From the beginning, man has tried to harness the means that nature puts at your wit and processing capacity to meet their needs and improve their living conditions. In addition to using energy wisely from the sun to increase yields and adapt their homes to the climatic conditions of the environment, man has used for millennia, the water power for grinding grain, wind push to move their boats , and heat of fire to extract metals from the earth.
Although the growth of energy demand has been constant throughout history, is at the end of the eighteenth century with the industrial revolution, when the energy becomes one of the most important factors, and even conditions for the development of human activities.
The need for flexible energy sources, not conditioned by a specific geographical location (on the banks of a river or in areas with abundant winds), or limited by natural phenomena, often unpredictable, leading to the promotion of the use of fossil fuels for energy production at the expense of water mills and wind, of limited usefulness in a world where energy transport was difficult and expensive, if not unknown.
The wood and then coal, were virtually the only source of energy supply to the late nineteenth century. From this date begins the massive exploitation of oil resources, in the early 70's, they would cover more than 40% of energy demand in industrialized countries. Finally, in mid-twentieth century, we discover and learn to use nuclear energy, with results so promising that they did foresee a future based on this type of energy.
However, and from the 70's, coinciding with the call <<crisis of petróleo>>, the landscape undergoes a radical change: fossil fuels are no longer cheap and are beginning to question both economically and socially, the profitability of nuclear power plants. These circumstances, coupled with the progressive social rejection of aggressive technology and environmental awareness of future consequences of overexploitation of limited fossil resources, led not only to search for new energy sources, but also to review disqualified or alternatives previously considered uneconomic.
In this context, the idea emerges strongly from the use of renewable resources as an alternative non-negligible in a situation of increased energy demand and progressive depletion of traditional fuels, a situation that undoubtedly will tend to worsen in near future, as science advances not provide access to new sources d and generous energy.
Renewables
More than 5000 million years the sun, a huge glowing sphere, located 150 million kilometers from Earth, and with a mass 334,000 times that of our planet, it emits energy that is manifested primarily in the form of light and heat.
Because of the fusion reactions take place continuously within it, the sun transforms every second, four million tons of its mass into energy, which is, according to Einstein's equation (E = mc squared), energy release of around 8600 billion toe per second
Although only two millionths of its radiation reaching the Earth's atmosphere, the sun, directly or indirectly, is the origin of all known forms of energy, except perhaps nuclear energy
Of all these forms of energy, particularly renewable energy are called alternative energy, to those whose use is not significantly alter an environment, are recoverable in a natural cyclical, at least in periods of time on a human scale and, unlike the so-called conventional energy sources, not from the exploitation of deposits of non-renewable and finite.
Types of renewable energy
• Solar energy directly radiated and that is not absorbed or transformed in a meaningful way, is called direct solar energy, or simply, solar power, and it will give the inhabitants of the earth light and warmth• The uneven distribution of energy absorbed by the atmosphere, and the consequent formation of thermal gradients is the primary cause of the movement of air masses, and therefore, the source of wind energy or wind energy• Part of the solar energy that passes through the atmosphere is absorbed by green plants through the process of photosynthesis, and it is stored as chemical energy. This energy, transmitted through the food chain to other living beings and also present in the waste they generate, is called biomass energy• Geothermal energy is the energy contained in the interior of the earth, also with remote origin in the sun, and is manifested as heat. Although, strictly speaking, is not an infinite resource, practically inexhaustible character usually does include it within the group of renewable energy• When water bodies present in the Earth's surface absorb solar energy, raise its temperature, evaporating in part, passed to the atmosphere and then fall back to earth as rain or snow that accumulate at different levels. The potential energy of these water bodies, which naturally is transformed into kinetic energy by moving to lower altitude areas, is hydropower, which, in particular, is known as mini hydro power, when its use is done through small installations, less aggressive to the environment• Finally on the oceans of the moon's gravitational forces. The heat of the sun and wind, is the source of energy from the sea in its three manifestations, tidal energy or tidal energy, wave energy and thermal energy of the teeth or maremotermica
The renewable energy today
Despite significant technological advances that have taken place in recent years in the field of renewable energy, its contribution to the energy balance is still modest. Of the 8000 million tonnes of oil equivalent (toe) which puts the world's primary energy in 1989, less than 1% is obtained from renewable resources. In Spain, this quantity is the order of 3% and in Galicia, with a total production of primary energy over 9.5 million toe, barely 2% of this figure
In the near future, and as far as Europe is concerned, the European Commission considers that the renewable energy contribution to the total of these energies could represent between 2 and 8%. With respect to Galicia, the current state of technologies to apply, and based on a reasonable consideration its foreseeable development, implementation and application, one could conclude that the share of renewables in the overall energy balance could reach Galician 5% of total
Solar energy
Of all the energy from the sun affects the Earth's atmosphere, only a part (a little over half), reaches the surface of our planet. At the upper levels of the atmosphere is removed most of the ultraviolet radiation, another part of the radiation is returned to space by reflection, refraction and diffusion, and finally, some is absorbed by water vapor and other components the atmosphere.
Still, solar energy reaching the surface of the earth in vast quantities: every ten days are about sixty million tep billion, equivalent to all the known reserves of coal, oil and natural gas. However, their use presents certain difficulties, which differentiate and distinguish it from other energy sources.
Difficulties
The first of these difficulties is that it is a widely dispersed energy (ground level received a maximum power of 1 kW / m squared), which requires consideration of a rethink on the use and distribution of energy quite different from now considered classic
Second, the characteristics of intermittent and random, pose serious problems in the optimization of systems based on solar energy utilization, especially for not being sufficiently developed, so far, no sufficiently effective system for storing energy produced
Finally, the large-scale solar energy collection systems require large area, with significant land-take and an aesthetic, at least arguably, in a time when society is particularly sensitive to alterations to the natural environment
However, despite the conditions described, it is clear that, both in quantity and quality, solar energy sources is one of the most important energy supply available to mankind and therefore with all the limitations impose a very recent technology implementation, can and should be exploited
Harvesting techniques
In addition to its passive use (sunlight and shading), used in many architectural elements from ancient times, there are two routes for the active use of solar energy, its transformation into heat, or thermal conversion and direct conversion into electrical energy, or photovoltaic conversion.
The thermal conversion
The thermal conversion is based on the use of an item (panel or collector) which exposed to solar radiation, to absorb the heat and transfer to a fluid for later use, either directly (heating, hot water ...) either for conversion into electricity through turbine-generator groups
Thermal conversion systems are typically classified into three types, in melting temperature of the fluid used for heat transfer. Thus we speak of low-temperature working fluid when below 90 ° C, medium temperature when it does between 90 and 300 ° C, and high temperature to values above 300 ° C
- Low temperature systems
They are characterized by the use of fixed flat plate collectors and energy uptake, and its main use is for domestic use (hot water and heating). The collector, a key element of the system is a surface exposed to solar radiation, absorbs and transmits its heat to a fluid, usually water or antifreeze liquid
Flat plate collectors usually used in low temperature systems are composed of the following:
- A sensor or receiver plate, made of material (copper, stainless steel and even plastic) that can absorb heat from the sun's radiation. To enhance its effectiveness, the board usually painted or coated electrolytically in black- A circuit for the circulation of the fluid, responsible for transporting the heat produced in the plate to the rest of the installation. Circulation may be natural or forced, as the effect using a pump or driving torque to the fluid motion- A transparent cover, and protect the plate from external agents, uses the greenhouse to increase the efficiency of the collector- A suitably insulated enclosure, containing the above elements.
In addition to the collector, the low-temperature solar systems have an energy storage device consisting of one or more storage tanks for hot fluid from the panels, in order to save the excess heat to take advantage when captured demand requires it, and not only at times that this uptake occurs
- Medium temperature systems
For the utilization of solar energy medium temperature collectors are used for consultation. These are devices that concentrate the sun's radiation in a small area, so it is possible to reach temperatures of 300 ° C, sufficient to produce steam, which can be used to generate electricity by conventional methods, or even directly in industrial processes
For proper operation, concentrating collectors need to be constantly facing the sun, so they require effective monitoring device, allowing them to receive at all times the solar radiation in the optimum position
Although there are various systems to concentrate sunlight (combinations of mirrors, lenses, parabolic mirrors, etc..), At present, the technique most used is the parabolic trough collector, which is below cylinder-parabolic mirror reflecting the radiation the sun on a glass tube provided in the focal line of the optical system, within which is the absorber and the heat carrier.
- High-temperature systems
The production of electricity on a large scale from the thermal use of solar energy required to achieve high temperatures, higher than can be obtained by flat plate collectors and parabolic trough
The thermal conversion system most commonly used is called heliostats central receiver, which consists of a set of reflective surfaces (heliostats), individually adjustable, which concentrate solar radiation onto a receiver located on top of a tower. The energy collected in the receiver is used to heat a fluid to a temperature to allow, either directly or using a heat exchanger to generate steam, a group fed conventional turbine-generator to produce electricity
Photovoltaic conversion
The direct conversion of solar energy into electric energy is through solar cells, devices that use the photovoltaic effect, ie the ability of some semiconductor materials to generate electricity by impacting on them a light radiation
A typical solar cell is constituted by a sheet of high-purity silicon, chemically treated with boron and phosphorus, and metal electrodes on both sides. The solar energy that strikes the cell, with some of the links on the silicon atoms, creating electron-hole pairs (negative-positive) that give rise to an electric field, and therefore to an electromotive force capable of supplying a current electrical
Since the voltage and power levels provided by a solar cell are very low, are usually grouped in panels, so that cells connected in series or in parallel, it is possible to obtain the voltage and current required by each application
In most low-power applications, the panels are connected in parallel with a battery and, in order to avoid losses, consumption takes place directly in DC. However, when the receivers need to use AC power, or when the installation is planned for operation in connection with the general distribution network, you must install an inverter, a device that converts alternating current from direct current of panels or battery
Wind energy
Solar radiation absorbed by the atmosphere unevenly, resulting in air masses with different temperatures and therefore different densities and pressures. The air, moving from high to low pressure, giving rise to the phenomenon known as wind
It is estimated that the energy contained in wind is approximately 2% of total solar energy reaching the earth, which is nearly two trillion a year and toe, but in practice could only be used a very small part of that number (approximately 5%), the amount of energy that this represents wind makes one of the renewable energy sources with the greatest potential
Like with solar power, wind power is characterized by randomness and dispersion, and therefore poses the same problem for its use in large scale, the need for expensive storage systems to adapt energy production the requirements of the demand
Although the use of wind power dates from the earliest times of humanity (there are recorded on sailing Egyptians dated 5000 BC), is from the XII-XIII when it starts to widespread use of windmills for raising water and grinding grain, based on rudimentary designs, which, with several improvements, especially in the control and guidance systems will be maintained well into the nineteenth century
The development of windmills is interrupted by the industrial revolution and the massive use of steam, electricity and fossil fuels as sources of motive power. It is however in the second half of the nineteenth century when it takes place one of the most important advances in the technology of harnessing wind, then the appearance of the highly popular <<molino multipal americano>>, used for pumping water almost everywhere in the world, and whose features were to lay the groundwork for the design of modern wind turbines
In 70 years, coinciding with the first oil crisis, begins a new stage in harnessing wind energy. The application of modern technologies, especially those developed for aviation has resulted in the emergence of a new generation of highly sophisticated wind machines, and with yields that enable its operation under the criteria of economic profitability, in areas with wind potential high
Harvesting techniques
Unlike the old windmills, used exclusively for pumping water and milling grain, almost all of modern wind turbines are oriented towards the production of electrical power, ease of handling and transport of such energy, as well as versatility in subsequent applications.
Wind machines
Machines are called wind those devices capable of exploiting the kinetic energy of wind into mechanical energy transforming
A wind machine consists of three basic elements, a collection system or rotor, whose mission is to collect and transform wind energy into mechanical energy, a guidance system that will detect wind direction and position the rotor in the most adequate for maximum energy efficiency, and a regulatory system to control the rotational speed of the machine and stop if necessary.
The collection system
The collection system or rotor is the most important element of a wind machine. It consists of a series of vanes or blades that rotate on an axis by wind and transform kinetic energy into mechanical energy
Depending on the spatial position of its axis, the classification is more usual wind rotors, rotor vertical and horizontal axis rotors.
Vertical axis rotors
Although best known wind machines are those that use horizontal-axis rotors have been designed and constructed vertical axis machines since man took his first steps in harnessing wind energy. In addition to greater structural simplicity, this type of machine has a significant advantage over devices horizontal axis, the rotor works for any wind direction and therefore requires no guidance system for
Among the many designs of vertical axis rotors are known, there are three that have a more favorable development prospects, the Savonius rotor, the Darrieus and Giromill
The Savonius rotor consists of two half cylinders, horizontally displaced a certain distance so that air can circulate between them, arranged vertically. This is a very simple device, easily constructed and, in general, small power.
The Darrieus rotor has two or three blades, straight or as a parable, attached to a vertical axis at its ends. Despite their inability to get going without other aids, is today one of the vertical axis rotors more advanced
The rotor type is basically similar to Giromill Darrieus, with the peculiarity that, through an eccentric mechanism, it automatically changes the pitch of the blades depending on their orientation to the wind, which results in better performance low speeds and provides the ability to boot itself.
Horizontal axis rotors
After onset mills vertical axis wind machines with horizontal axis rotor are currently the most widespread and sophisticated. Despite the need for a mechanism of high performance orientation has pushed the use of vertical axis rotors almost experimental purposes
Depending on the number of planes and, consequently, its rate of rotation, the horizontal axis rotors are classified into slow and fast
The rotors slow, with a number of blades between 12 and 36 and a diameter generally less than 8m, are used exclusively in low power applications. Because of its low speed and high torque, find their main use in water pumping
The rotors are built usually fast two or three blades. They have the advantage that, at equal power, are much lighter than the rotors slow, and its aerodynamic performance is higher. By contrast, require a relatively high wind speeds (about 5m / s) to begin work. Their wider application is the production of electricity.
The guidance system
Unlike primitive windmills, which was necessary to manually guide the rotor facing the wind, all modern wind machines are equipped with devices that automatically perform this function. Although various guidance systems, currently used only two of them in almost all facilities horizontal axis, the wings, stabilizers and servomechanisms
The first, used in machines of small capacity, consists of a simple fin set way behind the rotor vane so that it constantly faces the wind
Large wind turbines, the guidance system is an automatic mechanism, consisting of a small vane that captures the wind direction and governed by a servo which acts by rotating the rotor to place it in the right direction.
The regulatory system
Many applications of wind machines need their rotation speed is kept constant, avoiding fluctuations caused by variations in wind speed, and in all cases, we need a system that stops the rotor when the speed exceeds the limit of security. There are two basic methods for regulating the rotation speed regulation by varying the incidence of the rotor and regulation by variation of incidence of the blades
Regulation by variation in the incidence of the rotor is the most primitive, and currently only used in simple machines and small power. It consists of a vane rigidly attached to the housing of the rotor, causing a tilt of the wind turbine to the wind when the speed increases. As a result of the reduction of exposed surface, larger as the rotational speed remains constant, and the machine comes to a stop when the axis of the turbine reaches a position perpendicular to the wind
The regulatory system more efficient and more widespread use in machines of medium and high power is the regulation by variation of incidence of the blades, or variation of way. This system works by varying the angle of the rotor blades, which is increased or decreased performance, and consequently, the power of the machine. In machines of small and medium power devices are used to direct centrifugal action, by means of springs and balances, change the blade pitch, or part of them when its rotational speed increases, reaching them in a position to flag that is, parallel to the wind, when its speed reaches the limit of safety. In modern high-powered machines, the variation of the incidence angle of the blades is accomplished through a series of servo-mechanisms, governed by a microprocessor, which provides at all times the best position of the blades to the wind conditions champs.
Mini hydro power
In gross potential water power on our planet is estimated at one billion annual toe. Despite the constraints of technical, economic and even geographic, make possible the use only of something more than a third of this potential, the amount of energy that is around 1500 million toe per year, important enough for this kind of energy can be considered as a source of energy supply of the first magnitude
The use of mini hydro power has its origins in ancient Chinese wheels of action, built more than 4000 years. The first documented reference to a water mill on the mill is Roman and dates from the year 85 BC it was a water wheel with blades flat horizontal axis, and was widely used during Roman times for grinding grain. Although during the Middle Ages and the Renaissance hydro energy bring economic prosperity to many cities built along major rivers, the construction technique of the mills was hardly changes, and it is not until the mid nineteenth century when it starts the development of machines that give rise to modern hydraulic turbines
At that time, coinciding with the industrial revolution, the first turbines are constructed of reaction (Fourneyron 1832, and Francis 1848) was later recovered the use of the waterwheel, significantly improved (Pelton impulse turbine) and finally, in 1906 shows the Kaplan turbine. These machines, high performance and high rotational speeds, opened the way for a new application of water power, which would help meet much of the energy needs of industrialized countries during the first half of the twentieth century, the production of electricity through hydro-called
Although from the mid-50's, the share of hydropower in the energy market decreases rapidly, primarily because of the drastic reduction in fossil fuel prices, which boost the construction of large power plants, after the energy crisis occurred in the 70's, the small-scale hydroelectric again be taken into account. The proven existence of a significant yet untapped hydroelectric potential, coupled with technological advances of recent years which make the operation profitable, and growing social interest in the use of energy sources less aggressive to the environment, have returned to the small hydro lost the leading role in decades past.
Harvesting techniques
Today, almost all of hydropower in operation is used to produce electricity through hydroelectric plants.
Hydroelectric
It is called hydroelectric power to all facilities necessary to transform electrical energy into potential energy and kinetic energy of a water course, and in particular, adopting the name of mini hydro power when the installation does not exceed 5000 kW
In terms of its ability to store water from the river, are two different basic types of hydroelectric plants, water power plants with flowing and regulation
Of-river plants exploit a part of the flow of the river without any regulation is diverted and taken to the central for conversion into electricity. Since the flow rate used is variable depending on the supply of water at all times, the available power is directly related to the instantaneous flow of the river
In plants with regulation, there is the possibility of storing water through a dam, allowing its use at the time it is needed, adjusting production to consumption needs, regardless of the flows in each time the river provides
In-river plants, the work is a collection of small height wall (called azoud or prey), transverse to the flow of water and usually constructed of concrete or masonry, which aims to create a small haven in the river and channel part of its flow to the rest of central facilities. Regulation in plants with the work of recruitment also serves to raise the level of the river and store water by creating a reservoir
The water collected in the collection is conducted at nearly constant until close to the turbine via a channel, usually open, which follows the contours of the land with a gentle slope and provides the necessary water drop hydraulic use
The diversion canal flows into the forebay, which is not only a buffer tank whose mission is to absorb peak loads of the turbine starts, preventing the entry of air caused by a sudden drop in water level
Finally, through the pressure pipe or penstock, water is conducted to the turbine, where its potential energy and kinetic energy is converted into mechanical rotation, and later, and by means of a generator transformed into electrical energy .
Hydraulic turbines
Among the many types of turbines developed to Throughout history, today, there are three most commonly used, the Pelton, Francis and propeller, with its variant the Kaplan turbine
The Pelton turbine is in a group of so-called impulse turbines or turbine drive, is composed of a circular disc, or impeller, with a series of buckets mounted perpendicularly and symmetrically in the periphery, on which the water jet impinges of one or more nozzles distributed around.
Nozzles regulate the flow of water, and therefore, the power of the machine. This type of turbine, the axis can be arranged both horizontally and vertically, is used in large hydroelectric high and low flow. Its performance is superior to 90%
The Francis turbine comprises an inlet chamber, spiral-shaped, which channels the water into distributor, consisting of a series of moving blades, whose mission is to regulate the flow and direct it toward the impeller radially, consisting of a crown blade receiving stream and transforms their energy into rotational motion. As is the case with Pelton turbines, the shaft Francis turbine can be horizontal or vertical turbine type is the most versatile to adapt to different streams and waterfalls, and its maximum throughput is close to 90%
The turbine is a turbine propeller in which the impeller is reduced to a single propeller, four or five blades, arranged inside a chamber, usually cylindrical. When the slope of these blades is adjustable, sturdy turbine called Kaplan turbine, the turbine and propeller has the advantage of greater adaptability to variable flow regimes. These turbines are best suited for the utilization of low height and high flow, and its maximum output is around 95%
The energy of the sea
The oceans, which cover just over a third of the planet's surface, are a virtually inexhaustible energy source, yet little exploited. It is estimated that the energy potential of the seas is the order of 50,000 miles of toe / year, ie more than five times the total energy consumption at present
There are three major forms of ocean energy, tidal energy, wave energy and energy maremotermica.
The tidal energy
The rise and fall of sea level caused by the action of gravitational forces of the sun and the moon have been exploited by humans for energy production for many years. Already in ancient Egypt were used primitive tide mills for crushing the grain, and although there have been mills of this type throughout history, is in 1996 when, with the launch of the tidal plant estuary of the Rance River in France, performed the first major project for harnessing tidal energy. This plant, along with the Kislaya Bay, in the Soviet Union, putting into operation in 1968, are the only tidal power stations in operation today.
Harvesting techniques
The tidal power stations, like hydroelectric power, use the energy of a body of water that moves from a higher to a lower one. In its simplest form, a plant of this type consists of a reservoir formed by a natural estuary or bay, and a dam, which separates the sea and which are located a gate and a hydraulic turbine, similar to the turbines Kaplan used in hydroelectric power stations
Basically, the tidal power plant operation is the following, lie the tide rises, the gate of the dam remains open, and the estuary receives water from the sea. At the time of high tide, the gate closes, preventing the return of water to the sea as the tide. Finally, before low tide, the water in the estuary empties into the sea again through the turbine, resulting in energy production
Through this system, called single acting cycle is only possible to obtain energy for about six hours a day, in two periods of three hours, and coinciding with low tides. You can improve plant performance using reversible turbines, ie capable of operating in both directions. This so-called double-effect cycle, allows turbines during filling and emptying of the estuary, leading to greater and more regular energy production.
The wave energy
Although the first device designed to extract energy from waves dates from the late sixteenth century to the present has not built any of an industrial facility that allows the use of such energy
Tools that tidal variations are well known, the distribution and magnitude of the waves at a particular point are impossible to predict. This is a huge challenge for the design of devices of its energy collectors, to be able to respond effectively to waves with shapes, sizes and very different frequencies.
Harvesting techniques
Are currently being tested several systems for harnessing wave energy, all based on the same diagram of operation, the waves push a body, causing compression of a fluid which is then used to move a turbine and produce electricity. Among the most developed systems today are the <<pato>> Salter, the raft Cockerell, oscillating column converter, rectifier and the buoy nasuda Russell
The <<pato>> Salter is composed of a series of elongated floats, united by a longitudinal axis and a section that recalls the shape of ducks. The wave action causes the oscillation of the floats around the axis, oscillation that is utilized to drive an oil pump, which in turn is responsible for moving a turbine-generator group, for the production of electricity.
Cockerell's Raft is a group of floats, usually three, with a raft and articulated with each other. The relative motion between the floats produced by the waves is used to move a generator, by means of a hydraulic system installed in each joint
The converter uses oscillating column wave pressure as a piston to produce work. A variant of this system, developed in Norway, is harnessing the power of the waves that pass through the bottom of a semi-submerged cylinder attached to the coast, for compressing a column of air, which in turn drives a turbine located at the top
Russell rectifier consists of two chambers, fixed in the bottom of the sea and arranged one above the other, parallel to the direction of the waves penetrate the upper chamber by gravity flow to the bottom, turning a turbine
The buoy nasuda, developed in Japan, is a floating camera semisumegida, in which the wave motion is used to suck and push air through a unidirectional low pressure turbine, whose rotation is then used to produce electricity using a generator
The energy maremotermica
A portion of the solar energy striking the earth is stored by the oceans as heat. This energy, also called maremotermica energy can be transformed into electrical energy advantage of the thermal gradient of the sea, ie the difference in temperature between the surface layers, hotter, and deeper layers, but cold
Since 1930, the year he took the first mill practice capable of harnessing the heat energy from the sea, the research in this field have been constant. Although there are still many technical problems to solve, especially those related to the resistance of materials to the marine environment, the results obtained so far, although modest, allowing you seen this manifestation of energy as an important source of energy supply in the not too distant future.
Harvesting techniques
There are two fundamental techniques for the use of thermal energy from the sea, the open loop systems closed loop systems
In an open-loop system, the hot water from the sea surface enters a vacuum chamber, where it turns into vapor at low pressure. The steam, after driving a turbine, which generates power, it condenses again thanks to the cold water from the depths of the sea, which acts as a coolant
In a closed loop system, using a fluid of low boiling point, such as ammonia or freon, the duty cycle. The fluid in contact with hot water from the upper layers of the sea, evaporates, moves the turbine and finally, after cold water condenses the seabed, the cycle starts again
Importantly, the poor performance of this system (around 7%), mainly due to low temperature from the hot and the small difference in temperature between the cold and the hot.
Geothermal energy
It's called geothermal energy from the heat stored in the interior of the earth. Although not yet know what causes that have led to this heat, there are several theories attempting to explain this phenomenon. Some argue that it is due to the very high pressures that exist under the earth's crust, others assume that their cause is the natural decay of radioactive isotopes present in all rocks and finally there is a theory that attributes it to the incandescent matter in their origins formed the planet
This energy, which arises naturally or can be extracted from the bowels of the earth, it is well known since ancient times. By the accounts of Pliny the Younger described the use of hot springs, not only in swimming, but as a source of heat for the design of local housing and recreation. However, from the early twentieth century when the resources become used on a large scale. There are currently numerous geothermal exploitation around the world, both for domestic and agricultural and industrial. An example is a country like Iceland, where a third of its energy needs are met through geothermal sources
Of all the world's geothermal resources, estimated at around 20000 billion toe, only a small part can be used by the man with the currently available techniques. This requires that they comply at least two fundamental conditions, the first is that the high temperature zone is intended to operate is affordable at a depth, which can be reached with the technological means available. The second condition stems from the inability to extract heat directly from the rocks. It is therefore also necessary provision in the area of porous geological formations capable of retaining water, if possible extract the heat and transport to the surface
Depending on the temperature that can reach the water in contact with hot rocks, geothermal sites are divided into two types: low-temperature (low enthalpy) when its temperature is below 150 º C and high temperature (high enthalpy ), when its temperature is higher
The low-temperature geothermal reservoirs are the most abundant and better distributed on the planet, and in particular, the only existing in Galicia. With a temperature usually below 100 ° C, find their main application as a heat source for heating, either domestic, industrial or agricultural
The high-temperature deposits are located exclusively in areas of recent volcanic activity. The high temperature of the fluid, usually steam, allows its use for electrical energy production by means of a turbine-generator group.
Harvesting techniques
The scheme based on a geothermal operation is very simple, just make a hole to the area where the water is hot, remove it and use the heat to the application concerned. This system, however, has a number of drawbacks that make in practice, not used by one hand, large-scale extraction of geothermal fluids can alter in a significant way the hydrology of the area, both at groundwater and surface level. On the other hand, water from the interior of the earth has, in most cases, a high content of substances, often harmful, preventing their direct use by the contamination and corrosion problems that would result
These disadvantages can be avoided by emptying reinjecting geothermal fluid once used his power. Thus, a classical geothermal drilling consists of two, with their bombs, and a heat exchanger. The fluid extracted through one of the holes (production well), passes through the heat exchanger where it gives up part of its heat to a second fluid for use in the centers of consumption, and finally, is injected back into the ground through the second hole (injection well)
As previously mentioned technical means available today is only possible to extract heat from the rocks, when, because of its porosity allows the flow of fluid through them. To take advantage of large impervious geothermal sites exist in the subsoil, is investigating a system, called hot dry rock, which in essence, is to produce fractures in the rock, in order to provide an artificial porosity that allows the extraction of heat a fluid injected, according to conventional techniques.
The biomass energy
Biomass, primary source of energy used by man, is any organic matter originated as a result of biological processes. Biomass are therefore terrestrial and aquatic plants and their products, animals that feed on them, and all waste resulting from the activity of living beings
The energy component of the biomass comes from solar energy that green plants are able to capture and transform into chemical energy through photosynthesis. This energy, stored as carbohydrates, is transmitted to other living beings through the food chain and, therefore, is also present in the waste they generate
Biomass is a renewable resource whose use has unique characteristics and significant indirect benefits. Apart from being a virtually inexhaustible source, produced cyclically and continuously by the vegetable kingdom, the animal kingdom, the urban system and industrial system, there is at least in some form in almost all geographic areas
It has multiple applications, not just energy, since the relevant operations, the transformation is beneficial and even necessary, for the environment as well, the recovery of forest biomass is a significant increase in forestry yields and a significantly reduced risk of fire. In general, and for all media, is the ideal system of waste disposal, with subsequent improvement of natural environment, urban and industrial. Even, in some cases it may be a way to balance certain agricultural surpluses
Depending on the degree of transformation, are generally considered three types of biomass: the primary or plant biomass, animal biomass or high school, and finally the residual biomass
Plant biomass is produced directly from the photosynthetic activity of plants, ie, is formed by the plants themselves. Although the maximum yield of the transformation of solar energy in biomass is less than 5%, and only a small part of it is usable (40% is in the ocean and terrestrial plant biomass is widely dispersed), its potential as a source of energy supply is very important. It is estimated at 70000 Mtoe solar energy plants set in each year, equivalent to about ten times the energy of coal and oil consumed annually in the world
Inside the plant biomass, deserve special attention called energy crops, whose purpose is the production of biomass for conversion into fuel, and not to obtain food or industrial use, as in traditional agriculture
Animal biomass is composed of living things that feed directly or indirectly from plants. Due to the low efficiency of transformation of plant biomass into animal (about 15%), it is interesting only for use with energy
The residual biomass is made up of organic waste product of the activity of living beings that inhabit the planet, ie unusable comprises the processes that are performed on plant and animal biomass. Depending on their origin, residual biomass can be classified into three types: agricultural (agricultural residues, forestry and livestock), industrial and urban
The importance of the use of residual biomass as a source of energy supply is evident if one considers that currently generates an average of two tons of all kinds of waste per inhabitant per year, which represents the energy value of the order of 2400 million toe / year. A favorable aspect for energy recovery of this waste is the fact that, unlike other types of biomass, are often concentrated, making it easier and cheaper collection and treatment.
Harvesting techniques
In the state where the waste is recovered or collected directly from the field, biomass generally exhibit low physical and energy density and a relatively high moisture content, circumstances that prevent their direct use as fuel. Depending on the type of biomass, and state that is, using a series of processes for conversion into other useful products from the energy standpoint. These processes can be of two types: thermochemical and biochemical.
Thermochemical Processes
Thermochemical processes are based on the action of heat on biomass. Subjected to high temperatures, biomass undergoes a series of irreversible chemical reactions, depending on the amount of oxygen involved in the process, enter classified types: combustion, when the heating takes place with excess oxygen, gasification, when the amount of oxygen is limited and pyrolysis, when the heating is carried out in absence of oxygen
- The combustion
The combustion process is it simpler and more formerly used by man for the energy use of biomass, and involves the complete oxidation of the material, producing water vapor, carbon dioxide, ash and heat. Almost any biomass can be used through this process as long as their moisture content is low and present no appreciable amounts of sulfur, chlorine or fluorine, which can cause corrosion problems in the facility and the emission into the atmosphere gases contaminants
The combustion of biomass, whose energy can be used for producing hot water or air for domestic and industrial and electricity production, has particular application in industries that generate their own waste burnable, as the paper industry, sugar and of timber, since the biomass produced in the same place where it is consumed, it is extremely easy to use and eliminates the costs associated with transport. A similar case is that of waste treatment plants, solid waste, where every day is more common to use this technique for recovering energy from wastes.
- Gasification
Gasification is the process by which biomass heated to temperatures above 700 ° C in the presence of little oxygen, it produces a fuel gas consisting mainly of a carbon monoxide, carbon dioxide, hydrogen and methane, in varying proportions depending the composition of the biomass used and the conditions under which the gasification is carried out. In particular, the use as combustion air or oxygen, gives rise to two different types of gas, not only in composition and calorific value, but also in its possible applications
When the gasification occurs in the presence of pure oxygen, we obtain the so-called synthesis gas. This gas, whose calorific value is between 5000 and the 10000 kJ / m cubic, can be used directly, and has the same applications as traditional gas fuels (butane, propane, natural gas, etc.).. However, the synthesis gas interest lies in the possibility of transforming, by means of catalytic processes in liquid fuels (methanol, synthetic gasoline, etc..), With higher demand today and more interesting from the point of Economically, the gaseous fuel
If the gasification of biomass is carried out in air, the product obtained is called producer gas or gas tested. With a low calorific value (between 3500 and 5500 kJ / m cubic), but can be used as fuel, since the presence of nitrogen in its composition, prevents the conversion of this gas in other more elaborate products.
- Pyrolysis
The pyrolysis process traditionally used to obtain charcoal, biomass decomposition by the action of dry heat in the absence of oxygen. Depending on the temperature at which the process takes place (between 275 and 500 ° C), and the characteristics of the biomass are obtained as a result of solid products (coal, tar and ash), liquid (composed hidrocarbonatazos) and gaseous (gas poor ) in different proportions
As solid and liquid fractions resulting from the operation are most interesting, from the energy point of view, that the gaseous fraction, the latter is common to use as fuel for drying it before the biomass, resulting in a significant increase in process performance. In this case, and on average, from one ton of dry biomass, obtained around 2250 kg of liquid, with a calorific value of 25000 kJ / kg, and about 75 kg of solid products (coke) with a calorific half of 20000 kJ / kg
Pyrolysis processes are used for forest waste, agricultural waste, particularly municipal solid waste field where research is currently focused and where further development is expected from this technique.
Biochemical processes
Biochemical processes are those that exploit the action of a number of microorganisms contained in the raw or added during the process to break down biomass into other products simpler, but more energy value. In these processes, especially indicated for the treatment of biomass with high moisture content, the most used are two: the alcoholic fermentation and anaerobic digestion
- The alcoholic fermentation
The alcoholic fermentation is the biological transformation of sugar compounds in ethanol fuel with high energy, and carbon dioxide
Since plant biomass contains a high percentage of glucose and other simple sugars convertible compounds, it is an excellent raw material for this type of process
The transformation of biomass into ethanol takes place in three phases: pretreatment, which aims to prepare the biomass for fermentation, converting starch and cellulose present in fermentable sugars, fermentation, or conversion of these sugars into ethanol by the action of microorganisms, and finally, the distillation operation to purify and concentrate the ethanol obtained
Ethanol, also called thioalcohols, end product of alcoholic fermentation, is used industrially in the production of alcohol as a solvent, as feedstock for the manufacture of chemicals, and especially total or partial substitute for gasoline in nearly all applications.
- Anaerobic digestion
Anaerobic digestion is a process of decomposition of organic matter in the absence of air made by certain microorganisms (anaerobic bacteria), which gives rise to a mixture of gases, generically called biogas, weapons of a residue of solid and liquid products
The process, quite complex, takes place into containers called digesters airtight. It consists essentially of two stages, first, the complex organic compounds present in biomass are converted by bacteria in other acidifying lower molecular mass, such as acetic acid, carbon dioxide and hydrogen. In a second stage, and by methanogenic bacteria, acids are transformed into methane and carbon dioxide, a mixture of gases that make up the biogas. As waste, is obtained an aqueous slurry of solid material, composed of undigested products and bacteria responsible for the process
Anaerobic digestion, used for hundreds of years to obtain fuel gas, finds its main application in the treatment of livestock waste, food industry effluents and sewage sludge, high nutrient content which favors the development of the bacteria needed to digestion
Biogas is a mixture of methane (50-70%), carbon dioxide (30-50%) and other products, such as nitrogen, oxygen, hydrogen and hydrogen sulfide in small proportions. The low calorific value (on the order of 25,000 kJ / m cubic) compared with other gaseous fuels, does not justify their transport out of the zone where, so often used on site, either directly burning domestic type applications (heating, cooking, hot water) or using it as fuel for internal combustion engines for raising water by pumps or electricity through generators
The residue from the anaerobic fermentation process, comprising the undigested products, mainly proteins, fats, cellulose, and salts, is also a usable product. The biochemical changes that occur during digestion convert plant nutrients contained in biomass, such as nitrogen, phosphorus and potassium, into chemical forms more easily assimilated by plants, so that these residues are an excellent organic fertilizer far superior to the untreated biomass.
