Left-luggage lockers in Granada:
It is possible to leave bags and luggage in the left-luggage lockers at the Bus Station. For information about how to get to the bus station, see http://granadamap.com/airport/bus_stops.htm

Click on the bus station balloon.
Buses 3 and 33 buses go to/from the bus station and stop on the Gran Via and Avenida de la Constitución

Also there are lockers at the Alhambra. It is free if you have bought a ticket. The luggage office is located outside and downstairs from the main ticket office..