This is an unofficial expansion card to Power Grid published in the Spielbox magazine 1/2011 with approval of 2F Spiele. It appeared in the section "Besser Spielen" of the magazine and not as an "Edition Spielbox" game expansion. This means that the card is not included in the game, you get only rules and a picture of a possible card.
Every player can buy one of those cards for 10 elektros at any time of the game and place it next to the other power plants. The card does NOT count towards the maximum number of power plants allowed per player. If at any point after this player produces more energy than he needs, one energy point can be stored on this card for future use.