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What is energy - Реферат

People use some kinds of renewable sources.

At first, it is wind energy. We have been harnessing the wind's energy for hundreds of years. From old Holland to farms in the United States, windmills have been used for pumping water or grinding grain. Today, the windmill's modern equivalent – a wind turbine – can use the wind's energy to generate electricity. Wind turbines, like windmills, are mounted on a tower to capture the most energy. At 100 feet (30 meters) or more aboveground, they can take advantage of the faster and less turbulent wind. Turbines catch the wind's energy with their propeller-like blades. Usually, two or three blades are mounted on a shaft to form a rotor. A blade acts much like an airplane wing. When the wind blows, a pocket of low-pressure air forms on the downwind side of the blade. The low-pressure air pocket then pulls the blade toward it, causing the rotor to turn. This is called lift. The force of the lift is actually much stronger than the wind's force against the front side of the blade, which is called drag. The combination of lift and drag causes the rotor to spin like a propeller, and the turning shaft spins a generator to make electricity. Wind turbines can be used as stand-alone applications, or they can be connected to a utility power grid or even combined with a photovoltaic (solar cell) system. Stand-alone wind turbines are typically used for water pumping or communications. However, homeowners or farmers in windy areas can also use wind turbines as a way to cut their electric bills. For utility-scale sources of wind energy, a large number of wind turbines are usually built close together to form a wind plant. Several electricity providers today use wind plants to supply power to their customers.

At second, it is bio energy. We have used bio energy – the energy from biomass (organic matter) – for thousands of years, ever since people started burning wood to cook food or to keep warm. And today, wood is still our largest biomass resource for bio energy. But many other sources of biomass can now be used for bio energy, including plants, residues from agriculture or forestry, and the organic component of municipal and industrial wastes. Even the fumes from landfills can be used as an energy source.

The use of bio energy has the potential to greatly reduce our greenhouse gas emissions. Bio energy generates about the same amount of carbon dioxide as fossil fuels, but every time a new plant grows, carbon dioxide is actually removed from the atmosphere. The net emission of carbon dioxide will be zero as long as plants continue to be replenished for bio energy purposes. These energy crops, such as fast-growing trees and grasses, are called bio energy feedstocks. The use of bio energy feedstocks can also help increase profits for the agricultural industry.

I think, that it is very important to use sun energy. The Sun is the center of our solar system and the source of life on the planet earth. Moreover, as petroleum continues to pollute and destroy the earth, what better way than to look to the Sun for a solution?

The earth and either being used or simply bouncing off are always capturing the heat from the Sun. Solar technology utilizes this heat energy and converts it to electrical energy, which is then fed into the power grid for users. That, albeit, is not all. One of the benefits of solar energy is its ability to be used widely and in specialized situations. For instance, "Small systems can be installed on the roofs of homes to heat water for domestic use. Moderate-size systems can supply hot water, steam, and hot air to schools, hospitals, businesses, and industries. Large solar thermal electric installations can generate electricity in quantities comparable to those generated in intermediate-size utility generating plants (that is, 100 to 200 megawatts [MW] of electricity)."

One myth about solar power is that it requires large areas of land in order to be deemed useful. One example of this falsity is "Solar collectors covering less than half of Nevada could supply all of the United States' energy needs." While that seems like a lot of land, that area divided my 50 states and spread out could almost go unnoticed. One of solar powers biggest advantages is cost. For 1% of the construction cost on a building, solar panels installed could save up to 50% on heating bills. In addition, at a more consumer level, a resident of a home could save almost $500 within just the first year of installation. As an added bonus, the savings are likely to increase over the years due largely to increase in electrical bills. Thus, a solar heating system is capable of paying for itself in less than 10 years. The answer to the energy crisis the world is seeing could be to simply return to that with we depends on already, the Sun.

Flowing water creates energy that can be captured and turned into electricity. This is called hydropower. The most common type of hydropower plant uses a dam on a river to store water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn activates a generator to produce electricity. But hydropower doesn't necessarily require a large dam. Some hydropower plants just use a small canal to channel the river water through a turbine. Another type of hydropower plant – called a pumped storage plant – can even store power. The power is sent from a power grid into the electric generators. The generators then spin the turbines backward, which causes the turbines to pump water from a river or lower reservoir to an upper reservoir, where the power is stored. To use the power, the water is released from the upper reservoir back down into the river or lower reservoir. This spins the turbines forward, activating the generators to produce electricity.

The ocean can produce two types of energy: thermal energy from the sun's heat, and mechanical energy from the tides and waves. Oceans cover more than 70% of Earth's surface, making them the world's largest solar collectors. The sun's heat warms the surface water a lot more than the deep ocean water, and this temperature difference creates thermal energy. Just a small portion of the heat trapped in the ocean could power the world. Ocean thermal energy is used for many applications, including electricity generation. Ocean mechanical energy is quite different from ocean thermal energy. Even though the sun affects all ocean activity, tides are driven primarily by the gravitational pull of the moon, and waves are driven primarily by the winds. As a result, tides and waves are intermittent sources of energy, while ocean thermal energy is fairly constant. Also, unlike thermal energy, the electricity conversion of both tidal and wave energy usually involves mechanical devices. A barrage (dam) is typically used to convert tidal energy into electricity by forcing the water through turbines, activating a generator. For wave energy conversion, there are three basic systems: channel systems that funnel the waves into reservoirs; float systems that drive hydraulic pumps; and oscillating water column systems that use the waves to compress air within a container. The mechanical power created from these systems either directly activates a generator or transfers to a working fluid, water, or air, which then drives a turbine/generator.


Thus, humanity uses many kinds of energy: renewable and non-renewable. To make sure we have plenty of energy in the future, it's up to all of us to use energy wisely. We must all conserve energy and use it efficiently. It also up to those of you who will want to create the new energy technologies of the future. One of you might be another Albert Einstein and find a new source of energy. It's up to all of us. The future is ours but we need energy to get there.

The world has changed dramatically over the last 200 years, thanks largely to fossil fuels – coal, oil and natural gas. These have provided us with cheap and convenient energy, which we use to heat and cool our homes and to run our cars, appliances and industries. But there has been a cost. No city in the world is immune from the polluting effects of fossil fuels, and they contribute vast quantities of greenhouse gases to the atmosphere, something that many scientists believe causes global warming. So, in the last few decades, scientists have been looking for ways to produce energy without adverse side effects. Promising renewable energy sources such as wind, direct solar and biomass are dealt with in other Nova topics (see links at the end of this page). Now we'll have a look at hot dry rocks, waves and hydrogen. It may be some years before these energy sources make a big impact but they illustrate the diversity of options that are available.

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