(1) At sundown, the robot will generate generous power and cooling by
orienting arrays toward the sun. The robot won't experience such low
angle in the morning, since landing doesn't occur for an earth-day after
lunar dawn. On the Tranquility Trek mission, the robot will experience
sundown, but not sunrise.

(2) At all elevations, power and cooling are adequate when the sun
impinges from the side or front quarter.

(3) At one earth-day before lunar noon, if the sun impinges from the
radiator end, then the robot will turn 180 degrees for better power and
cooling. This orients arrays generally toward the sun, and it orients
the radiator generally away from the sun. That does not dictate
direction of travel, since driving is bi-directional, and off-axis
driving azimuth is common. Half-turns are useful for maintaining
highest power-to-cooling ratio. Spinning makes no difference at lunar
noon, when the sun is top-down. When the sun is overhead, thermal loads
are highest, though cooling is still adequate, and solar power is
sufficient.

(4) Best power generation occurs when the robot is driving toward a sun
that is elevated mid-morning and mid-noon. In that configuration, solar
impingement illuminates the entire array, and much of that insolation is
at favorable incidence.

From AstroboticBlogPhotos