Electricity 11th Edition Answer Key

[Sebastian Thorndike]

Believeit or not, there are vampires lurking in your house at this very moment. Not the bloodthirsty sort from Twilight, but energy vampires: appliances that silently suck electricity from your wall outlets and discreetly inflate your power bill. The small rechargeable appliances you mention are all guilty of wasting watts, as are other common household electronics like computers, televisions and microwaves. Even when turned off or in standby mode, these energy vampires continue to feed on the lifeblood of your electricity. What's to be done?

You first ask about the energy consumption of a device left plugged in after it has been fully charged. You could walk around your house with a wattmeter to investigate your fully powered appliances, but luckily the Lawrence Berkeley National Laboratory has already done just that for you. Their Standby Power Summary Table shows that almost all the electronics we use consume electricity even when off or idle, and even when fully charged. A fully charged cell phone plugged into the wall is consuming about 2.24 watts, or 60 percent of the power it consumed while charging. Even worse is a charged laptop that's still plugged in, which consumes 29.48 watts, 66 percent of the 44.28 watts consumed while charging. If you left it plugged in all year, it would consume as much electricity as running your coffeemaker for 12 days straight. (Now are you wondering whether or not you should work with it plugged in? That's a whole other question, and a surprisingly complicated one. The short answer is that plugged in is probably better, but there's a full discussion here.)

Just unplugging our chargers won't save the world, but it's an simple step in the right direction. Do your part to slay the energy vampires in your life and both the environment and your wallet will thank you.

Can I use wind energy to power my home? More people across the country are asking this question as they look for a hedge against increasing electricity rates and a way to harvest their local wind resources. Although wind turbines large enough to provide a significant portion of the electricity needed by the average U.S. home generally require 1 acre of property or more, approximately 19.3% of the U.S. population lives in rural areas[1] and may own land parcels large enough to accommodate a wind energy system.

Small wind electric systems can contribute to our nation's energy needs. This guide will provide you with basic information about small wind electric systems to help you decide if wind energy will work for you.

Wind energy systems can be one of the most cost-effective home-based renewable energy systems. Depending on your wind resource, a small wind energy system can lower your electricity bill slightly or up to 100%, help you avoid the high costs of extending utility power lines to remote locations, and sometimes can provide DC or off-grid power.[2] In addition, wind energy is clean, indigenous, renewable energy.

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.[3] Their blades are aerodynamically designed to capture the maximum energy from the wind.[4] The wind turns the blades, which spin a shaft connected to a generator or the generator's rotor, which makes electricity.

Before choosing a wind system for your home, you should consider reducing your energy consumption by making your home or business more energy efficient. You can start by learning how electricity is used in U.S. homes. Reducing your energy consumption will significantly lower your utility bills and will reduce the size of the home-based renewable energy system you need. To achieve maximum energy efficiency, you should take a whole-building approach. View your home as an energy system with interrelated parts, all of which work synergistically to contribute to the efficiency of the system. From the insulation in your home's walls to the light bulbs in its fixtures, there are many ways to make your home more efficient.

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.

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.[9]

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.[10] 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.

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 (see How Can I Make My Home More Energy Efficient?). 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.[11] 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.[12] 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.

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.

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.[13]

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.

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.[14] Relatively small investments in increased tower height can yield very high rates of return in power production.

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