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Talk:Energy density
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Admin
Do your math before changing anything on the energy page. Also read the NASA doc on handling Hydrogen.
some user
The quoted information you have here about PV energy content appears to be seriously out of date:
- As of today (2007), it takes about 20 years of constant use to get the energy used in manufacturer back out - if the life span of solar cells that long. Perhaps lower energy manufacturing methods will one day be figured out - they would have to be a magnitude or two improved to make these practical.
PVs have an energy payback somewhere in the area of 2-5 years for crystalline silicon and the latest thin films are thought to have a energy payback somewhere in the area of a few months. These systems last at least 25 years. So payback is somewhere between 5 and 150 depending on the system and location.
===Admins note=== I've heard this more than once, but I've yet to see a reference to real numbers. There is work on other forms of PVs(Photo Voltaic) that will have lower manufacturing energy, but they also produce much less power at this time. If anyone has real source data on this (not marketing hype), please pass it along.
reply
Here are some links quick links from Google. Also, the NREL has gone over these problems before many different times. I don't know why this myth has really stuck with some people.
Admin
My read of this paper - it neglects losses due to failure (hail etc) - it is still 3 years.. I don't see where they get their insolation number - no mention of clouds or dirt accumulation on the cells. Of course there is no comparison of lifetime-cost per lifetime-KWH. It was published in 1998 - so why do you think electric companies are ignoring it? Could it be that they might have engineers on staff that can do arithmetic?
admin
Funny - I can't find any PV for sale for less than $4/watt (2008)
Admins note
Show me where I can buy ANY PV for $1/watt - and the fact is they are not interesting until they cost $0.10/watt.
A 1 Watt panel can generate about 5 Wh/day on average - Now when you look up the price of electricity on your electric bill - notice it is in kWh -that K stands for thousands.
Admin reply
PV cell DO last much longer than 20 years. Much much more.
I don't believe that. It is hard to get asphalt roofs to last 20 years. In Kansas, hail damage can require the replacement of band new roofs. I don't think these arrays will stand up to golf-ball hail hitting at terminal velocity. Protective plastics will deteriorate from UV radiation and start reducing performance in only a few years.
There is no half life down here on earth. Sure in space there is due to radiation.
I don't think you understand - all devices have a failure half-life. And - there is radiation here on the surface of earth - called sunshine and it contains UV - something that breaks down paint and protective plastics. Again, the numbers from the referenced web sites are overly optimistic. If PV could produce electricity cheaper than power plants, the utilities would be installing them wholesale. I think the analysis of practicality based only on energy pay back is dubious in itself (and meaningless if PV fails economically). Find 50 people who installed PV systems 5 years ago and measure their current output. It won't be what it was when new. Ask them what it costs to maintain. Do they get dirty? What is the cost of high workers to clean them? Write again when PV panels cost $0.10/watt.
Hydrogen comment
Gasoline is explosive at ~ 1.5% concentration and has the bad habit of lingering around accident sites; hydrogen, alternatively, flies up into the atmosphere as soon as it is released. Hydrogen has the same ignition energy characteristics as gasoline or methane up until about 10% concentration. It has lower ignition energy beyond 10%, but it would be difficult to reach that point in anything but a small, poorly ventilated room. Hydrogen vehicles are equipped with sensors that sound an alarm when too much hydrogen is detected in the air around the vehicle. Besides the most economical way to produce hydrogen is from oil - Best way to store hydrogen is as gasoline - as there is more hydrogen in a gallon of Gasoline than in a gallon of liquid hydrogen. Gasoline is the ultimate fuel for vehicles due to its high energy density.
from krementz: Another alternative for storing hydrogen is anhydrous ammonia (NH3). It has a much higher H content than even liquefied H, is combustible in internal combustion engines with modification, and with high compression engines has a 30% higher fuel efficiency than diesel. It has an energy density about half of gasoline, so is reasonable (unlike compressed natural gas).
Ammonia can be produced from renewable energy, although presently most is formed from natural gas. Ammonia is carbon-free, has no greenhouse gas effects, and does not deplete the ozone layer. Ammonia is not explosive at any concentration at STP, and is not considered flammable by the Department of Transportation. It is the most produced chemical in the world except for petro-fuels, so the technology for storing and transporting is well-developed. While there is a perceived risk from ammonia, the strong smell means a leak is instantly identified (and fixed), unlike gases and gasoline vapors which are explosive. Ammonia gas is lighter than air, so spills go up, and there is no long term pollution issues in spills as there is with petroleum products.
+
+ Hydrogen has been attacked from many angles. It is not a magic bullet, however with advances in technology it is becoming more affordable and safe. They are often compared unfavorably to battery
+ electric vehicles ("why use the energy to make the hydrogen when you can just send it to car?"). But
+ BEVs are not ready for primetime either, still too expensive and not durable enough to compete
+ with what people expect from conventional ICE cars running on the ultimate transportation fuel, gasoline.
+
+ One important advantage to hydrogen is that it can be stored much more cheaply, long term ( > 5 days), than electricity. That makes it a good system for storing excess power from PV and wind.
Admin
The best - cheapest - way to make Hydrogen is from oil. Oil is easy to store. The best way to store hydrogen is in the form of gasoline.
admin
Easy - we burn it off.. Why waste energy? Of course you could litter the highway with little diamond pellets.. I want the carbon in my gasoline - gives much better millage.
Please do your home work - find real numbers do the math etc before posting here.
Admin Reply
No - I think Hydrogen is simply a boondoggle aimed at separating tax payers from their money. The science is not controversial - it would take a major breakthrough - not minor details to change this.
Admin
I'm fine with CO2. See http://xtronics.com/reference/globalwarming.htm What will happen, is that oil will eventually get more expensive, to point where other things developed - I'm thinking cellulose to sugar to a fuel that is much like gasoline is about the only thing cooking right now.
admin
You need to get a BS filter - Life will go on - (with or without us <grin>). If we start killing off the ocean - enough people will die to greatly reduce CO2 - a self limiting function. Anyway - won't happen that way - Oil will cost to much. You should worry about your currency going to zero instead. The green crazed babyboomers are about to find they don't have enough savings to drive much anymore.
admin
You have not been shut-up but your arguments lack good reasoning and hard science. Site one paper that conclusively shows that a 100ppm increase in CO2 causes a 2degC/cent increase in global temp. (There isn't even one that proposes a complete theory). Besides, any paper claiming a hockey stick HAS to explain why the satellite data shows the current cooling or MUST be considered nullified. That's how real science works - if the theory fails to explain the facts you need a new theory.
The fear-mongers may have scared the government out of more money, but their science is still lacking. Just because the idea that the world is coming to an end is popular with the religious-right and the green-left does not mean it is true - or even likely.
The graph at the top of http://xtronics.com/reference/globalwarming.htm fails to show a hockey stick - that means the theory is wrong or there is some sort of gross error in the data - but it is the BEST data we have at this time.
There were past times on earth when CO2 was much higher - it is not any more - there wasn't a thermal runaway. (There is some interesting speculation by Spenser about a misunderstanding of the feedbacks and forcing backed with some evidence of ice-crystals that may very well play this role by their effect in the tropics).
Admin
My suggestion to people that think that humans should leave no ecological foot-print: Please join - (the sooner you do the sooner the planet will be saved) this organization:
I plan to leave a few foot prints - I am an environmentalist - I want a nice environment - I also want to keep living and realize that burning carbon saves a lot more lives than it takes.
ADMIN
I'm not going waste time explaining why this is so wrong - read about it here: http://www.tinaja.com/glib/trashelc.pdf
MWarren us posting
Moved this to Discussion
it takes about 2 years of constant use for a photo-voltaic cell to return the energy used in its manufacturing.[1]
[2] Much longer payback times were often estimated in the past.Even lower energy manufacturing methods are being figured out[3] - they are a magnitude or two improved and are making modern solar cells competitive with other forms of grid generation.
Admin reply
The above links are not of the quality needed to support your point - all of them have economic connections that want reality to be something other than what it might be. I've moved it here for now.
There are no production systems where the total system has paybacks in the time claimed - if these made economic sense the power companies would be installing them big time to cover peak demand - the only installations are show case propaganda to pacify the publics want of the undeliverable.
Rebuttal to Admin reply
Discussions of energy payback periods versus economic payback periods need to be clearly separated.
Don Lancaster's article "Some Energy Fundamentals" clearly considers economic payback for photovoltaics and references no studies.
admin comment
The burdon of proof is on is proving they have a payback. I have yet to see a study cite any commercially available cells at $1/watt (they need to be $0.10/watt) that anyone can buy without subsidies. There are lab items that sound interesting, but you can´t buy them at any price.
from DBJ
The graph at the top of http://xtronics.com/reference/globalwarming.htm shows raw satellite data and does not reflect the actual temperature of the atmosphere. The discrepancy between the apparent lack of warming and the warming projected by the IPCC has been identified and corrected. See http://www.uah.edu/News/newsread.php?newsID=60 and http://www.uah.edu/News/newsread.php?newsID=60 for detailed explanations.
admin Response
Your understanding is not correct - the data shown has been corrected for the degraded orbit problem some years ago.. There just isn't any hockey stick.
from DBJ
No, the graph is of the raw data. Check again.
Admin Response
Not sure what you are basing that on - it is calculated from levels of radio signals - not at all raw data. It has been cross checked with data from weather balloons. You can email Spencer and Christy and find out for yourself how they went back and corrected for the degrade of orbit. It wasn't a big change anyway...
from DBJ
I don't need to email Spencer and Christy. The Spencer-Christy data set and analysis is from a 2000 study (see http://www.ncdc.noaa.gov/oa/climate/research/uah-msu.pdf). The more recent evaluations of the data are from 2005 (see http://www.ssmi.com/msu/msu_data_description.html#rss_msu_data_analysis). The raw data you are graphing has been analyzed using compensations for satellite drift and other factors and the warming has been proven to be more robust. See http://www.ssmi.com/data/msu/support/Mears_and_Wentz_TMT_TTS_TLS_submitted.pdf
Admin Response
I just looked at your links - I have no idea what your point is - there is no hockey stick in the data no matter whose method is used. The graph I have states that it is only accurate to +/-0.5degC - more than any trend. The trend is less than the noise - you can pick start and stop points to show warming or cooling. 0.2deg per decade is not the same as 2 deg/decade as is being claimed. Going further - if there was a trend of 4 deg/decade it does not prove CO2 caused global warming - and if there was a negative trend of 4 deg/decade it does not DIS-prove CO2 caused global warming. There are too many uncontrolled variables to prove anything..
from DBJ
The reason atmospheric temperature is relevant is not that it will show a hockey stick, but that a lack of warming was a key source of skepticism for the overall theory of AGW. In essence, the AGW theory predicted that there would be some level of warming in the atmosphere and the fact that satellite data failed to show that warming seemed to undermine the theory. The 2005 Mears/Wentz study explained why there actually was the expected level of warming and removed a key question regarding the validity of the AGW theory. This does not in-and-of itself prove anything other than there is one more reason not to doubt AGW theory.
Admin Response
The problem is that the proponents of AGW are claiming 2degC/decade - that is 10 times what even your favorite version of the data shows. There have been trends in both directions for long periods in the past. I'm simply saying there is not enough evidence of AGW to restrict the release of CO2.
I believe you are referring to the Global Land-Ocean Temperature increase - and it is 0.2degC, not 2degC per decade. See http://www.giss.nasa.gov/research/news/20060925/ and the graph at http://www.giss.nasa.gov/research/news/20060925/158227main_warm_trend_lg.jp
