Harnessing Water and Solar Power: Technologies and Applications
Water Power
Hydropower is generated using water as it moves through a channel (kinetic energy) or when it is impounded at a certain height (potential energy). When water is dropped, the potential energy turns into kinetic energy (speed), which can be exploited for various purposes. It is a renewable energy (not alternative).
There are two main applications of water power:
- From approximately 100 BC until nearly the end of the nineteenth century, all hydropower was transformed into mechanical energy with specific applications in Nones, grain mills, ironworks and forges, textile mills, and so on.
- From the early twentieth century, it was also used to obtain electricity. The first hydraulic unit for this application was built in 1882 in the United States to supply 250 electric lamps (invented by Thomas A. Edison).
Today, virtually all hydropower is used to obtain electricity.
A. Components of a Hydroelectric Center
Reservoir: Represents all the accumulated water. This has a thick wall of concrete, called a dam, whose function is to retain water. There are two basic types:
- Gravity dam: Its weight counteracts the force of water. It is usually straight or slightly concave (on the water side). Its cross-section is triangular, forming a right angle between the base and side of the reservoir. Its construction is expensive (Fig. 6.2).
- Arch dam: It works by the push of water that passes it to the slopes of the mountain. It is usually convex, so that the more water drives from the reservoir, the more it “keys” to the sides of the dam on the slopes of the mountain. This feature reduces the size of the dam, so that its construction is cheaper for the same performance as the previous case (see Figure 6.3).
Water Ducts: There are two types of channels:
- Gates (Fig. 6.6): Their mission is to evacuate the water in the reservoir without passing through the engine room (turbines). They are used when necessary by releasing water for irrigation or safety reasons (excessive rain).
- Flowlines (Fig. 6.4): The transfer of water from the reservoir to the turbines. There are two important parts:
- The water intake, which is usually placed at 1/3 of the height of the dam so that the sludge, stones, and various materials that the water pulls are deposited at the bottom and are not drawn into the turbines, which could break them. It also tends to have a grid to avoid entering the pipe branches, logs, etc.
- The surge shaft, which consists of a small tank connected to the flowlines, in which water accumulates. This prevents variations in water pressure when it regulates the flow at the exit.
Engine Room: In the engine room (Figure 6.5) are two very important elements:
- Turbines: Their function is to transform the kinetic energy of water into mechanical energy of rotation. The Evolution of waterwheels and turbines is summarized on the previous page. Today, the most used turbines are Kaplan (with high yields) and improved Pelton.
Characteristics of the Kaplan Turbine
This is a vertical axis turbine and a propeller-shaped rotor with blades (usually 4 or 5) of variable inclination, which is enclosed in a cylindrical chamber whose upper reaches by water.
It is used for water falls below 25 m with long flow.
Their performance is usually between 93% and 95%.
It is one of the most commonly used turbines today.
Features of the Pelton Turbine
This is a very sophisticated waterwheel, which has a series of “scoops” placed on the periphery of a circle that can withstand the shock of a very powerful water jet.
Spoons receive water in one direction and eject it almost in the opposite direction (150°). In very large installations, they reach up to 50 tons of thrust.
It is used when there is a large waterfall, but not much flow. Its performance can reach 90%.
It rotates more slowly than Kaplan (300 to 1800 rpm). To increase power, it is enough to increase the number of jets.
Alternatives: With a Pelton turbine, the alternator is usually integral with the shaft of the turbine because the speed of rotation can be regulated by placing one or more jets. Kaplan turbines spin very rapidly, and therefore it is necessary to insert a speed reducer between the turbine and generator.
Transformers and Transmission Lines: The transformers are responsible for raising the output voltage of the alternator (which is typically about 20,000 V) up to 400,000 V, usually the voltage used to carry the current between distant points. If the plant is connected to the national grid (which is logical), it must be synchronized to the whole network so that its contribution joins the others.
C. Plant Types
Captive: Its power is less than 10 MW. Historically, they have been the basis of electricity production in small towns and businesses that were located close to rivers.
Large plants or hydroelectric dams: Their power is greater than 10 MW. They are located in the basins of rivers with large flows.
There are two types of plants: pure pumping and mixed pumping.
Pure Pump Stations: They have two reservoirs (the lower one is natural and very small). During peak electricity demand, they function as any central; that is, the upper reservoir water passes through pipes to the turbine, rotating it and generating electricity. When energy demand is low, it uses the surplus electricity from this plant or other nuclear power stations to pump water from the lower to the upper reservoir. To obtain a higher reservoir, water must be pumped previously because there is no river passing through. That is, the upper reservoir serves as a reservoir.
Mixed Pump Stations: They can produce energy equally with or without prior pumping. There is no need to pump water to the upper reservoir to produce power, as this lake is fed by the river bed. Only when there is a surplus of electricity and the upper reservoir has little water, because at that time the river flow is small, can it pump water from the lower to the upper reservoir.
D. Hydropower and Environment
This system of energy production is one of the cleanest in existence, as it does not emit fumes or waste into the atmosphere.
In addition, dams can regulate river flows, preventing floods and personal and material misfortunes in case of heavy or torrential rains. They also contribute to storing water that will later be exploited for human consumption and irrigation.
The main problems are that when the dam and reservoir are built, they usually inundate fertile tracts of land or, in some cases, whole villages, and sometimes disrupt the vegetation and fauna (it should be borne in mind that the reservoir may sometimes reach up to 400 km long).
Solar
The sun is the main energy source on Earth. Through nuclear reactions that originate inside, much of the released energy reaches Earth in the form of electromagnetic waves.
A. Harnessing Solar Energy
· • The solar energy are two key application areas: power conversion and transformation into thermal energy or heat. The attached table shows the machines used to carry out this task.
· · Conversion into thermal energy: flat collectors or collectors. Converting solar energy into heat energy is based on the fact that all sun-exposed body absorbs some of the sun’s rays fall on him. Depending on their color, absorb more or less radiation.
· · Theoretically, a matte black body would absorb all radiation, while a bright white reflect all the (perhaps the mirrors are the materials that best reflect the radiation that falls on them). This is not entirely true, but for practical purposes, be taken for valid.
· The devices used for the thermal energy or heat energy from the sun are called collectors or collectors.
· A solar collector is a box, usually metal, inside which has arranged a series of tubes, painted black, through which water circulates. The interior of the collector is painted likewise matte black to absorb sunlight.
• In the top has a glass, which allows the passage of the rays and makes the outer insulation. The collector is oriented toward the sun to capture maximum sunlight.
· · We manufacture three types of collectors:
· Up to temperatures of 35 ° C. It would be the simplest model collector and the pipes would not have any insulation that is, they would be without glass, so it would be in contact with the outside. The most usual applications are: air conditioning of swimming pools, heating greenhouses, drying rooms, outdoor showers, etc..
Up to temperatures of 60 ° C. In this case, the collector shall keep a glass exterior and the interior will be thermally insulated by fiberglass or polyurethane. The interior is painted matt black and pipes. They are used to heat hot water for heating homes, industrial uses and so on.
Up to temperatures of 120 ° C. The collector carries inside it a vacuum insulation. Therefore, for sealing will not be opened. It is used for industrial applications where water is required or high temperature.
· · Conversion into heat energy: passive use. There are many applications where this system is used. In fact, the man and living things take forever to warm building. As an example, there are two applications of this type of use for industrial use:
· · Greenhouses. Plastics allow incoming electromagnetic radiation. By impacting on soil, its wavelength changes and trying out the plastic, due to reflection, are retained. The result is the increase of temperature.
· · Desalination of seawater. It consists of two separate containers and external insulation. On one side is a crystal that will have an orientation of about 45 ° to the horizontal. At bottom, a reflective materialrays on the salt water. When water evaporates from the sea, remains at the bottom of salt. Water droplets condense and fall to another container.
Heliostat field. It consists of a series of heliostats, or mirrors directional (1), of large dimensions, which reflect sunlight fairy tower (3), concentrating solar rays on the boiler (2). The heat input is absorbed by the fluid from the boiler and taken to the steam generator (5). Then the energy is transmitted to a second circuit, where the water has evaporated and reaches the turbine-generator group (6), which produces electricity. Finally, the fluid is condensed in the air-condenser (7) to repeat the cycle.
Parabolic trough. They concentrate sunlight on a pipe containing a liquid (oil). This system can achieve temperatures up to 300 ° C.
The fluid (oil) transfers heat from the collector to a heat exchanger that is in the boiler. With this heat to evaporate water is obtained, which passes through the turbine and spins. The alternator, in solidarity with the turbine, is responsible for generating electrical current.
Solar oven. Is to focus on a small area or point solar rays that affect a very large surface area compared to the previous one. It uses a parabolic mirror, as seen in Figure 6.15. Temperatures can get very high (even to 4000 ° C) and are mainly used in research as the study of the melting point of materials. Commercial exploitation is not feasible at present due to its high cost. The largest solar furnace in the world is in Odeillo (France) with an output of one megawatt.
Photovoltaic panels. Each module or photovoltaic panel is formed by a series of solar cells (usually 36 in number), built of silicon as base material. When sunlight strikes the cells, it generates a small voltage (0.58 volts) at the ends of the terminals. The cells are placed in series, achieving a final voltage of 18 V and an intensity of approximately 2 A. The energy efficiency of these plates usually reaches 25%, depending on their orientation and the temperature at which they are submitted. The yield decreases with increasing temperature.