The practicality of wind energy part I: Why ours doesn’t work

As most have probably suspected, our wind turbine at Macalester is completely useless from a practicality standpoint. Not only does the thing barely produce enough energy to power 13 standard light bulbs a year, it is significantly more expensive than simply getting the energy from other “green” sources. Keep in mind this is without factoring the $35,000 worth of expenses that were paid for by Xcel Energy.

What went wrong here? The fact of the matter is, even if the world’s greatest scientists and engineers met to give Mac wind power from a single on-campus turbine, the project would still end up being a failure. This is due to two factors localized to Macalester that will forever doom the viability of any turbine being constructed at our college. Critically, these factors are grounded in physics, not in the ability of engineers.

Factor number one is the height and blade length of our turbine. Commercial wind turbines are truly massive structures. In fact, many are taller than the Statue of Liberty. The reason for this is obvious to anyone who has flown a kite: winds are much better at higher altitudes. But there is more to the matter than this. The power from wind actually increases by the cube of the wind speed. So at an altitude where the wind blows twice as fast, it is in fact (2x2x2) 8x as powerful.

Due to zoning restrictions, the wind turbine at Mac was unable to be constructed any larger than 90 feet in the air. Furthermore, the blades that turn the turbine are quite short since the minimal amount of airflow cannot turn larger blades. This means that the total area from which power can be extracted is quite small, especially when comparing it proportionally to a larger turbine.

But ok, that is a zoning restriction. Let’s lobby the legislature and get this wind turbine restriction removed. If we can build a larger turbine it will start to become economical right?

Unfortunately, this is simply not the case. The final problem with the wind turbine is the location of the turbine itself. You might have noticed that around cities, wind turbines are a very rare site. There is a very good reason for this: wind is not very strong in cities. To get the best possible winds, it is important to be in areas where tall buildings are not obstructing wind flow.

Based on the data that Macalester has given about the annual energy output of the wind turbine, we can calculate that the average wind speed in our area is ~8.7 mph. For comparison’s sake, turbines in many areas of the Great Plains capture average wind speeds of 18 mph. That might not sound like much, but remember that double the wind speed is 8x the power that can be derived.

Of course, if the turbine were taller a greater wind speed could be recorded. But even at the high altitudes of larger turbines, the wind speed in the city limits of St. Paul is simply not sufficient for a truly sustainable source of power. This is why in the Department of Energy’s map on wind speeds at high altitudes, the Twin Cities metropolitan area is not even listed. The area does not have strong enough wind to be considered a viable source of electricity.

I am not going to go into the exact specifics of cost right now, since that is an article in itself, but suffice to say, our wind turbine is not economical. It is theoretically a piece of “sustainable” energy, but it’s installation, upkeep and repair costs will not outweigh the savings from the marginal energy we derive from it each year.

On the other hand, if I have made it sound like wind power has no purpose at all, I don’t mean to imply that. Wind power is actually a pretty awesome source of energy. This has a lot to do with why the Department of Energy intends for the US to get 20 percent of its power from wind in the next 15 years. Next week I will tie in why the failures of our own turbine actually make the case for wind energy in several other areas of the country.