Control the use of A/C
Almost every hostel we have visited in Brazil has some way of controlling the use of the A/C. Either if it’s done manually from the reception where the power can be switched off during the day time, or the fuse for the air conditioner switches off and on automatically at set times.
At Aju Hostel in Aracaju they have found a clever way to insure that the A/C is not in use when the guests leave the room. On every room key they have attached a socket that simply completes the circuit, without the socket the power to the A/C is disconnected. As you can see on the picture below it really is a simple contraption, completely homemade, and it contributes to saving a lot of energy.