How does latitude affect the solar energy that reaches the earth?

At equator sun rays drop at a 90* angle  -  full power
at tropiques they drop at (90-23.5)*angle - ~70% power
at polar circles they drop at 23.5* angle - ~30% power
at poles it's just 0* that means they're tangent to ground -  0% power

(that's valid only at equinox)

the general idea is that the energy is proportional to cosy where y is the angle that sun rays make with the ground

the higher the latitude, the lower the angle => less energy