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,Management of Renewable Energies and Environmental Protection, Part I 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).
Keywords: Environmental Protection, Renewable Energy, Sustainable Energy, The Wind, Sunlight, Rain, Sea Waves, Tides, Geothermal Heat, Regenerated Naturally.
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
Solar energy means the energy that is directly produced by the transfer of light energy radiated by the Sun into other forms of energy. This can be used to generate electricity or to heat the air and water. Although solar energy is renewable and easy to produce, the main problem is that the sun does not provide constant energy over a day, depending on the day-night alternation, weather conditions, season.
Solar Panels generate electricity approx. 9h/day (the calculation is minimal, the winter is 9 h), feeding the consumers and charging the batteries at the same time.
Solar installations are of two types: Thermal and photovoltaic.
Photovoltaics produce electricity directly, thermal ones help save 75% of other fuels (wood, gas) per year. A house that has both solar installations (with photovoltaic and vacuum thermal panels) can be considered “energy independence” (because the energy accumulated in the day is then sent to the grid and used as needed).
The use of solar radiation for the production of electricity can be done by several methods:
The use of photovoltaic modules – by capturing the energy of the photons coming from the sun and storing it in free electrons, thereby generating an electric current, solar photovoltaic panels generating electricity
The use of solar towers
Using Parabolic Concentrators – This type of concentrator consists of a gutter-shaped parabolic mirror that concentrates solar radiation on a pipe. A working fluid is circulating in the duct which is generally an oil that takes up the heat to give it water to produce the steam that drives the turbine of an electric generator. The concentrator requires adjusting the posture position of the sun in the apparent daytime displacement
Using the Dish-Stirling system
Solar installations work even when the sky is dark. They are also resistant to hail (in the case of the best panels).
Solar-thermal systems are mainly made with flat-bottomed solar collectors or vacuum tubes, especially for smaller solar radiation in Europe. In the energy potential assessments, applications concerning water heating or enclosures/swimming pools (domestic hot water, heating, etc.) were considered.
Locations for solar-thermal applications (thermal energy).
In this case, any available space can be used if:
Allows the location of solar thermal collectors
Preferential orientation to the South and inclination according to location latitude
This is the case for roofs of houses/blocks, adjacent buildings (covered parking lots, etc.) or land on which solar-thermal collectors can be located (Aversa et al., 2017 a-d; 2016 a-d; Petrescu et al., 2016 a-b; Mirsayar et al, 2017; Blue Planet; World Tree, From Wikipedia; Giovanni et al., 2012).
For the solar photovoltaic potential, both photovoltaic power grid applications and autonomous (non-grid) applications for isolated consumers were considered.
Solar energy can be used very easily – with a photovoltaic system. This type of system transforms the sunlight into electricity throughout the year, with the point that only high-quality photovoltaic systems that produce electricity over a long time are profitable. The system also allows other energy sources to be coupled with solar energy such as wind energy produced by a turbine. Obviously, besides the converter, it is also necessary to have a battery that is strong enough to retain as much energy as possible during the night, or when the consumption amount is very low and to release it when necessary. A system for producing, distributing and maintaining renewable energies for a house, cottage, motel, hospital, even located in isolated places, where the power grid does not reach, is presented in the figure 3. If the wind does not blow in a long period and the sky is not sunny, it is necessary to have an electric generator inserted into the system.
The winds are due to the fact that the Earth’s equatorial regions receive more solar radiation than the polar regions, thus creating a large number of convection currents in the atmosphere. According to meteorological assessments, about 1% of the solar input is converted to wind energy, while 1% of the daily wind energy contribution is roughly equivalent to the world’s daily energy consumption. This means that global wind resources are in large, widespread quantities. More detailed assessments are needed to quantify resources in certain areas.
Wind energy production began very early centuries ago, with sailboats, windmills and grain mowers. It was only at the beginning of this century that high-speed wind turbines were developed to generate electricity. The term wind turbine is widely used today for a rotating blade machine that converts the kinetic energy of the wind into useful energy. Currently there are two categories of base wind turbines: Wind turbine Wind Turbines (HAWT) and Vertical Wind Turbines (VAWT), depending on the axis orientation of the rotor.
Wind power applications involve electricity generation, with wind turbines operating in parallel to network or utility systems, in remote locations, in parallel with fossil-fueled engines (hybrid systems). The gain resulting from the wind energy exploitation consists both in the low consumption of fossil fuels as well as the reduction of the overall costs of generating electricity. Electric utilities have the flexibility to accept a contribution of about 20% of wind power systems. Combined Eolian-diesel systems can offer fuel savings of over 50%.
Wind power generation is a fairly new industry (20 years ago in Europe, wind turbines had not yet reached commercial maturity). In some countries, wind energy is already competing with fossil fuel and nuclear energy, even without considering the benefits of wind energy for the environment.
When estimating the cost of electricity produced in conventional power plants, their influence on the environment (acid rain, effects of climate change, etc.) is usually not taken into account. Wind energy production continues to improve by reducing costs and increasing efficiency.
The cost of wind energy is between 5-8 cents per kWh and is expected to fall to 4 cents per kWh in the near future. Maintenance of wind energy projects is simple and inexpensive. Amounts of money paid to farmers for land renting provide additional income to rural communities. Local companies that carry out the construction of wind farms provide short-term local jobs while long-term jobs are created for maintenance work. Wind energy is a rapidly growing industry in the world.
An indispensable requirement for the use of wind to produce energy is a constant flow of strong wind. The maximum power Wind Turbines (WTS) are designed to generate is called “rated power” and the wind speed at which nominal power is reached is “wind speed at rated power”. This is chosen to suit the wind speed in the field and is generally about 1.5 times the average wind speed in the ground. One way to classify wind speed is the Beaufort scale that provides a description of the wind characteristics. It was originally designed for sailors and described the state of the sea, but was later modified to include wind effects in the field.
The power produced by the wind turbine increases from zero, below the starting wind speed (usually around 4 m/s, but again, depending on the location) to the maximum at wind speed at rated power. Above the wind speed at rated power, the wind turbine continues to produce the same rated power, but at lower output until it stops, when the wind speed becomes dangerously high, ie over 25 to 30 m/s (vigorous storm). This is the shut off speed of the wind turbine. Exact specifications for identifying the energy produced by a wind turbine depend on the wind speed distribution during the year in the field.
Air currents can be used to train wind turbines. Modern wind turbines produce a power of between 600 KW and 5 MW, the most used being the 1.5-3 MW output power, being more simple and constructive and more suitable for commercial use. The output power of a typical wind turbine is dependent on the wind speed at the third power so that wind speed increases, the power generated by the turbine increases with the wind speed cube, the increase being spectacular. The world’s technical potential for wind power can provide five times more energy than it is consumed now.
In the strategy for capitalizing on renewable energy sources, the declared wind potential is 14,000 MW (installed power), which can provide an amount of energy of about 23,000 GWh/year. These values represent an estimate of the theoretical potential and must be reproduced in correlation with the possibilities of technical and economic exploitation. Starting from the theoretical wind potential, what interests the energy development forecasts is the potential for practical use in wind applications, which is much smaller than the theoretical potential, depending on the possibilities of land use and the conditions on the energy market. That is why the economically profitable wind potential can be appreciated only in the medium term, based on the technological and economic data known today and considered as valid in the medium term.
Under ideal conditions, the theoretical maximum of cp is 16/27 = 0.593 (known as the Betz limit) or, in other words, a wind turbine can theoretically extract 59.3% of the airflow energy. Under real conditions, the power factor does not reach more than 50%, as it includes all wind turbine wind turbine losses. In most of today’s technical publications, the cp value covers all losses and represents the product cp * h. The power output and the extraction potential differ depending on the power coefficient and the turbine efficiency.
If cp reaches the theoretical maximum, the wind speed immediately behind the rotor – v2 is only 1/3 of the speed in front of the rotor v1. Therefore wind turbines located in a wind farm produce less energy as a result of the reduction in wind speed caused by the wind turbines in front of them. Increasing the distance between wind turbines can reduce energy loss as wind flow will accelerate again. A correctly designed wind farm may therefore have less than 10% losses due to mutual interference effects.
Average annual power will vary from land to land. In high wind speeds, more energy will be obtained. This highlights the importance of strong winds and hence the implications of the wind climate on economic issues related to wind energy production.
Blasts are responsible for mixing air and their action can be considered in a similar way to molecular diffusion. As the vortex passes through the measuring point, the wind speed takes the value of that whirlpool for a period of time proportional to the magnitude of the whirlpool; this is a “gust”. In most cases, load variation is not significant. However, if the vortex scale is of the same magnitude as the scale of a component of the turbine, then the variation in load may affect the overall component. A gust of 3 sec corresponds to a whirl of about 20 m (e.g., similar to the length of a rotor blade), while a 15 sec burst corresponds to a 50 m swirl.
To calculate the maximum possible load for a turbine or its components over the lifetime of the turbine, the highest burst value is used for a relevant period of time. This is formulated as the maximum wind speed and gust speed over a 50-year period. Of course, wind speed can be exceeded during this period, the sizing reserve will allow for some overtaking. Calculation of stresses is particularly important for flexible structures, such as turbines, which are more susceptible to wind-induced damage than rigid structures such as buildings.
A wind turbine can be placed almost anywhere in a sufficiently open terrain. Nevertheless, a wind farm is a commercial project and therefore it is necessary to try to optimize its profitability. This is important not only for the profitability during the lifetime of the exploitation but also for the mobilization of capital in the initial phase of project development. For economical planning of investments in wind energy, it is necessary to know as safely as possible the prevailing wind conditions in the area of interest.
Due to lack of time and financial reasons, long-term measurement periods are often avoided. As a substitute, mathematical methods can be used to predict wind speeds at each location. Wind conditions and energy production resulting from the calculation can serve as the basis for economic calculations. In addition, simulation of wind conditions can be used to correlate wind measurements at a particular location with wind conditions in neighboring locations in order to determine the wind regime for a whole area.
Since wind speed can vary significantly over short distances, for example several hundred m, wind turbine location assessment procedures generally take into account all regional parameters that are likely to influence wind conditions.
Such parameters are:
Obstacles in the immediate vicinity
Topography of the environment in the measure region, which is characterized by vegetation, land use and buildings (description of the roughness of the soil)
Horoscopes, such as hills, may cause airflow acceleration or deceleration effects
For the calculation of the annual average power density in the field, a more accurate estimate of the average annual wind speed is required. Then, information on the wind speed distribution over time is needed. To obtain these trusted data, data sets that cover several years are needed, but usually these data are estimated using appropriate models from shorter-date data sets. After that, it is possible to determine the potential energy produced in relation to the performance of the wind turbine.
The most widespread procedure for long-term prediction of wind speed and energy efficiency in a land is the WAsP Wind Atlas.
The model quantifies the wind potential at different heights of the rotor shaft above ground for different locations, taking into account the distribution of wind speed (in time and space) at meteorological stations (measurement points).
The reference station could be up to 50 km away from the site. The projected energy output for this location can be calculated in relation to the power curve associated with the wind turbine (wind power). A key element of the WASP model is that it uses polar coordinates for the origin of the location of interest.
The WAsP incorporates both physical atmospheric models and statistical descriptions of the wind climate.
The physical models used include:
The similarity in the surface layer – considering the logarithmic law
The Geostrophic Wind Law
Stability corrections-to allow for variation from neutral stability
Change of roughness-to allow changes in land use throughout the area
Shelter model-modeling the effect of an obstacle on wind flow
Orographic model-modeling the effect of accelerating the wind speed in the field
The wind regime is described statistically by a Weibull distribution derived from the reference data. The Weibull distribution is designed to best fit the high wind speeds.
Depending on the complexity of the examined regions, different procedures are used to determine the wind conditions. In addition to the WAsP model mentioned above, there are other procedures such as mesoscales models.
Such measurements, usually performed over a period of one year, may be related to neighboring areas or may be extrapolated to the height of the rotor axis of certain types of turbines using the flow simulation described above.
Evaluating wind resources at a location ideally asks for data series for as long as possible at the location of the turbines. In addition, it is useful to understand the turbulence in the field and the rotor axis for the design of wind turbines. To do this, a quick time sample and spatial distribution of measurement points is required. In practice, time and expenses often exclude such a thorough investigation. Imitations are provided in the section on meteorology and wind structure.
Wind velocity measurements are the most critical measurements for wind resource valuation, performance determination and energy production. In economic terms, uncertainties are transformed directly into financial risk. There is no other branch in which the uncertainty of the measurements is as important as in wind energy. Due to the lack of experience, a lot of wind speed measurements have inaccurately high uncertainties, as best practices in the anemometer selection standards, anemometer calibration, anemometer fitting and measurement field selection have not been applied.
Investigations have shown that certain anemometers are highly susceptible to vertical air flow, which, under real conditions, even appear in open ground due to turbulence. In complex terrain these effects are of great importance and lead to over or underestimation of real wind conditions. Only a few types of anemometers can avoid these effects.
A representative positioning of the measuring point within the wind farm shall be chosen. For large power plants in complex terrain, 2 or 3 representative positions should be chosen for the installation of the pillar. At least one of the measurements must be made at the height of the rotor shaft of the future turbine to be installed, since extrapolation from a smaller height to the height of the rotor shaft gives rise to additional uncertainties. If one of the measuring posts is positioned close to the wind farm area, it can be used as the reference wind speed measuring pole during the boiler operation and for determining the wind energy performance by sectors.
Measurement of wind speed and direction are obviously necessary, but also other parameters, particularly air pressure and temperature. The equipment used for these measurements must be robust and safe, since it will generally be left unattended for long periods of time.
Average wind speed is usually collected using cup anemometers because they are safe and cheaper. These anemometers often have better response characteristics than those used at weather observation centers. Wind direction is measured with a girue. Giruetes are usually wound potentiometers. Giruge will be affected by the shade of the pillar and is often oriented so that the pillar is in the least likely wind direction. If data about the vertical flow of air is required, three-dimensional data is useful. These are obtained if lesser robust propeller anemometers are used, or sonic anemometers, which are more expensive.
These anemometers indicate information about both speed and wind direction. The data should be taken at a high frequency, possibly 20 Hz.
It is important that data transmission and storage is secure. For this purpose, the logger must be carefully isolated from atmospheric conditions, especially rain. Many experiments have suffered significant data loss due to various problems, including water infiltration or loss of electricity. The most promising locations for wind farms are usually in hostile environments, but a host of trusted data loggers are available on the market.
It is possible to collect data remotely and download data via a telephone line. The advantage is that data can be monitored on a regular basis and any other problems that occur with the tools can be resolved quickly. For the development of a wind energy project it is essential to carefully plan the data collection step.
Daily weather information is usually available free of charge from weather services. However, for statistical data and consultancy services fees are charged.
In South Europe, the wind regime is dominated by seasonal winds. Winter cold weather is associated with the northern and northest winds. These variations can be seen in station records for wind speed and temperature.
Certain studies suggest that a minimum of 8 months of data is required for the adequate estimation of wind resources. Other researchers have suggested that winter wind is the most important because it coincides with peak demand for electricity. The data can then be sorted into ranges or “boxes” for wind speed or wind direction, either as a whole. The number of measurements in each box is then counted and the sorted data is plotted as a percentage of the total number of readings to indicate the frequency distribution.
From these data it is possible to calculate the average wind speed and wind speed most likely. It is possible to obtain the distribution of the wind power density (proportional to the cubic wind speed). Data may also be presented as the probability of a higher wind velocity than another given value, usually zero, u> 0. These data can be represented by two parameters from the Weibull distribution, the k and C parameters resulting from the use of certain techniques such as the moment method, the least squares method and many others. The two parameters of the Weibull distribution match for many wind data with acceptable accuracy.
The data collected are representative, for example, that the year is not particularly windy or calm. To be sure, data is needed for about 10 years. Obviously this is not practical for a location. However, it is possible to compare the wind data from the location with those of a nearby weather station and apply a MCP-type methodology to increase the data set actually measured at 10 years.
There are a number of available MCP methods, such as:
Calculate the Weibull parameters from the location of interest and the reference location and correlate them over the measurement period and then apply the correction for the rest of the reference data
Calculation of the correction factor (coefficient) for the wind speed between the location of interest and the reference point, during the measurements and on each step of the wind direction
Correlate measured data with reference data by determining a continuous function between the two for all data over the measurement period and applying it for the rest of the reference data
Once the wind distribution probability density is established, the power curve of a turbine can be correlated with wind data to determine the turbine power density density. The data can of course apply to different types and configurations of turbines for optimizing results.
The annual energy output of a wind turbine is the most important economic factor. Uncertainties in determining the annual speed and power curve contribute to the overall uncertainty of predicted annual energy production and lead to a high financial risk.
Annual energy production can be estimated by the following two methods:
Wind velocity histogram and power curve
Theoretical wind distribution and power curve