Extraction energy from charged Vaidya black hole via the Penrose process

In this paper, we consider the analogy of the Penrose process in charged Vaidya spacetime. We calculate the border of the generalized ergosphere, in which the charged particles with negative energy might exist, and show that it is temporary. We show that there are no closed orbits for particles with negative energy inside the generalized ergosphere. We investigate the question about the efficiency of the Penrose process and show that one cannot extract large energies from a black hole if the velocities of ingoing and outgoing particles are of the same order. In the case of the extremal black hole, we show that the upper limit is restricted by the absolute value of the electric charge per mass.