The following information may have errors; It is not permissible to be read by anyone who has ever met a lawyer. Use should also be confined to Engineers with more than 370 course hours of electronic engineering and should only be used for theoretical studies. All content entered becomes and is (C)2007 Transtronics, Inc. the property of Transtronics, Inc. Rest assured that your contributions won't be sold and will be publicly available.
Talk:Energy density
From Transwiki
The quoted information you have here about PV energy content appears to be seriously out of date: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.
Contents |
[edit] 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.
[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.]
[No numbers to work with here..]
Even the first links shows payback times of half of what you are claiming.
The administrator of this site asked for data showing that the Energy Payback Times of Photovoltaics for average US solar irradation have been reduced to just one (1) year for thin-film PV and about 1.5 years for crystalline silicon PV. The paybacks for the SW are even better. Several peer-reviewed articles, based on audited, detailed material and energy inventories for 13 European and US PV manufacturers can be found in the web sites of Columbia University (www.clca.columbia.edu) and that of the National PV Environmental Research Center www.pv.bnl.gov. Furthermore, PV technologies are evolving and their cost and env. profiles are getting even better. Vasilis Fthenakis Brookhaven National Lab and Columbia University (email vmf@bnl.gov)
[edit] Admins note
I have no idea of the cost of these new PV - I can't find anything anywhere where PV power costs less than 4 times what a utility charges.
From http://www.cornellsolar.com/whoallocatesthefund.html
A 1kW PV array will produce approximately 1,600kWh AC per year in Ithaca on an average, south-facing sloped roof.
and also from the same page
How long will it take to pay for itself? - At the average cost, it would take about twenty years for the PV system to pay for itself through electricity savings if put on an off-campus building.
My hunch is all of these numbers are a bit fudged in favor of the 'venture vultures'. My real world take is that the PV won't last 20 years, and there is never a cost break-even point reached with today's PVs.
My hunch is the failure half life of a PV cell on a roof would end up being 3-4 years - I doubt there is a net energy gain in the real world.
[edit] 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. Again it is my "hunch" that 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?
[edit] 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.
+
+ 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.
[edit] Admin reply
This comment seems to want reality to be quite different than it is - we store cars in garages where hydrogen collects, We drive through tunnels.
It is a waste of energy to convert the form to hydrogen. The best way to store hydrogen today is in the form of gasoline.
There is no economic reality in Wind and PV - I would point you to Don Lancaster's |Energy Fundamentals fro details.
[edit] 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.
[edit] 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.
[edit] 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.
[edit] 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 that anyone can buy without subsidies. There are lab items that sound interesting, but you can´t buy them at any price.
[edit] Reply to admin comment
The CIS ST40 modules described in the Knapp & Jester paper are available for purchase. Searching Google for "st40 cis solar panel" found a number of vendors selling these modules at market prices and they do not require a subsidy. Similarly, searching Google for "sp75 solar module" found a number of vendors willing to sell the modules at market price without subsidies.
I'm focussing on energy payback and not monetary payback. I agree with this article's supposition that current, retail PV installations usually have a 15-20 year monetary payback (we'll see how well the Nanosolar PV power plant in Germany works out). Different forms of energy command different amounts of money; photovoltaic energy currently commands more money than other forms of energy. PV modules, however, easily generate enough energy in 5 years to match the energy used to manufacture the module. Whether a PV module is a good economic investment depends on the particulars of a given situation. From an energy point of view, however, PV modules are a net win.
[edit] Rebuttal to Admin reply
My citations address energy payback because the text in the article clearly directs the focus toward energy: "years of constant use to get the energy used in manufacturer back out". If the point of the article is to discuss economic payback, then the text should be updated to so state.
[edit] admin comment
They really are one and the same, the cost is directly dependent to the energy used in manufacturing.
[edit] Rebuttal to admin comment
Energy is just one of the inputs to cost. Labor, profit, materials and politics also play into the monetary cost. Different forms of energy generation cost different amounts of money. For example, nuclear energy production is an example where politics plays a large part in greatly increasing the monetary cost of the energy. Energy and money are not directly related (unlike Don Lancaster's supposition).
[edit] Rebuttal to Admin reply
Note: the Tesla blog is a jumping off point for the other citations - Karl E. Knapp & Theresa L. Jester, Home Power #80 Dec 2000/Jan 2001, Alsema, Frankl & Kato,2nd World Conference on Photovoltaic Solar Energy Conversion, Vienna, 6-10 July, 1998, etc...
What are the quality problems with the citations provided? How do the articles err in their energy analysis?
[edit] admin comment
The Lancaster paper artical covers this - the power generated is theoretical, not measured. When you really figure in the total losses from all factors inculding degredation and real life span of the cells, and pointer system and the Total energy content of the systems manufacture takes too long to recover to ever be a net gain. If it were a gain there would be measured studies showing it.
[edit] Rebuttal to admin comment
The Knapp & Jester paper does not claim a specific generation output in their calculation; instead, Figure 1. in the paper allows for a range of power generation and a range of paybacks. The Moore, Post, et. al., "Photovoltaic Power Plant Experience at Tuscon Electric Power" paper uses actual, measured power generation for a 5MWac installation over a four year period and cites a 2.8 year energy payback for that system.
[edit] admin reply
That is not for the whole system .. you need to read ref 13 with your BS filter tuned in.
