An old fogy's website
Not a trendy site. Just a dos dinosaur playing around.
Solar Panel Alignment
In early 2021, as noted in the "Solar Panel" blog article, I installed a solar panel and components for my house in Nicaragua. Noted in the same article was a javascript routine to calculate efficient noon-time angles for a solar panel.


Since our earth is tilted relative to her orbit around the sun, the noon sun strikes the earth at different angles at different times of the year. So, to optimize its efficiency, the solar panel should be adjustable so as to remain more or less perpendicular to the sun's rays. (fig.1)

Optimal Noon Angles

The angles in the sketches and noted below are for my house at 13° north of the equator. The base panel position for the equinox months March & September is 13° to the south of horizontal so as to face the noon sun at 13° south of vertical. For other latitudes, rotate the sketch so that this base position equals the latitude of your location. Everything else will work the same, relative to that base angle.

Note also that, as asserted in the later "Solar Panel Efficiency" blog article, absolute precision is not necessary. The angles used in design and fabrication need only stay within a few degrees of the ideal, keeping adjustments to a minimum. For this reason, the two solstice positions are only 21° from the base equinox position, not the full 23.5° of the earth's tilt. Thus 21° to the south of base (34° south of horizontal) works well from early November to early February. 21° to the north of base (8° north of horizontal) is good from early May through early August.

As to fabrication, it seemed simplest to support the panel in its base position (in this case, 13° to the south of horizontal), which works for the spring and autumn equinox seasons. Then hinge and elevate it on the north and south ends so as to attain the desired angles for other times of the year.

  fig.2  Position 3 is the base position; in this case 13 degrees to the south of horizontal. Hinged on the south end and elevated on the north end for positions 1 & 2. Hinged on the north and elevated on the south for positions 4 & 5. See table for date ranges and angles.
  Date ranges & angles:
positiondatesfrom basefrom horiz
17 nov - 6 feb21° S34° S
27 feb - 6 mar11° S24° S
37 mar - 6 apr013° S
47 apr - 6 may11° N2° S
57 may - 6 aug21° N8° N
47 aug - 6 sep11° N2° S
37 sep - 6 oct013° S
27 oct - 6 nov11° S24° S

These date ranges and angles are from the above mentioned javascript routine for my Nicaraguan latitude.

Morning & Afternoon Angles

The above sketches and geometrical calculations pertain to noon-time angles, and to seasonal adjustments. More importantly, of course, the sun rises in the east and moves west during the day. This movement is more familiar and easier to understand (no need for graphical figures). But adjusting the solar panel several times a day to face the sun is a bit more of an engineering challenge.

My current design is simply to mount the seasonal adjustment mechanism atop a semi-circular wheel, allowing it to roll from east to west to follow the sun from dawn to dusk. The key idea here is to align the rolling movement with the earth's axis of rotation, so that, as the earth rotates under the sun, the girasol rolls in the exact opposite direction, thus maintaining its position relative to the sun. This is achieved by raising one wheel of the mechanism according to the base angle mentioned above, which is also the site's latitude on earth. In my case, the mechanism is raised on the north end 13° from horizontal, to match the latitude of 13° north, and is thus aligned with the earth's axis of rotation.

As of April 2022, the rolling movement is manual. Am playing with some ideas on how to automate the daily movement with a stepper motor on a timer. May follow up with an update if/when am able to do this.

Field Photos

OK, applying the above principles: the girasol mechanism is fabricated from ordinary mild steel angles and tubes, and is oriented in the field according to compass points, and to the field latitude of 13° north of the equator. The rough stone support in photo 1 lifts the north track 13°. Photos 2 & 3 show how it is oriented according to compass points. Notice the timestamp of photo 2 (orange numbers at lower right, magnified photo): 11:44 am, which at this longtitude is high noon according to the sun (as opposed to clock time). This is the time of day when the sun is most directly overhead, so that in March a vertical stick casts a shadow directly to the north. Notice the construction string oriented in line with that shadow, thus defining a north-south line. Then in photo 3, another string at 90° defines east-west, the direction of sun movement.

The girasol mechanism is then placed on plastic tracks (to help keep the girasol oriented in an east-west direction as it rolls back and forth), with a little house to shelter the batteries, controller, and inverter. The seasonal adjustments are a simple matter of raising the north or south ends of the upper frame of the mechanism 11° or 21° with steel X braces.

1.  stone support  

2.  orient north-south  

3.  orient east-west  

4.  girasol mechanism  

5.  w/ battery house  

6.  batteries, etc.  

7.  panel & tracks  

8.  elevated (position 5)  

Here are 8 photos showing how the girasol mechanism can roll the panel to face the sun at various times of day, and can elevate the panel for the various seasonal positions (only 2 positions shown here). Click on the radio buttons for the time of day / season. Photos taken from a few feet northeast of the girasol, so east is to the left in the photo.

pos.3:    early    mid morning    mid day    late
pos.5:    early    mid morning    mid day    late

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Copyright (c) 2022-2022 Gerald DePyper
rev. 2022.06.13