http://www.wwindea.org/technology/ch05/estructura-en.htm

What's a remote site? There's no hard and fast rule. Utilities will build a power line almost anywhere if someone will pay for it. As a rule, anyone more than a one kilometer from existing utility service will find it cheaper to install an independent power system than to bring in utility service.

Even today, three-fourths of all small wind turbines built are destined for stand-alone power systems at remote sites. Some find their way to remote homesteads in Canada and Alaska, far from the nearest village. Others serve mountaintop telecommunications sites where utility power could seldom be justified (see Remote Telecommunications).



Remote Telecommunications. Hybrid wind and solar power system powering
a telecommunications tower on the frontier between Argentina and Chile.
The 2-kW AgroLuz turbine is modeled after the 1930s-era Jacobs windcharger and
uses a pitch-regulated rotor 4.1 meters (13 feet) in diameter. © Paul Gipe




Surprisingly, an increasing number are being put to use by homeowners determined to produce their own power even though they could just as easily buy their electricity from the local utility. Bruce Simson, for example, is a vice president for strategic planning at British Columbia Hydro, a Canadian electric utility. Yet Simson has lived off-the-grid since the early 1990s. When the lights in nearby Vancouver went dark during a power outage, he jokingly asked the BC Hydro's operations manager why he couldn't make the utility more reliable.

Because the wind is a variable resource, remote applications generally require some form of storage. For remote homes, where a fairly steady supply of electricity is expected, battery storage becomes a necessity. Batteries store surplus energy during windy days for later use during extended calms. In battery-charging wind systems, direct current (DC) from the batteries can be used, as is, in DC appliances or inverted to alternating current (AC) like that from the utility.

At many remote sites, small wind turbines produce power at less cost than gasoline or diesel generators. At such sites, says Mike Bergey of Bergey Windpower, wind systems are also more cost-effective than solar photovoltaics alone.




Hybrids
In the early days of the wind revival, solar and wind proponents wore blinders. If you wanted a wind system for a remote site, the dealer would happily oblige, sizing the wind turbine and the batteries to carry your entire load. If you'd asked a solar dealer to do the same, they would have covered your roof with solar cells (PV modules). Never the twain would meet.

Fortunately, that's not so today. All now agree that hybrids using both wind and solar capitalize on the other technology's assets. In many locales, wind and solar resources compliment each other. Strong winds in winter are balanced by long sunny days in summer, thus enabling designers to reduce the size of each component. They've found that these hybrids perform even better when coupled with small backup generators to reduce the amount of battery storage needed.




Low-Power Applications
There are numerous applications for low-power, off-the-grid systems where battery storage isn't required. One classic application is the cathodic protection of pipelines where a small wind turbine provides an electric charge to the surface of the metal pipe. The charge counteracts galvanic corrosion in highly reactive soils. Storage isn't needed during calm winds because corrosion is a slow process that occurs over long periods. Eventually, the wind returns and again protects the exposed metal. All cathodic protection in rural areas was, at one time, provided by wind turbines. Today, pipelines primarily use small PV modules for cathodic protection, but wind machines are making a comeback (see Cathodic protection).



Cathodic protection. Rafael Oliva's Bergey 1500 powers a cathodic
protection system for a natural gas well on the windswept Patagonian
steppes near Rio Gallegos, Argentina. © Paul Gipe.




In other cases, small batteries may be necessary for proper operation of the windcharger and for storing small amounts of charge for windless periods. Two examples are the powering of walklights and the charging of electric fences (see Electric fence charging).



Electric fence charging. This Marlec 910F is charging an electric fence
at the Folkecenter for Renewable Energy in Denmark. The Marlec's battery
is hidden in the grass at left. © Paul Gipe.




One popular low-power application is the charging of batteries on sailboats. In yacht harbors around the world, multiblade micro turbines such as Ampair and Marlec are a common sight. Mounted on the decks or in the rigging, the turbines maintain the boats batteries while in dock. (See On-board battery charging.)



On-board battery charging. Ampair 100 on the deck of a sailboat
in Copenhagen's inner harbor. Thousands of micro turbines are used
in marine applications worldwide. © Paul Gipe.





Village Electrification
One-third of the world's people live without electricity. In China alone, half the population lives without access to utility power. Many Third World nations are scrambling to expand their power systems to meet the demand for rural electrification. Most are following the pattern set by the developed world: build new power plants and extend power lines from the cities to rural areas. However, with the advent of reliable hybrid power systems using wind and solar energy, this approach to rural electrification doesn't make as much sense today as in the past.

Developing nations will find it more cost-effective, says Mike Bergey, to install hybrid power systems rather than to stretch heavily loaded, and often unreliable, central-station power from the large cities. Though these hybrid systems generate little power in comparison to central power plants, Third World villages need little power. One kilowatt-hour of electricity provides 10 times more services in India than it does in the U.S. state of Indiana.

Hybrid power systems featuring small wind turbines, because of their relative low cost, enable strapped governments to get power into villages quickly. As the central power system expands to these villages, the hybrid systems can be removed and sent on to even more remote villages.

The strategy works in the developed world as well. Rather than pay for line extensions to remote farms in the foothills of the Pyrenees, France at one time paid for installation of hybrid wind and solar systems.




Interconnecting with the Utility
Some small wind turbines generate electricity identical to that supplied by the electric utility: constant-voltage, constant-frequency alternating current. Since the late 1970s homeowners, farmers, and businesses in nearly all countries have been permitted to connect these wind turbines with the utility network. Literally thousands of wind turbines have been interconnected with local electric lines around the globe. For example, Bill Hopwood's 20-kW Jacobs wind turbine has been in near continuous operation for twenty years on his farm in western Pennsylvania.

Though the concept is technically simple, and the law affecting interconnection in many countries favorable, there are numerous obstacles. First, you must deal with the utility company and its network, a task that too often could try the patience of biblical figure Job. Second, if there's a power outage, your wind machine will typically be idled as well, though there are ways around this. And because your wind turbine will be competing with bulk electricity supplied by the utility, the economic requirements are more stringent than for an off-the-grid system. Electric utilities have had more than 100 years of experience producing electricity. They've had ample time to learn how to do it cheaply and reliably.




How It Works
There are two types of wind turbines suitable for producing utility-compatible power: those that use induction (or asynchronous) generators, and those that use inverters. Regardless of which is used, their interconnection with the utility is the same. The wind turbine is connected to terminals within your utility service panel or connected directly to the utility's transformer. In effect, the wind turbine becomes a part of the building’s electrical circuit not unlike that of any large electric appliance.

If the wind turbine is on the customer’s side of the utility's kilowatt-hour meter, the wind system reduces the consumption of utility-supplied electricity. The wind turbine will power your clock, your stereo, your refrigerator or your lights. If you're a farmer, it will run your milkers or your feeders. In short, wind-generated electricity will be used wherever utility power is presently used.

When the wind is blowing, the wind turbine produces electricity that flows to the service panel. From there, it seeks out those circuits where electricity is being consumed. With electricity, it's first come, first served. Electricity will flow to the first circuit where it's needed. If more energy is being generated than can be used by the first circuit, it will flow to the next, and so on. When the wind machine can't deliver as much energy as needed, the utility makes up the difference. There are no fancy electronics controlling which circuit gets what. It's all accomplished silently and effortlessly. That's the beauty of electricity.

If there’s little or no consumption and the wind turbine is operating, the excess generation flows from the service panel through the utility's kilowatt-hour meter and out to the utility's lines. In some cases, utilities permit running their kilowatt-hour meters backward. It seems mysterious, but it works. And it does so neatly, cleanly, and without fuss. Other utilities require the use of two separate meters to accomplish the same task.




Farming the Wind
Under the right conditions, for example when the utility pays a sufficient price for wind-generated electricity, you may be able to farm the wind for profit. You can do so by selling surplus generation from a wind turbine connected to your farm, home, or business. Or, you could install a group of wind turbines intended solely for generating electricity for sale to the utility.

A commercial wind farm, or wind power plant, is nothing more than a large-scale version of a wind turbine interconnected with an electric utility on the customer's side of the kilowatt-hour meter. But rather than meeting the domestic demand of a home or business, all the electricity generated by these wind power plants is delivered to the utility.

In the early 1980s, some small wind turbines originally designed for farms or small businesses found their way into California's mushrooming wind industry. Literally thousands of such wind machines were installed on California wind farms.

These were wind turbines that just a few years before were being installed in backyards in the United States, Denmark, and Germany. The biggest machines of that era produced about 50 kW with rotors from 13 to 15 meters in diameter. Today these are considered small, or more specifically household-size wind turbines.




Heating
In temperate climates heating comprises most of a home's energy demand. In many areas of the world, there is a good correlation between the availability of wind energy and the demand for heat. It's not surprising then that there have been numerous attempts to use small wind machines strictly for heating. Advocates of the wind furnace concept believed that the same winter winds that rob a house of its warmth could be used for heating. They argued that generating low-grade energy with either an alternator or a mechanical churn would be less costly than producing the same amount of utility-compatible electricity. It's simpler, proponents said, than trying to produce the high-grade electricity demanded by the utility.

Unfortunately, it never worked out that way. Both Danish and American companies tried to commercialize the concept during the 1970s and early 1980s, and again in the 1990s. None have proven popular. Experience has shown that in most cases it's cheaper and easier to interconnect the wind system directly with the utility than to generate heat and store the surplus for windless periods. Often, it's more cost-effective to produce a high-grade form of electricity that can be used for all purposes, including home heating if desired, than to build a wind turbine that can only be used for one function (see U Mass Wind Furnace).



U Mass Wind Furnace. Circa-1980 experimental wind turbine at the University
of Massachusetts designed for heating the experimental building nearby.
Several firms tried to commercialize the concept with little success. © Paul Gipe.




There are several examples where household-size turbines have been used to provide supplemental heating. For years, Bergey Windpower has marketed their Excel model to North Americans in "all-electric" homes, where the wind turbine will provide some or all of the heating load. But the Excel produces utility-compatible electricity that can be used anywhere in the home--or sold back to the utility. Similarly, French manufacturer Vergnet has had a long-running installation on Britain's windswept Orkney Islands, generating electricity that is used for heating. Like Bergey's Excel, Vergnet's turbines can also be used to produce utility-compatible power as well as electricity for heating.




Pumping Water
Wind machines have historically been used to pump water, and pumping water remains an important application of wind energy today in both the developed and the developing worlds. The American farm windmill, known as the Chicago mill in some parts of the world, dependably pumps low volumes of water from shallow wells. These multiblade wind pumps are still extensively used for watering remote stock tanks on North America's Great Plains, Argentina's Pampas, Australia's outback, and South Africa's veldt. There are probably more than a million of these wind pumps still in use worldwide.(See Wind pumping.)



Wind pumping. Foreground: American farm windmill on a Colorado ranch
near the Wyoming state line. Background: 700-kW NEG-Micon turbine
part of the Ponnequin wind power plant. © Paul Gipe.




Researchers at West Texas A & M University's Alternative Energy Institute and the U.S. Department of Agriculture's Agricultural Research Service have made major advances in water-pumping technology, first with wind-assisted irrigation in the 1980s, and then with wind-electric pumping systems in the 1990s. In cooperation with small wind turbine manufacturers, these researchers have developed pumping systems that couple modern electronics to small windchargers that eliminate the need for cumbersome batteries. Under certain conditions, these wind-electric pumping systems will deliver more water at lower cost than the traditional farm windmill.

From pumping water in North America’s southwest to boiling water for tea on the Mongolian steppes, small wind turbines are finding increasing application worldwide.




Paul Gipe
Califonia, USA
www.wind-works.org




The report has been adapted from the book Wind Power - Renewable Energy for Home, Farm, and Business, Chelsea Green Publishing (ISBN: 1-931498-14-8), 2004 by Paul Gipe:
http://www.wind-works.org/books/wind_power2004_home.html