Solar targeting reticle

Solar panels work best when pointed directly at the sun, but the exact angle can be difficult to eyeball. This device, attached to a panel with 2-sided tape, takes out the guesswork.

When the panel is off-angle, as in the second picture, the shadow of the arches will be off-center of the reticle on the base. When the shadow is brought in line with the reticle, as in the third picture, it means that the panel is perfectly orthogonal to the light source.