Why can’t we have hybrid towers, too?

Bob Doyle, Columnist

Advantages of height

When I first started teaching college in Jackson, Tenn., in the 1970s, a nearby college (Lane College) had a well known alumnus playing on the line for the Dallas Cowboys. His name was Ed “Too Tall” Jones, at a height of 6 feet 9 inches.

I find it ironic that the biggest objection to the proposed wind turbines for Western Maryland are the heights of towers, quoted as being taller than the Statue of Liberty at Ellis Island in New York. (From base to tip of the flame, the Statue of Liberty is 305 feet tall, dwarfed by hundreds of sky scrapers in New York. St. Louis’ golden arch is twice as high, the Washington Monument is 250 feet taller and a smokestack for New Page at the Luke facility is also taller.)

Why should wind turbine towers be so high? First, the higher you are above the ground, the faster the wind blows. This is because friction with the surface slows down the wind. The amount of power generated is proportional to the cube of the wind speed squared.

So if the wind speed doubles, the amount of power increases by a factor of (2 times 2 times 2) equals eight. Second, with a higher tower, you can have larger blades to capture more moving air, produce more torque (turning force) and generate more electricity. The amount of electrical power generated is proportional to the square of the length of the blades. The area of a circle is Pi (or 3.14) times the radius squared. So a higher tower allows you to access stronger winds, have larger blades and thus generate much more power.

The principle for large towers is the same for large stores — economy of scale. Large discount stores (where many of us shop) offer lower prices for the same goods than small stores; big stores with their larger volumes of goods get a bigger discount from suppliers compared to small stores.

A real objection to wind turbines is that their power is intermittent; when there’s no wind, they generate no electricity. Over a year’s time, wind turbines typically deliver only 20 to 30 percent of their rated power. So a wind turbine rated at 1 megawatt (1,000,000) might only produce an average of 6,000 kilowatt hours each day. (A kilowatt hour is 1,000 watts for an hour).

But there is another power source that the wind turbines can tap. On many sunny days, the wind dies and the wind turbine blades are still. It’s estimated that in a matter of five years, thin film solar cells will be mass produced in such quantities that their price will be $1 per watt, making the electricity from these solar cells competitive in cost with electricity from fossil fuel power plants. Then you will likely see many solar panels on the rooftops of big stores and some home roofs to produce DC electricity to defray the cost of daytime lighting and air conditioning.

The manufacturers of wind turbines could install a set of study solar panels below the wind blades that could turn to face the sun, both in altitude and direction. So when the wind is negligible, deploy the solar panels on the tower to capture the sunlight.

With a gimbaled mounting, the panels could be positioned to receive the sun’s rays straight on (to get the strongest sunlight intensity). During the day, the solar panels would follow the sun to get the most solar power (capturing more than twice as much energy as a static rooftop array of same area.). Then from a distance, the wind towers on a sunny, windless day would resemble a garden of enormous flowers with their leaves facing the sun.

These hybrid towers on a sunny, windless day could still generate electricity at a rate of about half of their average wind generated electricity. This power generated would be entirely green without any emissions to the atmosphere or require large amounts of water to cool (as coal burning, natural gas and nuclear power plants).

What other large towers could be made into hybrid towers, generating electricity using solar cells? Most communities have tall cell phone towers that could also be outfitted with solar panels.

So on days with little wind, the solar cells could unfurl and generate electricity. Then at night, the solar cells would be folded back.

What kind of devices rely on such solar panels for their electricity? The first devices to use solar panels were our orbiting satellites. The International Space Station when passing over us can now outshine the bright planet Jupiter due to its large arrays of solar panels. Even in space with micrometeorite impacts, these panels supply most electrical power for Earth orbiting satellites.

August sky sights

The very bright planet Jupiter dominates the low southern evening sky. Jupiter appears as bright point of light that shines steadily, unlike the twinkling stars. At dusk on Aug. 1, you can see a very slender crescent moon underneath the dull planet Mars. To the right at the same level is the planet Saturn.

The Perseid meteor shower is best seen in the early morning hours of Aug. 12. The moon will be close to Jupiter on the evening of Aug. 12th. The moon will be full on Aug. 16, appearing in the dim star group Aquarius. Nearly overhead on August evenings is the very bright white-blue star Vega. Vega is the brightest star of the Summer Triangle, whose long sides point towards Jupiter.

The Big Dipper appears about halfway up in the north-northwest with its handle on top and scoop below. The bottom two stars point right towards the North Star.

Bob Doyle is available for brief talks and discussions for clubs or groups (call above phone number). He invites comments and questions from readers; his email is rdoyle@frostburg.edu .