Introduction

The total installed capacity of small wind systems—100 kW or less—operating in the United States in 2006 was an estimated 61 MW, according to the American Wind Energy Association (AWEA). Of this capacity, less than one-third—approximately 15 MW—was grid-connected. Most small, grid-connected wind generators used for residential applications are between 1 kW and 25 kW. Larger grid-connected generators, up to 100 kW, are typically found on small farms and businesses.

The major U.S. companies that manufacture and sell small wind turbines are Abundant Renewable Energy (ARE), Bergey Windpower, Southwest Windpower, and Wind Turbine Industries. In addition, wind turbines manufactured abroad by companies including Eoltec, Kestrel, and Proven are imported for sale into the United States.

Finally, a few U.S. companies remanufacture and sell wind turbines. One is Halus Power Systems (Hayward, California), which rebuilds Vestas turbines formerly used in California wind farms. Another company, Energy Maintenance Service LLC (EMS) of Gary, South Dakota, formerly remanufactured and sold wind turbines. EMS continues to remanufacture wind turbines, but they are now sold through Next Generation Power Systems, Pipestone, Minnesota. Next Generation sells the NG Twelve-Five, a rebuilt German wind generator.

A rebuilt wind turbine is likely to have a new finish, repaired or replaced rotors, an overhauled brake system and gearbox, replaced cables and junction boxes, and a rewound or reconditioned generator, among other improvements and upgrades.

New and Emerging Technology Advances

Numerous improvements have been made to small wind generators over the past few years. These include advanced blade manufacturing methods. Manufacturers are using such techniques as injection molding and compression molding to produce more durable wind rotors. Although these techniques have reduced fabrication time, lowered parts costs, and increased repeatability, they have led to higher tooling costs. Another new technique—reaction injunction molding—has been prototyped but is not yet used in production.

Another improvement entails the use of rare earth permanent magnets. These magnets are replacing ferrite magnets, until now the industry staple. Rare earth permanent magnets, which have superior magnetic properties, result in more compact and lighter wind generators.

Manufacturers also have lowered the “cut-in” threshold—the wind speed at which a turbine begins producing energy, usually about 9–11 miles per hour (mph)—to enable turbine operation at lower wind speeds. Other improvements made by manufacturers include slower rotor speeds to reduce sound levels and alternatives to rotor furling—yawing and/or tiling out of the wind to protect against excessive rotor speeds in high winds—to control rotor speed. Among the alternatives are stall control, dynamic braking, mechanical braking, and pitch control—methods that have been demonstrated in utility-scale wind generators.

Small turbines—10 kW and less—used induction generators in the early 1980s. But those generators, which connect directly to the utility grid, were replaced with permanent magnet generators, which require an inverter to connect to the grid. Now a few companies are reintroducing induction generators in their machines. By eliminating the inverter, these companies seek to reduce the cost of a wind turbine while improving reliability.

According to several experts, inverters are the least reliable component in small wind systems. But some manufacturers are addressing this issue by adapting inverters from the photovoltaic (PV) market for use with wind turbines. By using an existing, proven product, they have lowered the cost of wind-specific inverters and been able to get them to the market more easily.

In addition, manufacturers are designing the electronics in wind generators for safer and more reliable performance. Some models also feature wireless display units for consumer convenience.

There appears to be general agreement among industry experts that no major technology breakthroughs are likely. Rather, companies will continue to improve and refine their products.

To address the relatively high cost of production, some manufacturers—such as Southwest Windpower—are designing turbines that can be produced in high volume and to high quality standards. To increase its market share, however, the small wind turbine industry needs to realize cost breakthroughs and new business models that will get its products to the market, in the view of some industry experts.

Bergey Windpower, for instance, is experimenting with large rotor diameters and more powerful alternators for use in low-wind regimes. In addition, the company’s wind turbines have progressed toward lower tip speed ratios—which reduce noise levels—as the cost of permanent magnets has declined. ARE has designed its ARE 442 model with a tip speed ratio of 7, which the company noted is considered slow. But the slow speed comes at a price—more expensive blades and heavier alternators. ARE is also working to eliminate the sound caused by rectifying the output of a very stiff and highly efficient alternator.

Bergey hopes to introduce its third generation of grid-intertie inverters in the spring of 2008. Another company, Wind Turbine Industries, is conducting research on an inverter that will be certified to Underwriters Laboratories (UL) 1741. And ARE is redesigning inverter controls to reduce cost and improve reliability.

There are physical limits to the low-wind performance that is possible in a competitive price range, according to ARE. The only way to achieve significant performance gains is by using larger rotors. But increasing rotor size and controlling a larger rotor at a reasonable cost is a substantial engineering challenge. ARE is considering the use of large rotors and passive pitch control for some of its new models.

Technical Challenges

The United States does not have a system for certifying small wind turbines. The lack of a certification system hinders the ability of consumers to make decisions based on turbine safety, functionality, and durability, and may constrain financial support for state incentives. Three elements are needed to establish certification, according to the Interstate Renewable Energy Council (IREC). One is a turbine hardware performance standard, the second is turbine field tests, and the third is an independent certification body. AWEA, IREC, and the National Renewable Energy Laboratory (NREL) of the U.S. Department of Energy (DOE) are working to establish these components.

PERFORMANCE STANDARDS

At present, small wind turbine performance specifications have not been widely accepted by the small wind turbine community because they are considered too expensive. As a result, consumers often have no realistic and comparable performance ratings for various wind turbines. AWEA has drafted a small wind turbine performance and safety standard that would describe the tests required for turbines. The standard provides a method for evaluating turbine systems in terms of safety, reliability, power performance, and acoustic characteristics. It is derived largely from international standards developed under the auspices of the International Electrotechnical Commission (IEC), including power curve, annual energy performance curve, sound pressure levels, strength and safety test, and duration test. Approval of the AWEA standard is expected in spring of 2008.

FIELD TESTING

Once the AWEA standard is approved, it will provide a basis for testing wind turbines and verifying product claims. The DOE’s NREL issued a request for proposal (RFP) in the spring of 2007 asking for commercially available small wind turbines to be tested at the NREL’s National Wind Technology Center in Colorado. To be accepted for testing, a wind turbine has to be a commercial product with 12 months of operating history.

In its RFP, the NREL noted that one of the barriers for the distributed wind market is the lack of small turbines that are independently tested and certified. The objective of testing is to provide high-quality, detailed, and independent test results for a number of small turbines and allow them the opportunity to earn certification by an independent certification body.

The NREL has accepted four proposed wind turbines for testing, including Abundant Renewable Energy’s ARE 442 turbine and the EW15, a 50-kW wind turbine made by Entegrity Wind, a Canadian company. Bergey chose not to submit a proposal, noting that it conducts testing at the factory. The National Wind Technology Center began testing three of the four turbines in December 2007 and expects to begin testing the fourth in September 2008. Testing is expected to run for 13–15 months. The center will test the turbines on the basis of the IEC standards, as the AWEA performance standard will not be approved in time for the launch of testing.

Through its Small Wind Verification Project, NREL conducted power performance, noise, safety, and duration tests on three small wind turbines. The results are available here, under Small Wind Verification Project. In another study, NREL examined the IEC standard for small wind turbine design through modeling and testing; the results are available here.

Turbine testing also has been conducted in North Carolina, under the auspices of the Small Wind Initiative. The initiative—supported by the North Carolina State Energy Office, the Tennessee Valley Authority, the DOE, Appalachian State University, as well as several small wind turbine manufacturers—established a small wind technology research and demonstration center on Beech Mountain in the western part of the state. The research and development (R&D) center is located at an elevation of 5,136 feet, with an average wind speed of approximately 18 mph at 164 feet.

Six turbines were tested at the Beech Mountain R&D site between June 2004 and June 2005: Southwest Windpower’s Air X, Whisper 100, and Whisper 500; Bergey’s XL.1; African Wind Power’s AWP 3.6; and Wind Turbine Industries Jacobs 31-20.

Through its Alternative Energy Institute, West Texas A&M University also has tested small wind turbines, often in cooperation with the U.S. Department of Agriculture (USDA). The results of some of these tests are available at the USDA’s Conservation and Production Research Laboratory website. Recent studies of small wind turbines include one on airfoil evaluation and one on solid-state sensors for control and data acquisition.

CERTIFICATION

Currently, small wind turbines can be certified to the IEC standard—IEC 61400-2—for testing wind turbine power performance. This standard is increasingly used by U.S. manufacturers in their wind turbine designs.

The formation of a U.S. certification body is under way. An organizational plan for the new North American Small Wind Certification Council (SWCC) has been adopted by the Small Wind Certification Working Group. The organizational plan provides the blueprint for the start-up and launch of the SWCC. The council will work with the small wind industry, governments, and other stakeholders to develop and implement quality certification programs.

The working group includes 15 representatives from several states, small wind turbine manufacturers, and other interested parties as well as three facilitators, including the IREC. In addition, the group has 26 alternates and observers.

The role of the SWCC, which is expected to become operational in 2008, is to verify and certify the results of small wind turbines tested to the AWEA standard. The corporation’s initial scope will include newly manufactured turbines that fall below the IEC 61400-2 limit of a swept area of 200 square meters, approximately 65 kW. The SWCC board of directors may consider expanding certification to larger turbines at a later date.

According to the IREC, a SWCC certification label will include rated annual energy (at a one-year average wind speed of 11.2 mph, although this may change), a rated sound level (which cannot be exceeded 95% of the time by average wind speed of 11.2 mph), and rated power (24.6 mph).

The IREC expects the first set of certifications in late 2008 or early 2009, assuming sufficient funds and adoption of the AWEA performance standard. Fees are expected to cover one-third of the first year of expenses, increasing to 100% in the fifth year.

Why Member-Consumers are Interested in Small Wind Systems

When asked why member-consumers installed a small wind system, three reasons where given, according to a small sampling of member-consumers in seven states. In addition to the production of green power, they cite energy independence and reduced utility bills.

ENVIRONMENTAL CONSIDERATIONS

In the 2003 Home Power survey, 18% of readers said they supported small-scale renewable energy because of its positive environmental impact. In the 2006 survey, 19% said they were interested in renewable energy because it would minimize their impact on the environment. Some environmentally conscious consumers will choose to invest in a wind turbine even when it does not save them money.

REDUCED UTILITY BILL

Of respondents to the 2006 Home Power reader survey, 14% said they supported small-scale renewable energy as a means of reducing their utility costs. Properly sited and installed, the right small wind system could potentially reduce a consumer’s utility bill significantly, in some cases by up to 80%. Experts caution, however, that a small wind turbine should not be seen as a moneymaker. Consumer expectations about the economic value of wind investments often outstrip reality. Whether a small wind turbine will actually save a consumer money in the long term will depend on a range of factors discussed in greater detail elsewhere in this guide.

OPERATIONAL COST MANAGEMENT

As volatile energy costs put added pressure on profitable farming operations, small wind systems can provide energy cost stability over the life of the wind turbine. It is sometimes more important—especially to contract livestock operators where margins are prenegotiated—to be able to predict future operating costs, including energy, than basing contracts on current prices. Farm wind turbine systems can offer these types of management opportunities.

OTHER REASONS

In the 2006 survey, 17% said they were interested in experimenting with the technology. Many homeowners are enamored by the new technology and are more interested in being on the cutting edge than even in saving money.

Other Sources of Information

There are several good sources for additional information on small wind system, such as the state renewable energy organization or energy office. The Iowa Energy Center has a renewables section on their wed site that provides state wind maps, economic analysis as well as other good references. The National Association of State Energy Officials’ website provides contact information for state energy offices. Regional organizations, such as the Midwest Renewable Energy Association (MREA) might also be able to help.

The U.S. DOE’s Small Wind Electric Systems: A U.S. Consumers Guide  and the EERE also provide information on small wind systems.

Interconnection

Member-consumers may think that interconnecting a small wind system to the grid can be accomplished easily and cheaply. In some cases they may be right, in others, the process may be significantly more complicated. A small wind system can affect the safety and reliability of the distribution system and the quality of power received by neighboring consumers. The cooperative’s technical interconnection rules are designed to address such effects on safety, reliability, and power quality.

Interconnection will also entail costs for the consumer. These include: equipment that must be installed on the consumer’s side of the meter to protect the generator and the consumer’s own electrical system; equipment that must be installed on the consumer’s side of the meter to protect safety, reliability, and power quality on the grid; and possibly upgrades to the distribution system. Such upgrades may be required to address reversed power flows, increased short-circuit voltage, or even to provide three-phase service to the new generator. The consumer will also be expected to pay for the cooperative staff time and resources required to process the interconnection application and to conduct any necessary studies needed to determine whether the generator poses risks to the system, and if so, what upgrades are needed to address those risks. Finally, depending on the choices made by the local system, the consumer may also be required to carry additional liability insurance to protect the cooperative in the event an equipment malfunction causes harm to life or property.

In some cases, the process, fees, and contracts for interconnection will be mandated by state law or regulation. Some states have developed interconnection standards and a few have precertified models of distributed generation (DG) units for interconnection. In most cooperative systems, the rates, terms, and conditions of interconnection will be established by the cooperative.

Net metering

A member-consumer may expect to receive credit at the retail rate for any net excess electricity sent to the grid, that is, for any generation produced at any particular time in excess of the consumer’s load at the time. This is called net metering. Manufacturers of distributed generators and environmental advocates strongly support net metering because it increases the economic viability of small wind generators. Some consumers and government officials believe (incorrectly) that if a utility does not offer net metering then the consumers cannot interconnect to the distribution system or will not be compensated at all for any net excess generation.

On the other hand, most cooperatives either do not offer net metering or limit net metering to a limited number of generation types and sizes of generation. Those cooperatives are concerned that net metering overcompensates consumer-owned generators for their net excess generation. Most cooperatives pay for net excess generation at the level required by the PURPA, which is the cooperatives’ avoided cost (the cost that a utility would incur if it had generated the power itself or purchased it from another source).

To limit conflicts, it can be helpful if a cooperative’s policy for purchasing net excess generation is adopted well before any consumer seeks to interconnect generation, is extremely clear, and is supported by data demonstrating that the policy is necessary to ensure equitable rates for all consumers on the system. It may help if the materials the cooperative hands to consumers interested in self-generation explain the cooperative policy, explain what net metering is, and if they are different, explain why the cooperative does not offer net metering. An issue paper on net metering is available on the NRECA’s Web site.

The use of two meters or a single advanced meter capable of reading power flows each direction provides a way for member-consumers to pay their fair share of costs for electric service while benefiting from their small wind system. One meter measures electricity coming from the grid and one meter measures electricity being delivered to the grid. This approach is consistent with the PURPA, where the consumer buys power from the cooperative at the retail rate and sells power to the cooperative at the avoided—or wholesale—cost.

Member-consumers may ask about the difference between net metering and net billing. In net metering, the electricity being delivered to the grid by the member-consumer is netted against the electricity being delivered to the member-consumer. The value of power imported and exported, therefore, is the same. Consumers are paid full retail value for the wholesale power they export to the grid. By contrast, net billing nets the value of power exported against the value of power imported, allowing the retail and wholesale power to be valued at different levels. The netting occurs in the billing process. Under both approaches, the consumer has first call on generator output. The utility only buys that portion of the consumer’s output that exceeds simultaneous demand. The consumer only buys from the utility that portion of the consumer’s load that exceeds the simultaneous output of its generator.