The use of Renewable Energy Sources (RES) together with improved Energy Efficiency (EE) can contribute to reducing energy consumption,Management of Renewable Energies and Environmental Protection, Part III Articles reducing greenhouse gas emissions and, as a consequence, preventing dangerous climate change. At least one-third of global energy must come from different renewable sources by 2050: The wind, solar, geothermal, hydroelectric, tidal, wave, biomass, etc. Oil and natural gas, classical sources of energy, have fluctuating developments on the international market. A second significant aspect is given by the increasingly limited nature of oil resources. It seems that this energy source will be exhausted in about 50 years from the consumption of oil reserves in exploitation or prospecting. “Green” energy is at the fingertips of both economic operators and individuals. In fact, an economic operator can use such a system for both own consumption and energy trading on the domestic energy market. The high cost of deploying these systems is generally depreciated in about 5-10 years, depending on the installed production capacity. The “sustainability” condition is met when projects based on renewable energy have a negative CO2 or at least neutral CO2 over the life cycle. Emissions of Greenhouse Gases (GHG) are one of the environmental criteria included in a sustainability analysis, but is not enough. The concept of sustainability must also include in the assessment various other aspects, such as environmental, cultural, health, but must also integrate economic aspects. Renewable energy generation in a sustainable way is a challenge that requires compliance with national and international regulations. Energy independence can be achieved: – Large scale (for communities); – small-scale (for individual houses, vacation homes or cabins without electrical connection).
The purpose of this project is to present an overview of renewable energy sources, major technological developments and case studies, accompanied by applicable examples of the use of sources.
Renewable energy is the energy that comes from natural resources: The wind, sunlight, rain, sea waves, tides, geothermal heat, regenerated naturally, automatically.
Greenhouse gas emissions pose a serious threat to climate change, with potentially disastrous effects on humanity. The use of Renewable Energy Sources (RES) together with improved Energy Efficiency (EE) can contribute to reducing energy consumption, reducing greenhouse gas emissions and, as a consequence, preventing dangerous climate change.
At least one-third of global energy must come from different renewable sources by 2050: The wind, solar, geothermal, hydroelectric, tidal, wave, biomass, etc.
Oil and natural gas, classical sources of energy, have fluctuating developments on the international market. A second significant aspect is given by the increasingly limited nature of oil resources. It seems that this energy source will be exhausted in about 50 years from the consumption of oil reserves in exploitation or prospecting.
“Green” energy is at the fingertips of both economic operators and individuals.
In fact, an economic operator can use such a system for both own consumption and energy trading on the domestic energy market. The high cost of deploying these systems is generally depreciated in about 5-10 years, depending on the installed production capacity.
The “sustainability” condition is met when projects based on renewable energy have a negative CO2 or at least neutral CO2 over the life cycle.
Emissions of Greenhouse Gases (GHG) are one of the environmental criteria included in a sustainability analysis, but is not enough. The concept of sustainability must also include in the assessment various other aspects, such as environmental, cultural, health, but must also integrate economic aspects.
Renewable energy generation in a sustainable way is a challenge that requires compliance with national and international regulations.
Energy independence can be achieved:
Large scale (for communities)
Small-scale (for individual houses, vacation homes or cabins without electrical connection)
Today, the renewable energy has gained an avant-garde and a great development also thanks to governments and international organizations that have finally begun to understand its imperative necessity for humanity, to avoid crises and wars, to maintain a modern life (we can’t go back to caves).
Materials and Methods
The Geothermal Energy Potential
Geothermal energy is defined as the natural heat coming from within the Earth, captured for electricity, space heating or industrial steam. It is present anywhere beneath the earth’s crust, although the highest temperature and therefore the most desirable resource, is concentrated in regions with active or young geologically active volcanoes.
The geothermal resource is clean, renewable, because the heat emanating from the Earth’s interior is inexhaustible. The geothermal energy source is available 24 h a day, 365 days a year. By comparison, wind and solar energy sources are dependent on a number of factors, including daily and seasonal fluctuations and climate variations. For this reason, the energy produced from geothermal sources is, once captured, more secure than many other forms of electricity. Heat that continually springs from within the Earth is estimated to be equivalent to 42 million megawatts (Stacey and Loper, 1988). One megawatt can supply the energy needs of 1000 homes.
Geothermal energy originates from the thermal waters, which in turn extract their heat from the volcanic magma from the depths of the earth’s crust. The Earth’s thermal energy is therefore very large and is virtually inexhaustible, but it is very dispersed, very rarely concentrated and often too deep to be exploited industrially. Until now, the use of this energy has been limited to areas where geological conditions allow a transport medium (liquid or gaseous water) to “transfer” heat from hotspots from the depth to the surface, thus giving rise to geothermal resources.
The environmental impact of the use of geothermal energy is rather small and controllable. In fact, geothermal energy produces minimal atmospheric emissions. Emissions of nitrogen oxide, hydrogen sulphide, sulfur dioxide, ammonia, methane, dust and carbon dioxide emissions are extremely small, especially when compared to emissions from fossil fuels.
However, both water and condensed steam from geothermal power plants contain different chemical elements, including arsenic, mercury, lead, zinc, boron and sulfur, the toxicity of which obviously depends on their concentration. However, most of these elements remain in solution, in water that is re-injected into the same tank from which fermented water or steam was extracted. The most important parameter in the use of this type of energy is the temperature of the geothermal fluid, which determines the type of geothermal energy application. It can be used for heating or to generate electricity.
Going from the surface of the earth to the depth, it is noticed that the temperature increases progressively with the depth, with 3°C on average for every 100 m (30°C/km). It is called the geothermal gradient. For example, if the temperature after the first few meters below ground level, which on average corresponds to the average annual outdoor air temperature, is 15°C then it can reasonably be assumed that the first temperature will be 65-75°C at 2000 m Depth, 90-105°C at 3000 m and so on for the next few thousand meters.
Regions of interest for geothermal energy applications are those where the geothermal gradient is higher than normal. In some areas, either due to the volcanic activity of a recent geological age, or due to the cracked cracks of hot water at depths, the geological gradient is significantly higher than the average, so temperatures of 250-350°C are recorded at depths of 2000-4000 m.
A geothermal system consists of several main elements: a heat source, a reservoir, a carrier fluid that provides heat transport, a recharge area and a rock to seal the aquifer. The heat source may be a very high magmatic intrusion (> 600°C) that has reached relatively low depths (5-10 km) or, in some low temperature systems, the normal Earth’s temperature, which, as explained earlier, increases with the depth.
The tank is a volume of permeable rocks from which the carrier fluid (water or steam) extracts heat. The reservoir is generally covered by either impermeable layers or rocks whose low permeability is due to the self-sealing phenomenon consisting in the deposition of minerals in the pores of the rocks. The tank is connected to a surface recharge area through which the meteoric waters can replace the fluids leaving the tank through springs or by extraction to boreholes. The geothermal fluid is water, in most cases meteoric, liquid or gaseous, depending on temperature and pressure. Water often carries along with chemicals and gases such as CO2, H2S, etc. The mechanism underlying geothermal systems is generally governed by fluid convection. Convection occurs due to heating and thermal expansion of fluids in a gravitational field. The low density heated flame tends to rise and be replaced by a cooler, high density fluid coming from the edge of the system. Convection, by its nature, tends to increase the temperature at the top of the system, while the bottom temperature decreases. Frequently, a distinction is made between geothermal systems dominated by water and vapor-dominated systems. In water-dominated systems, liquid water is the continuous fluid phase controlling the pressure. Vapors may be present, generally as discrete bubbles. These geothermal systems, whose temperature may vary from 225°C, are the most widespread in the world. Depending on the temperature and pressure conditions, they can produce hot water, water-steam mixtures, wet steam, or, in some cases, dry steam. In vapor-dominated systems, liquid and vapor co-exist in the reservoir with continuous steam controlling the pressure. Geothermal systems of this type, of which the best known are Larderello in Italy and The Geysers in California, are quite rare and are high-temperature systems.
Generating electricity is the most important use of high pressure geothermal resources (> 150°C). Medium and low temperature resources are suitable for various applications. The classic Lindal Diagram (1973) shows the possible uses of geothermal fluids at different temperatures. Fluids at temperatures below 20°C are rarely used under very particular conditions, or in heat pump applications (DiPippo, 2004).
In the case of temperatures below 90°C, geothermal waters can be used directly rather than for conversion to electricity.
The most common form of use is for space heating, agricultural applications, aquaculture and some industrial uses.
When the water temperature is below 40°C, heat pumps are used to heat or cool the spaces. If groundwater is not available then heat pumps can be combined with heat exchangers with the ground.
A heat pump is a thermal machine which allows the extraction of heat from the basement and the aquifer at low depths (tens or hundreds of meters) at low temperatures and transferring it at higher temperatures to the medium to be heated. The advantage of heat pumps is related to the fact that for each unit of electricity consumed, approximately three units of heat in the form of heat, with the contribution of geothermal water, are obtained.
In the case of cooling, the heat is extracted from space and dissipated in the Earth; In the case of heating, the heat is extracted from the Earth and pumped into space.
A heat pump is governed by the same limitations of the second principle of thermodynamics (any energy transformation implies a dissipation of a heat-treated part that can no longer be used) like any other thermal and that maximum efficiency can be calculated from the Carnot cycle. Heat pumps are normally characterized by a performance coefficient that represents the ratio of its heating power to the electrical power absorbed by the grid.
High enthalpy geothermal energy is most commonly used to generate electricity. The typical geothermal system used to produce electricity has to produce about 10 kg of steam to produce a unit (kWh) of electricity. The production of large amounts of electricity in the order of hundreds of megawatts requires the production of large volumes of fluid. Thus, one aspect of geothermal systems is that it must contain large amounts of high temperature fluid or a tank that can be recharged with fluids that are heated as contact with the rocks.
The three basic types of power generating installations are “dry” and “flash” central stations, where the hot water pressure (usually over) is low. The production of electricity in each type of installation depends on the temperatures and pressures of the tank and each type produces different environmental impacts.
The most common type of power plant today is the “flash” with water cooling system where a mixture of water and steam is produced by the spring. The steam is separated into a surface vessel and led to the turbine and the turbine trains a generator.
In a dry installation, the steam comes directly from the geothermal tank to the turbine that drives the generator and no separation is required because the source produces only steam.
Recent advances in geothermal technologies have made it possible to produce electricity in economically advantageous conditions and geothermal low temperature resources of 100-150°C. Known as “binary” geothermal plants, these plants reduce emissions due to geothermal energy almost to zero. In the binary process, geothermal water heats another liquid, such as isobutane (most often n-pentane), which boils at a lower temperature than water and has high vapor pressure at low temperatures compared to steam. The two liquids are kept completely separated by using a heat exchanger to effect the transfer of thermal energy from geothermal water to the working fluid. The second fluid passes, vaporizes and turns into gaseous vapors and the force of expanding vapors drives the turbines that train the generators.
If the geothermal plant uses air cooling, geothermal fluids never make contact with the atmosphere before being pumped back into the underground geothermal reservoir. Developed in the 1980s, this technology is already in geothermal power stations in the world. The ability to use low-temperature resources increases the number of geothermal tanks that can be used to produce energy.
Binary geothermal power stations, along with flash systems, produce almost zero emissions. In the case of direct use of thermal energy from geothermal hot water, the impact on the environment is negligible and can be easily reduced by adopting closed cycle systems, with the final extraction and re-injection of the fluid in the same geothermal reservoir.
The economic aspect of the use of hot water is still limiting for a wider spread in the energy sector. In fact, the economic benefit derives from its prolonged use over many years with low operating costs, although the initial investment may be considerable.
Identifying a geothermal reservoir is a complex activity consisting of different phases, starting from exploring the surface of a given area. This consists of the preliminary assessment of current geothermal events (hot water springs, steam jets, geysers, etc.), followed by geological, geochemical, geophysical and drilling exploration wells (several hundred meters deep) Measure the temperature (geothermal gradient) and evaluate the earth’s heat flux. The interpretation of the collected data will suggest the location where deepwater exploration is to be carried out by well drilling (even at depths above 4000 m) that will confirm the existence of geothermal fluids. In the case of positive results, the geothermal field that has been identified will be exploited by drilling a sufficient number of wells to produce geothermal fluid (hot water or steam).
The largest geothermal power plant in the world is in California – “Geysers”, with an installed power of 750 MW.
Geological and hydrogeological studies have an important role in all phases of geothermal research. They provide basic information for interpreting the data obtained with other exploration methods, and ultimately for the realization of a realistic model of the geothermal system and the assessment of the potential of the resource.
Geothermal areas should be further analyzed using geophysical techniques (gravimetry, magnetic and electrical tests, hot water chemical analysis, etc.) to locate specific reservoirs, the source of geothermal fluid. Geophysical analysis aims at indirectly determining physical parameters of depth geological formations from the surface or at depths close to the surface.
These physical parameters include:
Temperature (temperature measurement)
Electrical conductivity (electrical and electromagnetic methods)
The propagation velocity of elastic waves (seismic studies)
Density (gravity analysis)
Magnetic susceptibility (magnetic methods)
Geothermal exploration is done through a sequence of several steps:
Study on thermal conditions by collecting heat flow and map information
Study on hydro-geological maps for assessing the distribution of groundwater resources
Drilling wells for fluid extraction
Only after the surface exploration has shown that there is a workable potential, one can proceed to drill wells.
Biomass is the “biodegradable fraction of products, wastes and residues of biological origin in agriculture (including vegetal and animal substances), forestry and related industries, including fisheries and aquaculture and the biodegradable fraction of industrial and municipal waste”.
The benefits of biofuels compared to traditional fuels are aimed at greater energy security, lower environmental impact, currency savings and socio-economic issues related to the rural sector. The concept of sustainable development embodies the idea of inter-connectivity and balance between economic, social and environmental concerns.
The bioenergy production chain in a given territory must be achieved taking into account the technologies and types of biomass needed to achieve the best results. Therefore, the classification and characteristics of different biomass resources must be known.
An overwhelming part of biomass available for bioenergy comes from plant material and animal products. Some of the important features of different types of biomass are shown below. A first distinction can be made taking into account the origin of biomass from different sectors, such as agriculture, forestry, industrial and urban sectors. Another classification can be made by its nature: Energy crops, agricultural or forest residues and waste.
Biomass is mostly represented by energy crops from the agricultural and forestry sectors.
Herbaceous plants (monocots) represent the largest part of modern large-scale farming. Multi-annual grass crops include cereals such as grains, barley, oats, rye, other minor cereals: sugar beet, sugarcane, fodder crops and clover. The seeds of these cereals, stems and tubers of other plants are a good source of starch that can be used in technological processes for energy production and biofuels.
Selective reproduction (especially for non-food crops) has been used to modify seed/plant ratio for many biomass species with high seed production.
This type of biomass can be used as a raw material for the production of bioenergy when economically viable. Rapid reed and cane species are examples of grassy crops that can make good use of available nutrients to increase biomass productivity; But at the same time other agronomic features still present weaknesses, such as floral sterility, prohibitive costs for setting up culture, relatively low harvest mechanization, high humidity of the harvested product and high ash content.
Oil crops include annual crops of oilseeds and oleaginous perennial crops. The most representative oilseed crop in the European regions is sunflower and soybean. Vegetable oil is typically extracted by mechanical pressing and/or solvent extraction and is used in the food industry, soap and cosmetics. Oils in these crops also contain other seed constituents (proteins or starch). The lignocellulosic part of oleaginous crops, which is traditionally used as a mulch or feed, can also be burned to produce energy or heat, while vegetable oils can be used for higher value bioenergy applications, especially as a substitute for Diesel fuel.
Vegetable oils derived from these cultures and modified in m-methyl esters are commonly referred to as “biodiesel” and are the main candidates for becoming alternative fuels. But the use of edible oils for energy purposes can cause significant problems, such as hunger in developing countries. The double use of palm oil increases competition between the edible oil and biofuel market, resulting in higher prices of vegetable oil in developing countries.
The use of non-edible vegetable oils when compared to edible oils is very significant in developing countries because of the huge demand for edible oils, which are far too expensive to use as fuel today. The production of biodiesel from various non-edible oils has been intensively researched in recent years.
Residue and waste biomass analysis is more complicated due to the variety of materials and sectors of origin (from agriculture to urban).
Wastes are those generated in the production process, industrial waste and solid municipal waste. The typical energy content is from 10.5 to 11.5 MJ/kg. Waste management practices vary from country to country, from urban areas to rural areas, from industrial to residential.
The situation of waste management in a developing country differs from that of an industrialized country. Transfer of technology from one country to another may be totally inappropriate, although technically the technology is viable and accessible.
It is very important to understand local factors such as:
Characteristics and seasonal variations of waste
Social issues related to habits regarding solid waste and the attitude of political institutions
Awareness of other resource limitations the role of sustainable waste management is to reduce the amount of waste released into the environment by reducing the amount of waste produced
Large quantities of waste can’t be eliminated. However, the impact on the environment can be reduced by sustainable waste use. This is known as the “waste management hierarchy”. The waste management hierarchy refers to reduction, re-use and recycling and the classification of waste management strategies according to their desirability to minimize waste. The purpose of the waste management hierarchy is to obtain the maximum practical benefits of a product and to generate a minimal amount of waste.
Biomass from residues and wastes includes plant and animal waste. These are agricultural residues such as straw, vegetable and fruit shells, residues and forest waste, such as leaf layer, sawdust residues, food waste and the organic solid waste mining component. Energy can be generated from these wastes, as globally there are several billion tons of biomass contained in them.
There are many options available for converting waste and waste into energy. These technologies are: Waste disposal, incineration, pyrolysis, gasification, anerobic digestion and others. Energy density and physical properties of biomass are critical factors for the raw material and need to be understood in order to choose the processing technology.
The choice of technology must be based on the type of waste, its quality and local conditions, but a classification of different types of waste is not easy. In the countries of the European Union waste is classified according to the European Waste Catalog.
In recent years, the production of energy and biofuels from waste and residues has become very important due to the positive economic and environmental effect. The use of urban waste for energy purposes could avoid an increase in the surface of urban waste landfills, resulting in a reduction in greenhouse gas emissions and greater independence from fossil fuels.
Major agricultural waste includes plant residues, straw and shells, olive stones and nut shells. More specifically, residues can be divided into two general categories: – Waste from the field: The material remaining in the field or in orchards after harvestings, such as cocci, stems, leaves and seed pods. – Processing residues: Material left after harvest processing, shells, seeds, roots.
Much of the wood from the forest sector is a major source in some countries and is used as the main fuel for small-scale energy production in rural areas, where gas heating is unusual. Wood is thus a competitor for fossil fuels and is used both in the household for cooking and heating water, as well as in industrial and commercial processes (for water heating or process thermal energy). The alternative to the use of waste from the forestry sector or related industrial activities, such as timber factories, is an attractive source of biomass and a successful example for the generation of waste energy. Forest residues are wood from cuttings, logging residues, trees, shrubs, tree bark, etc. Normally forest residues are considered to be a better fuel than agricultural residues, but their density and the collection system (especially when the land is high) lead to a high cost of transport; The net CO2 emission produced for each unit of energy provided by forest residues is lower than that produced by other agricultural waste due to fertilizers and pesticides used in agriculture.
The energy content of different vegetable materials determines their calorific value. The calorific value depends on the percentage of carbon and hydrogen, which are the main contributors to the biomass energy value.
In order to obtain maximum energy, plant materials should be dried, as the amount of energy contained in plants varies depending on the moisture content. In the case of firewood, the calorific value decreases linearly with the increase in moisture content.
The biomass potential is the total amount of source that is present on a given territory; It is common to refer to the potential of biomass in several ways: Theoretically, technically, ecologically and economically. In practical terms, biomass actually available for energy uses derives from the application of certain restrictions (technical, environmental, other restrictions on land use competition) to the theoretical potential.
Boiler combustion is the most widespread biomass energy utilization technology. Types of boilers for combustion of wood biomass are very varied and could be classified into three groups:
Boilers with grilling
Boilers with under floor heating
Bias gasification is a complete gas conversion process using air, oxygen or steam gasification media. The biomass gasification is achieved by two main methods:
Thermal gasification using air, oxygen, steam or their mixture at temperatures of about 7000 C
Biochemical gasification using micro-organisms at ambient temperature and under anaerobic conditions
For the gasification of wood, three main types of gasification reactors were developed and applied:
Fixed bed gasogens
Fluidized bed gasifiers
Ascending current gas