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Crops for Ethanol versus Solar Arrays

  1. Mar 25, 2007 #1
    There has been much talk in the U.S. about growing corn and switch grass for the production of ethanol. The purpose being to use ethanol as a fuel additive.

    Would it not be possible to produce more energy by putting solar arrays in place of these crops? It would seem that ethanol production would require a few extra steps that solar energy does not.
     
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  3. Mar 25, 2007 #2

    Ivan Seeking

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    The return on invested energy from ethanol, from corn, is supposed to be around 10%. Ethanol from corn yields about 500 gallons per acre-year, or about 50 usable gallons per acre-year. If you play with the numbers a bit, it becomes clear that we could never grow enough corn to replace petro with ethanol. Also, ethanol from corn puts energy into direct competition with food and clean water for both livestock and human consumption.

    Notably, George Bush is the only person that I have seen get excited about ethanol from switchgrass. This option is probably at least twenty or thirty years off, even in principle.

    As was indicated by another member who just deleted his post, the cost of solar panels is presently far too high to be practical as a total energy solution.

    If you go through this thread
    https://www.physicsforums.com/showthread.php?t=108344
    after a few pages you will find a fairly extensive review of the basic numbers on solar panels, and biodiesel from algae. AFAIK, biodiesel from algae is the only solution that promises a nearly complete replacement option for petro. Claims as high as 20,000 gallons of fuel per acre year can be found, with all sources claiming at least half that much. Also, the return on invested energy for biodiesel from algae is alleged to be about 60+%; or about 6000 to 12,000 usable gallons per acre-year.

    late edit: conflicting methods of comparison.
     
    Last edited: Mar 25, 2007
  4. Mar 25, 2007 #3

    ShawnD

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    From a business standpoint, the idea of solar power seems infeasible. Look at a few simple differences between solar and alcohol/diesel.

    Alcohol and diesel can be made from basically any kind of plant. Diesel is essentially just another name for thick oil (corn oil, olive oil, peanut oil, sunflower oil, etc). Solar power can only be made with 1 thing - solar panels, and unlike a stalk of corn, which can be made into alcohol or diesel, a solar panel cannot be eaten.

    Having a hail storm take out a crop of corn sucks, but it's not the end of the world. Having a hail storm destroy a field of solar panels might actually be the end of your solar farm if it costs upwards of a million dollars to fix/replace all of the panels every time this happens. The area east of the rocky mountains is actually called "Hail Alley" because these storms happen every year. In fact, the year I bought my car there was a local shortage of Honda Civics because the storage lot in Calgary (Canada) was heavily damaged by a hail storm.

    Alcohol and diesel (especially diesel) have very high energy density, which makes it easy to store energy. North America has huge stockpiles of electricity in the form of coal; alcohol and diesel are the same basic idea. Solar power is different from oil or coal in that energy cannot be stored efficiently; even the best lithium batteries in the world are extremely heavy and expensive relative to how much energy they contain. The energy in 1000 pounds of batteries is probably less than that stored in 20 pounds of diesel.

    The startup cost for alcohol and diesel is relatively low because the infrastructure is already in place. We already have fields of corn, we already have fields of sunflowers, we already have distilleries. I don't think we have biodiesel refineries but it wouldn't be too hard to set that up because it's a 2 step process of filtering then saponification, which is just a fancy word meaning titrate with base then let it settle. Solar panels, on the other hand, are extremely expensive, and we don't have a lot of solar panels in existence so basically all of this stuff would need to be purchased new.


    Alcohol and diesel are the future. Solar panels might find their way onto buildings with the help of some tax deductions, but overall I don't think we'll ever have fields of solar panels.
     
  5. Mar 25, 2007 #4

    Ivan Seeking

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  6. Mar 25, 2007 #5
    This may sound a bit like a conspiracy theory, but I think that solar voltaic could be a lot cheaper than it is. Most new technology follows a pattern of becoming cheaper as it goes into mass production. Solar never did. Why not?
    Sure silicon is expensive, but now we have thin film which requires no silicon.

    Look at how much the price of thin screen TV's has dropped in just the past three years.

    Exxon is the second largest producer of solar, following closely behind Siemans. Siemans main production has tended to stay with small array equipment and small tech such as solar yard lights ect.

    I suspect that Shell, Phillips and Exxon don't really want to see solar brought into the picture. They could if they wanted to, they have a lot of patents on solar devices. As this link shows:

    http://sciencecop.info/wiki/tiki-pagehistory.php?page=Cartel Solar Patents&source=5

    I can see where China may be the country where cheaper solar originates.

    At Costco I paid only 90 bucks for a set of sixteen solar yard lights, made in China of course. That is a fraction of what they cost just a few years ago.
     
  7. Mar 25, 2007 #6

    Ivan Seeking

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    The price per watt has dropped significantly but is still far too high as a practical replacement for petroleum. I think the current cost for silicon panels is about $4 per watt peak. However...

    http://news.mongabay.com/2005/1010-nmsu.html
     
    Last edited: Mar 25, 2007
  8. Mar 26, 2007 #7

    Sorry Ivan. I wanted to look at some numbers before I finalized what I said. :tongue: I ussually don't like to delete posts, but I felt that my post was a little bit premature.
     
    Last edited: Mar 26, 2007
  9. Mar 26, 2007 #8

    russ_watters

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    ....and look how expensive LCD tv's are still. Prices have come down, as Ivan said, but I don't think I'd say that solar cells are in mass production. How many are sold a year? I don't know, but I doubt the number of good-sized (say, 1x2m) cells is greater than 100,000.

    No, I don't think the logic is logical there.

    Here is a good list of panels. With one at $3 per watt, all the rest are from $4-$5 per watt: http://www.ecobusinesslinks.com/solar_panels.htm

    Something in favor of solar: It is expensive if the goal is to seamlessly integrate it with municipal power, but what if instead of a full-backup with an autotransfer switch and a huge bank of batteries for night-time, you just sized it and designed the electronics for running your air conditioning system? I've always been curious about this, but I've never done the research on this specific issue. Maybe I'll throw something together tonight...
     
    Last edited: Mar 26, 2007
  10. Mar 26, 2007 #9

    Astronuc

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    I don't think we are there yet in mass production of solar cells, and the industry still needs to recover upfront R&D costs as well as capital investment for production facilities.

    If solar yard lights fail, you easily replace (like a light bulb). If a solar panel fails - it is a major issue - so lifetime and reliability (related to product quality) keep the cost higher.

    Some people for some reason seem to expect technologically sophisticated products to sell for commodity prices. Well, you get what you pay for. If one wants cheap, don't expect it to last as long.
     
  11. Mar 26, 2007 #10
    If you guys are looking for alternative energy sources not being nuclear, how about methane. It burns clean with minimum of pollution and, for whomever it may concern, with the lowest CO2 signature of all carbon fuels.

    And there are thousands of gigatons available on the ocean floors.

    http://www.google.com/search?hl=en&q=methane+hydrate+energy&btnG=Google+search&lr=

    removing that stuff may even make the world safer:

    http://www.google.com/search?hl=en&...lr=&q=methane+hydrate+release&btnG=Search&lr=
    NOT!
     
  12. Mar 26, 2007 #11

    Ivan Seeking

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    Methane is not a viable option for combustion because the world has decided to reduce carbon emissions. However, it is the most efficient source of hydrogen.
     
  13. Mar 27, 2007 #12

    Ivan Seeking

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    http://www.businessweek.com/bwdaily...0070316_016207.htm?campaign_id=rss_topStories

    Something else caught my attention today: Although ethanol from corn is heavily subsidized, it was reported today that there are only about 1100 E85 pumps in the US, which agrees with wiki
    http://en.wikipedia.org/wiki/E85_in_the_United_States
    - no more than the number of biodiesel pumps, with the latter being primarily a grass roots movement that has not enjoyed broad support or subsidies. In other words, unlike E85 from corn, the biodiesel industry has grown based on merit.

    Another consideration is that ethanol from sugar beets yeilds about twice as much fuel per acre-year.

    Here is a nice discussion from The News Hour, on PBS. Note that opponents still argue that when taken in total, ethanol from corn yields a net ZERO energy gain. Above I cited the number that I have seen used most often - a 10% gain.
    http://www.pbs.org/newshour/bb/transportation/jan-june07/ethanol_03-26.html
     
    Last edited: Mar 27, 2007
  14. Apr 9, 2007 #13

    Ivan Seeking

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    http://abcnews.go.com/WNT/story?id=3024574&page=1

    We don't want to put food - esp corn - into direct competition with fossil fuel alternatives.
     
    Last edited: Apr 9, 2007
  15. Apr 15, 2007 #14

    Ivan Seeking

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    http://www.physorg.com/news95749527.html
     
  16. Apr 16, 2007 #15

    chemisttree

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    Last edited: Apr 16, 2007
  17. Apr 16, 2007 #16

    D H

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    I just did a quickie calculation. There are about 8766 hours in a year, but the number of interest is the number of hours per year the solar cells will produce power. Solar cells won't produce any power at night, and will produce little power during the morning, evening, and during a rain storm.
    I assumed the equivalent of 2000 hrs/year of peak power sunshine falling on the array.

    With this number, a lifespan of 25 years, and a cost of $4/watt, the cost of the power produced by the array is 8 cents per kilowatt hour. This number compares favorably with the current cost of electricity in the US, 8.8 cents per kilowatt hour. Caveats: This is a hand-waving number, and I have ignored amortization costs.

    I would assume that materials, labor, benefits, taxes, general and accounting, and profit account for the bulk of the $4/watt cost. This answers chemisttree's question: There is no way the energy costs to produce solar cells exceed the energy produced by the solar cells. The manufacturers would have to charge a lot more than $4/watt if this were the case.
     
  18. Apr 16, 2007 #17

    Ivan Seeking

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    This assumes that the source of power for production costs the same as electrical consumer rates. How much energy is spent from gasoline, diesel, or coal power used to mine and process the materials? What is the price of fuel and electrical power in China? Also, I would bet that 4$ per watt is mostly due to the energy needed for manufacturing.
     
  19. Apr 16, 2007 #18
    Speaking of rising costs of corn due to ethanol production...
    Someone I know who works with Coca-Cola said that Coke's Philadelphia plant was considering using sugar instead of corn syrup because the price of corn is rising so much. Who woulda thunk?
     
  20. Apr 16, 2007 #19

    ShawnD

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    Good news for people who drink coke. Bad news for the people who pay for that coke :wink:
    Doesn't Mexican coke use real sugar in it?
     
  21. Apr 20, 2007 #20

    Astronuc

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    Interesting SciAm article, which somewhat puts into question the efficacy of using ethanol as an alternative to gasoline.

    Want to Reduce Air Pollution? Don't Rely on Ethanol Necessarily
    Fueling the automobile fleet primarily with ethanol rather than gasoline might increase air pollution, a new study finds
    We have E85 in our area. :rolleyes: I can't say that it has helped.
     
    Last edited: Apr 20, 2007
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