A high fence with the warning sign "High Voltage, Danger to Life!" stretches out. Behind it, there are poles, lines, and transformers as far as the eye can see. Such substations can be found far and wide across the country. Here, power lines from different sources come together, are transformed to a standard voltage of 110 kilovolts, and fed into the public electricity grid. It all comes down to simple physics: the higher the voltage, the lower the losses in transmission – and the longer the power lines. So, do the wind farms of Prokon also have to connect to a substation? The answer is: Not always – but more and more often. "In the older facilities, the electricity is usually fed into the medium-voltage grid through a small transfer station," explains electrical engineer Hauke Henningsen, who is responsible for network connections and data transmission at Prokon.
The medium-voltage grid provides a maximum of 15 megawatts of power. However, with the current wind farm projects having significantly increased rated capacities, this limit is quickly exceeded. "Then the system must be connected to a substation," explains Henningsen. This is also the case in Friedersdorf, Brandenburg. Prokon has obtained permission to build four wind turbines with a total capacity of 22 megawatts (4 x 5.5 MW).
The wind farm, which is expected to be operational in spring 2025, also includes a new substation with a capacity of 63 megavoltamps, equivalent to 63 megawatts. The additional reserves are necessary: Nearby, at the Podelzig-Lebus site, a repowering project involving six Nordex turbines, each with a capacity of 7 MW, is planned under the leadership of Prokon. Repowering involves replacing old wind turbines with new, more powerful ones. In this case, 14 AN Bonus turbines will be replaced.
"The substations of the grid operators hardly have any available capacity left. Therefore, we have to build the facilities ourselves."
Hauke Henningsen, Electrical engineer
"Theoretically, we could also feed the electricity from the wind farms into a nearby grid operator's substation," explains Henningsen. "Unfortunately, they hardly have any free capacities left. This can lead to us having to throttle down the power of our facilities during peak times." The topic of electricity feed-in will therefore become increasingly relevant in the future. 90 percent of repowering projects connect to the high-voltage grid. Therefore, Prokon will have to build its own substations more frequently - and thus contribute a part to the urgently needed grid expansion.
In practice, this also means more bureaucracy in project planning, as the approval procedures for building a substation are more complex than for constructing a simple transfer station. However, the financial planning is seen as the bigger challenge. The costs for building a substation have recently increased to up to five million euros. Three years ago, it was still 1.5-2 million euros. "This means that we have to calculate differently in tenders," says Henningsen. The reasons for the price increase are diverse: increased demand due to intensive grid expansion, higher raw material prices, and supply chain bottlenecks following the destruction of a steel plant in Ukraine."
Prokon already operates ten of its own substations. The technically complex facilities are planned and constructed by the Saxon company WT Energiesysteme – including the one in Friedersdorf, whose construction is set to begin in July. Another substation is being built simultaneously in Nadrensee, where Prokon has been awarded the contract for a 28 MW repowering project. “At both sites, air-insulated switchgear is being installed, which does not require the climate-damaging gas SF6,” emphasizes Prokon expert Henningsen.
For optimal energy yield, Prokon will also rely on storage technology alongside substations. For the first time, Prokon is using such a power terminal in the new Solar Park Walshausen (Image). However, storage solutions for wind parks are more technically challenging. In the region, Prokon is also planning a stand-alone battery storage system that will also be connected to the substation. So far, they are still looking for a suitable manufacturer to tackle this innovative project alongside the energy cooperative.
Prokon will pioneer here and gain practical experience in dealing with battery storage. Storage is necessary to fully utilise the wind energy installations even during peak times. Excess electricity will then charge the battery modules - to be fed back into the grid at a later time. It is already clear: "In order to optimise the grid connection point, we must consider storage systems in the future," says Henningsen."
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