Before spending a great deal of money on wind energy you probably want to know if this is going to work for you or not. If so, this section is for you. It explains the relation between wind, electricity production, and economics. No advanced degree in corporate finance needed! The plan is to extend this with technical information as well in the near future, so check back in a bit. Meanwhile, you can find the following sections:

• Wind Energy Potential

• Predicted Electricity Production Potential

• Economic Return on Investment

For a quick summary take a look at the table on the Scirocco page. It shows electricity production, cost per kWh, Return-On-Investment time, and profit or loss for business/farm as well as home use with net metering. This table was produced using realistic cost numbers and the current electricity price. If you want to know exactly where the numbers came from, they are explained in the sections below.

In case you are thinking about wind energy, also consider solar: Wind makes a wonderful complement to solar energy: When there is no sun there is often wind, when there is no wind the sun is usually shining bright.

Wind Energy Potential

Wind energy potential of a site is largely determined by its average, or mean, wind speed. If you have the opportunity it is a good idea to actually collect your own wind speed data, specifically for your site. Alternatively, for most larger places the meteorological office keeps wind speed data, then there are wind speed atlases that can fill in the blanks. While wind speed data can be measured at different heights, it is almost always recalculated and published as wind speed at 10 meters above the ground, in an area free of obstacles.

In addition, there is also the concept of "wind class" to quantify a site's potential for wind energy production. Classes are based on the average power available in the wind, and range from 1 ("Not enough wind to make any money") through 7 ("All your money will go to repairing your wind turbine"). Here is a table showing wind speeds and wind classes:

Keep in mind that wind classes are about average wind speed. While, for example, an absolute wind speed of 7 m/s contains 210 W/m², a site with an average wind speed of 7 m/s contains about twice as much power in its wind. This is in part because of the way wind speeds over land are typically distributed (called a Weibull distribution), and in part because those times the wind blows harder than average contribute proportionally more to the power made from wind. Energy in the wind is related to the cube of the wind speed, so when it is blowing harder than average the wind will contain far more power than what's lost during the times the wind is blowing less than average.

So what do these wind classes feel like? Take a look at the next table:

Again, wind class is about average wind speed, much of the time (especially in winter) it will be much windier than the mean wind speed. A class 3 site, which is considered by many to be the least amount of wind to be economically viable, will feel as if the wind is just about always blowing at a pretty good clip. The message to take home from the previous table is that good wind potential sites are very windy places indeed!

Predicted Electricity Production Potential

The next step is to determine how much energy we can expect from our wind turbine. Electrical energy is commonly measured in kilo-Watt-hours, or kWh, just as you pay the electricity company for the number of kWh you consumed. One kWh is the amount of energy used if you let 1000 Watt of light bulbs (=1 kW) burn for exactly one hour. In other words, kWh = load (in kW) * time (in hours). Knowing the mean wind speed, turbine height for your site, and turbine type largely determine how much the wind turbine is going to produce. The next table shows expected production for a few wind turbines:

You should keep in mind that these production numbers are largely the maximum one can expect, and for the Whisper 500 very likely quite a bit more than the maximum, as this is based on a very improbably power curve supplied by the manufacturer. Many site-specific factors conspire to actually make it less: Turbulence, tower interference, cable losses, inverter losses, down time, etc. A very big one in this short list is turbulence. Wind is turbulent when the air is moving at different speeds and directions, creating swirls and eddies instead of flowing nicely parallel to the ground. Turbulence is very bad indeed for wind turbines, it not only kills energy production, it also causes excessive wear-and-tear on the wind turbine parts because it constantly has to speed up, slow down, and reorient itself. The rule-of-thumb to get away from turbulent air is to place the turbine at least 10 meters (30 feet) plus one blade length higher than the highest obstacle in a 100 meter (300 feet) radius around the turbine, and this should really be regarded as the very minimum. For that reason there is not much point in placing a turbine on a tower of less than 60 feet (18 meters).

As mentioned elsewhere; Pine Ridge Products in Montana has been flying a Scirocco on a 100' tower, next to a Bergey Excel-S on an equally high 100' tower. In the 1½ years both were up, they measured Scirocco production to be 87% of Excel production. Theirs is a high-wind site, for lower wind sites the expectation is that production of both would be even closer together.

Economic Return On Investment

The wind may be free, as they say, but it sure costs a lot to catch it! Wind turbines and their associated towers, inverters and so on are not cheap. Cost, and return on investment, are not everyone's main concern. Maybe you need a wind turbine to power your off-grid house, or lake-side cottage, and only care if there's enough energy in the wind to do so? In that case even wind class 1 can work fine for your needs. Possibly you place great value on clean, renewable energy, even if it is more expensive than the utility company. If so, cost may be secondary. On the other side, maybe you have a farm and simply need it to make money for you.

Now that we know what to expect in terms of electricity production, it is time to take a look at how long it will take to earn back our investment. Since we sell Eoltec Scirocco turbines, that is what we will use in these examples. We will go for a grid-connected application, no batteries. Here is our list of common expenses (an estimate, though it should be fairly close to reality):