It's all about the cosine of the angle between the panel's normal and the direction toward the sun. If that angle is 0, the cosine is 1 and you get maximum effi

It's all about the cosine of the angle between the panel's normal and the direction toward the sun. If that angle is 0, the cosine is 1 and you get maximum efficiency. The error angle has to increase to 60 degrees before the cosine decreases to 0.5. Meaning you can tolerate a lot of slop before you lose half your output. Trackers were a big deal when PV panels were 10x or 20x more expensive than they are now. Back then every bit of added efficiency was worthwhile. Not so much now. Edit: It's more complicated than this: You have to compute two cosines (azimuth and elevation) and average over both days and seasons, but the basic point is still true.