Abstract: Apparatus and method are disclosed which include a string of units including at least two electrical energy producing units connected in series and providing string current. Each of the units is adapted to provide the electrical energy via output terminals. The apparatus further comprising a current equalization unit. The current equalization unit is adapted to individually control the magnitude and direction of current via that current equalization unit so that the algebraic sum of the current produced by its respective electrical energy producing unit when operated at a defined operational point and the current flowing via said current equalization unit equals to said string current. The operation of the apparatus enables transfer of energy from units with high production capacity to units with low production capacity without having to use a dedicated bus for that. The energy is transferred via the cabling of the string.