Wikipedia:Reference desk/Archives/Science/2009 November 19

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November 19

Photo-electric cells for the home?

a) Will they eventually become cheap enough to cover the roof and walls of your house with, or is there any fundamental reason for them staying expensive? b) If you did cover the roof and walls of your house with them, what proportion of the electricity useage would they provide, for somewhere like London for example? 92.29.45.37 (talk) 00:24, 19 November 2009 (UTC)

Rule of thumb: in moderate climates, one square meter of a roof photovoltaic system provides about 0.5 - 1.0 kilowatt-hour of electric energy per day. Average Domestic energy consumption in UK is about 2000 kg of oil equivalent a year, which is 8.4 gigajoules per year = 8.4x10⁶/3600 kilowatt-hours per year = 2300 kilowatt-hours per year = 6.4 kilowatt-hours per day. So you need something in the ballpark of 10 m² of solar panels to satisfy energy needs of an average UK household. Regarding the prices: yes, they will come down, but not dramatically and not very soon. You need 10 m² of semiconductor on your roof, for crying out loud. However, simple solar water heaters discussed in one of the previous questions are dirt-cheap (they are essentially copper tubes painted black) and can save some significant bucks / pound sterling / euro / whatever your currency is. --Dr Dima (talk) 03:06, 19 November 2009 (UTC)

10 square meters is not all that large. 3.3 x 3.3 meters square should adequately fit on the roof of a single family home; that amounts to a square about 11 feet on a side. Other configuratiosn, such as 2 meters x 5 meters (6 1/2 feet by 16 1/2 feet) would also work nicely, and may fit better on some roofs. It's a lot of semiconductor material, which is where the cost comes in; the material cost is largely due to supply and demand. If everyone in a large metropolitan area started installing solar electric panels, prices would drop drastically. --Jayron32 03:12, 19 November 2009 (UTC)

Um - technically - the law of supply and demand says that if everyone started installing these things, the price would go UP not down! However, "economies of scale" might push the price down - so I don't entirely disagree with Jayron's point. SteveBaker (talk) 12:52, 19 November 2009 (UTC)

You are both right. Initially the cost would go up, but the increase in demand would very likely cause the people who make the things to raise production levels and increase the supply so prices would eventually drop. Googlemeister (talk) 14:33, 19 November 2009 (UTC)

I think Dr Dima's estimate may be low. If a typical house is oriented with the roof crest East-West, then the entire roof-half facing the sun might, in the future, be covered with photovoltaic solar cells, tied into the grid through an inverter. When the sun is shining brightly, the solar electricity could well exceed the usage, and the meter would "spin backward," or more realistically the homeowner would accrue credit against electricity used when the sun is not shining. Solar energy striking a square meter oriented normal to sunlight, i.e. at an angle appropriate for the latitude(horizontal at the equator, 45 degree angle at 45 degree latitude, vertical at the poles,) receives about a kilowatt per square meter. Then the efficiency of the solar cell (currently still not all that high), and the degree of cloudiness must be factored in, as well as the efficiency of the inverter. I believe that solar shingles will be in common commercial use in a few years. See [1] and [2]. Such companies as Dow and Johns-Manville have tested solar shingles which can be installed by just nailing them down, like regular shingles, with easy electrical connections. A house roof might be 20 square meters on the side facing the sun, with peak solar input of 20 kilowatts. The DC output from the solar installation can be fed through an inverter to one circuit on the normal breaker panel, and a smart meter can credit the homeowner for any generation larger than demand. Generation smaller than demand would simply slow down the spinning of the meter and reduce the electric bill. The Museum of Science and Industry in Chicago presently has on its grounds a "smart house" which has solar panels on the roof and a small wind generator, There is synergy in this combination, because the wind is often blowing when the sun is not shining brightly. On most days, the electrical records show that the house has, for some period during the day, generated more electricity than it has used. If the solar energy striking the sun-facing roof half is not turned into electricity then (in the summer at least) it is just a wasted resource, or it heats up the house (in the summer) and requires more air conditioning. Edison (talk) 04:49, 19 November 2009 (UTC)

There are several efforts to drive down the price of solar panels - and if one of these comes off then perhaps the price might drop significantly enough. However, the big problem with solar panels is with energy storage. You get all the power you need (and then some) during the day (when you're probably out at work) - but zero at night when you mostly need it for lighting, cooking and heating. The amount of batteries you'd need to store that energy would be enormous...far more than most householders have room for. Right now, you can solve that in many parts of the world by effectively selling your excess daylight energy to the power utility and using the money to buy it back at night. Not all electric companies allow that - but many do. However, that model is only sustainable while your 24 hour production is less than your usage. If you are simply using your electricity provider as a large battery without giving them money for the privilage - they aren't going to want your business for long! If this model of borrowing electricity at night and paying it back during the day becomes the norm for 99% of households - then that will require a new pricing model for these utilities - and that's an unknown quantity right now. The utilities might manage to keep things together by selling excess daytime power to factories and such - and using the profits to generate power for homes at night. But there is also a longer term issue in the more extreme latitudes - that your solar production in the winter is much lower than in summer - but the winter has longer nights and colder weather - so more power is needed for lighting and heating. In the summer, there is plenty of power - but warm nights and long days mean less power is needed. While it's possible that storage solutions might cover the day/night problems - there is unlikely to be a solution for storing power in those quantities over 6 months of the year. SteveBaker (talk) 12:52, 19 November 2009 (UTC)

As for long-term storage of energy, one way to do that is by pumping water from a low reservoir to a high one, then later use this gravitational potential energy to run turbines, as the water goes back down to the lower level. StuRat (talk) 13:40, 19 November 2009 (UTC)

@Dima: I think you are off by at least a factor of 10. 100m2 is a more likely estimate for the required area. @Steve: The storage of energy is a problem only if solar becomes our ONLY source of energy. A combination of solar, wind and hydro might solve that problem quite easily. Biofuels and Nuclear power are also likely to remain important components of our energy portofolio even after we run out of fossil fuels. Dauto (talk) 13:31, 19 November 2009 (UTC)

Yeah - Dima is WAY off on energy requirements for a typical US/European home. Our article Photovoltaic_system#System_performance agrees that the best you're going to get from solar panels is 1kW/hr per square meter each day. At worst (and I'd guess that London is close to the worst) you'll get maybe a third of that on average - assuming average cloud cover over the year - and some way to store unused summer power for the winter (tough!). Remember: London is pretty far north (Americans: It's at the same latitude as Southern Alaska) - and it can be cloudy for weeks at a time. So 0.3kW/hr per sq.m is about right for London. The Domestic energy consumption article gives the average energy in a household a year consists of 20,000kW-h (and breaks that down according to usage) - which is close to ten times what Dima estimated. So you need 55kW/hr per day. That means that you're going to need 160 square meters of panels in London. 50 sq.m in Texas/Arizona. Completely covering the rooftop might be enough if you have a large-ish house - but not if you live in an apartment! Covering the walls is less useful because vertical surfaces are at entirely the wrong angle to the sunlight at the times of day (around noon) when the energy is mostly being delivered. The reality seems far, FAR worse. Look here [3] - this is for systems sold in Austin, Texas - where there is a LOT of sunshine. A $17,000 installation comprising 15 one meter panels produces 2,800 – 4,000 kWh per year. Between a fifth and a tenth of what you need...in Texas. So expect to pay $80k to $170k to completely power your home - and expect to need between 80 and 150 square meters of panels to do it...which fits very well with my estimates. This manufacturer claims a 30 year lifespan for the product - but fails to mention that the amount of power they produce steadily declines over the years. But at (say) $100k capital cost - you'll be paying perhaps $300 a month on top of your mortgage to pay for them. So unless your electricity bill is well over $300 a month - it's not a money-making proposition until the price of panels comes way down...and that's in sunny Texas...in London...forget it! SteveBaker (talk) 18:49, 19 November 2009 (UTC)

Steve, careful with your notation - there is a very big difference between kilowatt/hr (a rarely-useful rate of power-per-unit-time) and kilowatt·hr (a unit of energy). I think you have repeatedly used "kilowatt/hr" when you mean "kilowatt·hr". I think your calculations are all square, but other readers may naively misinterpret your notation, especially when trying to calculate energy and power consumptions over average time periods. Nimur (talk) 19:31, 19 November 2009 (UTC)

A couple thoughts:

1) How much electricity a home uses depends greatly on whether you use electricity for heating and A/C. If not, then a small patch of solar cells on the roof and a way to store that energy for night (either with batteries or by using the power company) should satisfy your demand. If you do heat and cool your home with solar energy, then even a house completely covered with solar cells might not be enough.

2) Solar cells are quite inefficient, in that they only change a few frequencies (colors) or light into electricity (this is also true of leaves converting sunlight into chemical energy). Passive solar heating, on the other hand, can change all frequencies of visible light, and even infrared and ultraviolet, into heat. So, you can heat your home much better by just letting light in large, insulated windows than by having solar cells convert it into electricity that you then use to generate heat inside. A/C is more of a problem, though, as any method of using light to cool your home is highly inefficient. StuRat (talk) 13:50, 19 November 2009 (UTC)

I qwonder if a world electricity grid would be theorectically feasible, allowing electricity to be moved from day to night and summer to winter. 78.146.97.208 (talk) 20:14, 19 November 2009 (UTC)

Transmission-line losses would be huge. Take a look, for example, at HVDC. Loss estimates range widely; our article claims "3% per 1000 km" (for example, so says Siemens' marketing brochure); but I think it would be significantly higher (researchers I work with have cited dramatically higher numbers - at least an order of magnitude worse). HVDC Transmission Systems Technology Review is a good overview, but does not quote power-loss estimates for any of the case studies. This dismal but well-sourced policy analysis indicates that it is more efficient (in terms of energy and dollars) to ship energy in the form of rail-cars full of coal, than to turn said coal into electricity and pipe it by transmission lines. Though the proposal for piping solar-electric power via long-range electric transmission lines does not bear the direct carbon-related costs due to the burning of coal, this analysis is helpful in establishing the ballpark kinds of efficiency numbers. This is not to say such projects are never undertaken - the Pacific DC Intertie is an HVDC line largely designed to sell cheaper-to-generate hydroelectricity from the Pacific Northwest to the electricity-starved Los Angeles area. Nimur (talk) 21:14, 19 November 2009 (UTC)

The Nord Pool is the first multinational exchange for trading electric power between Norway, Denmark, Sweden and Finland.. Cuddlyable3 (talk) 12:17, 20 November 2009 (UTC)

What about super-conducting electricity cables? If technology can put several gas piplines from one side of europe to the other and beyond, then a super-cooled conductor inside some liquid gas and insulation is not impossible. 92.27.157.99 (talk) 19:42, 20 November 2009 (UTC)

Definition of “taxon”

Monkeys are a paraphyletic group (because the Old World monkeys are closer relatives to certain non-monkeys than to the New World monkeys). Does it follow that monkeys are not a taxon? Our article taxon says: “Today it is common to define a good taxon as one that reflects presumptive evolutionary (phylogenetic) relationships. But this is not mandatory” (emphasis added). If a taxon can be paraphyletic (such as reptilia, an example given in the taxon article), then our article monkey is wrong when it says “The term 'monkey' is an artificial grouping; it is not a taxon..., but instead it is a paraphyletic group, like ‘fish’.” This question was asked here three months ago but the answer given then is inconsistent with the discussion in the taxon article. —Mathew5000 (talk) 05:22, 19 November 2009 (UTC)

The entire Linnean system is not terribly internally consistant on these issues. The classification of "monkeys" as two seperate taxa, while classifying reptiles (reptilia) into a single taxon is simply a statement of existing practice. Monkeys ARE currently classified under two seperate taxa, and reptiles ARE currently classified under a single taxon. That this is not consistant is moot; perhaps monkeys should be put into a single taxa, OR perhaps reptilia should be removed entirely from the classification system and replaced with more appropriate taxa, however neither of these reflects what is actually being done. Should either of these things be "officially" adopted by whatever body is in charge of officially adopting this stuff? Maybe. Is it inconsistant as it stands now? Possibly. --Jayron32 05:38, 19 November 2009 (UTC)

'Not a clade', might be better than, 'not a taxon'. A taxon is pretty much any name for a group of organisms that has ever been published by a taxonomist. A phrase like "All primates that are not prosimians (lemurs and tarsiers) or apes" hints at a 'ragbag', indicating that further work is required. William Avery (talk) 11:31, 19 November 2009 (UTC)

I've taken a shot at improving the wording in the monkey article; please check that I got it right if you can. Looie496 (talk) 18:27, 19 November 2009 (UTC)

The term '"good" taxon' went through my mind later. I think that's clearer. William Avery (talk) 21:02, 19 November 2009 (UTC)

Thanks; the edit improved the article. It would be good to have a bit more discussion in the Etymology section of that article. I assume that when Europeans first encountered the platyrrhines in the Americas, they called them "monkeys" because they looked more similar to the cercopithecoids than either group did to the apes; then at some point later (but when?) it was realized that cercopithecoids were closer to apes. Or am I wrong about that; maybe it is only in English that there is one term applying to the platyrrhines and cercopithecoids? This goes beyond etymology; it belongs in an encyclopedia article on the broad subject of monkeys. —Mathew5000 (talk) 01:39, 20 November 2009 (UTC)

Out of curiosity I had a look at articles from other-language Wikipedias, and it turns out that the English turn “monkey” is unusual: most other languages have no single term encompassing platyrrhines and cercopithecoids but not great apes. For example, the French article fr:singe says “Les anglophones distinguent deux types de singe, Apes et Monkeys, le premier terme regroupe les Hominoidea et les gibbon, ceux-ci sont donc plus grand et sans queue contrairement aux seconds. Également polyphylétique, ces distinctions anglophones n'ont pas de correspondances précises en français.” (Anglophones distinguish two types of singe, Apes and Monkeys, the first term including Hominoidea and gibbons, which are bigger and lack a tail, in contrast with monkeys. Equally polyphyletic, these anglophone distinctions do not have precise correspondences in French.) The Dutch article nl:apen says “In verscheidene talen wordt een onderscheid gemaakt tussen apen en mensapen (bijvoorbeeld het Engels: monkey (aap) en ape (mensaap)). Het Nederlands maakt dit onderscheid niet, en mensapen worden ook apen genoemd.” (In several languages, a distinction is made between apen and mensapen (for example in English: monkey (aap) and ape (mensaap)). Dutch does not make this distinction; mensapen are also called apen.) The Spanish article es:mono says “Los términos mono y simio son sinónimos, pero en la jerga zoológica suele distinguirse entre ambos por influencia del inglés, idioma en el que los términos equivalentes monkey y ape tienen diferente significado.... Este uso de la palabra simio como traducción de la palabra inglesa ape, restringida a los primates sin cola, es erróneo, y no corresponde al castellano. Se recomienda para este uso la palabra hominoideo.” (The terms mono and simio are synonymous, but in zoological jargon they usually distinguish between the two under the influence of English, a language in which the equivalent terms monkey and ape bear different meanings.... The use of the word simio as translation of the English word ape, restricted to primates without tails, is erroneous, and does not correspond to Castilian. For this use the word hominoideo is recommended.) —Mathew5000 (talk) 03:00, 20 November 2009 (UTC)

Nut

What's the nut inside of peach/nectarine stones? jc iindyysgvxc (my contributions) 11:15, 19 November 2009 (UTC)

As far as I know, they are called pits and are not nuts. The Peach is a relative of the Almond, and Amaretto is flavoured using the pit from inside an Apricot.Popcorn II (talk) 12:10, 19 November 2009 (UTC)

You can call it a nut, just as with the related almond, but it's actually the seed of the peach tree, not a true nut. The "pit" or "stone" is the endocarp of the fruit, a drupe. These nuts are not necessarily safe to eat (in quantity), as plants in this family usually contain some amount of cyanide. See bitter almond and apricot kernel. --Sean 13:18, 19 November 2009 (UTC)

Least Densest Fabric

I don't know if I spelled that right, but what fabric is most like "light as air"? --Reticuli88 (talk) 19:49, 19 November 2009 (UTC)

for clothing? --Reticuli88 (talk) 19:55, 19 November 2009 (UTC)

I would guess that would be paper clothing. You're probably familiar with the paper gowns you get to wear in the hospital, but there was also a fad of wearing disposable paper dresses in the 1960's: [4]. StuRat (talk) 23:27, 19 November 2009 (UTC)

I doubt that paper clothing would be lighter than fine silk. But there aren't any fabrics that are literally "light as air" because the lightest solids known to man are 'aerogels' - those are not quite as light as air (although they come amazingly close) - but they aren't really robust enough to make into fabrics. SteveBaker (talk) 03:14, 20 November 2009 (UTC)

What about a birthday suit? :-) Mitch Ames (talk) 08:10, 20 November 2009 (UTC)

Lace and gossamer are mostly air.--Shantavira|^{feed me} 08:17, 20 November 2009 (UTC)

And a good thing, too! "Boss, I, er, let our, uh, $100,000 slab of aerogel float away. Sorry." --Sean 19:03, 20 November 2009 (UTC)

@Steve: According to the article aerogel, the lightest solid is indeed slightly lighter than air (1 mg/ccm vs. 1.2 mg/ccm).--Roentgenium111 (talk) 15:12, 23 November 2009 (UTC)

Looking for a particular female scientist.

I'm trying to remember the name of a particular female scientist. All I remember about her currently is that her given name started with S and was German-sounding, she was some type of Germanic or Eastern European, and she worked in the early 20th century. Any suggestions? --✶♏‭ݣ 20:35, 19 November 2009 (UTC)

That's probably a pretty big category. Could you be a bit more specific about the scientist? What area of research (biology, physics, chemistry, medicine)? Major award winner of some sort? TenOfAllTrades(talk) 20:42, 19 November 2009 (UTC)

I think it was physics or chemistry (or both). Were there really that many Eastern European female scientists whose given names started with S in the early 20th century? (I mean prior to World War II.) --✶♏‭ݣ 20:53, 19 November 2009 (UTC)

Oh, and she definitely never won a Nobel, since I went over the list of female Nobel laureates. Other than that, I can't speak to awards. If you could point me to lists of female science award winners for awards that were created before 1940, that might be helpful (but I wouldn't know where to start looking for such lists). --✶♏‭ݣ 20:55, 19 November 2009 (UTC)

Hmmm. I thought you may have be thinking about Maria Skłodowska, much better known under her married name Marie Curie, but she has a Nobel (well, she has two ;-). --Stephan Schulz (talk) 20:58, 19 November 2009 (UTC)

How about Sulamith Goldhaber or Stephanie Kwolek, although they did most of their work after WWII I assume. Mikenorton (talk) 21:07, 19 November 2009 (UTC)

It wasn't either of those two. Her given name was very Germanic sounding. --✶♏‭ݣ 23:05, 19 November 2009 (UTC)

Any of these? Gertrude Scharff Goldhaber, Luise Meyer-Schützmeister, Hertha Sponer. Red Act (talk) 00:33, 20 November 2009 (UTC)

I do realize that's it's not the given name that starts with S on those, but they all do at least have a name starting with S. Red Act (talk) 00:38, 20 November 2009 (UTC)

A wild guess, which does not quite satisfy the criteria, but Sofia Kovalevskaya. (Igny (talk) 00:37, 20 November 2009 (UTC))

Lise Meitner does not start with S, but contains an S, and she was a notable Austrian-born physicist working before WW2 who never won a Nobel Prize. --Anonymous, 00:50 UTC, November 20, 2009.

Take a look at:

• List of physicists
• List of women scientists
• Contribution of 20th century women to physics
• and, if you are really dedicated to the task: Category:Lists of scientists or Category:Women scientists

Let us know if you find what you are looking for. Abecedare (talk) 01:09, 20 November 2009 (UTC)

Assuming that you mixed up the given and surname, there's Hertha Sponer, one of the first women to get a PhD in physics in germany. It could also be Stephanie Kwolek, inventor of Kevlar and with a given name which could be pronounced in a very german way. If you recalled what the person was famous for, it would help. There's too many female physicists from the 20th century to easily check them all. Which when you come to think of it, is really great. :-) Too bad most of us can only recall the names of Marie Curie and Lise Meitner. EverGreg (talk) 13:32, 20 November 2009 (UTC)

None of the above is it, but thanks to everyone who contributed. I'll look through the lists more. Now I'm starting to wonder if I just imagined it. Thanks, and I'll post again if I find her. --✶♏‭ݣ 16:20, 21 November 2009 (UTC)

Boating the Amazon River

Has anyone recently, like NatGeo, navigated the whole (or most) of the Amazon river? Strictly for exploratory, scientific reasons? --Reticuli88 (talk) 20:37, 19 November 2009 (UTC)

Navigating the whole Amazon is actually not much of a feat, because at the point in Peru near Iquitos where the Ucayali and Maranon join to form the Amazon, they are both already huge rivers. If you want to go farther upstream, you have to decide which river to follow. Looie496 (talk) 22:38, 19 November 2009 (UTC)

We don't need no steenkin' boats! --Sean 19:11, 20 November 2009 (UTC)

smoke stream

Moved from Computing desk by Falconus^{p t c}

In thomas the tank engine tv show the trains make loads of smoke. how is this done, and where can one make such a device to make smoke —Preceding unsigned comment added by 82.44.55.114 (talk) 15:38, 19 November 2009 (UTC)

This might get a better answer on the science desk. We have an article on fog machines. I would speculate that the tv show uses dry ice and a little water, which spews out steam and condensed water mist (not smoke). Dry ice is cheap and comparatively safe; and the fumes are just carbon dioxide and water mist. However, because the "fog" it produces is mixed with CO2 (which is heavier than air), the smoke often appears to hug the ground. It's possible that other techniques are used, like glycol theatrical fog, or even just a real steam boiler. Nimur (talk) 15:50, 19 November 2009 (UTC)

Is this the same questioner from this archived question? Our article on Thomas and Friends has a section about animation and one about models which talk about some of this. The 1:32 model trains had smoke generators (which are discussed in the archived section I just linked), and CGI seems to be the preferred method now. --LarryMac | Talk 16:23, 19 November 2009 (UTC)

Yes it's the same questioner, and sorry I missfired and posted on the wrong desk. Could you move my question to the right desk? Thanks, and sorry for the mistake —Preceding unsigned comment added by 82.44.55.114 (talk) 16:37, 19 November 2009 (UTC)