Interview by Rikki Stancich

As the US wind energy market matures, developers are being forced to site their projects in rugged terrain as the number of undeveloped, less complex sites dwindles.

Rugged, forested terrain introduces a host of issues relating to increased wind speed, turbulence and wind behaviour that can make turbine siting and installation a very costly exercise.

To address this issue, France-based wind modeling and climatology software developer Meteodyn has developed a CFD software for wind resource assessment in complex terrain, called Meteodyn WT, which has been adopted and endorsed by US wind energy consultant, EAPC.

Wind Energy Update speaks to Jay Haley, engineer and partner at EAPC, to learn more about the challenges associated with siting wind farms in rugged terrain, and how tools such as Meteodyn’s can ease the process.  

Wind Energy Update: To what extent - and where - are we seeing the development of more complex sites?

Jay Haley: What is happening in the US is that the less complex sites are getting developed so the choices are limited and developers are having to go to the complex sites by default. In the North East, for example, you have a higher population density but the question is how and where to site?

Wind Energy Update: How would you classify 'complex terrain'?

Jay Haley: Complex sites are not as flat – it is more rugged terrain, steeper with hills and slopes and often in proximity to forested areas. This contrasts with the plains of the Midwest where you have prairies.

Wind Energy Update: What tools are required to identify good sites in complex terrain?

Jay Haley: In less complex terrain, the standard tools are used. WAsP is the model that has been used for the last twenty years. It’s a well-known proven model. However, it is a linear model, so it can’t pick up second or higher order effects. Meteodyn’s, on the other hand, can model second order or higher effects.

So when a developer looks at putting up a wind farm in complex terrain, you need a model to identify where the wind resource is best, but where it is not too turbulent. Meteodyn can help determine where the turbulent spots are, which can overload the turbine and lead to early failure.

Wind Energy Update: What are the main challenges associated with identifying sites in complex terrain?

Jay Haley: It is all down to predicting wind speed and turbulence intensities across sites, and predicting the inflow angles of the wind. A slope changes the angle of the wind as it hits the turbine rotor, which in turn, has an effect on the turbine loading and production.

Wind Energy Update: How can wind-modeling tools like Meteodyn assist developers in the site selection process in such an environment? 

Jay Haley: Higher turbulence and increased loads leads to early failure. This means that O&M costs are higher, while production from the turbines is lower if they are sited incorrectly.

It is more difficult to identify the optimal sites for turbines in complex terrain, but tools like Meteodyn enable you to select sites where the load is manageable. You want to maximise production and minimise loads – it’s a balance.

Wind Energy Update: How much more costly and challenging is it to develop wind farms in complex terrain?

Jay Haley: The cost of developing wind farms on complex sites is higher. You have fewer options on things like road access to the turbines and underground cable trenching routes, because the physical terrain features force you to route in other directions i.e. not necessarily the shortest path.

It is also difficult to move large equipment when you have such limited access, so a big question is: “how do you get the equipment to site?”

But if the turbines are positioned in the right location where the cost of electricity justifies the installation cost, then it makes sense to do it. 

Complex terrain is often at higher elevations, which generally implies a better wind resource. But along with higher wind speed, you have higher turbulence. Again, software like Meteodyn’s can help identify these spots.

Wind Energy Update: How many software solutions like Meteodyn’s are available to developers, and what made EAPC decide to exclusively use Meteodyn’s? 

Jay Haley: There are two or three other packages out there performing the same function.

We opted for Meteodyn given that it has consistently demonstrated a high degree of accuracy in third party testing. It has always performed very well. The fact that it is user-friendly is also a big plus. Often these software packages can be fairly complicated, which can have added costs in terms of the time invested in understanding and operating them.

Wind Energy Update: What other tools and processes complement the site selection process in complex terrain?

Jay Haley: There is WAsP, which I mentioned before, and then the other major workhorse tool is WindPRO, which is the comprehensive package. Ninety percent of the wind farm design is carried out using WindPRO (for positioning the turbines, mapping exercises etc.)

For calculating the energy and turbulence, you can use WAsP for flat sites  (such as in the mid-west), or on complex sites you would use Meteodyn. Those results would be incorporated back into WindPRO to finish the job.

Wind Energy Update: To what extent does software such as Meteodyn's promise to broaden the existing wind market

Joe Haley: It is hard to put a number on it, but as a general trend we are at the point where most of the simple sites have been developed. The CFD tool really has become commonplace  - it is a necessity nowadays, whereas five years ago it was not.

To respond to this article, please write to the editor: Rikki Stancich