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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The quoted information you have here about PV energy content appears to be seriously out of date: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. This would be PV with peak costing less than $4/Peak-watt installed with controller etc..
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) Still in 2011..
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.
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. [admin: you might ask yourself why? And we don't need that for gasoline]
Admin
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).
[Admin:You might look up the industrial accidents involving NH3 - there is a reason it is not used.]
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
Remind me - who is developing this? I don't think anyone - most often a reason for that
Admin
The best - cheapest - way to make Hydrogen is from oil. Oil is easy to store. The best way to store hydrogen is still the form of gasoline.
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. I think a lack of oil would kill many. We should be using nuclear..
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 now that this country no longer produces any wealth...
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 here 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. It seems likely to me that the AWG crowd has confused a cause with an effect - they are not real scientists as their email correspondence has revealed - real scientists don't strive to "hide the decline" in their data. ).
Admin
My suggestion to people that think that humans should leave no ecological foot-print: Please join [ http://www.vhemt.org/ VHEMT] (the sooner you do the sooner the planet will be saved).
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.
2 years in orbit? Ignoring the fuel cost for all the support structures and positioning, cleaning etc?
Rebuttal to Admin reply
Discussions of energy payback periods versus economic payback periods need to be clearly separated.
[admin ] Not really - money = k x energy where k is pretty much a constant.
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.
