Wind Energy

Across this country and certainly here in Oregon we see wind turbines going up all over the place. I routinely have discussions with students about their desire to but up small wind turbines at their homes. The questions in this homework are intended to help clarify your understanding and thinking about wind energy, how much there is, where it is, and the economics of personal wind power.

Math Stuff: Don't forget the various conversion constants we have been using so far this term. Some new ones you may need: 1 square mi is 2.6 square km; 1 square km is 1 Mega (square meter) – this is very awkward to write and would look like this mathematically – 1 km² = 1 Mm². 1 acre = 4000 m². 1 mi² = 2.6 km²

1) In Britain David Mackay calculates that there are about 4000 m² of land area per person. We will calculate the average land area available per person for the whole country in class. If we thought of Oregon as it's own “country” how much area is available per person in Oregon? Is this bigger or smaller than an average house lot which is 680 m²? Is this bigger or smaller than a standard Central Oregon ranchlet (5 acres) which is 20,000 m² ?

2) Ask someone who isn't in this class where in this country (which states) is there the best wind potential for wind energy. Where does the map from the National Renewable Energy Lab indicate is the answer to this question?

3) Using the map of wind energy resources for the state of Oregon (for some reason it's gotten harder to find this info so I gave you the link. Here is the general link to all NREL maps) where are the regions that have the greatest potential for wind energy (that are not along the crest of the Cascades)?

4) When I go and look at a map of the Shepards Flat Wind Farm which is listed as covering 30 mi² I am struck by the many empty spaces inside the area covered by the wind farm. Presumably these are areas where installing wind turbines is not as practical for some reason. What could those reasons be? The and that is leased for the wind farm covers 30 mi² but a reasonable estimate for the overall area occupied by the wind farm is probably 50 mi². When we did the calculation in class we determined that the facility produces 3 W/m². How would this number change if we had used 50 mi²for the area? To do this go back to our calculation in class and change the 30 to a 50 and see what the impact is. Think about whether you expect the capacity to up or down as a result.

5) As we found in class it can be remarkably difficult to find all the data we need to determine the production of energy by other wind farms (just got lucky with Shepard's Flat I think). After digging around in the NREL data base Here are some numbers from an Oklahoma wind farm called Blue Canyon. The nameplate capacity is 75 MW and in a good month (not year!) it generates 25 GWh of energy. In a bad month it generates 15 GWh of energy. Looking at the map of the region it looks like this wind farm covers at least 30 mi² spread through the ridges and farm country there. How many W/m² does this facility generate? Remember that these numbers are for a month of production not a year.

6) Using the links from our discussions in class find the wind rose for Redmond Oregon in May. Analyze the wind rose and calculate how many hours during May is the wind blowing faster than 5.4 m/s. How many hours during May does the wind blow faster than 8.4 m/s?

7) Let’s assume that the wind speed 30 m above the ground (where the wind rose in question 4 was generated) is 50% greater than at the ground. How many kWh of energy could you generate from 2000 m^2 of land (0.5 acres) during the May described by the wind rose in question 4? To do this first increase the wind speeds for each color in the wind rose by 50%. Then figure out how many Wh you can generate at each wind speed using these numbers: at a wind speed of 13 m/s you can generate 18 W/m^2 and at 8 m/s you can generate 5 W/m^2.

8) Here’s a link to the basic specifications for a small residential wind turbine. What is the minimum operating speed for this wind turbine? If you assume that the Aeolos 500 is generating 500W whenever the wind speed is above the minimum operating speed how much energy (kWh) would you expect to generate in May in Redmond? You will need to know how many hours the wind is above that speed from your answer to number 7!

9 The power curve describes how much power is actually generated at a particular wind speed. Here is a link to the power curve used for the Aeolos 500. What is a more realistic estimate of the total energy generated by this wind turbine in May in Redmond? What is the value of this energy at $0.07 per kWh? Just for comparison this wind turbine costs about $1000.00 with a simple guyed tower included.