Tracker efficiencies, etc. [RE-wrenches]

[John Raynes]

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At 12:26 PM 3/24/02 -0800, you wrote:

>Hiya Carl, etal,
>I've just returned from a two day seminal at the University of 
>Oregon-Eugene that dealt with the use of solar radiation data. One graph 
>(by NREL if memory serves, but I could be wrong) showed about a 3% yearly 
>difference between single and dual axis trackers. Before you jump to any 
>conclusions based on that, keep in mind that none of their data was 
>designed with offgrid battery charging systems in mind where the relative 
>difference in winter charging could have a far greater impact.
>bob-O


I was there too and second Bob-O's comments.  It was Craig Christiansen 
from NREL that gave the talks that he's referring to.  One one hand, 
Craig's data tended to re-affirm the industry rule of thumb that trackers 
can gain you potentially 25-30% more total energy production.  What was 
surprising though, was his data showed that departing from optimum tilt, or 
azimuth (departure from true south), up to +/- 15% or so for fixed arrays, 
has little effect on total daily KWh.  At least, it has much less effect 
than most of us intuitively think.  Hmmm.

He actually had some data that indicated in south latitudes, with near 
perfect tilt angles, azimuth angles of up to +/- 60% won't ruin you.  I'm 
not sure I'd take it that far, I'm just passing on what he reported.  The 
data was fairly convincing though.  Enough to make me a trifle less fussy 
with my customers about obtaining absolute optimum panel orientations in 
the future.

John Raynes
RE Solar

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