20.+Classifying+Energy+Types

= = Christopher, Sara, Blayde, Jessica

20.1 CLASSIFYING ENERGY TYPES
There is no shortage of effort being devoted to finding new and sustainable energy solutions. Even amidst the current economic challenges, the U.S. government is supporting these efforts with nearly a 50% increase in funding for energy-related research that includes energy efficiency and renewable energy, “smart” grid and efficient electrical transmission, green cars, as well as many other areas of research. Within this chapter there are a number of goals that will be addressed. First and foremost a general knowledge of alternative energy sources, along with there specific advantages and disadvantages that go along with them will be presented.

Seeing as the topic of this chapter is sustainable energies it would be advantageous to give a proper definition of sustainable energy, but before we classify what sustainable energies actually are it will be beneficial to develop a process for understanding where we are using energy and how we can improve upon it. Before the idea of new power is considered, all opportunities for reducing the need for power should be considered. If an area has reached its perceived limitations for energy use it may be beneficial to first evaluate possible ways to reduce the area’s need for power through reducing energy use in buildings, passive design strategies, using energy efficiently, or reducing demand through transportation changes.

Once all available power reducing options have been explored the next step to a more sustainable output is improving the energies productivity. This could be achieved with something as simple as replacing standard incandescent bulbs with a much more efficient LED light. Or as complicated as replacing outdated wasteful power lines with new GE Energy Compact Power Lines.

Macro Sources of sustainable energy can be defined four our purposes as large scale energy used to power cities or communities. While this scale of Sustainable energy is certainly convenient and can reduce our dependence on fossil fuels, that doesn’t mean that it has no drawbacks. Figure 14-1 depicts one of these very well, space. Land use is one of the predominate drawback when dealing with sustainable energies on a macro scale. When delved into deeper past the blatantly visible land use for sustainable energies and you consider the land use for mining and processing coal and natural gasses for Power production, that most certainly starts to tip the scales in the other direction.



Micro source sustainable energies are not designed for large scale power production, however they serve as an excellent tool on a much smaller measure. There are a number of micro generation renewable technologies now available that can be incorporated into both new developments and existing homes. These can reduce greenhouse gas emissions and save money by providing endless cheap energy and using less gas and electricity. While at this scale the number of ways to produce energy is incredible we will only address four types later in this chapter.

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20.2 Solar Power
//Solar thermal energy (STE)// Solar thermal energy is a technology for harnessing solar energy for thermal energy. Solar thermal collectors are classified by the United States Energy Information Administration as low-, medium-, or high-temperature collectors. Low-temperature collectors are flat plates generally used to heat swimming pools. Medium-temperature collectors are also usually flat plates but are used for heating water or air for residential and commercial use. We will come back to these forms later in the chapter. What we will focus on in reference to Macro Scale energies is High-temperature collectors concentrate sunlight using mirrors or lenses and are generally used for electric power production. STE is different from and much more efficient than photovoltaics, which converts solar energy directly into electricity.

20.3 Wind Power
Wind energy is actually indirectly a form of solar energy. Winds are caused by the uneven heating of the atmosphere by the sun, the irregularities of the earth's surface, and rotation of the earth. Wind flow patterns are modified by the earth's terrain, bodies of water, and vegetative cover. On a Macro scale wind turbines are often grouped together into a single wind power plant, also known as a wind farm, and generate bulk electrical power. Electricity from these turbines is fed into a utility grid and distributed to customers, just as with conventional power plants.

Horizontal Axis Wind turbine are composed of: Wind energy is very abundant in many parts of the United States. Wind resources are characterized by wind-power density classes, ranging from class 1 (the lowest) to class 7 (the highest). Good wind resources are class 3 and above. These have an average annual wind speed of at least 13 miles per hour and are found in many locations (see Figure 20-). Wind speed is a critical feature of wind resources, because the energy in wind is proportional to the cube of the wind speed. In other words, a stronger wind means a lot more power.
 * Blade or rotor, which converts the energy in the wind to rotational shaft energy;
 * Drive train, usually including a gearbox and a generator;
 * Tower that supports the rotor and drive train
 * //Wind Energy in United States//**



20.4 Hydro Power
Hydro power is one of the worlds oldest forms of Hydro Power can be separated into two basic categories; energy that can be generated by harnessing the kinetic energy in a body of water (Wave power, Ocean Thermal Energy Conversion, Tidal Power), or the energy generated by gathering the potential energy within a body of water (Hydroelectric damns, Tidal power).

A typical hydro plant is a system with three parts: an electric plant where the electricity is produced; a dam that can be opened or closed to control water flow; and a reservoir where water can be stored. The water behind the dam flows through an intake and pushes against blades in a turbine, causing them to turn. The turbine spins a generator to produce electricity. The power extracted from the water depends on the volume and on the difference in height between the source and the water's outflow. This height difference is called the head. The amount of potential energy in water is proportional to the head and how much water moves through the system.
 * //Hydroelectric Dams//**



Tidal power is a form of hydropower that converts the energy of tides into electricity. Although not yet widely used, tidal power has potential for future electricity generation. Tides are more predictable than wind energy and solar power. Among sources of renewable energy, tidal power has traditionally suffered from relatively high cost and limited availability of sites with sufficiently high tidal ranges or flow velocities, thus constricting its total availability. However, many recent technological developments and improvements, both in design and turbine technology such as new [|axial turbines] and [|cross flow] indicate that the total availability of tidal power may be much higher than previously assumed, and that economic and environmental costs may be brought down to competitive levels.
 * //Tidal Power//**

20.4 Geothermal Energy
Below the Earth's crust, there is a layer of hot and molten rock. Heat is continually produced there, mostly from the decay of naturally radioactive materials such as uranium and potassium. The amount of heat within 10,000 meters (about 33,000 feet) of Earth's surface contains 50,000 times more energy than all the oil and natural gas resources in the world.d Geothermal springs for power plants. The most common current way of capturing the energy from geothermal sources is to tap into naturally occurring "hydrothermal convection" systems where cooler water seeps into Earth's crust, is heated up, and then rises to the surface. When heated water is forced to the surface, it is a relatively simple matter to capture that steam and use it to drive electric generators. Geothermal power plants drill their own holes into the rock to more effectively capture the steam.

There are three basic types of geothermal power plants: ====
 * **Dry steam plants** use steam piped directly from a geothermal reservoir to turn the generator turbines. The first geothermal power plant was built in 1904 in Tuscany, Italy, where natural steam erupted from the Earth
 * **Flash steam plants** take high-pressure hot water from deep inside the Earth and convert it to steam to drive the generator turbines. When the steam cools, it condenses to water and is injected back into the ground to be used over and over again. Most geothermal power plants are flash steam plants.
 * **Binary cycle power plants** transfer the heat from geothermal hot water to another liquid. The heat causes the second liquid to turn to steam which is used to drive a generator turbine.

The choice of which design to use is determined by the resource. If the water comes out of the well as steam, it can be used directly, as in the first design. If it is hot water of a high enough temperature, a flash system can be used, otherwise it must go through a heat exchanger. Since there are more hot water resources than pure steam or high-temperature water sources, there is more growth potential in the heat exchanger design.

= = = MICRO SOURCES =

20.5 WIND ENERGY
Vertical-axis wind turbines have the main rotor shaft arranged vertically. Key advantages of this arrangement are that the turbine does not need to be pointed into the wind to be effective. This is an advantage on sites where the wind direction is highly variable, for example when integrated into buildings. The key disadvantages include the low rotational speed with the consequential higher torque and hence higher cost of the drive train, the inherently lower power coefficient, the 360 degree rotation of the aerofoil within the wind flow during each cycle and hence the highly dynamic loading on the blade, the pulsating torque generated by some rotor designs on the drive train, and the difficulty of modelling the wind flow accurately and hence the challenges of analysing and designing the rotor prior to fabricating a prototype.[13]
 * //Vertical Axis//**



Horizontal Axi//s// turbines on a small scale have a large potential for small scale energy production provided the area has consistent unidirectional wind. Verses its more versatile counterpart, the vertical axis windmill can produce larger amounts of electricity with the same size windmill. Its major drawback is that it can only be pointed in one direction. Horizontal axis wind turbines have the main rotor shaft and electrical generator at the top of a tower, and must be pointed into the wind. Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive an electrical generator.
 * //Horizontal Axis//**

20.6 Solar
These collectors could be used to produce approximately 50% and more of the hot water needed for residential and commercial use in the United States In the United States, a typical system costs $4000–$6000 retail and 30% of the system qualifies for a federal tax credit and additional state credit exists in about half of the states. Labor for a simple open loop systemcan take 3–5 hours for the installation. Northern system require more collector area and more complex plumbing to protect the collector from freezing. With this incentive, the payback time for a typical household is four to nine years, depending on the state.
 * //Solar Thermal//**



A solar cell (also called a photovoltaic cell) is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect. It is a form of photoelectric cell which, when exposed to light, can generate and support an electric current without being attached to any external voltage source. The efficiency of a solar cell may be bro ken down into reflectance efficiency, thermodynamic efficiency, charge carrier separation efficiency and conductive efficiency. The overall efficiency is the product of each of these individual efficiencies. Some devices are now approaching the theoretical limiting power efficiency of 33.7%
 * //Photovoltaic//**




 * __REFERENCES __**
 * 1) []
 * 2) Denholm, P. (March 2007) (PDF). [|//The Technical Potential of Solar Water Heating to Reduce Fossil Fuel Use and Greenhouse Gas Emissions in the United States//]. National Renewable Energy Laboratory . Retrieved 2007-12-28.