Barcelona Airport has two left luggage offices. One is in the terminal T2B hall, beside the arrivals area, and other office in terminal T1.
It is a payment service and you will have to choose among three types of lockers, according to the size of the luggage which you want to leave. The prices are the following ones:
Small (35cm x 80cm x 45cm) 3,80 € day (24 horas) or fraction.
Medium (35cm x 80cm x 60cm) 4,40 € day (24 horas) or fraction.
Big (50cm x 80cm x 90cm) 4,90 € day (24 horas) or fraction.
If you need to travel with a very big or voluminous object, and you want to leave something here several weeks, there is the storehouse service. This service cost 1,97 €/ day, but you have to pay first the transfer from the left luggage office to the storehouse 39,34 €. Other economic option is rent a mini storage room from 1 euro per day.