
expand
"When photons hit the silicon plates, electron-hole pairs are created (with a probability depending on the quantum efficiency) and separated. The electric field across the p-n junction draws the electrons and holes in opposite directions, and they then diffuse to the front and back contacts."
- how are the pairs created? can we have more details about this process? - Omegatron 22:52, Jan 8, 2005 (UTC)
production energy
I have heard that more energy goes into producing solar cells than they will ever produce. I am doubtful of this but have been unable to find and information on the production of solar cells. Does anyone know anything about the amount of energy required to produce a solar cell or array?
- I'm pretty sure this isn't true, though I can't find a reference. I've heard that it takes n years or so for an installation to pay for itself, and they last >n or more, so if money is energy (it isn't, but close enough), then you are making net profit in energy. - Omegatron 18:07, Jan 21, 2005 (UTC)
- I have some numbers for poly-Si but they are quite old (1994). If someone has better ones, please add them. 16.0 kWh are needed for each Watt-peak installed (of the finished module). This is split in the following way : Production of Silicon ingot 7.9 kWh / production of the wafers 2.9 kWh / Cells production 3.7 kWh / Grouping cells in modules 1.5 kWh. Assuming an efficiency of 14%, 7 Years are needed in central Switzerland to make an installation profitable. Of course it takes a shorter amount of time in sunnier areas at lower latitudes. Furthermore, due to the fact that those figures are pretty old, today's real values are probably lower. Furthermore, thin film technology allows the productions of cells for less energy. Therefore, it is wrong to say that it takes more energy to produce a solar pannel than it will ever give. Glaurung 20:59, 21 Jan 2005 (UTC)
LEDs and solar cells
Solar cells seem at first to be kind of a dual of LEDs. They take in light and convert it back to electrical energy. But they aren't really opposites:
LED: Has a fixed voltage drop across it. Voltage must increase above this drop for LED to emit light. After switched on, the current sent through the LED (determined by the resistance of other components in series) determines the intensity of the LED, while the voltage stays constant.
Solar cell: Voltage output varies with intensity of light? I think so, anyway...
- TMW: No!! The output CURENT of a solar cell depends on the incident light intensity. The voltage remains (alomst) constant. You are right though, they ARE almost like large-area light-emitting diodes operating in reverse.
- So is this just an effect of low load impedance? What kind of source impedance do they have? - Omegatron
LED: Emits only a single frequency. Voltage drop across LED depends on frequency of light emitted? (Which depends on construction. You can't change the voltage on the fly and change the color emitted (although that would be pretty cool...))
Solar cell: Converts different frequencies into electrical energy? I imagine it has a bandpass response, but I'm not sure.
Can we get a physics explanation of the similarities and differences between these processes? - Omegatron 15:20, Mar 8, 2005 (UTC)
- Hmm...
- "Photovoltaic modules (solar panel) convert all wavelengths within the visible light spectrum to DC electricity but are optimized for the wavelengths that occur most commonly. For peak performance a solar module should face the brightest part of the sky. Most modules are installed at a fixed azimuth and tile angle in order to maximize their energy output.
- Solar modules are made up of "cells" manufactured from various forms of silicon. The greater the light intensity falling on the cells the greater the current produced (light intensity and output current are proportional). However, the voltage produced is not proportional to light intensity but rises considerably in low light ensuring that charging can take place." - Omegatron 15:29, Mar 8, 2005 (UTC)
- We should cover the information on this page. http://www.solarserver.de/wissen/photovoltaik-e.html#char - Omegatron 15:34, Mar 8, 2005 (UTC)
Full Cost Comparison?
The comparison of the cost per kw/hr between p.v. and nuclear is only a good figure, really, if it includes some accounting of the cost of building the installation and maintaining it (including replacement-component cost) amortized over the expected lifetime of the installation.
As an analogy, if you look at the cost of running two different cars for a year with gasoline of equal cost per litre or gallon, over the same roads and streets, with the same number of passengers - but leave out the comparative cost of acquiring and maintaining the two vehicles - it's not a complete comparison. In other words, a comparison could be made more informatively.
Hasn't Rocky Mountain Institute (Amory Lovins, et al.) developed the kind of figures I'm referring to? If not, someone else may have. - J.R.
Major Revamp
10 April 2005 (darkside2010). I am in the process of rewriting and revamping this page "solar cell". The page needs a lot of work. Some of the information on it is just plain wrong, and other things are either poorly described or simply overlooked. (Sorry, no offense intended to the people who already contributed to this page). I am currently doing my PhD in solar cell research, so I think I am fairly well qualified to write about solar cells.
I like the page "solar panel". It should definitely not be merged with "solar cell". However, I am a bit concerned about the page "photovoltaic cell". I feel it would be best to make it into a stub which directs readers to "solar cell". I don't see any distinction between photovoltaic cells and solar cells, and solar cell is by far the more commonly used term. I don't see any advantage to duplicating information on these pages. darkside2010
- I agree : one should merge the info on the photovoltaic cell to this page and create a redirect. I also agree that this page needs some clean up and organization. Perhaps we should discuss about a better paragraph layout, starting by explaining the absorption of photons by a semi-c and then move to the main realisation of solar cells (mono, poly, thin film, III-V, Greatcell) Glaurung 11:30, 11 Apr 2005 (UTC)
- Ok, I am happy to merge the information on photovoltaic cell (which is not much) to this page, and then create a stub, redirecting here. Do you really think that photovoltaic cell should "automatically" redirect to solar cell? I feel it is better to say a few words about the origin of the term "photovoltaic" on that page, and then redirect readers here. I know that a lot of wikipedians don't like stubs, but I think that an informative stub is better than an automatic redirect.
- Certainly, lets discuss a better paragraph layout for solar cell. As you can see, I went ahead and made some rearrangement of the structure of the article, but I'm sure there is still plenty of room for improvement.
- On another note, I intend on replacing the lonely picture on this page. I think that for the top of the article, a photograph of a solar cell would be more appropriate, and that drawings such as the one currently there would be better in the "workings" section. I intend making a few copyright-free drawings of electron-hole pair creation, the equivalent circuit of a solar cell, etc for the page as I find time in the coming weeks. darkside2010 13:59, 11 Apr 2005 (UTC)
- Another thing is, there are, to my mind, far too many external links on this page. I haven't taken the time to follow any of them yet, But I'm sure they are not all neccessary.
- Photovoltaic cell should redirect here, and any explanatory text should be in the first paragraph of this. - Omegatron 15:45, Apr 11, 2005 (UTC)
- Ok, Omegatron, if that is the way things are done, then let it be so. I have rewritten the first paragraph to include a discussion of the etymology of the term photovoltaic. Perhaps there should be a page called Photovoltaics, though, to describe all the institutions and research departments who work in that field. I noticed that Photovoltaic(s) redirects to solar cell, and i would argue that these are not actually the same thing. darkside2010 13:31, 12 Apr 2005 (UTC)
- That's a great idea. I'm no expert in the field, so I don't know which are discrete ideas. - Omegatron 18:23, Apr 12, 2005 (UTC)
- Glaurung, Perhaps rather than discuss a new paragraph layout for this page, let's just edit the page itself, and see where the wikipedia process takes us. I mean, we all have the same goal here, right? To produce the best encylopaedic article of a solar cell in the world! So lets not spend our time and energy discussing, but rather making the page the best it can be. If you have an idea for a better structure, just change it. After all, that's what wikipedia is all about, yeah? darkside2010 13:31, 12 Apr 2005 (UTC)
I pulled that image which was at the top of the article, and replaced it with one which, in my opinion, increases understanding for the general reader as to what a solar cell is. The old picture was a baffling barrage of different coloured arrows which, without a detailed accompanying explanation (which was absent), added no understanding as to what a solar cell is, or how it works. At least with the photograph of the solar cell, people can say "Oh, yeah, I have seen one of those somewhere". darkside2010 16:18, 12 Apr 2005 (UTC)
- Rather than replace it, just move it down the page and add the new image. then if you find a better image that covers the same idea as the confusing arrows, use that to replace them. - Omegatron 18:23, Apr 12, 2005 (UTC)
- I reinserted the image where the photon absorption is explained. But I will try to find a better one (or maybe even make one). This one looks nice, but is not really clear. I think a simplier 2D schema would be better. Glaurung 20:01, 12 Apr 2005 (UTC)
Tesla
Nikola Tesla patented a primitive solar cell in 1901 when he received the patent US685957 (http://patimg2.uspto.gov/.piw?Docid=00685957&homeurl=http%3A%2F%2Fpatft.uspto.gov%2Fnetacgi%2Fnph-Parser%3FSect1%3DPTO1%2526Sect2%3DHITOFF%2526d%3DPALL%2526p%3D1%2526u%3D%2Fnetahtml%2Fsrchnum.htm%2526r%3D1%2526f%3DG%2526l%3D50%2526s1%3D685957.WKU.%2526OS%3DPN%2F685957%2526RS%3DPN%2F685957&PageNum=&Rtype=&SectionNum=&idkey=3D035366337E) (Apparatus for the Utilization of Radiant Energy).
- I believe this is a pretty controversial statement. - Omegatron 23:09, May 19, 2005 (UTC)
- Yeah, I just read the patent and it's certainly not a solar cell. It appears to collect energy from collisions of ionizing radiation via the photoelectric effect, not light. - Omegatron 00:12, May 20, 2005 (UTC)
- but light causes the photoelectric effect to happen so would have powered the apparatus I believe. Greenpowered 21:46, 20 May 2005 (UTC)
- I'm reading about this a lot right now and learning a lot of new things. The work function for metal is too high (4.5 eV) for light to cause a photoelectric effect. The radiation hitting it has to be above near UV in frequency. This is really neat. The photoelectric effect actually causes spacecraft to acquire a positive charge and levitates dust particles on the moon! - Omegatron 21:50, May 20, 2005 (UTC)
- I'm going to add some details to Talk:Photoelectric effect#Tesla / radiant energy - Omegatron 00:12, May 21, 2005 (UTC)
A thought toward the major revamp
The current article says, in one place: "Typical module efficiencies for commercially available screen printed poly-crystalline solar cells are around 17%." What might be a useful and informative addition would be discussion - or preferably a graph - explaining what the increase in efficiency has been (starting from some point in, say, the 1960s or early '70s) leading up to the currently typical efficiency achievement.
It probably goes without saying that this would suggest the positive future of solar-cell applications. I know a lot of people who have languished and rather given up on the potentials of pv, but it is not justified. A discussion or graph could bring home the trajectory toward wide practicality. - J.R.
- A graph would indeed be a good idea. If you have the data at hand showing the evolution of efficiency versus time, feel free to make one. Glaurung 06:02, 20 May 2005 (UTC)
- I don't have the data - wish I did. I put the suggestion out for Darkside, since he is working on a PhD on the subject and wants to re-write the Wiki article. I thought he might be in touch with the stats. I do know that at times I've read about current typical solar cells being so much more (i.e., several times more) efficient than in the early 1970s, which was when I, as a kid, first became aware of the exciting idea of "solar energy." I believe a lot of people became aware of the general potentials of pv in the 1970s, which is one reason why I feel the comparative stats would be valuable.
- I have seen books that state it's up to 35% now so a graph could show a lot. Also I have heard solar power was thousands of dollars a watt over 20 years ago, and is now under $4.00. A graph showing the cost prices dropping over the years would really show the doubters solar is the power of the future. Greenpowered 21:50, 20 May 2005 (UTC)
Cost Analysis
I removed this sentence from Cost Analysis, The present cost benefit to consumers is pretty bad. I do not think that is fair or correct. If you are in an area with subsidies it is not pretty bad, it's pretty good! Even if your not it can still easily be the best option. I know someone the utility companies wanted to charge over $100,000.00 to run grid electricity to his home and solar power was extremely cost effective. And there are even ways to make it cost effective if you are hooked up to the grid and in an area without subsidies. Also the subsidies for solar are compared to the cost of the grid. It does not mention that there are more subsidies on that end then in solar. Greenpowered 21:43, 20 May 2005 (UTC)