Renewable energy resources are easily accessible, constantly replenished and do not negatively affect the environment or life. By contrast, energy from oil, coal, and natural gas comes from finite, non-renewable fossil fuel resources. Access to fossil resources for non-renewable energy is difficult and expensive. In addition, the use of fossil fuels causes damage to the environment and life.
Introduction
Much of the renewable energy comes directly or indirectly from solar light and heat: 1. The sun influences the direction of the winds that are captured to generate wind power. 2. Solar heat encourages the evaporation of water on the planet, whose vapor is transformed into rain that flows into rivers and lakes where it can be captured in dams to generate hydroelectric energy. 3. Sunlight and rain favor the development of plants that contain organic matter known as biomass that can be used to generate energy. 4. The heat from sunlight heats the surface waters in the oceans, and the temperature difference between surface and deep waters in the oceans can be used as a renewable energy resource.
However, not all renewable energy resources come from the sun. Geothermal energy comes from internal heat on the planet, and can be used to generate electricity and heating.
The tides in the oceans generate renewable energy due to the gravitational effect of the moon on the Earth. The energy in the oceans is also generated by the movement of waves and tides.
Hydrogen is the most abundant element on planet Earth, and it is also an important source of renewable energy, present in all the water and air on the planet, as well as in many organic compounds. Hydrogen does not occur naturally as a gas in itself, but always combined with other elements such as oxygen found in water (H2O). Once hydrogen is separated from another element, it can be used as a renewable energy resource. Here are key technologies for harnessing our renewable energy resources.
Wind power
Wind energy (wind) was used in ancient times to grind grains and pump water through windmills. Today the equivalent of windmills are the wind turbines that are used to generate electricity. Like windmills, wind turbines are mounted on towers to capture wind energy. At thirty meters above the ground or more, wind turbines receive the fastest and least turbulent winds to generate electrical power. The turbines capture the energy of the wind that turns their two or three blades mounted in such a way to form a rotor that activates the generator to produce electricity.
Wind turbines can be used either interconnected together to generate large amounts of electricity; combined with solar cell systems; or by themselves in rural regions to pump water and provide electricity. Likewise, they are used to improve the supply in electrical power distribution systems.
Wind meter:
It measures the wind speed and transmits the data to the controller.
Brake:
The disc brake can be operated mechanically, electrically or hydraulically to stop the rotor in an emergency.
Controller:
The controller turns on the equipment when the wind speed is between 13 and 25 kilometers per hour, and turns off the equipment when the winds are greater than 100 kilometers per hour. Wind turbines should not operate with winds greater than 100 kilometers per hour because they overheat the generators.
Gear box:
The gearbox connects the Low Speed Bar to the High Speed Bar and increases the rotational speed from around 30 or 60 revolutions per minute (RPM) up to 1200 and 1500 revolutions per minute which is the speed required by most engines. generators that produce electricity. The gearbox is expensive and heavy, so engineers are exploring the possibility of direct drive that does not require a gearbox.
High Speed Bar:
The high speed bar runs the generator.
Low Speed Bar:
The rotor spins the low speed bar between 30 and 60 revolutions per minute.
The turbine rotates by means of three blades facing the wind. Two-blade wind turbines pick up less wind. Wind turbines produce 50 to 750 kilowatts. Small turbines (less than 50 kilowatts) are used in ranches, houses, to pump water, etc.
Solar energy
1. Concentration of Solar Energy
Conventional power plants use fossil fuels as a heat source to boil water whose steam turns a turbine to activate the generator that produces the electricity. However, new generation electric power plants are using concentrated solar heat instead of fossil fuels to obtain water vapor. There are currently three main types of systems to concentrate solar heat: Parabolic, Flat and Tower.
The Flat System
It uses dish-shaped mirrors that concentrate solar heat into a receptacle. The heat is transferred to the fluid in the machine. Solar heat causes the fluid to expand against a piston or turbine that produces mechanical energy, which is used to activate a generator or alternator that produces electricity.
Parabolic Systems
they concentrate solar heat through long, curved rectangular mirrors. These mirrors concentrate light and solar heat on the pipe in the center of the mirrors. The heat of the solar rays heats the oil that flows inside the pipe, which is used to boil the water whose steam activates a conventional steam generator to produce electricity.
The Tower System
uses large mirrors to concentrate solar heat into a receptacle containing salt, installed on top of a tower. Solar heat melts the salt that flows into the receptacle. The heat from the molten salt is used to generate steam and obtain electricity through a conventional steam generator. Molten salt retains heat so effectively that it can be stored for days before being converted into electricity. This means that the electricity through this system can be produced on cloudy days or at night.
2. Passive Solar Energy
Some buildings are designed to take full advantage of the benefits of solar energy, when it comes to lighting and heat. The south side of the buildings always receives a good part of heat and sunlight. For this reason, large windows are built on the south side of buildings and facilities. Likewise, materials that absorb solar energy are installed on floors and walls. These floors and walls heat up during the day, and release heat at night when it is most needed.
On the south side of some buildings, "sun spaces" are built, which are actually like greenhouses, made of transparent materials, through which sunlight passes that heats the interior space. In an appropriate "sun space" design, fans and ducts are installed to transfer and distribute the heat from inside the "sun spaces" to the interior of buildings. These systems during the hot season are "closed" by curtains that reduce the entry of sunlight.
3. Photovoltaic Solar Energy
It is used to produce electricity directly from sunlight. Solar cells, called photovoltaics, convert sunlight directly into electricity. These types of cells are also used to power calculators and watches. They are made of semiconductor materials, similar to those used in computer "chips." When sunlight is absorbed by these materials, solar energy strikes the loose electrons in their atoms, allowing them to flow through semiconductor materials to produce electricity. This process of converting sunlight (photons) into electricity (voltage) is called the Photovoltaic Effect
The solar cell combination typically consists of ten flat modules containing about 40 solar cells each. These modules can measure several meters on each side, and are installed, either fixed at an angle to the sun, or on rotating mobile devices that chase sunlight throughout the day. Several interconnected modules can be used when large amounts of electricity are required.
In thin films of solar cells, layers of semiconductor materials with a thickness of only a few microns are used. Thin film technology has made it possible to double the number of solar cells in the same space. The cells can be used in roof construction. Some solar cells are designed to operate in high concentrations of sunlight. These solar cells are built in concentrating collectors that use lenses to focus and capture more sunlight on the cells. This system, which consists of taking advantage of as much sunlight as possible, has advantages and disadvantages. The advantage of the system is that it uses little semiconductor material which is expensive. The downside is that the lenses only work well in regions with a lot of sun.
The performance of solar cells is measured in terms of their efficiency in transforming sunlight into electricity. Only part of the sunlight can be transformed into electricity, the other part is reflected or absorbed by the material from which the solar cells are made. Because of this, a typical commercial solar cell is approximately 15% efficient. That is, one sixth of the sunlight that reaches the cell generates electricity. In such a way, the low efficiency requires a greater number of solar cells, which increases the cost of electricity. Much of the research has been focused on improving the efficiency of solar cells. It should be noted that the first solar cells were built in 1950, and had an efficiency of less than 4%.
4. Solar Energy for Water Heating
We know that heat by physical law tends to rise, and that shallow waters are warmer than deep waters. Sunlight warms the bottom of shallow water areas. The hot bottom transmits heat to the water. This is the natural way that the sun heats water.
In some systems, flat solar collectors are generally installed on the south side of the roofs. Most systems for heating water in buildings have two main parts that are: a collector and a storage tank. The commonly used flat collector is installed on roofs, and consists of a thin rectangular box with a transparent cover facing the sun. Interconnected tubes inside the box contain the fluid, which can be water or another substance, which will be heated. The tubes, in turn, are installed on a black painted solar absorber plate, to capture the heat of the sunlight. In this way, the heat accumulated in the collector heats the fluid that passes through the tubes, and in turn the water to be heated.
Hydroelectric power
The flow of water that generates energy can be captured and transformed into electricity. This is hydroelectric or hydropower. In the common hydroelectric system, dams are used in rivers to store their water in dams. Water from the dam flows through turbines and turns them. As the turbines rotate, the generators are activated to produce electricity. Dams are not always required to obtain hydroelectric power. Some hydroelectric plants use only a narrow channel to channel all the water from a river through the turbine. A micro hydroelectric plant can produce enough electricity for a ranch, farm or house.
Biomass Energy
Human beings have used biomass or bio-energy energy for thousands of years. This energy that comes from vegetables and their derivatives has been used since the beginning of humanity to cook and maintain body heat by burning wood mainly. Currently, wood remains the largest biomass energy resource. However, other biomass energy resources can be used. Among them the waste of crops; woody and oily vegetables that are residues of agriculture and forestry; and organic components resulting from industrial and municipal waste. Even gases (methane) in garbage dumps can be used to obtain biomass energy. Biomass can be used for fuel,production of energy and products that would otherwise be made with fossil materials from which non-renewable energy is obtained.
Burning biomass releases the same amount of carbon dioxide as burning fossil fuels. However, fossil fuels release carbon dioxide captured by photosynthesis in plants millions of years ago. This essentially adds a "new" amount of carbon dioxide to the environment, while biomass releases only the carbon dioxide captured by plants during their recent development. The main sources of biomass for energy are found in waste from paper mills, sawmill waste and municipal organic waste. On the other hand, the main sources for obtaining biofuels are found in the surpluses and residues of corn (ethanol) and soy (bio-diesel).
Unlike other renewable energy resources, biomass can be directly converted into liquid fuels called bio-fuels, which can be transported. The most common biofuels are ethanol and bio-diesel. Ethanol is an alcohol like beer and wine, made by fermenting any type of biomass high in carbohydrates, and it is obtained by a process similar to that carried out for the manufacture of beer. Currently ethanol is made from starches and sugars. In the near future, ethanol will also be able to be manufactured from cellulose and hemicellulose from fibrous waste materials that make up the majority of vegetables. Ethanol is mostly used as an additive in gasoline to increase octane number and reduce carbon monoxide emissions.Bio-diesel is made by combining alcohol (usually methanol) with vegetable oil, animal fat or recycled vegetable oil, and can be used as an additive, typically 20%, to reduce gas emissions in vehicles, or 100% in engines diesel as an alternative renewable source of energy.
Hydrogen Energy
Hydrogen can fill vehicle fuel tanks instead of using gasoline. It is possible to pipe it for cooking and heating in homes. Also with hydrogen, electricity can be generated in the same place, instead of sending electricity through transmission. Hydrogen does not pollute at all, because when it is used it only emits water vapor.
Fuel cells electrochemically combine hydrogen and oxygen to produce electricity, making hydrogen an ideal universal fuel. Hydrogen is the most abundant element on the planet, because it is found in all water (H2O) combined with oxygen, and in the air. However, it does need to be removed from the water for transport, storage and use.
Hydrogen production is currently made from natural gas, which is a rare and expensive fossil fuel that releases carbon dioxide. Hydrogen has very high energy relative to its weight, but low energy relative to its volume. For this reason technology is required to store and transport hydrogen. In this sense, technological research to improve the efficiency and durability of fuel cells is still under development. Researchers are working to make hydrogen the most important source of energy on the planet soon.
Research topics include the following:
- Improve technology and materials for fuel cells. Develop efficient and competitive techniques to obtain hydrogen from renewable energy resources. Develop technology to be able to store and transport hydrogen efficiently and competitively.
1. Fuel Cells
The ability of fuel cells to produce energy from hydrogen and oxygen, without generating pollution, is what makes them attractive. Fuel cells work in a similar way to a battery that generates energy by chemical reaction rather than combustion, except that fuel cells require a supply of hydrogen to function. Fuel cells typically consist of small layered cells, and various types of cells use different catalysts and electrolytes.
2. Hydrogen Production
The simplest and most common element among us on the planet is hydrogen, but this is found in combination with other elements. In such a way, for hydrogen to be usable it is necessary to use other energy resources to extract it from water and other compounds where it is found. The following are some of the methods for producing hydrogen from renewable energy:
- Thermochemical Hydrogen: When heating biomass in an environment without oxygen, or with limited oxygen, a gas mixture is produced that contains hydrogen and carbon monoxide. Hydrogen is extracted from this gas mixture: The mixture can be catalytically converted to increase the amount of hydrogen available through a water-gas reaction.Electrolytic Hydrogen: By electrolysis, it is electrochemically possible to separate hydrogen and hydrogen from water (H2O). oxygen Photovoltaic Electro Chemical Hydrogen: Semiconductor material is used to generate the electricity required in the reaction that separates hydrogen from oxygen in water Photovoltaic Biological Hydrogen: Research on the development of microorganisms that ferment sugars and cellulose to produce hydrogen instead of alcohol.
Hydrogen as a renewable energy resource to generate electricity is not very competitive, because until now the wind is the cheapest renewable energy source. However, hydrogen could be used as a fuel in transport vehicles.
3. Hydrogen Storage
Due to its low density, hydrogen requires large space to be stored and transported. This is obviously impractical for transport vehicles and storage tanks. Hydrogen is currently compressed in pressurized tanks, but this method is still insufficient because its volume is greater than desired for its transport, storage and processing.
In liquid hydrogen the density of the fuel doubles, but a large amount of energy is required to lower its temperature to -253 ° C in order to increase its density. Likewise, expensive tanks are necessary, made with insulating materials to maintain the temperature and, even so, the hydrogen volume continues to be greater than desired for its handling.
Research on hydrogen storage is mainly focused on the use of nano-tubes, as well as other geometric forms of simple carbon atoms (nano-structures), whose size is not much larger than hydrogen molecules, and maintain a high density-space radius. That is, high density in little space. These nano-structures have the ability to absorb hydrogen on their surfaces. Researchers have developed the nano-scale whose unit is equal to one billionth of a meter. The characteristics of nano-structures, mainly single-walled nano-tubes, that can increase the hydrogen storage capacity are investigated. This type of storage is still promising.
Geothermal energy
1. Direct Use
Geothermal hot water reserves are generally found more than two kilometers below the earth's surface, and using their energy can directly provide heating. That is, a well is drilled in the geothermal reservoir to obtain a constant flow of hot water. The hot water is pumped, piped and controlled to be distributed to where heating is required. After use, the cold or warm water is injected into the subsoil or used on the surface. The direct use of this energy for heating can be applied for domestic, industrial, municipal and greenhouse use.
2. Electricity Production
Most electricity generation systems require steam to produce electrical energy. The steam turns the turbine that activates the electricity-producing generator.
Geothermal power plants use steam that emanates from the deep. In this way, the use of fossil fuels to heat water and generate steam in the production of electricity is avoided.
In geothermal power plants that work with dry steam coming from the subsoil in geothermal reserves, they directly pipe the steam that emanates from the wells and is directed towards the turbine-generator unit.
Another type of geothermal power plants use water, whose temperature is greater than 182 ° C, which flows from the wells towards the surface by its same pressure. As the water flows, its pressure decreases, and much of the water is transformed into steam that is separated from the water to be used in the turbine-generator unit. The water and steam residues are injected into the subsoil so that the resource is sustainable.
In binary cycle geothermal power plants, water that is at lower temperatures (107 ° C to 182 ° C) is used. In this system, hot water is used to boil a fluid that is generally an organic compound with a low boiling point (ammonia). The fluid is vaporized in the heat exchanger and used to turn the turbine and activate the electricity generator. The residual water is injected into the subsoil to be reheated. Fluid and water are kept separate throughout the process. Small-scale geothermal power plants have potential in rural areas where geothermal energy resources exist.
3. Heat Pumping
Within the first three meters of depth in the subsoil, the temperature remains constant between 10 ° C and 16 ° C. This constant temperature range in the subsoil is higher in winter and lower in summer than on the surface. Through pumping and temperature distribution, use is made of the constant temperature range in the subsoil, either for cooling or heating in buildings. The system consists essentially of three parts: 1. Underground heat exchanger. 2. Pump. 3. Ducts. The heat exchanger basically consists of a series of tubes buried underground near the building. A fluid, generally water and antifreeze, circulates inside the pipe absorbing or repelling the heat from the subsoil. During winter,The pump takes heat from the heat exchanger and pumps it to the ducts that distribute it in the building. In summer, the pump takes heat from inside the building and pumps it to the underground heat exchanger.
Ocean Energy
The oceans produce two types of renewable energy: 1. Thermal, due to the heat of sunlight. 2. Mechanics, due to tides and waves. The oceans cover 70% of the planet Earth, and are the largest collectors of solar energy and heat. Only a small part of the heat trapped in the oceans could supply energy to much of the world. The sun's heat is greater at the surface than in the depths of the oceans. This difference between temperatures generates the thermal energy.
1. Thermal Energy
Thermal energy in the oceans is used in various applications including electricity. There are three conversion systems for generating electricity: open cycle, closed cycle and hybrid. The closed-loop system uses warm water at the ocean's surface to vaporize a low-boiling fluid, whose steam turns the turbine and activates the generator to produce electricity.
In an open cycle, seawater is boiled operating at low pressure to generate steam that powers the turbine and generator. The hybrid cycle is the combination of open cycle and closed cycle.
2. Mechanical Energy
Mechanical energy in the oceans is very different from ocean thermal energy. Although the sun influences all ocean activities, tides are caused by the gravitational force of the moon, and waves are formed mainly by winds. Thus, tides and waves are an intermittent source of energy, while the thermal energy in the oceans is more or less constant. In this way, devices are necessary to obtain mechanical energy in the oceans. Dams are typically used to convert tidal energy into electricity, channeling seawater into turbines that turn on generators.
On the other hand, basically three systems are used to transform wave energy into electricity: 1. Channel systems that trap the waves in reservoirs. 2. Floating systems that operate hydraulic pumps. 3. Oscillating water column systems that use waves to compress air within a container. The mechanical energy created by these systems activates generators or is transferred to fluids, air or water, to run the turbine-generator unit.
3. Thermal Energy Conversion
This process uses the heat energy stored in the planet's oceans to generate electricity. This process works best when the difference between the temperatures of surface water, which is warmer, and water from the depths, which is colder, is around 20 ° C. These conditions of difference between temperatures occur mainly in tropical coastal areas, between the Tropic of Cancer and the Tropic of Capricorn. In order to raise the cold water from the ocean depths, to create a difference between temperatures, large pumps with large diameter pipes are required, which are submerged at ocean depths greater than 1500 meters.
This system is not new, as in 1881 the French physicist Jaques Arsene d'Arsonval presented studies to take advantage of the thermal energy of the oceans. However, it was the disciple of Jaques Arsene d'Arsonval, Georges Claude, who in 1930 built in Cuba the first plant to take advantage of thermal energy in the ocean. The system produced 22 kilowatts using a low pressure turbine. Georges Claude himself, in 1935, built another plant aboard a 10,000-ton cargo ship docked off the coast of Brazil.
4. Hybrid System
Through the mentioned hybrid system, fresh water can be obtained from the oceans. A plant that generates two megawatts of net electricity can produce around 4,300 cubic meters (four million three hundred thousand liters) of desalinated water per day.
5. Tidal Energy
In all coastal regions there are two high tides and two low tides in a period a little longer than 24 hours. Tidal energy can be converted into electricity when the difference between high and low tide is at least five meters. There are only about 40 regions on the planet where there is this difference in the magnitude of the tides. It is also possible to use turbines to harness the energy of the tides. Turbines are placed underwater in the oceans, ocean currents pass through them and make them spin. Some currents whose speed is between 5 and 8 knots, can generate more energy than high capacity windmills (wind energy). This is because the density of seawater is much higher than that of air. In such a way,ocean currents carry more energy than wind.
6. Wave Energy
Various devices directly extract energy from surface waves, or from pressure fluctuations under the ocean surface. Analysts estimate that waves in the oceans could provide up to three trillion megawatts of electricity. Wave energy can be harnessed, either through oceanic or coastal systems. Oceanic systems are generally installed at a depth greater than 40 meters. These systems use sophisticated mechanisms that take advantage of the movement of the waves to activate a pump that generates electricity. Other ocean systems use hoses connected to floats that travel with the waves. The vertical up and down movement of the floats stretches and relaxes the hose, which pressurizes the water that turns a turbine. On the other hand,Specially designed platform ships can also harness wave energy. These floating platforms create electricity by funneling waves into internal turbines.
Coastal systems use to extract energy from the waves, procedures such as the oscillating water column, which consists of a metal or concrete structure, submerged in the coasts, which has an opening towards the sea, below the line of water. This structure stores a column of air above the column of water. The waves when penetrating the air column, make the water column rise and fall. These two reciprocating movements compress and depressurize the air column. Then, when the wave withdraws, the air is pulled through the turbine due to the reduction in air pressure.
Another system consists of a narrow channel, built into reefs. The narrowness of the channel causes the waves to reach the channel increase in height. The waves spill over the canal walls and are captured in a pond where the stored water is used to move the turbine and activate the generator.
Additionally, the pendulum system consists of a rectangular box open towards the ocean on one side where a hinged lid is installed so that through the action of the waves it oscillates in and out. The oscillating movement of the cover generates energy that is used to operate a hydraulic pump and a generator.
References: Renewable Energy Laboratory.
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