Talk:Solar cell/Archive 1

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)


 * energy payback is in the 2-3 year range in southern UK. The issues is economic payback used to be un-achivable. Now with increases in effiancey, choice of material and mounitng (the pannel only makes up arround 50-70% of system cost) it is looking like you can achive viable paybacks.

I last updated this list five years ago, My list actually goes back to 1839 but this gives an idea of the technology advances:

1981 	Amorphous silicon cells made by RCA with efficiencies of around 4 percent. 1981 	Reid Mickelsen and Wen Chen of Boeing made CuInSe2 cell with 10 percent efficiencies. 1984 	Yuan-Sheng Tyan of Kodak made 11 percent efficient cells of CdS/CdTe. 1984 	Roger Little of Spire Corporation develops 20.3 percent efficient GaAs cells. 1985 	Arco Solar announced 10.5 percent efficient cells of SnO2/CdTe. 1985 	Texas Instruments improves Jack Kilby's cell composed of single crystalline silicon spheres. Reaches 15 percent efficiency. 1986 	Dr. Alvin Marks experiments with Lumeloid and Lepcon for solar electric conversion. Not the photovoltaic effect. 1988 	Richard Swansen of Stanford University makes silicon concentrator cells with efficiencies of 28 percent. 1990 	Paul Smith of Kopin Corporation demonstrates a thin-film tandem junction solar cell with 26 percent efficiency. Structure top to bottom: glass, adhesive, GaAs, adhesive, CdAnS/CuInSe2, glass. GaAs is 5 microns thick. 1993 	Rommel Noufi of the National Renewable Energy Laboratory in Golden Colorado developed a polycrystaline thin film single junction cell with 15.9 percent efficiency. 1994 	Subhendu Guha of United Solar Systems Corporation (Troy Michigan) makes a 10.2 percent efficient polycrystaline silicon cell on a stainless steel substrate at high speed. 1999	An NREL's GaInP/GaAs multijunction solar cell achieved almost a 30% efficiency. 2000	United Solar and Energy Conversion Devices (ECD) fabricated 9%-10% stable thin film photovoltaic cells. --Mmunroe 9 July 2005 07:16 (UTC)


 * The questions is whether or not there is a positive net energy gain in producing a device. Although it might be cost effective to own a device, it may not produce as much energy as it took to make it. Considering alot of the worlds energy comes from fossil fuels, the real question is what is the net gain in energy? Money DOES NOT equal energy. And if the cells on your roof were made with fossil fuel energy, and there is not a positive net gain, then aren't you just polluting the environment.  This is an important question, with very little data to support either side. I would like to see someone show me a well researched, peer reviewed article that demonstrates a positive net energy gain. ~Anthony

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 (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 - 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)


 * Solar concentration needs to be better integrated here, rather than just mentioned as a side-item. Of course, solar concentrators could be a wiki article in and of themselves, and should be as PV cells are not the only possible target for them.  However their role in PV needs to be presented more prominantly in this article as well.  The reasons are: 1) The extremely high efficiency cells that operate at multiple suns apparently are only that efficient if multiple suns worth of light are actually applied (something to do with device physics.)  Confusing efficiency figures between flat panels and concentrator cells should be avoided.  2) The number of suns a cell can utilize is a parameter of import that will become more and more critical in deciding the worth of a given module or technology (Energy Innovations, the Sunflower 250 manufacturers, are using a normal off-the-shelf Si cell intended for flat panel use and feeding it tens of suns without signifigant degradation as long as it is cooled.  CVP cells made specifically for this purpose tolerate hundreds of suns.) and 3) perhaps most importantly, concentrated photovoltaics are an important trend that will greatly impact the market viability of solar PV installations.  You can't rigorously talk about market viability or payback periods without figuring this technology in. (24.218.106.196 02:11, 21 September 2005 (UTC))


 * Oh, how interesting. Thank you for mentioning it.  I googled a bit and found this May 2005 conference agenda on the topic that references dozens of papers http://www.nrel.gov/docs/fy05osti/38024.pdf  --noösfractal 02:28, 21 September 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)


 * in germany the econimics are so good for instilation that insitutions are installing large ammounts of them to use as a fixed income stream. If you are a farmer in the right area people will pay you large ammounts of cash to stick PV arrays on the side of your barn.

Greenhouse gases?
I just got my solar array installed, and one of the readouts BP Solar is hyping is how many pounds of greenhouse gases are saved. I'd love to know if that's really true, and to see this factiod reflected in the redesigned page. Also, just wondering, does anyone know how much energy and/or greenhouse gases goes into the manufacture of present-day solar panels?


 * A lot. The present day semiconductor/solar silicon manufacture uses carbon to reduce silcon from quartz: SiO2+2C -> Si + 2CO. Each mole of silicon generates 2 moles of carbon oxide. But it doesn't stop here. Then the silicon is reacted with chlorine/HCl to produce silicon tetrachloride SiCl4 or trichlorosilane, SiHCl3, which is be purified by distillation. Distillation consumes humongous amount of heat, obtained by, you guessed it, most likely by fossil fuel combustion these days, though technically nuclear or hydropower energy could be used. Once purified by distillation, then the trichlorosilane, or silicon tetrachloride/hydrogen mix, are passed into a hot zone reaction chamber, to decompose to pure silicon, which is then doped, processed (including melted, lots of energy required here too.) A silicon solar panel will have about 40 years of useful lifetime, or even more, the very first built solar panels are still cranking out electricity, though their efficiency has fallen to something like 80% of what it was 40 years ago, but remember, these were the very first solar panels built, current ones might last even better. During these 40 years, depending on your location (whether you are in low solar dose UK, Canada, or high solar dose California/Mexico/Sahara Desert) you get 6 to 30 times the energy invested in creating your solar panels. So overall, over a few decades you do save energy that would otherwise would have had to be obtained from fossil fuels. Consider it an investment - lots of fossils could have been burnt, but instead, they were invested into your solar panels, and, usually after less than 5 years, you're out of the red zone, and you and  our environment profiting by not releasing more greenhouse gases. See the Net_energy_gain article. Just make sure no baseballs/hurricanes/accidents break your panels, and they do last those 40 years. :) I'm not being totally sarcastic here, but it's more a serious advice, because what you're doing is a very nice thing.


 * Ultimately, we'll have to get off the fossil fuel/carbon metallurgy bandwagon, and silicon and all other metals will be produced purely by electricity/noncarbon heat sources, such as solar furnaces, nuclear furnaces, and hydrothermal/solar electricity. But these days we're not there yet, and chances are that your panels did generate quite a bit of atmospheric greenhouse gases, simply because nobody has the money not to listen to economics and just take some ethical high road. When natural gas is cheap, because its only cost is that of extraction+delivery+profit, without accounting the screwing ourselves in the long run with these greenhouse gases, who the heck are you, as an individual, to deviate from the norm, and not use the currently cheapest method of carbon based silicon production and energy generation? Sillybilly 04:06, 17 October 2005 (UTC)

Thin-film Photovoltaic cells using metal foil
This could be added to the Solar cell article if someone knowledgeable enough is found: http://www.daystartech.com/product.htm

Not the actual product of course, but the principle. Mostly because it seems to be usable non-SI solar cell - the only one I've come across.


 * You mean non-Si, not non-SI. :-) Looks interesting... - Omegatron July 7, 2005 17:57 (UTC)

Question
Does anyone have information on specialized solar cells for use in satellites? I imagine there would be very different types for use in places close to the sun with high insolation (like SOHO at earth L1) or for deep space missions where low temperature would allow higher efficiency using materials sensitive to a broader spectrum reaching further down to the infrared. (see ) 84.160.209.236 09:17, 2 October 2005 (UTC)

I have had a discussion with a designer of cells for space, they are indeed quite different in how they use light. The effect of being in a vacuum is that heat from the sunward side can be dissipated on the other side. What this means is that the cells can be pumped up to a temperature of a couple of thousand degrees Kelvin making their absorption compatible with the light from the Sun. The basic benefit of this is efficiencies of close to 60%. This is unfortunately impossible on Earth because of inadequate heat dissipation. Sorry I don't have the source of the info, but it's a start. --70.20.191.207 01:51, 17 October 2005 (UTC)

I wonder what solar cell materials would stand up to a couple of thousand Kelvins without melting, even if their "absorption is compatible", whatever that means. Sillybilly 03:43, 17 October 2005 (UTC)

Remove BIPV section int he introduction
The the three last paragraphs of the introduction about the BIPV technology are very enthusiastic, and to me they sound like a commercial for XsunX. I'd like to replace them with a shorter and more objective text, like this one:

"Another approach is to integrate thin, transparent photovoltaic cells into ordinary window glass. This would allow windows in homes and office buildings to produce electric energy from sunlight, while at the same time staying transparent enough to see through. The technology is propietary and is currently being marketed by XsunX."

I don't think it is a good idea to talk about this "One particularly promising technology" already in the introduction, which is supposed to give a general overview over the topic. I would not completely omit it though, since the technology seems quite interesting and promising. What do you think? Alex

Explanation why I removed a section
Materials and efficiency ... Efficiency is the ratio of the electric power output to the light power input. Around noon on a clear day, the solar radiation at the equator is about 1000 W/m². So a 10% efficient module of 1 square meter has a power output of about 100 W. Solar cell efficiencies vary from 6% for amorphous silicon-based solar cells to 30% or higher with multiple-junction research lab cells.

The common method to express economic costs of electricity generating systems is to calculate a price per kilowatt-hour (kWh).

- begin section removed -

Part of this calculation which can be counterintuitive is that with no fuel cost and low maintenance cost, the economically relevant efficiency metric is not generally thermodynamic efficiency (e.g. energy in vs. energy out,) but rather capital efficiency &mdash; that is, the initial cost per watt of a solar cell is a stronger determinant of economic viability than is its efficiency. (e.g. a 30% efficient solar cell costing $2 is much less desirable than a 10% efficient cell costing $1 in most applications.)

- end section removed -

I deleted that section because I think the statements that are already there, such as "The common method to express economic costs of electricity generating systems is to calculate a price per kilowatt-hour (kWh)." are succint enough to represent the message from the erased section and the long winded discussion that follows here.

First of all, the very last statement is nonsense - a 30% efficient solar cell costing $2 is much less desirable than a 10% efficient cell costing $1 in most applications? Rephrased, into a specific example, this means that under identical, say 100 watt solar radiation intensity, the first unit will deliver 30 watts for $2, the second unit 10 watts for $1. The whole purpose of the unit is to generate watts, so the first one will give 15 watts/$, the second 10 watts/$. Which is better?

Now on to the discussion of financial vs. energy profitability, at least a perspective on it. The net energy gain article has a discussion on this topic, though it could be clearer. Basically energy in vs. energy out will translate into dollars in vs. dollars out sometime in the future, though it's true that future is not here yet. This is because energy prices will take on whatever price the market demands, energy is simply a must, no way around it. Prices will simply climb to whatever is necessary if demand is high but supplies are low, until it hits the pricepoint at which new supplies can generate. These days energy is extremely cheap, practically free, therefore the bulk of cost in solar cells is the human sweat and not the energy input. So while we have coal, natural gas, oil and cheap nuclear, it's financially-cheap energy-wise, but financially-expensive human-sweat-wise to create silicon. This is only sustainable while you have practically free coal, natural gas, etc, whose cost is basically punch a hole in the ground and put the finished product it in a barrel, or on a railcar, but such supplies are finite and are rapidly getting used up. The millions of years used by biomass to accumulate all the fossils underground are treated as an economic externality. When you completely run out of non-renewable energy sources, and you have to rely on energy generated by your solar panel or windmill to make new solar panels and windmills, and then you have to add the worker's labor cost on top of that, the picture becomes much grimmer. So yes, if you, as the microeconomic consumer need to make a decision right now, this moment, all that counts to you is capital cost per delivered watt + expected lifetime, for the solar panel you buy today. It doesn't matter to you if the price of panels goes up or down after you bought your panel and it's installed, it's installed, it's done, you sunk your cost to it, can't change the past, you may be angry that you missed the boat if the price falls, or snicker in glee how lucky you were to buy the panels before their prices rose, but yes, as far as a financial microeconomic decision goes today, all you care today is delivered watts per dollar. That is a short sighted view though, it doesn't solve the big problem, ultimately the real macroeconomic problem has to be solved of having something that's sustainable long term, and then the dollars in vs. dollars out will be closer to energy in vs. energy out, but in the meantime we can use the energy in vs. energy out as a closer approximation to reality trying to decide what works, what's sustainable, until the financial world wakes up to same reality and catches up in pricing. Basically cheap fossil fuels can sustain cheap solar panel prices as long as you have cheap fossil fuels, but when you're out of fossils, what will count is energy in vs. energy out, the energy required to make the panel will have to come from the energy generated by the panel, and not from practically free fossil energy. You can basically buy some time - instead of burning this pile of cheap coal, let's make a cheap solar panel out of it, that will return 10x the energy over 40 years compared to if we just burned it now, so you can have cheap solar panels for a while. You can also have wars in the meantime, to take over more cheap energy supplies, to protect the luxurious way of life, but sooner or later what you took from others will run out too, and what happens then? Will there be an abundant cheap supply of energy where we can live in this current luxury world where energy costs are practically nil? If not, then using the energy in vs. energy out metric is a lot closer to reality than the current financial price of renewable/sustainable supplies that's pegged at the cost of nonrenewable fossils. Of course human labor sweat costs will always matter, and add to the picture, I'm not saying they won't, but 5-10 cent/kWh prices these days may be so far off from the sustainable scenario that we might as well ignore current prices and look at the net energy gain instead, see what inherent price that allows. However, if the answer is yes, and there will be cheap energy, such as if we can successfully develop fusion, then this whole discussion is mute, because we're back to the good life the easy, wasteful ways, and we simply don't give a ..., because we don't have to care. But it's very hard to run reactors that don't evaporate at a couple million degrees that fusion reactions require, even with all that magnetic containment. Cross your fingers for fusion - and cross your toes too extra for ITER not to succumb to intellectual property licensing quabbles and simply go up in smoke, end in a standoff, in a showdown, because it took half a decade to settle on where to do it in the first place, forget about trying to decide who gets what from the chickens that get counted long before they hatch, when the whole point is trying to find a darn way to hatch them at all so that people on this planet can live at all without a massive drop in world population. Without fusion, in the meantime, looking at what we got, what's doable, energy in vs. energy out, rate of energy return is a very important parameter in any kind of long term sustainable financial analysis, unlike the dollars/watt, which only deals with the current transient situation that will massively fluctuate anytime the market goes haywire - demand surges because everyone wants to buy before prices go even higher so prices go even higher because everyone wants to buy til they reach so ridiculously sky high that the market finally wakes up, and everyone stops buying because they are waiting for prices to fall further before they buy so prices fall even further because nobody buys, to a ridiculously low point, where the whole cycle repeats. To tame all this, the long term sustainable pricepoint determined by the energy in vs. energy out besides the human labor factor is what a lot of sensible people will go by, and ignore the occasional price fluctuations, and if the price is above their sustainable energy in vs. energy out price estimate, they won't buy, so prices will not reach sky high. See the entertaining tulip mania for further details on what current price that's not in sync. with some long term sustainable estimate, how the dollars per watt not in sync with energy in vs. energy out, what all that can lead to. Sillybilly 19:20, 7 January 2006 (UTC)

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

Rules for whose thumb?
As of November 12, 2007: "A rule of thumb commonly used is that peak power times 20% gives average power...." That rule applies fairly well for desert locations between about 30 and 35 degrees latitude, such as southwestern desert areas of the United States. At higher latitudes and in cloudier climates, the capacity factor can be much less. For example, developers of the large solar plant under construction near Brandis, Germany, on the north German plain, are estimating a capacity factor of 11 percent.

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)