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Panel tilt on East facing "flat roof"

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Posted by Dallas Dick/Jean Rystrom/Clay on April 9, 2010, 4:39 pm
 
What is the ideal panel tilt on an East facing "flat roof".  The roof
actually has a slight angle sloping down ~7-8 degrees toward the
east.  The roof is on the non-street side of the house. Would it be
best for optimum electricity generation to lay the panels flat on the
roof or to tilt them?  What would be the difference in output?  If
tilting makes sense, then should they be tilted East or South?  Thanks

Posted by dold on April 9, 2010, 5:10 pm
 

Optimum for energy production is probably equal to your latitude.
Optimum for money production might depend on the rate plan in your area if
you are grid-tied.
Optimum overall value might depend on how much it costs to tilt the panels.

East facing is more of a problem, so you might need tilt adjustments to get
good production.

My panels are flat on a 4/12 pitch roof, too flat for optimum energy
throughout the year, but it turns out they are near optimum for payback
from my local utility, because the flatter tilt provides more energy in the
summertime.  The azimuth is toward about a 2pm sun, also optimum for dollar
payback.

You can play with numbers on the PVWatts site to see a percentage effect of
different angles.  For this purpose, I would leave the sizing at default,
and adjust the angles.

http://rredc.nrel.gov/solar/codes_algs/PVWATTS/version1/
Predicted solar energy available, based on real observation points around
the US and the world.

--
Clarence A Dold - Hidden Valley Lake, CA, USA  GPS: 38.8,-122.5

Posted by Josepi on April 9, 2010, 6:42 pm
 You would need to do some 3D trig for that one. I often thought about doing
a trial and error spreadsheet to do just that but ran out of time for "that
project"...LOL

I want to point my panels a little west about 3 PM solar, as I get many
overcaset days and, if it clears up, for only 1 hour, it is at 4-6 PM,
almost everytime. Your micro-climate will determine this mostly.



What is the ideal panel tilt on an East facing "flat roof".  The roof
actually has a slight angle sloping down ~7-8 degrees toward the
east.  The roof is on the non-street side of the house. Would it be
best for optimum electricity generation to lay the panels flat on the
roof or to tilt them?  What would be the difference in output?  If
tilting makes sense, then should they be tilted East or South?  Thanks



Posted by ghio on April 13, 2010, 12:14 pm
 On Apr 10, 2:39am, "Dallas Dick/Jean Rystrom/Clay Rydick"

The correct angle for your panels is facing north if your are southern
hemisphere and south if you are northern hemisphere.

Posted by Martin Riddle on April 13, 2010, 11:06 pm
 

message

I believe its still your Latitude. SE facing is where most experiments
have been done.
A quick search says 35 degrees for east facing roof. -20% loss versus
south.
Advantages, are Clear mornings with out the haze and water vapor found
in the afternoon hours.

Cheers
 



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