After a quiet year, power from the wind is set for strong growth.
By Paul Hull
Last year was not a banner year for construction of wind-powered energy sites-for many reasons that may be irrelevant today. This year is more promising, with wind farms proposed and approved across the North American continent. Some sites are on land, usually in the middle of farms and open fields, but others are in the ocean, offshore, something like oil rigs. Even if last year's progress was slow, there is one aspect of wind power that has been impressive. It works. The wind we meet everywhere in every season of the year has the potential to generate considerable energy and it is proving useful as it enhances the sources of power we already have.
Did you ever have a little, colorful windmill on a stick when you were a child, or are you too young to have enjoyed such pleasures? The principles of wind power and the construction of its reliable equipment remind me of those childish windmills. The wind blows and it turns the mill. What is new is that the power generated is now sent down to generate electricity that can be used anywhere. In historical terms, wind has always been a helpful (and usually free) source of power-for the ships of people such as Drake, Magellan, Cook and Columbus that crossed the world to find new countries, for windmills like those well-known, often painted and photographed ones in Holland that power the stones to grind the wheat into flour, for helping people sailing on their local lakes, and for flying kites. If we extend the concept of wind, we'll think of engines that drive planes and of turbines that provide power in many industrial and commercial applications.
Turbines are the keys. Those tall objects that look like huge propellers on poles have turbines. One of the leading manufacturers, Siemens (for its Wind Power Americas), is confident of the growth for this sector of the energy industry. Last December, Siemens received an order from MidAmerican Energy for 448 turbines. The company also announced a pair of projects in Texas that will use its turbines, adding up to 250 MW of clean energy to the grid. According to the American Wind Energy Association (AWEA), there is enough wind power under construction in the US to power the equivalent of 3.5 million American homes-or all of the households in Iowa, Oklahoma and Kansas. That's more than 12,000 megawatts.
Farming with a Crop of Practical Power
I must admit that, when I think of turbines, my first images are of cylindrical machines that drive about anything that needs power. They have very few, if any, moving parts inside, which makes maintenance much easier. A few years ago I read about a turbine, about the size of an office waste basket, that could fit on the roof of a single house to give it all the power it needed for everyday use. What surprised me was that the turbine required only a little wind to make it work well. I had read only a few minutes before that the success of wind power depends on the strength of the wind. Everything related to wind power seems to involve those tall turbines; they are becoming a common sight. I asked myself if those were the only types of turbines that could produce energy. I found a story about turbines that work on the roof of a building to serve only that building. Then I came across many articles that gave differing views of the efficiency of different types of wind power turbines. There is still much argument about what works and what doesn't, and it's all broadcast by people who have something to gain (or lose) either way. Nothing changes in that respect.
0Some 30 years ago I was invited to visit the research labs of a large company to see what could be possible in engineering. The most fascinating exhibit was a small car (the same size as many today); it could be driven without gasoline or electricity. I learned a few weeks later than an oil company had bought the patents to the invention, and it has never been seen or heard about since. Most of the arguments I have seen against wind power have come from those with rival systems or those who perceive they will lose business if wind power is accepted by a public desperate for reliable power. That does not mean public utilities are opposed to wind power; some of the biggest wind farms are owned by public utilities.
Like all new technologies, wind power has its special names and initials. How often, for example, have you used the word nacelle? It's probably best known as the name for the cover of an aircraft engine. In wind power it's that "box" at the top of the tower; loaded, it weighs several tons. It contains the turbine, gearbox, generator, transformers and several mechanical and control devices. This system is driven by three blades (each more than 100 feet long), which are designed to produce power from the wind. The towers themselves, made of steel, can be more than 200 feet tall. Generally, the supplier of the tower and turbine will subcontract the erection of towers, nacelles and blades, but will be responsible for the final commissioning of it all.
Most of the construction work done for the installation of wind power towers will be done by the equivalent of a general contractor, contracted with the owner. This contractor, often called the developer of the project, negotiates for differing roles with the owner, which can include the initial proposition for the wind farm and go on to engage in its operation and maintenance, without being the owner.
Construction for Wind Farms
We see the tall towers and it would be easy to ignore what must be built to support them during and after their installation. First, how do those towers get there? You can't just dig a hole and drop it in. Key to the installations are cranes. Essential for the cranes are access roads and a crane pad near each tower site. Roads are built for the vehicles that bring the cranes to the correct locations, roads that must accommodate the size of the cranes and their balance during transportation. There is careful, skilled, basic construction done before the owners put up towers. There are excavators, dozers, cranes and other everyday construction equipment needed to make the installation safe and durable.
The towers may be supported by a thick concrete ring. For one installation I read about, the ring was two feet thick, cast-in-place, post-tensioned and it ranged up to 32 feet in length. The contractors had to drill and blast into rock about two feet lower than the design depth of the foundation. They could drill three foundations a day and then do the necessary blasting. The excavators then moved in and managed two holes a day. There are other procedures with concrete, including the floor for the tower with its 5,000-psi compressive strength. It's clear, when you read the specifications of the support for wind energy towers, that strength and safety are of paramount importance. They are much stronger than the windmills we used to see on some farms and ranches.
Not only does reading about wind energy towers show us how careful the construction of the sites for the towers is, it also reminds us that wind power is not just a passing fancy of a few people. The contents of the towers' nacelles are high technology from companies such as Siemens and GE. The towers are carefully designed and built to catch the winds they require to generate the required power-and built with integral safeguards against stronger-than-needed winds. The equipment used to install new towers is recognized construction equipment, its size and capability matched to the needs of each situation: tall cranes with enormous strength, strong excavators, equipment for building access roads, and all those smaller but vital machines that make any construction site the seat of perfection.
More towers for wind power are being built. This year could be a banner year for the industry. From all I have read, it seems the towers will be proof of our country's ability to respond to the demands of the public with strength and safety.