How wind farms slow each other down

Nor is wind an inexhaustible source of energy, the researchers explain: Using offshore farms in the North Sea, they show how surprisingly much systems slow down the wind. As a result, electricity efficiency can suffer significantly: according to modeling, the shadow effect can reduce the efficiency of neighboring wind farms by up to 25%, especially in stable weather conditions. The researchers say the results could now pay off in terms of optimizing the use of the area’s limited potential.

Wind energy has become an important component of the renewable energy energy mix. So-called offshore wind farms are considered particularly efficient: more and more countries are building sometimes huge offshore systems to get their energy from the mostly constant air flow. The expansion of wind power in the German Gulf and the Baltic Sea has also led to considerable success: today wind turbines with a capacity of around 8,000 MW are rotating there, which is the equivalent of around eight nuclear power plants. You’d think you could just put up more wind turbines there. Unfortunately, the power of the wind is not as inexhaustible as it seems: the rotors slow the flow of air and can thus take away the propulsion of the next one.

Shadow effect in view

Due to this well-known braking effect, individual wind turbines in offshore installations are positioned at a minimum distance from each other. It is also known that wind farms also have a great influence on air currents due to the shadow effect and therefore can affect neighboring systems. As location options are limited and wind farms are sometimes built as close together as possible, it is important to evaluate this effect and its impact on the profitability of the plant. Scientists from Naveed Akhtar at the Helmholtz Hereon Center in Geesthacht have now dedicated themselves to this research topic.

For their research, they used a modeling system for the entire North Sea that includes data from weather services. This allows you to break down the weather situation in the region in detail and calculate how the weather and climate or wind conditions behave. Data on the location and dimensions of existing and planned wind farms in the North Sea were then included in the calculations. Researchers used 2015 North Sea planning as a basis. This also includes wind farms, some of which have yet to be built. The study therefore looks ahead – to some extent towards the target status of maritime expansion.

Braking effect under stable weather conditions

The results show how extensive the braking effect can be: on average, it ranges from 35 to 40 kilometers – up to 100 kilometers under certain weather conditions, scientists say. This can reduce the production of a neighboring wind farm by 20 to 25 percent, ultimately translating into economic losses. However, it depends on the season, as the results clearly show: the braking effect of wind farms is very large, especially in stable weather conditions – when there is little turbulence in the atmosphere. This is especially true in March and April. In turbulent times – especially in November and December – the atmosphere is so varied that, according to model simulations, the shadows of the wind farms are insignificant. Scientists were then able to confirm that the theoretical results were accurate by comparing them with wind measurements from two North Sea research platforms in 2008-2017.

As they emphasize, the peculiarity of the work is that the full ten-year period was calculated for the first time for the entire North Sea: “Traditional flow models for wind farm analysis have very high spatial resolution, but only consider the wind field over short periods of time,” says Akhtar. “In addition, it cannot be used to determine how a wind farm changes airflow over a large area.” Scientists have managed to do so. The results are important for wind energy development in Germany and can now be used in expansion planning or in energy loss assessment arranged wind farms.

In further research, scientists now want to focus on the ecological effects of coastal parks’ shadow effects caused by deterioration in energy efficiency. Because wind and waves mix the sea, thereby changing the salt and oxygen content of the water, as well as its temperature or the amount of nutrients at certain depths. “We now want to find out how limited mixing affects marine life,” says Akhtar.

Source: Helmholtz-Zentrum Hereon, technical article, scientific reports, doi: 10.1038 / s41598-021-91283-3

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