Proteinoid microspheres are stable hollow spheres of diameter of the order of 5 microns. Their stability is discussed in terms of macroscopic energies. It is shown that bulk and surface energy contributions alone cannot lead to stable microspheres. If electrostatic energy, due to transmembrane voltage, is taken into account, stable hollow spheres are proved to exist. For several reasons, however, this result should not be regarded as the ultimate explanation of microsphere stability.