Solar Tracker Code - how to limit steppers to max & min angle?
The only sure way is to use one or more position or limit switches. Steps can be lost (motor didn't move as commanded due to, f/ex, overload), the motor could be back-driven while powered down or if over-powered by the mechanical system, or your step counting could be faulty due to a bug or a power glitch.

At power-up or at any time your software thinks it might have got out of sync with the mechanicals, back into the limit switch at low speed (so you don't hard-crash), and reset your software counters, and reposition from there.