Hi John;
John Popelish wrote:
mike wrote:
Then I turned the panel ever so slightly away from the sun.
I was amazed at how dramatically things changed with just
a small angle. Looks like I'd gain WAY more watt-hours/day
by tracking the sun than by anything else I could think of.
Bingo, that is my opinion also.
Yep. It doesn't take much of an angle from perpendicular
for a silicon cell to act as a pretty fair mirror.
Basically the power output will be:
COS(angle) * Watts
Watts is the output of the panel when aimed normal to the sun.
Angle is how far off of normal the panel is oriented.
0deg = 100%
8deg = 99%
11deg = 98%
18deg = 95%
30deg = 87%
45deg = 70%
However somewhere around 45deg or a bit more the cover glass
begins to act more like a mirror and the panel outputs much
less than allowed by the COS rule. Some panels can improve
on this with anti reflective coatings. These coatings may
not have a long lifetime though.
Now if you use a solar tracker the panel can be oriented
close to the ideal angle throughout the day. This significantly
improves the energy captured per day.
As an example:
At summer solstice where I live, 45deg latitude, the sun
subtends an angle of 270deg. That's an 18 hour day.
6 hours of the day the sun is actually behind a fixed panel.
Another 6 hours or so the sun is at an angle where the output
is low or negligible.
Only during 6 hours or so will the panel output significant
power. And the average power output is less than optimal.
A solar tracker in my location can theoretically harvest
3 times as much energy as a fixed panel.
OK, practically, due to weather and thick atmosphere the
output is 2.4 times according to the NREL data.
Other times of the year the improvement is not as much.
But even at winter solstice the improvement in output
is 1.4 times the fixed panel.
Solar trackers, at least the electronic bits, are really
low in cost, $35 for mine. The total cost including the
tracking mount is much cheaper than the cost of adding more
PV panels for the same outputs.
There are places where the tracking costs aren't cost effective.
The california sea coast and in maybe 50 miles or so is an
example. The local weather has lots of fogs which lower the
solar insolation except when the sun is high in the sky.
One must study the NREL data to see how cost effective
your location may be.
--
John Popelish
Duane
--
Home of the $35 Solar Tracker Receiver
http://www.redrok.com/electron.htm#led3X[*]
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