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This discussion relates to Technology Review's article Chasing the Sun.

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  Zweibel
  

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  06/26/2009 08:35 AM

  cheaper than any other source

  Some PV has been in use for over 30 years. The track record is they still work fine. In addition to long life (60-90 years perhaps - do you know how long you will live?) PV is utterly simple - some systems have no moving parts. Thus they cost essentially nothing while they put out energy for 30 or more years after they are paid for. Is this too hard for a nuclear scientist to grasp? PV has some unique attributes, like no fuel, simplicity, and long life, in addition to no pollution or CO2.

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    DockScience
    

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    06/26/2009 02:31 PM

    Re: cheaper than any other source

    silicon semiconductor structure is damaged by irradiation, it has a limited life in the sun before recombination exceeds electron generation.
    
    and the tracking panels in Chicago are indeed mechanical and subject to serious wind, snow and ice exposure, not exactly the kind of weather conducive to low repairs.

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      Zweibel
      

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      06/29/2009 12:49 PM

      Re: cheaper than any other source

      Radiation damage occurs in space. Surely you know iot doesn't apply here on Earth? Trackers do have additional O&M costs, and most systemns don't use them. But I expect they are minimal versus most anything else.
      
      power plants are used for 50 or more years. These are very cheap to operate compared to any others.

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  eyu100
  

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  06/26/2009 11:54 AM

  Most efficient?

  In less sunny regions and at times other than the middle of the day, when electricity prices are high and solar cells are most efficient, the power produced by photovoltaics is still far too expensive.
  
  Should this be "least efficient," or are solar cells really more efficient in those times and places?

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    Zweibel
    

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    06/29/2009 01:09 PM

    Re: Most efficient?

    efficiency as a technical term implies output per unit input, and in that case, you are right - solar cells, like everything else, are less efficienct at high temps (by a few relative percent). In terms of total output, the best days are the longest days and with the fewest clouds. One is seasonal and lattitudinal; the other is climate. Be that as it may, statements that solar is well matched to daytime demand are accurate.

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  erbium
  

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  06/26/2009 04:21 PM

  PV the best investment?

  I'm not saying you are wrong but I am curious as to the cost differences between PV and solar thermal. 
  
  Both in building a  big field of mirrors with a central tower, and the modular approach where a 10 to 20 foot mirror like a satellite dish has own focus point above the dish and thermal generator module.  A field full of these modular units are much easier to construct than those with a huge central tower I'd think.
  
  The small modular solar thermal have the same advantages that PV do in that you generate electricity immediately after a section is installed while you are still building the rest. 

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  Zweibel
  

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  06/29/2009 01:05 PM

  PV and solar thermal

  Solar thermal electric prices are always quoted in the highest sunlight, because where they are used. And they don't work where there are many clouds, like Chicago. Actually, PV and solar thermal are neck and neck in the desert in terms of price.

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    erbium
    

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    07/01/2009 04:18 AM

    Re: PV and solar thermal

    Thanks Zweibel
    
    If they're about the same in capital costs, what about other costs: reliability for example, are PV really damaged by sun?   or in slighly rainy area, would rust damage tracking gear on solar thermal over time? 
    
    over 10, 20, 30 years there must be differences, possibly a matrix of advantages and disadvantages of each depending on climate and location instead of a simple answer that one is better?

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  Zweibel
  

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  07/01/2009 08:56 AM

  too much detail

  90% of costs are capital costs. But there are lots of differences in the 2nd order things like CSP using water for cooling towers, as currently configured (Brightsource towers do not); and CSP maybe using natural gas as backup; and CSP possibly having molten salt storage (this is big); and CSP not working as well in the winter (doesn't warm up fast enough and too many clouds); and PV having sudden changes with clouds coming over; etc. In general, PV is a way simpler system and has fewer issues. the radiation damage comment is from the Van Allen belts for PV in space. Doesn't apply on Earth.

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    TooMany
    

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    07/04/2009 11:57 PM

    Re: too much detail

    PV is very expensive. Engineering of solar thermal is in its infancy is potentially more practical than PV.  Heat can be stored and relatively cheaply.  Large quantities of electrical power as yet cannot be. Existing solar thermal attempts have low efficiencies because they operate at relatively low temperatures (400-500C)and have large cooling needs.  At 800C, 50% thermal efficiency is achievable and beats even the best PV which at 40% efficiency is ridiculously expensive.  Glass with aluminum backing is cheap.  Tracking the sun cheaply is a mechanical engineering problem that should be solvable.  I'll bet on solar thermal for truely practical solar power.

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