Photogalvanic Cells and Where to Aim Them

Photogalvanic Cells and
Where to Aim Them

Earth tilts 23.44 degrees on its axis (north-south) in relation to celestial north / the ecliptic. The result is that while the Sun still appears to rise in the East and set in the West, throughout the year it will also appear to crawl a bit North and a bit South. Since Earth's tilt is 23.44 degrees, the Sun's apparent movement North and South will be 23.44 degrees. To get the most out of a photogalvanic power cell, it "should" be aimed directly at the Sun: to do this, one must know one's geographic latitude, and the season.

Here is a drawing of the planet Earth showing the aproximate tilt. As the Earth rotakes on its axis, the Sun will appear to rise in the East and set in the West--- therefore in this image the earth would be rotating counter-clockwise. The yellow line indicates the solar ecliptic: the direction the Sun will appear in the sky over the horizon. Note that the solar ecliptic (yellow line) is 23.44 degrees from Earth's equator (west-east line).

To show why the Sun appears to move North and South of Earth's equator, two more images, showing Earth on opposite sides of the Solar System, are here presented. In the first image we see Earth at the Summer Solstice: the Sun appears to be at its farthest North. In the second image, the Sun appears to be at its farthest South. If one now imagines Earth in orbit around the sun, one can see that as Earth appears to pass "behind" the sun, the Sun will appear to creep closer to the euquator; when the Sun is directly "behind" Earth, it will appear to be directly on the equator--- this is called the Fall Equinox. As the Sun appears to come out from "behind" Earth, it will appear to creep Southward. When the Sun appears to be directing "in front of" Earth, it will again appear to be on the equator--- this is the Spring Equinox.
Keep in mind that even though this cycle takes one entire year, Earth is still rotating on it axis once a day. We therefore get the Sun rising and setting, creeping North or South a bit every day (depending on the season of the year).

This image shows Earth on one side of the Solar System: since the Northern Hemisphere is tilted towards the Sun, the Sun is in its apparent Northern Latitude: it is Summer in the North on Earth, and Winter in the South.

Now the image shows Earth on the other side of the Solar System: Earth's Southern Hemisphere is now tilted towards the Sun--- it is Winter in the North on Earth, and Summer in the South.

S 22.70 1-Jan-01

S 16.19 1-Feb-01

S 6.40 1-Mar-01

N 4.57 1-Apr-01

N 15.17 1-May-01

N 21.92 1-Jun-01

N 23.16 1-Jul-01

N 18.48 1-Aug-01

N 8.961 1-Sep-01

S 2.45 1-Oct-01

S 13.48 1-Nov-01

S 21.32 1-Dec-01

This table shows the Sun's apparent latitude throughout the year. The graph was plotted using 377 data points, so it is an accurate representation of the apparent motion day by day. Therefore this graph shows the apparent North-South movement of the Sun.

Throughout the year the Sun changes the times it appears to rise in the East and set in the West. In this graph I have plotted, using a nautical almanac, 377 data points for both the rising and setting of the Sun. The times were calculated for the geographic latitude near Los Angeles California USA, at 35 degrees North. (Another image is via this link.)

What this tells us is that there are two apparent solar motions we need to be aware of in order to aim a solar panel directly at the sun: a daily motion, and a seasonal motion. If one wants the best production of electricity from one's solar panels, one will wish to have one's solar panels track the sun.
The problem is that for the daily movement, this would require constant adjustment--- it requires a motor to move the panels every few minutes as the sun appears to cross the sky from East to West. If one does not wish to install a motor and electronic tracking system, one will have to ignore this daily motion. This means that the solar panel will not produce the wattage at which it has been rated.
One may still tilt the photogalvanic power cell towards the sun on the seasonal cycle, by manually adjusting the tilt at the start of every month. The table to the right shows the aproximate solar latitude at the start of every month. One may use this table to calculate the degree of tilt one needs to have the panel face the sun. One must know one's geographic latitude to make this calculation.

One example: Los Angeles is located at about 35 degrees North of the equator. To have the solar panel face the Sun on January First when living in Los Angeles, one must add 22.70 degrees to 35 which is 57.70 degrees. Since laying flat on the ground means the panel is tilted 0 degrees, one must pick up the edge of the solar panel and tilt it towards the sun 58 degrees to have the panel aimed properly. As the sun appears to move north, the tilt of the panel should decrease; around Summer the Sun will be at its farthest North latitude, so the tilt will only be about 12 degrees (almost laying flat). The Seasonal tilting for January would therefore be 58 degrees. To add the diurnal (daily) tilt, one must aim the panel towards the East in the morning, straight up in the afternoon, and to the West in the after-noon.

To show why the Sun appears to move North and South of Earth's equator, two more images, showing Earth on opposite sides of the Solar System, are here presented. In the first image we see Earth at the Summer Solstice: the Sun appears to be at its farthest North. In the second image, the Sun appears to be at its farthest South. If one now imagines Earth in orbit around the sun, one can see that as Earth appears to pass "behind" the sun, the Sun will appear to creep closer to the euquator; when the Sun is directly "behind" Earth, it will appear to be directly on the equator--- this is called the Fall Equinox. As the Sun appears to come out from "behind" Earth, it will appear to creep Southward. When the Sun appears to be directing "in front of" Earth, it will again appear to be on the equator--- this is the Spring Equinox. Keep in mind that even though this cycle takes one entire year, Earth is still rotating on it axis once a day. We therefore get the Sun rising and setting, creeping North or South a bit every day (depending on the season of the year).
	This image shows Earth on one side of the Solar System: since the Northern Hemisphere is tilted towards the Sun, the Sun is in its apparent Northern Latitude: it is Summer in the North on Earth, and Winter in the South.
	Now the image shows Earth on the other side of the Solar System: Earth's Southern Hemisphere is now tilted towards the Sun--- it is Winter in the North on Earth, and Summer in the South.