In that case you will probably get pretty close. The Rule of 12ths is
actually a way to estimate the slope of a sine wave and except for a few
minor variations the seasonal variation in day length is sinusoidal.
--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
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"Geoff Schultz" wrote in message
.. .
I'm not thinking about solar panels. I was just watching the daylight
disappear while thinking having to move BlueJacket from the Chesapeake to
Ft. Lauderdale at the end of the month. I was thinking about how quickly
we're loosing daylight and wondered if rate of change was the same as
tidal
change and thus the rule of 12ths. I couldn't see why not.

-- Geoff

"Glenn Ashmore" wrote in
news:fHsVg.23885$rg1.377@dukeread01:

The angle of incidence of sunlight on a stationary flat panel would be
a sinusoidal curve between sunrise and sunset but I don't think the
power output would quite follow the Rule of 12ths. For one thing the
amount of atmosphere the light has to pass through would squeeze the
peak output towards the center where both the filtering and the angle
of incidence would be least. If the panel were mounted so it tracks
the sun the output curve would be flatter.