Sometimes it's the small screws you have to turn to change the big picture. This is also the case with the two wood-fired power stations of Holzwerke Weinzierl GmbH. Initially, as producers of electricity from renewable energies, they fired the energy transition with an output of over four megawatts. In the meantime, the power plants today also act as participants on the balancing energy market and compensate for grid frequency fluctuations within seconds.
But in order to be able to assume this responsibility for security of supply, adjustments were necessary. "Of course, you often hear 'That's not possible' when you want to change something," recalls Josef Brauneis, head of electrical engineering at Holzwerke Weinzierl. "In our case, however, only minor changes had to be made to the system hardware so that the bypass flaps for the silicone oil vapor react more quickly. After the parameters and the system control had been adjusted, the rest of the process ran smoothly. In the meantime the procedure has become the standard at our generator manufacturer - also for other customers".
In more than 300 deliveries of short-term balancing energy, the two power plants, for whose daily operation Josef Brauneis is responsible, have demonstrated that renewable energies can make their contribution to system stability by providing ancillary services to the TSO. They are ramped up and down via the Next Box telecontrol unit, which communicates via GPRS mobile radio with the central control center of the Virtual Power Plant Next Pool in Cologne. The duration of control reserve activations varies considerably depending on the grid situation. On some days, the balancing requirements of the transmission system operator last only a few minutes, but in rare cases they can also take up to 50 minutes. "At the start of the project, we mentioned the technical and organizational restrictions to Next Kraftwerke, such as the minimum capacity that must not be undercut. These parameters are now taken into account in the control system of the Virtual Power Plant, so that control reserve activations, which are passed on to us by Next Kraftwerke, can't even theoretically endanger the functionality of the plant" explains Josef Brauneis.
Holzwerke Weinzierl GmbH's motivation to become part of a Virtual Power Plant was also based on economic considerations. "Of course, we have an interest in operating our wood-fired power plants with optimum economic efficiency. The investment costs for the integration into the Virtual Power Plant are low and the necessary adjustments in everyday operation are manageable. And the additional revenues that we achieve through trading and balancing energy justify our participation. The fairness of Next Kraftwerke has also convinced us, for example when it comes to short-term schedule changes."