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3299Re: [hreg] Assistance RESPONSE

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  • SBT Designs
    Sep 3, 2005
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      Why don't we just stop kidding ourselves?  The entire concept of "payback" from a solar power system is a dinosaur from the 1980s when the government, academics and solar vendors alike were trying to justify to the American consumer (the most uneducated consumer in the world) why we should invest in solar.  At best this data is a weak marketing tool.
       
      So called calculations of payback are little more than fiction because all renewable energy systems are subject to the behavior of weather.  We have been trying to predict the weather for thousands of years with less than accurate results.  Because you cannot tell me what the weather will be like tomorrow you also cannot tell me how much power a renewable energy power system will produce.  I can offer you any "calculations" you like for a solar power system for any location in the world.   Your calculations, my calculations and anyone else's calculations would be just as accurate as gazing into a crystal ball.  And your crystal ball works just as well as mine.  Most American consumers don't read and would not even understand payback calculations and estimates.  And let's not even bring up the topic of efficiencies.  When I am asked about efficiency that is always the first indication of a clueless consumer.  The next indication would be that consumer concerned about the "imbedded pollution" of the solar manufacturing process.  Give me a break.  These concerns and payback concerns are the concerns of a consumer who probably has no intention of investing in renewable energy - plain and simple.
       
      The basic practical fact of investing in solar technology (or any renewable energy technology) is that a solar power system is an on site electric power generator capable of providing power if no utility power is available at all, capable of providing electricity in the event of utility failure and/or capable of producing distributed power that can be applied back to the grid at large.  The fuel for that generator is free, natural, nonpolluting sunshine.  If the American consumer cannot recognize the logic and practical nature of this basic fact (and they don't)  why waste time producing pages of nearly useless data that will end up in the trash can?  And what about the risk that some grubby lawyer might use that data against you in the future because your solar power system did not deliver as predicted by your payback estimates?
       
      I'd rather spare the trees.
       
      Steven Shepard
      SBT Designs
      25581 IH-10 West
      San Antonio, Texas 78257
      (210) 698-7109
      www.sbtdesigns.com
      ----- Original Message -----
      Sent: Saturday, September 03, 2005 7:15 AM
      Subject: RE: [hreg] Assistance RESPONSE

      All,

       

      There are many ways of calculating the “payback” of a pv system………some which make it look more appealing, some which make it worse, some using very basic calculations, some using complex financial analyses and calculated energy projections.

       

      The method however, that has been presented in this thread, is most peculiar.

       

      First of all, while acceptable to use the NREL average for back-of-the envelope calculations, it probably isn’t acceptable to simply de-rate the STC rating of the array by the inefficiency of it as there are many other inefficiencies that come into play by the time the power from the system in question gets put to work.

       

      This pitfall is illuminated in the example that a 3 kW array will provide the 450 kWh/month (average) or 5400 kWh/year.  To be clear: it would not, at least not in Houston . 

       

      Secondly, and regarding the basis for the calculations we have seen: 

      It will be very hard to install to functionality a quality 3 kW system installed for $18K.  Furthermore, it would seem that the example case is assuming a $.56/kWh rate (5400 kWh/Year for $3K).  Perhaps this includes environmental costs or other “intangibles”, which is most appropriate in a big-picture way, but maybe not so much for a bare-bones payback analysis. 

       

      I am a pv advocate and I believe that a true accounting should incorporate all social and environmental costs, in addition to the financial ones.  However, or perhaps because of that advocacy, I think that a clear representation needs to made as to the limitations, as well as the capabilities, of this technology with respect to people’s energy “needs”.

       

      See below for a more “real world” projection for what the 3 kW system in question might actually do in Houston :

       

      Station Identification

      City:

      Houston

      State:

      TX  

      Latitude:

      29.98° N

      Longitude:    

      95.37° W

      Elevation:

      33 m

      PV System Specifications

      DC Rating:

      3.0 kW

      DC to AC Derate Factor:

      0.770

      AC Rating:

      2.3 kW

      Array Type:

      Fixed Tilt  

      Array Tilt:

      30.0°

      Array Azimuth:

      180.0°

      Energy Specifications

      Cost of Electricity:    

      9.2 ¢/kWh

       

       

       

      Results


      Month

      Solar Radiation
      (kWh/m2/day)

      AC Energy
      (kWh)

      Energy Value (estimated)
      ($)

      3.68     

      252   

      23.18   

      4.12     

      251   

      23.09   

      4.82     

      321   

      29.53   

      4.98     

      315   

      28.98   

      5.24     

      335   

      30.82   

      5.53     

      337   

      31.00   

      5.43     

      338   

      31.10   

      5.44     

      342   

      31.46   

      5.40     

      332   

      30.54   

      10 

      5.19     

      334   

      30.73   

      11 

      4.33     

      277   

      25.48   

      12 

      3.34     

      226   

      20.79   

       

       

       

       

       

       

       

       

      Year 

      4.79     

      3660   

      336.72   

       

       

       

      And here for an output projection for the system one might need (with correct array orientation) to hit their 5400 kWh/year consumption mark:

       

       

      Station Identification

      City:

      Houston

      State:

      TX  

      Latitude:

      29.98° N

      Longitude:    

      95.37° W

      Elevation:

      33 m

      PV System Specifications

      DC Rating:

      4.5 kW

      DC to AC Derate Factor:

      0.770

      AC Rating:

      3.5 kW

      Array Type:

      Fixed Tilt  

      Array Tilt:

      30.0°

      Array Azimuth:

      180.0°

      Energy Specifications

      Cost of Electricity:    

      9.2 ¢/kWh

       

       

       

      Results


      Month

      Solar Radiation
      (kWh/m2/day)

      AC Energy
      (kWh)

      Energy Value (estimated)
      ($)

      3.68     

      377   

      34.68   

      4.12     

      376   

      34.59   

      4.82     

      481   

      44.25   

      4.98     

      472   

      43.42   

      5.24     

      502   

      46.18   

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