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What is the orientation of my house?

Discussion in 'Photovoltaics' started by [email protected], Dec 24, 2005.

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  1. Guest

    I want to know the orientation of my house.

    I happened to see that one wall of my house was oriented with the sun at
    2:55pm PST, 24 Dec 2005, at 38.8,-122.5.

    I know that Sunrise today was 7:26, at an azimuth of 120, and sunset will
    be at 16:53 at 240 degrees, according to heavens-above.com.

    A sweep of 120 degrees in 567 minutes is 4.725 minutes/degree.
    Sunrise, 120 degrees, +449 minutes to 14:55, (449/4.72)+120 = 215.

    Is it correct?

    My $5 compass indicated 218, after magnetic declination was taken into
    account.
     
  2. Guest

    Thanks for that. I thought it might not be linear, but I couldn't manage
    to form a Google search that would lead me to it.

    I suppose the non-linearity is because the altitude is changing throughout
    the day.
     
  3. you know. Solar orientation is not a rocket science.
    If you are within 15º of South your cool. esp. if you already own a
    place.
    A bigger concern might be trees blocking the sun.
    good luck, you're on the right path.
     
  4. SJC

    SJC Guest

    I would want a house with a patio cover facing south.
    (in the northern hemisphere of course) The 15 degree
    rule is a good one, but I would rather put my solar on
    a patio cover than my roof.
     
  5. Guest

    I looked at 5 degree swings in orientation, looking for the peak, but I
    actually didn't pay attention to how little difference there was.

    In California, where we get to push power back onto the grid at Time-of-Day
    retail rates, the orientation should be adjusted for maximum peak period
    performance. They tell me that is 225 degrees, 22 degree tilt for me.
    That would put direct sun azimuth at 3pm. The angle is based on their
    calculations for overall dollars of energy produced, not strictly watts, so
    it becomes a more difficult balance.

    But you are right. If there's already a place to put the panels, it
    becomes a choice of which location is best. I thought my 214 orientation
    wasn't so good for maximum power, but California is different.
    I suppose I went off on quite a tangent trying to figure out _exactly_ what
    the orientation was. It's not like I'm going to move the house, or put up
    a ground-mount installation.

    According to PVWatts:
    124 degree - 5220 kWh/yr one side of my house
    180 degree - 5637 kWh/yr south
    214 degree - 5512 kWh/yr the "west" side of my house

    Another annoyance, that I have no control over, is that I was looking at
    PVWatts, using a selection of "San Francisco". I should have been using
    "Sacramento", which is the right latitude. Those numbers are lower. ;-(
    http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/
    More of a difference there than shifting 34 degrees in orientation.
    214 degree - 5704 kWh/yr San Francisco.
    My nice big fat garage roof has a nice big fat tree next to it ;-)

    36 panels went up yesterday, some wiring is going on today.
    County building inspector on Monday, wait for PG&E to put in the
    Time-of-Day meter and do the cutover. I hope the sun is shining that day.
     
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