Talk:Solar energy/Archive 1

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This page needs some work. There are some very unclear paragraphs that probably ought to be deleted, re-worked and/or checked for bias.

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Yes, in particular:

"The basic cost advantage is that the home-owner does not pay income tax on electric power that is not purchased. " (2nd sent. of 2nd pp in Applying Solar Power)

I removed it for now. --Erauch 02:51, 11 Sep 2004 (UTC)

Removed one advantage

The advantage:

-Solar power is available to approximately half the planet at any given moment.

means the same thing as the disadvantage:

-It is not available at night and is reduced when there is cloud cover, decreasing the reliability of peak output performance..

So I removed the former, as it is not really an advantage.

minor edit needed

The generally accepted standard is for peak power of 1020 W/m² at sea level. The average power, which is an important quantity when one is considering using solar power, is lower. As an example, in North America average power lies somewhere between 125 and 375 W/m² 9 kWh/m².[1]

kWh/m^2 is not a unit of power, it is a unit of energy. Something odd is going on here. is that the energy gained over 1 day?

Look at the [1] link, and the images on that site cite daily, latitude tilt numbers, so the variation is due to line-of-sight atmospheric thickness, weather, clouds and "albedo", averaged over a year. Fixed now, and this subsection can be removed from the talk page after a while. Sillybilly 18:31, 11 December 2005 (UTC)

Help on solar power

Does anyone know a good place to find pictures of concentrated solar energies? i tried Google and Yahoo search and it came up blank. Help is appreciated

There are some nice pictures at www.stirlingenergy.com, but I don't know how you'd go about getting permission to use them. --Flatline 16:58, July 28, 2005 (UTC)

Fix this passage - public hot water

I removed this passage (under "Deployment of Solar Power") as confusing:

"For example, while certain European or U.S. states could benefit from a public hot water utility, such systems would be both impractical and counter-productive in countries like Australia or states like New Mexico. " Erauch 04:15, 23 Oct 2004 (UTC)

"such systems would be expensive in areas low population density" would be an accurate assessment. Are there examples of or proposals for public solar hot water?

I would have guessed that units on top of apartment buildings would be the most practical option, with the side benefit of reducing the Urban heat island effect by absorbing solar energy into the cold water.

Just my thoughts - I haven't edited the page as it's not my area of knowledge. Singkong2005 02:44, 19 November 2005 (UTC)

Power

can somebody confirm the 1.4 W number please? See Wikipedia:Reference_desk#http:.2F.2Fen.wikipedia.org.2Fwiki.2F1_E48_J. dab (ᛏ) 14:44, 6 Feb 2005 (UTC)

The article states that the earth recieves "1,410 W / m2 of energy, as measured upon a surface kept normal (at a right angle) to the sun." Thats 1.4 Kw not 1.4 watts. This intuitively sounds about the right order of magnitude but I cannot confirm it. Lumos3 11:00, 7 Feb 2005 (UTC)

A 0.25sq M solar panel can generate 20W hence 1 sq.m is around 80W. Solar is say 10% efficient, that is 800W. So it is ball park right --Rjstott 11:36, 7 Feb 2005 (UTC)

What timescale ? Day or hour ?--80.131.82.121 04:46, 23 August 2005 (UTC)

No timescale is needed. Watts (& kW) are rates, not amounts. 1 watt means 1 joule per second. Joules are the amount of energy, watts are the power (i.e. the rate of energy per unit time). 211.28.170.248 11:46, 19 November 2005 (UTC)

Calculations - power at sea level

from the article:

"As the Earth orbits the Sun, it receives approximately 1,400 W/m² of energy, as measured upon a surface kept normal (at a right angle) to the Sun (this number is referred to as the solar constant). Of the energy received, roughly 19% is absorbed by the atmosphere, while clouds on average reflect a further 35% of the total energy. The generally accepted standard is for the peak power 1020 W/m² at sea level."

This figure - 1020 - doesn't follow from the previous figures.

1400 W less 19% is 1134 W. Wouldn't this be be the peak power? (ie no clouds, equator at midday).

If we reduce it by 35% (assuming it's geometric, i.e. 1400*(1-0.19)*(1-0.35), we get 737 W, so that's not the reason for the different figure. And if we take the percentages arithmetically (i.e. add them) we get 1400*(1 - (0.19+0.35)) = 644 W.

Can anyone help explain this? --Singkong2005 13:28, 19 November 2005 (UTC)

Per Earth's_energy_budget and Solar_radiation about 1,366 W/m^2, 341.5 W/m² is the global average value. These are figures for above the atmosphere, so 19% is 1106 W/m^2 which reaches the surface, not including the further 35% reflected by clouds, though this is different then the 6% atmospheric reflection in the EEB article. So the 1134 and 1106 figures are close to the generally accepted standard for peak power of 1020 W/m^2, though it's still unclear where that figure comes from. In the end it's all best guesses anyway.

Potential Energy Generated

I'd like some info included on the theoretical maximum energy that solar energy could provide. I.e. if the entire earth were covered with solar panels, how much power would be generated? Would it meet the total energy requirements of the world? What's the practical maximum coverage we could ever hope to achieve? How much energy would that provide? Provide results with 90-100% solar cell efficiency, and with current efficiency. --CraigBuchek 24 Mar 2005

Why limit yourself to the surface of the Earth? Vast solar panels could be built in space and the energy they recieve beamed back to earth as microwaves. You would also have to build a system to tramsit the waste heat from this back into space or the earths temerature would increase. Lumos3 22:19, 26 Mar 2005 (UTC)

And on the other hand, for those of us who prefer something more within arm's length, what about a calculation based on 1/10 of 1% of the Earth's land area (disregarding the water)? And using the currently most advanved proven solar p.v. tech. This would give some idea of something tangible, even though we realize no one is going to cover that much land area with solar arrays. It would offer food for thought for the reader.

I won't attempt to define "proven" (as in "proven solar technology") -- that's out of my field of expertise. But I think you'll understand what I'm getting at.

Just a point for consideration with respect to the article. - J.R.

Eps, my first chat contribution... I'm not sure if this helps or not... The "standar" ratiation at sea level is 1 Kw/h but the photovoltaic panels have an efficiency of just 15-16% aprox... That means that for a standar on-grid installation (5 kW) we need some 50 square meters... Any hair dryer takes more than 1 Kw...

On the other hand, recently there has been an agreement acording the "equivalency" between PV solar panels - thermal solar panels, with some 700 wats/square meter... so you can produce 5 Kw with just 7 square meters (5 Kw used for heating water, for heating the house or swimming pool or even air conditioning, under development...). Maybe it's a better idea try to save energy instead of produce more...

JordiG june 2.005

Using http://www.greenandgoldenergy.com.au/images/DirectBeamAustraliaandNewZealand.GIF (5kWh/m2/day = 1825 kWh/m2/year

From http://uic.com.au/nip37.htm (In 2003-04 Australia's power stations produced 237 billion kilowatt hours)

237,000,000,000 / 1,825 = 129.86 km2 (1,000,000 m2 in 1 km2)

assuming 10% efficency =1298.63 km2

20-21 km wide circle , .0169 % total area of australia

assuming 100% efficency =129.86 km2

6-7 km wide circle , .00169 % total area of australia

using projected (http://www.eia.doe.gov/oiaf/ieo/world.html) worldwide energy use in 2015 is 162,068,301,805,239 kilowatt hours (per year)

690 times the energy

10% efficency = 11.660% the area of australia , 896,054.70km2 , 534km - 535km circle

100% efficency = 1.166% the area of australia , 89,605.47km2 , 168km - 169km circle

The problem is storing the energy (5 hours of sun(total) for 24 hours) and cost

Can someone check my numbers

catprog june 6.006

Here's my attempt at a calculation using figures circa 1997:

World consumption of gasoline for 1997=160 litres per person (wri.com)
World population for 1997=approx 5.7 billion
Thus, world consumption of gasoline for 1997=9.12*10^11 litres
Energy content of that gasoline=2.92*10^19 Joules
Solar energy production rate for panels in space=160 Joules/second per square metre
Time available for energy production=60*60*24*365.25=31557600 seconds
Production per square metre per year=160 J/s * 31557600 seconds=5049216000 J
For panels on the ground multiply by 0.5 due to night and 0.6 due to atmospheric losses,
for a total reduction to 0.3 (30%) of power generated in space.
Tracking the sun is harder on the ground as well.
Area required to equal energy of gasoline above=5.78*10^9 m^2 = approx. 76km by 76km
or 1.93*10^10 m^2 = approx 138km x 138km on the ground.

On the ground it would require the area the size of the state of New Jersey, but it would have to be somewhere closer to the equator and much more sunny. This would constitute 0.013% of the total available land on Earth. At $500 per square metre the total cost would be about 10000 billion dollars (10 trillion dollars).

A structure that size in space built with current technology would be much more expensive both in terms of energy and money required to put it up there. The extra cost would easily outweigh the extra energy collected. Solar power satellite has a good discussion of the issues.

Also oil constituted about 46% of global non-renewable energy consumption in 1998 so double again to get the area needed to replace all fossil-fuels.

PS: Can someone check my numbers? Pi lambda 06:06, 20 July 2005 (UTC)

To attempt to somewhat answer the original question, projected (http://www.eia.doe.gov/oiaf/ieo/world.html) worldwide energy use in 2015 is 162,068,301,805,239 kilowatt hours (per year), or 18,500,000,000 kilowatts continuously. Incident solar insolation near the equator is commonly cited as 1 kilowatt per square meter. At (unrealistic) 100% efficiency, this is equivalent to 18,500 square kilometers, near the equator, or an area 136 kilometers square (85 miles square). At current efficiencies, lets say 15%, it would require more like 351 kilometers square, or 219 miles square, near the equator. This is equivalent to approximately 3/4 of a country like Oman, 1/2 of Ecuador, or less than 1/2 of Malaysia. --Benjamindees 00:26, 19 October 2005 (UTC)

I have recently researched and sketched the areas required for solar power systems that are able to cover the total primary energy demand (assuming a rather conservative efficiency of 8%). The area is visualized by six red stars distributed over the world's desert areas - see the figure I have added to the article ( upper right, or http://www.loster.com/ml/xmas/xmas05.html ). The figure also contains the averaged solar irradiation over three years derived from satellite data. --Mlino76 12:08, 9 March 2006 (UTC)

I've just looked at your figure, and I had difficulties understanding it: As far as I'm concern, it is not obvious that the stars represent area. Maybe you should use squares instead of stars (their area is easier to compare) and give a more detailled legend. In my opinion, the two informations in your figure (solar irradiation and surface of solar panels required) overlap. Maybe two distinct figures could be better. But anyway, this is an interesting figure.CyrilB 12:16, 9 March 2006 (UTC)

In view of these facts it is astonishing that ohter forms than regenerative enegies are still in discussion! --Pelo 12:44, 9 March 2006 (UTC)

Solar energy requires a relatively large investment per unit of energy extracted. This is also the reason why wind energy is experiencing good growth ahead of solar in many areas. It's very cheap to install and already competitive with fossil fuels in many places. In the past fossil fuels have required smaller capital investment for the amount of energy you can get out of them, because there were some very large reservoirs which were quite easy to find. In some cases the oil was literally oozing out of the ground! As new oil gets harder to find and extract there will eventually come a point when solar becomes more economical than fossil fuels, if for no other reason other than the fact that it is very reliable (well, in some places anyway). Pi lambda 05:45, 11 May 2006 (UTC)

Thanks for your comments, CyrilB. The image originates from a card that I've sent out as season's greetings, thus the star-shaped areas. I admit that, although they have the geometrically exact surface area, the shape could be distracting. The solar irradiance overlaid with the required area for solar panels allows to identify other suitable locations, especially because the restriction to desert and centralized areas is only meant to give an idea about the required areas. I'll try to improve the figure caption ... --Mlino76 13:54, 9 March 2006 (UTC)

Environmental and Climatic impact

In the section above the remark is made: "At current efficiencies, lets say 15%, it would require more like 351 kilometers square, or 219 miles square, near the equator." Question: What happens to the other 85%? I guess most of it would become absorbed as heat wouldn't it? So now here is my question: Imagine that we have this 100 miles square sitting in the middle of Nevada, pitchblack, and converting 85% of all impinging solar energy into heat (and as minor spin-off 15% electrical energy send of to LA and environs, but we can safely neglect that for now). Any idea what that is going to do to the climate of Nevada, and perhaps the entire Southwest? We would be setting up an enormous convection cell rising up above Nevada, with an energy of --somebody pls calculate for me how many-- nuclear explosive devices. Air would be sucked in from 1000's of miles around it, sucking up all the moisture in from a wide area. It would setup a permament region of severe weather with thunderstorms and tornados, a sort of permament category 5 hurricane sitting in the middle of the Nevada desert. Baseball sized hail would be raining down permanently, shattering 10 trillion dollars worth of solar panels. Can somebody explain to me what is wrong with that scenario? JdH 21:23, 21 March 2006 (UTC) (doomsday prophet)

What about the pollution in the production process?

Response: You forget the fact that every square mile of land is constantly absorbing and re-radiating solar energy during the day. There is not much difference in the way this happens between a solar plant and, for example, a patch of desert. A dark gray patch of desert will absorb about 85% of the sunlight falling on it and re-radiate it as heat and reflect the other 15% back into space. The only difference with the solar panel is that it will convert the 15% into electricity. Either way 15% of the incident solar energy disappears from the local environment. A large solar plant might have some slight effect on local climate, but then so can any other land use such as farming, for instance. The effect of a change in land use on the weather might even be measurable but at the moment it is almost always ignored because it is generally quite subtle. Pi lambda 02:49, 3 May 2006 (UTC)

I think you underestimate desert albedo; it is in fact around 0.3 to 0.35. So if you decrease albedo it results in more visible and UV light to be absorbed, and re-emitted as IR that will be reabsorbed by the atmosphere, leading to an increase in air temperature. Another factor that comes into play is evaporation of water. How those changes will affect climate I can't say with some hand waving arguments, but it is not something you can dismiss without appropriate model calculations.

It are exactly these kind of changes that drive the desertification process in the southern Sahara and Sahel region of Africa. JdH 15:09, 3 May 2006 (UTC)

It was not my intention to suggest that there could be no impact but rather to say that, as far as change in local climate is concerned, what matters the most is the change in thermal properties of the land. If you build a huge solar plant on land that already has the same overall thermal properties I would expect no effect on the local climate. Then again, climate is a very complex phenomenon and any structure that size could be creating side-effects simply due to its size. Pi lambda 06:20, 11 May 2006 (UTC)

Economics of Solar Power

I think somebody ought to have another look at the section of this article dealing with cost-effectiveness. In particular, there's the part that asserts that at $9/watt, a solar panel yields a 9% ROI assuming the power can be sold at 9cents/kwh. That ROI figure seems wrong. Let's say I build a 1 watt solar power plant for 9 bucks. Every hour that it is sunny, I make a watt-hour worth of electricity that I can sell for .009 cents. If it's sunny 12 hours a day, every day all year round, thats (12 x 365 x .009) = 39 cents worth of power, for a one year ROI of 4.3%. This neglects costs of maintenance on the plant, which even at 1-2% per year will take the ROI down to what you could get from T-Bills (and with a lot less risk). Nobody in their right mind would invest in such a project unless the government were showering them with subsidies, in which case the plant can hardly be said to be cost-effective.

Response: What maintenance cost would you need? The panel would probably never require any maintenance for the entire life of its installation, especially a small 1 watt one (about the size of the palm of your hand). Its expected reliability means that the maintenance cost is usually included in the purchase price. Also, are you saying the sun is less dependable than the government? Pi lambda 06:46, 15 July 2005 (UTC)

Response: Yeah, maintenance -- who needs to consider that. We have to be very careful on this article to make sure that the fantasy world of the pro-solar crowd doesn’t add too much bias, and this is only a small example of how it creeps in.

The main point I want to make is that NET METERING IS A HUGE SUBSIDY. Solar is no where near competitive without this benefit. –jcp-

Response: Your point about net metering may be right but I don't think maintenance would lower your ROI by anything like 1%.
To use a real-life example: the Springerville solar plant cites their module failure rate for 2003 as 0.028% and overall reliability of 99.7%. They have almost 35000 modules over 44 acres but the whole array is controlled remotely. They don't say how much the array cost to build but assuming $50 million (which is very likely too low) they would have to spend $500,000 per year on maintenance to equal 1%. Given the reliability figures that seems at least 10 times too high. Pi lambda 01:51, 19 July 2005 (UTC)

Don't confuse peak generating power with average insolation. You can't get 12 watts a day out of a power plant like that. You can get maybe 4.4 watts a day out of it, assuming the thing is located in the sourthern US. linas 18:14, 22 July 2006 (UTC)

Inexaustible

Is solar power inexaustible, renewable, or nonrenewable?

Yes.

• Inexhaustible on practical terms, as long as the Sun shines and sunlight can reach the surface.
  • Exhaustible because there is a limit to how much can be gathered on the surface over any time period.
• Renewable because there is always more the next day.
• Nonrenewable because the Sun will eventually stop shining the way it now does.

The above becomes slightly different in space, for example by being able to build much larger collection structures and the ability to be closer to the Sun. (SEWilco 18:56, 12 May 2005 (UTC))

Ocean thermal energy conversion

Is OTEC technology a direct enough form of solar energy to be mentioned in this article? I know on some level even fossil fuels are indirect solar sorces, however since OTEC is based on the actual tempature differental created by solar heating of the upper ocean it might be listed as a type of solar power. I was trying to classify it in my mind anyway and that was the closets one I coudl come up with. Dalf | Talk 04:32, 24 Jun 2005 (UTC)

I think it deserves a mention, in the same way that wind power should be mentioned. As secondary solar energy or something. -- Ec5618 11:45, Jun 24, 2005 (UTC)

It is already mentioned under Indirect solar power. Lumos3 13:02, 24 Jun 2005 (UTC)

What about heat?

Solar power describes a number of methods of harnessing energy from the light of the Sun.

Shouldn't that be heat and light of the Sun (as received on Earth)...? --Just my 2 cents -- Hemanshu 16:10, 13 July 2005 (UTC)

It's all technically light. There is visible light, and IR/ultraviolet/etc. but it's all photons. In a strict sense, it isn't really heat until it strikes an object. So a change really only makes sense if you take an expansive view of heat (as including radiation). While it's common for students to be taught that way, it actually adds more complications to try to differentiate "heat" radiation from "visible" radiation. --Benjamindees 12:04, 17 November 2005 (UTC)

Solar Air Heating

There is no mention of solar air heating, which is more efficient and more cost effective than solar water heating and PV. The potential energy contribution of solar air heating is huge in the areas between 30 and 60 degrees north and south latitudes. The most cost effective systems within the type operate without system storage and provide direct daytime space heat. Currently there is a scarcity of equipment from which to choose, but presumably this will change.

Nov 14 reversion

What happened here? [1] the comment is rv vandal, but doesn't say to which old version, and I think we may have lost some good information. --D0li0 11:50, 15 November 2005 (UTC)

Agree the reversion seems to go back several weeks and lots of good changes have been removed. Lumos3 14:43, 15 November 2005 (UTC)

Agreed. I saw an odd edit, and did a simple revert. Somebody who knows the artcle well should be able to find a better revert point. Ronabop 15:12, 16 November 2005 (UTC)

Dead Link

The solar one solar two link in the body of the text states that the link has been moved. Can someone provide a new link?

• There is a Wikipedia article talking about Solar One and Solar Two, so I had the link direct to there. Pentawing 03:22, 13 December 2005 (UTC)

Link Removed?

I added a link to external links to www.solarfacts.net. Why was it removed? --Pippin88 21:47, 16 December 2005 (UTC)

Sunny days per year

The article claims that areas in California have the sunniest days per year-- Doesn't that neglect Hawai'i?

link removed?

I added a link to Solar ponds that was removed by Wtshymanski with the remark "rv Wikipedia style is no links in headings)". That is not very helpful; if it is not according to "Wikipedia style" then please move it someplace else, but don't just cut it out. The problem here is that there is a lot of redundancy, and unless there are appropriate links to clarify that it is bound to get worse over time JDH 7:10 PM, 26 January 2006