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Posted by jp838 on August 2, 2008, 12:48 pm
 

The Spectrolab 'terrestrial' FAQ states that the cells can work at
100C with little loss.


too bad :)


Thank you for your interesting posts. I can't add much.
I just made some basic computation to evaluate the necessary tracking
accuracy:

500 suns concentration on a 1 cm2 cell, means a 500 cm2 Fresnel lens,
lens size: 23 * 23 cm, with assumed focal distance of 23 cm

for very small tracking error angle:

Focus_Shift(FS) ~= Focal_Distance(FD)  * tg (Tracking_Accuracy(TA))

    FS(cm)       FD(cm)    TA(degree)     ~loss(%)
    1                23            2.489             10
    0.1             23            0.249             1
    0.01           23            0.0249            0.1

So, these cells, used in these conditions, require a tracking accuracy
greater than 0.5 degree! Such a tracking accuracy is a challenge for a
'solar affordable' outdoor systems (dust, snow, wind, ice, rain,
temperature, ??road traffic vibrations??, animals, ...). It seems to
me that a secondary concentrator, close to the cell - simple mirrors,
compound concentrator, ... -, allowing lower tracking accuracy, is
necessary/mandatory.

A better design may require less tracking accuracy: ?larger cell, ?
shorter focal distance, ?lower concentration, ...

A Fresnel lens model would show what exactly happens to focus when the
light source is not perfectly aligned for a lens ? My experience :)
shows that the spot turns elliptic?? Maybe it's not as bad as the
above numbers predict.

Sholl


Posted by jp838 on August 2, 2008, 9:21 pm
 

Oops ...


Focus_Shift(FS) ~= Focal_Distance(FD)  * tg (Tracking_Accuracy(TA))

    FS(cm)       FD(cm)    TA(degree)     ~loss(%)
    1                23            2.489             100
    0.1             23            0.249               10
    0.01           23            0.0249               1.0

~Loss were 10 times to small

Sholl

Posted by Chuck Olson on July 28, 2008, 4:09 pm
 
Check out http://www.greenandgoldenergy.com.au/  and
http://www.zolardistributors.com/index.html  



Posted by Chuck Olson on July 28, 2008, 4:15 pm
 Also, do a Google search on "Sunball".



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