In the drawings of the earth below, the top drawings are a view of the earth looking directly down perpendicular to the plane of the earth's orbit, and the bottom drawings are side views.

The left drawings show the earth's tilt at the summer solstice, and the right drawings show the earth's tilt at the winter solstice.

The shaded area (away from the sun) represents night and the unshaded area (toward the sun) is day.

The red ellipse in the top drawings (which shows up as a short tilted line in the lower sideview drawings) is the path traveled by a point on the earth's surface at 41.5 degrees north latitude - which just happens to the the latitude of the DeSoto Solar shop.

The longer red line in the lower drawings is the earth's axis, an imaginary line from the north pole to the south pole.

Earth at summer and winter solstices

Now notice the short black lines in the lower drawings that stick straight up from the earth's surface. These represent side (edge) views of a vertically-oriented solar heating panel at noon.

In the lower left midsummer drawing the earth (and therefore the panel) are tilted so that the panel points almost directly at the sun. To an observer on the ground in DeSoto, the sun is nearly directly overhead. At this angle the glazing on the front of the panel acts very much like a mirror, and nearly all of the sunlight striking the glazing is reflected to the ground in front of the panel.

In the lower right midwinter drawing the earth (and therefore the panel) are tilted so that the panel is much closer to perpendicular to the sun's rays. To our DeSoto observer the sun appears much lower in the sky. At this angle the glazing on the front of the panel passes nearly all of the sunlight striking the glazing to the absorber in the panel.

Notice also in the midwinter drawing that if the ground in front of the panel is covered with snow, additional sunlight will be reflected into the panel - and energy reflected from fresh, clean snow can nearly double the amount if energy collected.

To sum all of this up, a vertical panel produces almost no heat at midsummer - and produces a maximum amount of heat at midwinter. It's completely automatic and the only moving part required is our planet!