Wind Power Basics. Dan Chiras

needs at rates that are often competitive with conventional sources. In remote locations, wind or wind and solar electric hybrid systems can be cheaper than conventional power, which requires the installation of costly electric lines that transport electricity from power plants to end users.

      Fig. 1.5: Plug-In Hybrid. Electric cars and plug-in hybrids like the one shown here are the most promising automobile technologies on the horizon. They could be powered by electricity from the Sun and wind.

The Purpose of this Book

      This book’s principal focus is on small wind-electric systems — those with rated output ranges from 1 kilowatt to 100 kilowatts. Most of the turbines we’ll be discussing fall in the 1- to 20-kilowatt (kW) range. The blades of small wind turbines (1 to 100 kW) range from 4 feet to 32 feet in length. Small-scale wind systems serve a variety of purposes. The smallest units are generally sufficient to power cabins and cottages; larger small wind turbines power homes and small businesses as well as schools, farms, ranches, small manufacturing plants, and public facilities.

      This book is written for individuals who want a succinct introduction to small-scale wind systems that doesn’t require a degree in physics or engineering. My goal was to create a user-friendly book that teaches readers the basics of wind energy and wind energy systems. This book is not an installation manual, but it will help you learn about wind if you want to become a wind energy installer or install a wind turbine and tower on your property. It will also help you determine if wind energy is right for you, what your options are, and how much it is going to cost.

      When you are done with this book, you should have a good knowledge of the key components of wind energy systems. This book will help you when shopping for a wind system or an installer. You’ll also learn about maintenance requirements.

      If you choose to hire a professional wind energy expert to install a system — a route we highly recommend — you’ll be thankful you’ve read this book. The more you know, the more input you will have into your system design, components, siting and installation — and the more likely that you’ll be happy with your purchase.

      This book should help readers develop realistic expectations. Wind energy systems, for instance, require annual inspection and maintenance — climbing or lowering a tower to access the wind turbine to check for loose fasteners and blade damage and, much less commonly, an occasional part replacement. If you are not up for it or don’t want to pay someone to climb or lower your tower once or twice a year to check things out, you may want to invest in a solar electric system instead.

Organization of this Book

      After this brief introduction, we turn our attention to the wind itself, the driving force in a wind energy system. In Chapter 2, you will learn how winds are generated and explore the factors that influence wind flows in your area. We will also explore the factors that affect energy production by a residential wind turbine and why it is important to mount a wind machine on a tall tower.

      In Chapter 3, we’ll explore small wind energy systems. You’ll learn the three types of residential wind energy systems: (1) off-grid, (2) batteryless grid-tie, and (3) grid-connected with battery backup. You’ll learn about the basic components of each one and hybrid wind systems.

      In Chapter 4, you will learn how to assess your electrical energy needs and how to determine if your site has enough wind to make a wind system worthwhile. You’ll learn why energy conservation and energy efficiency will save you a lot of money on a wind energy system. You will also learn ways to evaluate the economics of a wind system answering the question: Does a wind system make sense from an economic perspective?

      Chapter 5 will introduce you to wind turbines — what types are available and how they work. We’ll also give you shopping tips — what to look for when buying a wind turbine. We’ll spend a little time discussing building your own wind generator.

      Chapter 6 describes basic tower options, the pros and cons of each one, and how they are installed.

      In Chapter 7, we’ll study storage batteries and charge controllers, two key components of off-grid wind systems.

      Chapter 8 addresses another key component of all wind energy systems, the inverter. You will learn how inverters work, what functions they perform, and what to look for when shopping for one.

      In Chapter 9, we’ll give a brief overview of wind energy system maintenance. We’ll also explore a range of issues such as homeowner’s insurance, financing renewable energy systems, building permits, electrical permits and zoning. This books ends with a resource guide that lists books, magazines, organizations, small wind turbine manufacturers and wind turbine tower kits.

       CHAPTER 2

       WIND AND WIND ENERGY

      As you learned in the last chapter, wind is a clean, abundant, and renewable energy resource that can be tapped to produce electricity. This chapter explores how wind is generated and introduces you to two types of wind — local and global. We’ll also explore ways local topography affects wind, introducing you to two key concepts: ground drag and turbulence. This information provides the practical knowledge you will need to select the best site for a wind turbine and the optimum tower height.

What is Wind?

      Wind is air in horizontal motion across the Earth’s surface. All winds are produced by differences in air pressure between two regions. Differences in pressure result from differential heating of the surface of the Earth. Heating, of course, is caused by sunlight striking the Earth’s surface.

      Like most other forms of energy in use today, even coal, oil and natural gas, wind is a product of sunlight — solar energy. Some wind advocates, refer to wind as “the other solar energy” or “secondhand solar energy.” Let’s begin by looking at two types of local winds: (1) offshore and onshore winds and (2) mountain-valley breezes.

      Offshore and Onshore Winds

      Offshore and onshore winds are generated along the shores of large lakes, such as the Great Lakes of North America, and along the coastlines of the world’s oceans. Offshore and onshore winds blow regularly, nearly every day of the year. They are produced by the differential heating of land and water, caused by solar energy.

Here’s how this happens: As shown in Figure 2.1a, sunlight shining on the Earth’s surface heats the land and water simultaneously. As the water and adjoining land begin to warm, they radiate some of the heat (infrared radiation) into the atmosphere. This heat, in turn, warms the air above them. When air is heated it expands, and as it expands it becomes less dense and rises. The upward movement of air is called a thermal or updraft.

      Although water and land both heat up when warmed by the sun, land masses warm more rapidly than neighboring bodies of water. Because air over land heats up more quickly than air over water, air pressure over land is lower than over neighboring surface waters. As warm air rises over land, cooler, high pressure air moves in to fill the void, resulting in a steady breeze known as onshore wind.

      At night, the winds blow in the opposite direction — from land to water — as illustrated in Figure 2.1b. These are known as offshore breezes or offshore winds.

      Like onshore winds that occur during the day, offshore winds are created by differences in air pressure between the air over land and neighboring water bodies. Here’s what happens: after sunset, the land and the ocean both begin to cool. Land, however,