[[email protected]]

Generally, it is recommended that fixed panels should be set so they
directly face the noon-day sun at the winter solstice, when sunlight is
scarcest.

That would maximize the output at noon, with lower outputs before and after.

With no ground reflection, an angle between the horizon and noon elevation
would maximize the daily output, no? Snow would favor more vertical tilts,
adding 0.5RIh(1-cosB) to the direct sun, where R is the ground reflectivity
(eg 0.6 for snow) and Ih is global horizontal radiation (eg 620 Btu/ft^2 vs
1000 for sun on a south wall (including a 0.2 ground reflectivity) on an
average January day in Phila), and B is the tilt up from horizontal. Snow
might increase the sun on a south wall from 1000 to 1000+0.5(0.6-0.2)620
= 1124 Btu/ft^2-day in January, ie 11 vs 90%.

... if the panels are closer to horizontal they will perform better in
summertime.

That might be good for a grid-tied vs standalone system.

Nick

 

[David Williams]

-> Moving on, Jack is at 37 degrees latitude, but for some reason has the
-> panels fixed at around 12 degrees. Anyone care to comment on
-> potentially why? I saw the response that suggested adjusting the
-> panels to 37 degrees. As a neophyte, I understand and agree that it
-> should be closer to 37 than 12. However, I remember that isn't the
-> latitude + or - 5 or 10 degrees recommended for some reason? I forget
-> exact details of this, but...hold that thought...

Generally, it is recommended that fixed panels should be set so they
directly face the noon-day sun at the winter solstice, when sunlight is
scarcest. The tilt of the earth's axis is about 23.5 degrees, so at the
(northern) winter solstice the sun's noon position in the sky is 23.5
degrees *south* of the equator. This means that the panels should be
inclined at an angle of L + 23.5 degrees from the horizontal, where L
is the local latitude. So at latitude 37 degrees North (actually, I
think the OP said he was closer to 38 degrees), the panels should be
inclined southward at an angle of 60.5 (or 61.5) degrees from the
horizontal, or about 29 degrees from the vertical.

A few degrees more or less than this won't make much difference and, if
the panels are closer to horizontal they will perform better in
summertime. So an inclination of 50 or so degrees from the horizontal
or 40 degrees from vertical is probably a good compromise.

dow

 

[Mel]

David Williams a écrit :

-> Moving on, Jack is at 37 degrees latitude, but for some reason has the
-> panels fixed at around 12 degrees. Anyone care to comment on
-> potentially why? I saw the response that suggested adjusting the
-> panels to 37 degrees. As a neophyte, I understand and agree that it
-> should be closer to 37 than 12. However, I remember that isn't the
-> latitude + or - 5 or 10 degrees recommended for some reason? I forget
-> exact details of this, but...hold that thought...

Generally, it is recommended that fixed panels should be set so they
directly face the noon-day sun at the winter solstice, when sunlight is
scarcest. The tilt of the earth's axis is about 23.5 degrees, so at the
(northern) winter solstice the sun's noon position in the sky is 23.5
degrees *south* of the equator. This means that the panels should be
inclined at an angle of L + 23.5 degrees from the horizontal, where L
is the local latitude. So at latitude 37 degrees North (actually, I
think the OP said he was closer to 38 degrees), the panels should be
inclined southward at an angle of 60.5 (or 61.5) degrees from the
horizontal, or about 29 degrees from the vertical.

A few degrees more or less than this won't make much difference and, if
the panels are closer to horizontal they will perform better in
summertime. So an inclination of 50 or so degrees from the horizontal
or 40 degrees from vertical is probably a good compromise.

dow

Jack gave us a pretty good hint in his email, he said his PV was for a
"summer cabin" so I would suggest that the best inclination will be one
that will maximise *summer* production. ie Something a lot flatter than
40 or 50°, and closer to the 15° to 30° range.



Mel

 

[[email protected]]

Generally, it is recommended that fixed panels should be set so they
directly face the noon-day sun at the winter solstice, when sunlight is

I am confused about which angle is being measured.
My panels are flat on a 6:12 pitch roof.
Are my panels at 26 degrees elevation, or 64 degrees elevation?
The installer's notes say 26 degree tilt.

http://solardat.uoregon.edu/SunChartProgram.html gives todays sun angle as
around 30 degrees max. On the basis of this chart, I would call my panels
"64 degrees".