Distances between wind turbines

After more than fifteen years of participating in the planning and implementation of wind farms in Spain, even today (and despite the uncertain situation experienced by renewable energies, including wind power) they continue to ask us this question: At what distance do we place wind turbines from each other? Our answer is immediate, not so when the question is What regulations are there in this regard? And here is the problem, since the solution we offer is the result of the experience accumulated in the wind farms in which we have participated. But as they say that Better late than never, we analyze here the different information flows in terms of distances between wind turbines and alignments and the reason for these regulations.

We started with the Endesa Red Chair, where Óscar Alexis Monzón Alejandro, in his project”Design of a 20 MW Wind Power Plant” indicates that the distance between wind turbines in the same row shall never be less than two rotor diameters and, between wind turbines in one row and the other, there will always be a distance greater than eight diameters. The reason for these minimum distances is to minimize the Shadow effect of some wind turbines over others. We already have here the first reason: avoid this shadow effect.

Charles Meneveau, a student of fluid dynamics at Johns Hopkins University, developed a model to calculate the optimal space between turbines in order to obtain the largest yield in large wind farms of the future, thus, using large scale computer simulations and small scale experiments in wind tunnels for 5 megawatt wind turbines, he concluded that the optimal space between the turbines should be approximately 15 times the diameter of the rotor, incredible distance for an incredible 5 MW where we've almost talked about offshore.

Technical Applications Notebook No. 12. ABB wind power plants indicate that wind turbines must be located at an appropriate distance between them to avoid aerodynamic interference and, with them, their two most serious consequences: increased turbulence and loss of power... the optimal separation is between 8 and 12 times the diameter of the rotor in the direction of the wind, and between 2 and 4 times in the direction perpendicular to the wind.

As can be seen, words such as shadow effect, performance, power loss, etc. We could fill pages and pages on the analysis of the distance between machines from the point of view of efficiency. However, until now distances have not been treated from an environmental perspective, but only from this prism of wind efficiency, a fact that, although important, is not what concerns us.

We are continuing to dive into scientific publications and texts and finally some regulations in this regard: Decree 32/2006, of March 27, which regulates the installation and operation of wind farms within the Autonomous Community of the Canary Islands. In its Article 25 it talks about the distances from wind turbines to homes or other wind turbines; and more specifically, in its heading 2, it indicates that the minimum distance between two wind turbines on the same line shall not be less than two (2) rotor diameters. The distance between two lines in the same park must be at least five (5) rotor diameters. This regulation does not seem to be due to performance reasons but neither (we believe) to environmental issues.

Reviewing various Environmental Impact Statements of wind farm projects in which we have participated (54 to be more exact), we found that the limitations that are established vary by autonomous community and even by province. However, the rule of separating wind turbines in the same alignment, three times the length of the rotor diameter and seven times that length between alignments, predominates. When these ratios are reflected in the Environmental Impact Statements, we can think that they may be the closest thing to an “environmental standard”, however, we have always believed that the scientific basis for this is diffuse and that this criterion is probably born from the first analyses presented: the purely technical ones and that therefore do not answer our questions.

We are still trying to shed some light on the issue, for which we reviewed the vast existing documentation on wind farms and environmental impact, and we did not find a faunistic criterion that defines distances between solvent wind turbines to reduce the impact of so-called “wind farms”. We also reviewed the recent publication: Understanding bird collisions at wind farms: An updated review on the causes and possible mitigation strategies, who mentions, in the section dedicated to the morphology of wind farms, that the position of wind turbines within an alignment did not influence the mortality rate of griffon vultures in Tarifa (De Lucas et al., 2012). It also describes that it is currently necessary to consider that the distance between machines must be greater due to their larger dimensions (we are already talking about ordinary 3 MW machines with rotors of up to 125 m). And that what birds once perceived as impenetrable walls now, due to the necessary distances, do not seem so much so. In fact, in Greece, it was found that the longer the distance between wind turbines, the greater the probability that raptors would attempt to cross the space between them (Cárcamo et al., 2011)

In short, and regardless of efficiency, we must say that we do not find clear environmental criteria that indicate the best distance between wind turbines and between alignments depending on the diameter of the rotor. Although it is true that the experience accumulated in environmental monitoring during the exploitation phase and these general guidelines described should continue to govern the decisions of designers, managers and evaluators, without prejudice to the fact that the present reopens the debate and we obtain references unknown to us and in the meantime we add this utility to the post published in 2015 so that you can check the compliance of the machines you consider.

After more than fifteen years of participating in the planning and implementation of wind farms in Spain, even today (and despite the uncertain situation experienced by renewable energies, including wind power) they continue to ask us this question: At what distance do we place wind turbines from each other? Our answer is immediate, not so when the question is What regulations are there in this regard? And here is the problem, since the solution we offer is the result of the experience accumulated in the wind farms in which we have participated. But as they say that Better late than never, we analyze here the different information flows in terms of distances between wind turbines and alignments and the reason for these regulations.

We started with the Endesa Red Chair, where Óscar Alexis Monzón Alejandro, in his project”Design of a 20 MW Wind Power Plant” indicates that the distance between two wind turbines in the same row shall never be less than two rotor diameters and, between wind turbines in one row and the other, there will always be a distance greater than eight diameters. The reason for these minimum distances is to minimize the Shadow effect of some wind turbines over others. We already have here the first reason: avoid this shadow effect.

Charles Meneveau, a student of fluid dynamics at Johns Hopkins University, developed a model to calculate the optimal space between turbines in order to obtain the largest yield in large wind farms of the future, thus, using large scale computer simulations and small scale experiments in wind tunnels for 5 megawatt wind turbines, he concluded that the optimal space between the turbines should be approximately 15 times the diameter of the rotor, incredible distance for an incredible 5 MW where we've almost talked about offshore.

Technical Applications Notebook No. 12. ABB wind power plants indicate that wind turbines must be located at an appropriate distance between them to avoid aerodynamic interference and, with them, their two most serious consequences: increased turbulence and loss of power... the optimal separation is between 8 and 12 times the diameter of the rotor in the direction of the wind, and between 2 and 4 times in the direction perpendicular to the wind.

As can be seen, words such as shadow effect, performance, power loss, etc. We could fill pages and pages on the analysis of the distance between machines from the point of view of efficiency. However, until now distances have not been treated from an environmental perspective, but only from this prism of wind efficiency, a fact that, although important, is not what concerns us.

We are continuing to dive into scientific publications and texts and finally some regulations in this regard: Decree 32/2006, of March 27, which regulates the installation and operation of wind farms within the Autonomous Community of the Canary Islands. In its Article 25 it talks about the distances from wind turbines to homes or other wind turbines; and more specifically, in its heading 2, it indicates that the minimum distance between two wind turbines on the same line shall not be less than two (2) rotor diameters. The distance between two lines in the same park must be at least five (5) rotor diameters. This regulation does not seem to be due to performance reasons but neither (we believe) to environmental issues.

Reviewing various Environmental Impact Statements of wind farm projects in which we have participated (54 to be more exact), we found that the limitations that are established vary by autonomous community and even by province. However, the rule of separating wind turbines in the same alignment, three times the length of the rotor diameter and seven times that length between alignments, predominates. When these ratios are reflected in the Environmental Impact Statements, we can think that they may be the closest thing to an “environmental standard”, however, we have always believed that the scientific basis for this is diffuse and that this criterion is probably born from the first analyses presented: the purely technical ones and that therefore do not answer our questions.

We are still trying to shed some light on the issue, for which we reviewed the vast existing documentation on wind farms and environmental impact, and we did not find a faunistic criterion that defines distances between solvent wind turbines to reduce the impact of so-called “wind farms”. We also reviewed the recent publication: Understanding bird collisions at wind farms: An updated review on the causes and possible mitigation strategies, who mentions, in the section dedicated to the morphology of wind farms, that the position of wind turbines within an alignment did not influence the mortality rate of griffon vultures in Tarifa (De Lucas et al., 2012). It also describes that it is currently necessary to consider that the distance between machines must be greater due to their larger dimensions (we are already talking about ordinary 3 MW machines with rotors of up to 125 m). And that what birds once perceived as impenetrable walls now, due to the necessary distances, do not seem so much so. In fact, in Greece, it was found that the longer the distance between wind turbines, the greater the probability that raptors would attempt to cross the space between them (Cárcamo et al., 2011)

In short, and regardless of efficiency, we must say that we do not find clear environmental criteria that indicate the best distance between wind turbines and between alignments depending on the diameter of the rotor. Although it is true that the experience accumulated in environmental monitoring during the exploitation phase and these general guidelines described must continue to govern the decisions of designers, managers and evaluators, without prejudice to the fact that the present reopens the debate and we obtain references unknown to us.