The Complexities of Wind Energy

Last week we commented on some of the potential problems of implementing Wind Energy. The idea is to illustrate the complexities behind developing and implementing these new technologies (Greentech).

This week we will try to illustrate the challenges of building an efficient wind turbine. THE POINT IS TO SHOW WHAT IS BEHIND THESE TECHNOLOGIES THAT SEEM SIMPLE, BUT ARE MUCH MORE COMPLEX ONCE YOU START DIGGING INTO THE DETAILS.

Before we start talking about the challenges of each component and type of turbine, the first issue pertains to the wind.

The efficiency for a single turbine or for a wind farm (multiple turbines) is a combination between turbine design and wind "quality". The wind quality is measured in terms of speed, air density, roughness (air flow affected by earth's surface or obstacles). All these factors have to me monitored throughout at least one year before deciding on turbine type and design. The reason is that the power obtained by a turbine is measured according to this formula:

(source http://ftexploring.com/energy/wind-enrgy.html)

Where (as you can see) the wind velocity affects the power output by a power of 3 (double the wind = eight times more energy output)

Furthermore, each turbine is designed to work under a specific wind speed. If the speed does not match the target for the design, the efficiency of the systems drops.

These are wind maps of Europe (red is strongest wind):

and USA:

Assuming we find a great spot for our turbine and that the conditions will not change much from one year to the next. Now we have to decide on the type of turbine we would like to install.

As shown in the picture (for in-depth knowledge go to http://www.windpower.org) the basic elements of a turbine are: the rotor blades, the gearbox and the generator. These three components are at the top of the tower that has a rotating base (or yaw) to allow the blades to follow the wind's direction and the electronic equipment to control and monitor the turbine.

The rotor blades are a key component because their diameter affects the power output by the power of two (see power formula above). Also, the blades are the main element on the aerodynamics of the turbine. If the blades have poor design, the turbine will work only under a short range of wind speeds and types and it will reduce the force transmitted to the gearbox and therefore reduce the electric output. One of the biggest challenges of today's turbine design is the minimum speed at which they can generate power, the lower the speed the more these turbines will be generating electricity non-stop and the more sites will become feasible for wind farms.

The electric output of these turbines has to be compatible with the electricity we use at home (the one coming from the grid). This electricity has a frequency of 60Hz (50Hz in Europe). This means that the generator shaft has to rotate at approximately 1500 rpm, whereas the blades of the turbine rotate at around 30 rpm.

To solve this issue all turbines have a gearbox. The gearbox converts the slow rotation of the blades into a constant and faster rotation speed for the generator.  Otherwise, the generator should have a mechanism to "smooth" the  power peaks and therefore lose power in the process.

Finally we get to the generator which converts the mechanical force into electrical output. There are several options for these generators, from the number of coils (or magnets), their capacity to the option of having synchronicity or asynchrony between the shaft and the poles.

After all this is studied and budgeted we still need to add the size of the tower and its foundation strength as well as the weight of the whole system as it relates to the "yaw" (the mechanism that allows the turbine to rotate 180 degrees over its horizontal axis to follow the direction of the wind)

(rotor size vs power)

And to finalize our assembly we need to have all the components monitored by electronics. Some components (depending on the design) need to be adjusted according to the monitoring system. The output has to be measured as compared to the wind measurements to account for the efficiency of the turbine. And safety mechanisms (such as mechanical brakes) have to be provided for extreme winds, electric peaks, and component failure.

At the end of the day the most efficient turbine is the one that provides most electricity per cost of its components times their working life. Keep in mind that wind is free, the cost comes from turbine components and their replacement cost (and perhaps also the land where they sit).

As you can see these technologies that seem straightforward at the beginning are much more complex when you get to the "nitty-gritty". The good news is that we are on a steep learning curve and sooner rather than latter we will get to a point where most hurdles will be left behind.

Until next week! SHALOM