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How do wind turbines work?

May 12, 2021 0 Comments

How do wind turbines work?

How Do Wind Turbines Work?

Wind is created by the unequal heating of the Earth's surface by the sun. Wind turbines convert the kinetic energy in wind into mechanical power that runs a generator to produce clean electricity. Today's turbines are versatile modular sources of electricity.  Their blades are aerodynamically designed to capture the maximum energy from the wind. The wind turns the blades, which spin a shaft connected to a generator or the generator's rotor, which makes electricity.

Is Wind Energy Practical for Me?

A small wind energy system can provide you with a practical and economical source of electricity if: Your property has a good wind resource. Your home or business is located on at least 1 acre of land. Your local zoning codes or covenants allow wind turbines. You can determine how much electricity you need or want to produce. It works for you economically (you may be eligible for state/utility or federal incentives). You're comfortable with long-term investments. Your average electricity bills are $150 per month or more or you don't have access to utility grid power. 

Zoning and Permitting Issues

Zoning refers to the general local regulations that allow and restrict various types of projects, whereas permitting refers to acquiring permits for a specific project within the scope of those zoning rules. The zoning and permitting processes for wind energy installations seek to address safety, aesthetics, and community interests and concerns. Some of these concerns might include sound level, visual impact, wildlife impact, TV/radio interference, ice shedding, or broken equipment. Practices vary dramatically across the country so becoming familiar with the local regulations, authorities, and general requirements is helpful. In some cases, zoning and permitting expectations are consistent and straightforward. In other cases, hearings may be required and the process is uncertain. A project designed within the existing limitations will experience a much smoother permitting process and will be more likely to receive a permit. But if your project falls outside of defined limits, it must usually undergo a special review process to obtain a variance from the existing rules and regulations — a  potentially expensive and time-consuming process that often involves at least one public hearing and has no guarantee of success. Before you invest in a wind energy system, you should research potential zoning and permitting obstacles. Some jurisdictions restrict the height of the structures permitted in residential-zoned areas, although variances may be obtained. Most zoning ordinances have a height limit of 35 feet.  You can find out more about zoning and permitting requirements by:

Contacting the local building inspector, board of supervisors, or planning board. They can tell you if you will need to obtain a building permit and will provide you with a list of requirements.

Visiting the Distributed Wind Energy Association'sPermitting and Zoning Resource Center.

Utilizing the Clean Energy States Alliance's

Distributed Wind Energy Zoning and Permitting: A Toolkit for Local Governments.

In addition to zoning issues, your neighbors might object to a wind turbine that blocks their view, or they might be concerned about the sound it produces. Most zoning and aesthetic concerns can be addressed by supplying objective data. For example, a typical 2-kilowatt wind turbine operates at a noise level of approximately 55 dB 50 feet away from the hub of the turbine.  At that level, the sound of the wind turbine can be picked out of surrounding noise if a conscious effort is made to hear it.

What Size Wind Turbine Do I Need?

The size of the wind turbine you need depends on your application. Small turbines range in size from 20 Watts to 100 kilowatts (kW). The smaller or "micro" (20- to 500-Watt) turbines are used in applications such as charging batteries for recreational vehicles and sailboats. One- to 10-kW turbines can be used in applications such as pumping water. Wind energy has been used for centuries to pump water and grind grain. Although mechanical windmills still provide a sensible, low-cost option for pumping water in low-wind areas, farmers and ranchers are finding that wind electric pumping is more versatile and they can pump twice the volume for the same initial investment. In addition, mechanical windmills must be placed directly above the well, which may not take advantage of available wind resources. Wind-electric pumping systems can be placed where the wind resource is the best and connected to the pump motor with an electric cable. However, in areas with a low wind resource, mechanical windmills can provide more efficient water pumping. Turbines used in residential applications can range in size from 400 Watts to 100 kW (100 kW for very large loads), depending on the amount of electricity you want to generate. For residential applications, you should establish an energy budget and see whether financial incentives are available. This information will help determine the turbine size you will need. Because energy efficiency is usually less expensive than energy production, making your house more energy efficient will probably be more cost effective and will reduce the size of the wind turbine you need . Wind turbine manufacturers, dealers, and installers can help you size your system based on your electricity needs and the specifics of your local wind resource and micro-siting. A typical home uses approximately 10,649 kilowatt-hours (kWh), an average of 877 kWh per month.  Depending on the average wind speed in the area, a wind turbine rated in the range of 5 to 15 kW would be required to make a significant contribution to this demand. A 1.5-kW wind turbine will meet the needs of a home requiring 300 kWh per month in a location with a 14 MPH (6.26 meters per second) annual average wind speed.  The manufacturer, dealer, or installer can provide you with the expected annual energy output of the turbine as a function of annual average wind speed. The manufacturer will also provide information about any maximum wind speeds at which the turbine is designed to operate safely. Most turbines have automatic overspeed governing systems to keep the rotor from spinning out of control in extremely high winds. Along with information about your local wind resource (wind speed and direction) and your energy budget, this information will help you decide which size turbine will best meet your electricity needs.

What Are the Basic Parts of a Small Wind Electric System?

Home wind energy systems generally comprise a rotor, a generator or alternator mounted on a frame, a tail (usually), a tower, wiring, and the "balance of system" components: controllers, inverters, and/or batteries. Through the spinning blades, the rotor captures the kinetic energy of the wind and converts it into rotary motion to drive the generator, which produces either AC or wild AC (variable frequency, variable voltage), which is typically converted to grid compatible AC electricity.

Wind Turbine

Small wind turbines can be divided into two groups: horizontal axis and vertical axis. The most commonly used turbine in today's market is the horizontal axis wind turbine. These turbines typically have two or three blades that are usually made of a composite material such as fiberglass. Vertical-axis wind turbines consist of two types: Savonius and Darrieus. A Savonius turbine can be recognized by its "S" shaped design when viewed from above. Darrieus turbines look like an eggbeater and have vertical blades that rotate into and out of the wind.  The amount of power a horizontal-axis turbine will produce is determined by the diameter of its rotor. The diameter of the rotor defines its "swept area," or the quantity of wind intercepted by the turbine. The turbine's frame is the structure onto which the rotor, generator, and tail are attached. The tail keeps the turbine facing into the wind.

Tower

Because wind speeds increase with height, the turbine is mounted on a tower. In general, the higher the tower, the more power the wind system can produce. The tower also raises the turbine above the air turbulence that can exist close to the ground because of obstructions such as hills, buildings, and trees. A general rule of thumb is to install a wind turbine on a tower with the bottom of the rotor blades at least 30 feet (9 meters) above any obstacle that is within 300 feet (90 meters) of the tower.  Relatively small investments in increased tower height can yield very high rates of return in power production.

There are two types of towers: self-supporting (free-standing) and guyed. Guyed towers, which are the least expensive, can consist of lattice sections, pipe, or tubing (depending on the design); supporting guy wires; and the foundation. They are easier to install than self-supporting towers. However, because the guy radius must be one-half to three-quarters of the tower height, guyed towers require space to accommodate them. Although tilt-down towers are more expensive, they offer the consumer an easy way to perform maintenance on smaller lightweight turbines (usually 5 kW or smaller). Tiltdown towers can also be lowered to the ground during hurricanes and other hazardous weather conditions. Aluminum towers are prone to cracking and should be avoided. Most turbine manufacturers provide wind energy system packages that include a range of tower options.  Balance of System Costs in addition to the turbine and the tower are the balance of system, including parts and labor, which will depend on your application. Most manufacturers can provide you with a system package that includes all the parts you need for your application. For example, the parts required for a water-pumping system will be different from the parts required for a residential, grid-connected application. The balance of system equipment required will also depend on whether the system is grid-connected, stand-alone, or part of a hybrid system. For a residential grid-connected application, the balance of system parts may include a controller, storage batteries, a power conditioning unit (inverter), wiring, foundation, and installation. Many wind turbine controllers, inverters, or other electrical devices may be stamped by a recognized testing agency, such as Underwriters Laboratories or Intertek. Batteries for Stand-Alone Systems Stand-alone systems (systems not connected to the utility grid) require batteries to store excess power generated for use when the wind is calm. They also need a charge controller to keep the batteries from overcharging. Deep-cycle batteries, such as those used for golf carts, can discharge and recharge 80% of their capacity hundreds of times, which makes them a good option for remote renewable energy systems. Automotive batteries are shallow-cycle batteries and should not be used in renewable energy systems because of their short life in deep-cycling operations. Small wind turbines generate direct current (DC) electricity. In very small systems, DC appliances operate directly off the batteries. If you want to use standard appliances that use conventional household alternating current (AC), you must install an inverter to convert DC electricity from the batteries to AC. Although the inverter slightly lowers the overall efficiency of the system, it allows the home to be wired for AC, a definite plus with lenders, electrical code officials, and future homebuyers. For safety, batteries should be isolated from living areas and electronics because they contain corrosive and explosive substances. Lead-acid batteries also require protection from temperature extremes. Inverters for Grid-Connected Systems In grid-connected systems, the only additional equipment required is a power conditioning unit (inverter) that makes the turbine output electrically compatible with the utility grid. Batteries are usually not required.

Is There Enough Wind on My Site?

Is the wind resource at your site good enough to justify your investment in a small wind turbine system? That is a key question and not always easily answered. The wind resource can vary significantly over an area of just a few miles because of local terrain influences on the wind flow. Yet, there are steps you can take to answer the above question. The highest average wind speeds in the United States are generally found along seacoasts, on ridge lines, and on the Great Plains;  however, many areas have wind resources strong enough to make a small wind turbine project economically feasible. Although there may be many methodologies for understanding the wind resource at a specific location, gathering on-site, measured wind data is typically preferred.

Prior to conducting an on-site measurement campaign, some small wind project developers use state wind maps to conservatively estimate the wind resource at turbine hub height. While these maps can provide a general indication of good or poor wind resources, they do not provide a resolution high enough to identify local site features. State wind maps cannot include information on complex terrain, ground cover, wind speed distribution, direction distribution, turbulence intensity, and other local effects. Purchased maps or services can often provide higher resolution and more flexibility with zooming, orientation, and additional features. Pay attention to a map's height above ground as it relates to the potential project's tower height. Adjusting the wind speed for the height difference between the map and the turbine height adds a potential source of error depending on the wind shear exponent that is selected, and the greater the height difference the greater the potential error. Therefore, for small wind generator applications, 30- to 40-m wind maps are far more useful than 10-, 60-, 80-, or 100-m wind maps. It is also important to understand the resolution of the wind map or model-generated data set. If the resolution is lower than the terrain features, adjustments will be needed to account for local terrain effects.  Local airport or weather stations can offer local wind data, but these data may be less reliable than actual site data. If airport data (typically recorded at 30 ft or 10 m above ground) or weather station data (typically recorded at 5 to 20 ft above ground) are used, inquire not only about the site's current equipment and location but also if it is historically consistent with the data collection equipment and siting. Equipment at these sites is not primarily intended for wind resource assessment, so it may not be positioned at an appropriate height or in a location free of obstructions. Unfortunately, airport and weather stations are usually far from the site of interest, with considerably different orography, tree cover, and monitoring height, making these data of questionable usefulness. Given the expertise required to effectively establish and correlate wind resource data, the data provided by airport and weather stations may only provide a rough screening assessment. 

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