EC_i^t = \alpha * altitude_i^t, computed as the potential energy of an object (mass*gravity*height) (less realistic)

EC_i = (\beta + \alpha*h_i)*\Delta t + P_{max}*h_i/U, where \alpha and \beta are motors coefficients, \Delta t is the amount of time the drone
i will stay at altitude h_i, P_{max} is the maximum power of the motors, and U is the vertical speed of the drone. (\beta + \alpha*h_i)*\Delta t
corresponds to the energy needed to maintain the drone at altitude h and P_{max}*h_i/U is the energy needed to rise the drone at the same altitude
(more realistic).