[Greenbuilding] PV Tracking ~ Fibonacci?

nick pine nick at early.com
Sat Aug 20 17:02:53 CDT 2011


Reuben Deumling <9watts at gmail.com> writes:

>What about this kid's idea?

>http://www.amnh.org/nationalcenter/youngnaturalistawards/2011/aidan.html

>... I needed to compare the tree design pattern's performance. I made a 
>second model that was based on how man-made solar panel arrays are 
>designed. The second model was a flat-panel array that was mounted at 45 
>degrees. It had the same type and number of PV solar panels as the tree 
>design, and the same peak voltage.

Not true. The graphs show about 5 volts peak for the tree vs 4 volts for the 
panel.

>My idea was to track how much sunlight each model collected under the same 
>conditions by watching how much voltage each model made.

And measuring "how much sunlight each model collected" requires measuring 
energy vs voltage, eg accumulating joules or watt-hours instead of measuring 
the number of hours per day with an output exceeding a certain threshold 
voltage. Trees might grow according to the voltage measure, but people buy 
and sell and use energy, not voltage or power. Politicians who don't know 
the difference might pass laws requiring PV trees, like cellphone trees :-)

>I measured the performance of each model with a data logger. This recorded 
>the voltage that each model made over a period of time. The data logger 
>could download the measurements to a computer, and I could see the results 
>in graphs... The Fibonacci tree design performed better than the flat-panel 
>model.

Perhaps, if one is a tree :-)

>The tree design made 20% more electricity and collected 2 1/2 more hours of 
>sunlight during the day.

The text and graphs have no evidence to support those claims.

>... in December, when the Sun was at its lowest point in the sky. The tree 
>design made 50% more electricity...

Nonono. And the configuration suggests the contrary. And a flat panel with a 
43lat+15 = 58 degree tilt would receive more sun than a 45 degree panel in 
Albany in wintertime, 2.5 vs 2.4 kWh/m^2-day, according to NREL. And why do 
trees need solar energy in December, with no leaves or ongoing 
photosynthesis?

Nick 





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