# Pop Quiz for Solar Professionals

Discussion in 'Photovoltaics' started by [email protected], Mar 11, 2005.

1. ### Guest

Pop Quiz for Solar Professionals (i.e. architects, interior designers,
landscape architects, builders, developers, HVAC engineers, energy experts,
and teachers of all of the above.)

You are a star if you get at least 10 right.
You are a moon if you get at least 5 right.
If you didn't get as many right as a solar professional should,
maybe you should get a conceptually clear heliodon.

Note that all questions refer to the northern hemisphere.

1. How many days per year do sunrays hit the north side of a building?

2. How many days each year does the sun rise due east and set due west?

3. How many days per year are there 12 hours of daylight and 12 hours of
darkness? Is that true for all degrees latitude? What are the exceptions?

4. How many degrees north of east does the sun rise on June 21?

5. What is the furthest north in degrees that the sun ever rises
in the northern hemisphere? Where?

6. What is the least north that the sun ever rises in the northern
hemisphere on June 21? Where?

7. How far south do you have to go so that the sun is directly overhead
on June 21 at 12 noon?

8. Does the sun always rise and set everywhere in the northern hemisphere?

9. What is the change in degree altitude from 12/21 to 6/21 at 12 noon?

10. What is the change in degree altitude from month to month?

11. Does the sun ever rise due south anywhere in the northern hemisphere?
Where and when?

12. On the equator, the sun is strongest on which day(s)?

13. At the equator, is it more important to shade the south wall
or the north wall?

14. What is the best shading system for north walls? (Circle answer)
a) Vertical fins b) Horizontal overhangs c) Combination of A & B

15. A certain south window has an overhang that is as wide as the window and
long enough so that even the December 21 noon is shaded. How long each day
is the window shaded before being outflanked by the sun?

From Norbert Lechner via the SBSE list...

Nick

2. ### CosmopoliteGuest

At my house, or at yours ?
It rises in the east, everywhere
It rises in the east, at my house
I don't have that much time to fly the hot air balloon
Depends on how high you want to go.
Days without clouds.
Which part of the equator is the northern hemiphere?
Lack of reflective surfaces on north side.
Need vector of " long ".

3. ### daestromGuest

Oh, sure, what the heck. But I'm 'shooting from the hip' here without
looking anything up.
This would be half the year regardless of hemisphere. Although near the
equinox's it just *barely* touches, at a very oblique angle, the side facing
the nearest pole.
The general answer would be two, the spring and fall equinox. But if
measured down to the second, that's only true along a particular great
circle around the planet at the exact moment of the equinox.
Well, in the continental US, 2 days a year (the equinox). Exactly on the
equator, every day. Depending on how exact you want to measure '12 hours of
daylight', locations near the equator see very little variation through the
seasons. And of course at the pole the sun doesn't set/rise on the equinox.
That varies with the latitude. At the equator, the sun rise is 23.5 degrees
north of east (the inclination of the planet's axis with the orbit around
the sun). At latitudes higher than the artic circle, it doesn't set so it
doesn't rise.
At the artic circle, the sun grazes the horizon on the summer solstice. So,
moving south from there a short distance you would find a latitude where the
sun rises and sets due north.
Just at the equator, it rises just 23.5 degrees north of east.
The Tropic of Cancer. (latitude ~23.5 N)
No, north of the artic circle the sun doesn't 'set' in the summer.
Similarly, the sun doesn't 'rise' during the winter. How many days of
'midnight sun' you have depends on exactly how far north of the artic
circle.
Of the sun? About 46 degrees, the same as the difference in latitude from
the Tropic of Cancer to the Tropic of Capricorn.
Various with which month. The most in March and September.

At the artic circle, at the winter solstice the sun *just* 'rises' to the
horizon, due south.
The two equinox. It rises due east, travels directly overhead and sets due
west.
Well, strictly from an astronomical point, the planet is closer to the sun
in December, so that would mean the south wall should be shaded first. Of
course, the local climate (rainy season) may override that.
In the northern hemisphere? Far north, the only sun that strikes the north
walls is early morning and late afternoon. So vertical fins would be
'best'.

At latitudes closer to the equator in the summer, the sun shines on the
north side for longer periods of the day (south of the Tropic of Cancer, it
strikes the north wall the entire day 1/2 the year). So very low latitudes
the horizontal overhangs would be better. Obviously, in mid latitudes, a
combination would be best.
It is only *completely* shaded when the sun is due south. So from sunrise
to sunset, at least a portion of the window is exposed to sunlight all day
except exactly at local noon. (at least whenever the sun is south of due
east and west)

daestrom

4. ### Guest

(i.e. architects, interior designers, landscape architects, builders,
developers, HVAC engineers, energy experts, and teachers of all of the above)

You are a star if you get at least 10 right.
You are a moon if you get at least 5 right.

If you didn't get as many right as a solar professional should,
maybe you should get a conceptually clear heliodon.

Note that all questions refer to the northern hemisphere.

1. How many days per year do sunrays hit the north side of a building?
182... half the year the sun rises north of east and the other half
it rises south of east.

2. How many days each year does the sun rise due east and set due west?
2 days... only on the equinoxes.

3. How many days per year are there 12 hours of daylight and 12 hours of
darkness? 2 days... the equinoxes.

Is that true for all degrees latitude? No.

What are the exceptions? At the equator, all days are 12/12,
and at the poles the answer is zero. At the poles, there are 24 hours
of sunlight each day for 6 months and 24 hours of darkness for the other
6 months. On the equinoxes the sun sweeps the horizon half above and half
below the whole day. Thus, on those days there are 24 of sunset (sunrise).
Wouldn't that be a great place and time for a honeymoon?

4. How many degrees north of east does the sun rise on June 21?
Varies with latitude.

5. What is the furthest north in degrees that the sun ever rises in
the northern hemisphere? Where? The sun rises 90 degrees north of east
(due north) on June 21 at midnight at the arctic circle.

6. What is the least north that the sun ever rises in the northern
hemisphere on June 21? Where? At the equator the sun rises 23.5 north of east.

7. How far south do you have to go so that the sun is directly overhead on
June 21 at 12 noon? The Tropic of Cancer.

8. Does the sun always rise and set everywhere in the northern hemisphere?
No... not above the Arctic Circle.

9. What is the change in degree altitude from December 21 to June 21 at 12
noon? 47...

10. What is the change in degree altitude from month to month? Varies!
The most change occurs around the equinoxes and the least around the solstices.

11. Does the sun ever rise due south anywhere in the northern hemisphere?
Where and when? Yes... On December 23 at the Arctic Circle the sun will
rise and set due south within minutes of each other.

12. On the equator, the sun is strongest on which day(s)? equinoxes - on
those 2 days the sun passes directly overhead. At the equator there are two
summers and two winters. [But the earth and sun are closest in January--Nick]

13. At the equator, is it more important to shade the south wall or the
north wall? Both equally! The sun shines symmetrically on north and south

14. What is the best shading system for north walls in the United States?
a) Vertical fins b) Horizontal overhangs (a)

15. A certain south window has an overhang that is as wide as the window and
long enough so that even the December 21 noon is shaded. How long each day
is the window shaded before being outflanked by the sun?

One instant before noon the overhang is outflanked from the east and after
12 noon it is outflanked from the west. This situation is most critical on
tall narrow windows. The solution is to either extend the overhang beyond
the window on each side or to use fins on each side.

From Norbert Lechner...

Nick

5. ### daestromGuest

Actually it's valid up to the pole. Even in mid latitudes, the sun rises
north of due east for 1/2 the year.

But as you say, at the pole there is no 'north side' ;-)

daestrom

6. ### daestromGuest

Given that the earth and sun are closest in January (as per your previous
annotation), there is a slight advantage to shading the south wall over the
north (if you can only shade one)

daestrom