Electricity generation from so-called renewables does not work like a conventional fleet of power plants. Two gas-fired power plants with the same output can generate twice as much electricity as a single gas-fired plant. They are also capable of baseload operation and are largely dispatchable. Wind turbines, by contrast, do not produce according to demand, but according to the weather. Installed capacity can therefore rise while actual annual output grows only weakly or even stagnates.
Germany’s energy transition follows a seemingly simple arithmetic of expansion. More installed capacity is supposed to mean more electricity.
The calculation is as simple as it is wrong. That stark realization lies at the heart of a new debate about German wind power. Installed wind capacity has continued to grow substantially in recent years. Yet the additional electricity generated has fallen far short of what a linear projection would have suggested.
Output Matters More Than Capacity
The Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) reported for 2025 that wind power was the largest source of net electricity generation in the public grid, although output fell 3.2% from the previous year because of weaker wind conditions. Onshore wind supplied around 106 terawatt hours (TWh), while offshore wind generated around 26.1 TWh. Over the same period, 4.5 gigawatts (GW) of new onshore capacity were added, while offshore capacity increased by 0.29 GW.
The difference between nominal capacity and actual electricity generation is crucial. Nominal capacity describes only what a plant can produce at most under favorable conditions. Annual output describes what it actually delivers. That output depends on wind speed, location, turbine height, technical availability, grid connection and curtailment. Doubling installed capacity does not automatically double the amount of electricity generated.
Small Cause, Big Effect
In wind power, this difference is especially pronounced because output rises with the cube of wind speed. Small changes in wind therefore have major consequences for yield. A low-wind year can outweigh the effect of many newly built turbines, as happened in 2025. In Germany, good locations are also becoming increasingly scarce. New turbines are increasingly being built where land is available, not necessarily where wind conditions are best.
Wind farms can also interfere with one another. Wind turbines extract energy from the airflow. Behind a turbine, a wake forms with lower wind speeds and stronger turbulence. In large wind farms and densely developed regions, this effect can noticeably reduce the yield of downstream turbines. That applies both onshore and offshore.
Costly Curtailment
Germany faces an additional constraint. Not every kilowatt hour that could be generated reaches the market. Grid congestion means that plants have to be curtailed. Much of Germany’s wind power is generated in the north, while major consumption centers are in the west and south. When power lines are missing or overloaded, grid operators have to intervene. They reduce generation in one place and ramp up power plants elsewhere. These interventions are grouped under redispatch and feed-in management.
The Federal Network Agency publishes additional data on this through the SMARD platform. It records congestion management, redispatch, countertrading and the grid reserve. For the second quarter of 2025, SMARD reported measures totaling 5,856 gigawatt hours and preliminary costs of around €623m. Clean Energy Wire also reported that compensation costs for curtailing renewable energy still amounted to €435m in 2025. The decisive question is not how many plants exist, but whether the system of generators, grid and consumers can absorb, transport and use the electricity when it is produced.
The Merit Order Effect
The more often generation runs into grid congestion, the smaller the gain from each additional plant becomes. The effect is not constant. It depends on weather, regional distribution, grid expansion, consumption patterns, storage, export options and the use of flexible loads.
Alongside the grid problem, there is also a market effect. Wind and solar plants have very low variable costs. When they deliver large amounts of electricity at the same time, they push down the wholesale price. This mechanism is known as the merit order effect. For consumers and large industrial buyers, it can have a price-dampening effect in the short term. For the plants themselves, it means lower revenues precisely when they produce a lot. Wind and solar also tend to undercut one another in the power market.
When Renewables Cannibalize Themselves
Scientific studies, including a 2025 study published in the Journal of Environmental Management, have described this relationship. As the share of variable renewable energy grows, its market value falls relative to the average electricity price. Wind can cannibalize wind, solar can cannibalize solar and cross-cannibalization between the two can compound the effect. Solar power lowers prices during sunny hours and can therefore also depress wind revenues if turbines feed into the grid at the same time. Conversely, strong wind can weigh on the revenues of other generators.
The trend is most visible during hours with negative electricity prices. Negative prices arise when supply exceeds demand and producers are willing to pay others to take the electricity.
The Financial Times reported as early as 2024 that negative prices in Europe had reached a record level. For Germany, several market observers cited new highs in 2025. High wind and solar production is increasingly colliding with limited flexibility in demand, storage and grids.
Negative Prices
Negative prices show that the value of electricity depends on when it is produced. The more strongly production is concentrated in the same hours, the more sharply the market value of additional plants falls. At this stage in the expansion of renewable energy, adding further generation capacity no longer increases the value of the system. On the contrary, it creates high market risks. The system would then have to cope with severe fluctuations and surpluses at the same time.
For Germany, this means that the number of wind turbines or the total installed gigawatts offers only the appearance of progress in the energy transition. A full picture emerges only from the terawatt hours generated each year, the timing of generation, the location of feed-in and the price achieved at that moment. An additional wind farm can produce a great deal of power under good conditions. If it feeds into an oversupplied market, however, the result is often costly curtailment. That can leave further expansion with little practical effect.
A Transition Going in Circles
The debate over more wind power is becoming circular. Where policymakers begin to rely on load management and flexible consumption, central planning has already made its way into the electricity market. Yet it cannot provide the energy needed by an industrial society. The energy hunger of artificial intelligence has not even been factored in.
A serious assessment of efficiency also has to take account of the enormous land use of wind and solar compared with other energy sources. A nuclear power plant with an output of 1.7 GW, which also emits no carbon dioxide, requires 1–2 square kilometers of land. Producing the same amount of electricity would require around 5–7 GW of onshore wind power. Roughly calculated, that would correspond to 250–700 square kilometers of wind farm area, in some cases requiring large areas of forest to be cleared.