What is solar energy and what are its advantages and disadvantages?

As a natural nuclear reactor, the sun releases small packets of energy called photons, the photons travel the distance of 150 million kilometers from the sun to the earth in approximately 5.8 minutes. These particles are sufficient to produce annual solar energy and meet global energy needs. Current photovoltaic power accounts for only one-fifth of the energy consumed in the United States; But solar technology is progressing and the cost of implementing this type of energy is decreasing at an impressive speed. There are many technologies to convert sunlight into energy used by buildings. The most common solar technologies for homes and businesses are solar hot water technology, passive solar design for ambient cooling and heating, and solar photovoltaic technology for electricity. Organizations and industries use these technologies to increase energy resources, improve efficiency and reduce costs. The most common type of solar energy is photovoltaic energy. Solar photovoltaic system is an electrical system that consists of solar panels, inverter and several other components (assembly, cable, etc.).

Solar cells: performance and types

The solar cell is the main component of the solar panel. Sometimes they are called photovoltaic cells or PV cells. These cells produce electricity by absorbing sunlight. The name PV is derived from the process of converting light (photons) into electricity (voltage), which is also called the PV effect. The PV effect was first discovered in 1954, when scientists at the Bell telephone station discovered that silicon produced an electric charge when exposed to sunlight. Shortly after this discovery, solar cells were used to power space satellites and smaller products such as calculators and watches.

A large silicon array mounted on the roof of a commercial building. Solar cells are made of semiconductor materials, the most common type of which is crystalline silicon. There are two types of crystalline silicon, but monocrystalline silicon is more common: this type of cell has a square structure, and its high silicon properties are stronger (and of course more expensive) than other solar panel materials. Another type of crystalline silicon, polycrystalline is a cheaper example with less efficiency and impact, this type is used in large spaces (for example, solar farms, non-residential areas). The second generation of solar cells are thin film cells that are made of amorphous silicon or non-silicon materials such as cadmium telluride. Thin film solar cells use layers of semiconductor materials with a thickness of only a few millimeters. Due to their high flexibility, these cells can be used for roof coverings, building facades or glass glazing of skylights. In addition to silicon, the third generation of solar cells are made from a variety of new materials, including solar composites, using conventional printing technologies, solar paints, and conductive plastics. Some solar cells use plastic lenses or mirrors to focus sunlight onto a small portion of the PV material. PV materials are more expensive but cost-effective due to the low need for them in industry and facilities. However, because the lenses must face the sunlight, the use of concentrating collectors is limited to sunny areas.

Mechanism and storage methods of solar cells

The potential of solar energy used by humans varies based on criteria such as geographical conditions, time changes, cloud cover and land. Geographical conditions affect the potential of solar energy, because areas closer to the equator receive more solar radiation, and hence the use of photovoltaics or solar cells can increase the potential of solar energy in areas far from the equator. Time changes also affect the potential of solar energy because during the night the solar rays that can be absorbed by the solar panels are less. Cloud cover can block sunlight and reduce the amount of light available for solar cells. Another important criterion is suitable land, the land must be unused and suitable for installing solar panels. Rooftops are a good place to install solar cells, in this way every household can provide its own energy directly. Suitable areas for installing solar cells are lands that have not been used for commercial purposes or other purposes and can install solar units. Solar technologies are divided into two categories, active and passive, based on the method of receiving, converting and distributing sunlight and controlling solar energy at different levels around the world, as well as the distance from the equator. In the active method, photovoltaics, concentrated solar power, solar thermal collectors, pumps and fans are used to convert sunlight into useful outputs. The passive method includes choosing materials with suitable thermal properties, designing spaces for air conditioning, and exposing the building to sunlight. Active solar technologies increase energy supply and are focused on supply-side technologies; While passive technologies reduce the need for alternative resources and are considered as demand-side technologies.

Energy production mechanism

PV solar panels generate direct current (DC) electricity. In DC electricity, electrons flow from one direction around the circuit. As an example of DC current, we can mention the amplification of the lamp with a battery. Electrons move from the negative pole of the battery, pass through the lamp and return to the positive pole again.

In AC electricity, electrons oscillate in an alternating path, similar to the cylinder of a car engine. When a loop of wire is wrapped around a magnet, the generator produces AC electricity. Many different energy sources such as gas, diesel fuel, hydroelectric energy, nuclear energy, coal, wind and solar energy can control this type of generator. Because AC power is cheap to transmit over long distances, the US power grid uses AC power. Meanwhile, solar panels generate DC electricity. Now the question is how to transfer DC power to AC network? The answer is to use a converter or inverter.

Solar inverter performance

The solar inverter receives the DC power from the solar array and converts it to AC power. Inverters are the brains of the system. In addition to converting DC power to AC, converters also display the system status, including voltage and current in AC and DC circuits, energy production, and maximum power tracking and prevent errors.

Since the beginning of the solar industry, central converters have been the most common types of converters. The advent of micro-inverters was one of the biggest technological developments in the PV industry. Micro converters optimize the performance of each panel independently and do not affect the entire system like central converters. In this way, each solar panel provides its maximum potential. Another disadvantage of the central inverter was that a problem with one solar panel (for example, being in the shade or getting dirty) would disrupt the performance of the entire solar array. Micro-inverters, such as those found in the SunPower Equinox home solar system, solve this problem. If one solar panel has a problem, the rest of the solar arrays will continue to work without any problems.

Solar panel system performance

It is better to explain this concept with an example. First, sunlight shines on the solar panel on the roof. The panels convert the energy into DC current to flow through the inverter. An inverter converts DC power to AC, which can then be used to power a home. This energy is simple and clean, economical and optimal. But what happens when you are not at home? Or, for example, what should be done at night when the solar system is not able to produce electricity? There is no need to worry, in this situation, the net metering system can be used. This system is a typical type of grid-based PV system that produces more energy during the peak hours of the day, so the excess energy is fed back into the grid. The consumer can use the extra energy at night or on cloudy days. net meter records the ratio of energy sent to energy received from the network. On a broader scale, there are three types of power plant systems for solar energy, which are:

Linear concentrator system

The linear concentrator system collects the sun’s energy using rectangular and parabolic mirrors. The mirrors are deflected toward the sun, focusing the sunlight onto tubes (receivers) located along the length of the mirrors. The reflected light heats the fluid flow inside the tubes. This hot stream is then used to boil water in a conventional turbine generator in order to generate electrical energy.

The dish/engine system uses a mirror dish similar to the large dish of satellites. Aiming to minimize costs, this system is made of a combination of flat mirrors that are placed together in a plate shape. The plate surface directs the sunlight to the heat sink, which absorbs and collects the heat and then transfers it to the motor generator. The most common type of heat engine used in dish/engine systems today is the Stirling engine. This system uses hot fluid to move pistons and generate mechanical power. Then this mechanical force is used to start the generator or alternator and produce electricity. A power tower system consists of a large, flat section of solar tracking mirrors called a heliostat, which it uses to focus sunlight onto a receiver at the top of the tower. The hot fluid in the receiver is used to generate steam, which is then used to generate electricity in a conventional turbine generator. Some power towers use steam or water as the hot fluid. Other advanced designs use this material due to its energy storage and heat transfer capabilities of molten nitrate salt. The ability to store energy or heat storage also provides the possibility of distributing electricity on cloudy days or at night.

Molten salt technology

Molten salt can be used as a thermal storage method to preserve the energy collected by the solar tower, which is ultimately used to generate electricity in bad weather or at night. According to predictions, the efficiency of this system is 99%. Salt melts at 131 degrees Celsius. And it remains liquid up to 288 degrees Celsius in a cold storage chamber. The liquid salt is pumped through the panels into a solar collector, where the temperature reaches 566 degrees Celsius. When electricity is needed, the hot salt is pumped to a conventional steam generator to provide hot steam for the turbine or generator in any of the nuclear, coal, oil, etc. power units.

Applications of solar energy

Solar technology for industrial, commercial and residential buildings is similar (photovoltaics, passive heating, daylighting and water heating). Of course, non-residential buildings can use types that are not for domestic use. These technologies include air conditioning, solar heating and cooling. In the following, the various types of solar energy applications on a domestic and industrial scale are briefly mentioned: Heating, cooling, ventilation: Solar chimney (thermal chimney) is a passive solar ventilation system that consists of a vertical axis. This axis connects the outside and the inside of the building. As the chimney heats up, the air inside the building heats up and draws air into the building. Seasonal plants and trees can be used as mediators to control solar heating and cooling. If the plant is located in the southern part of the building, its leaves will produce shade during the summer and provide bare branches without the possibility of light passing through in the winter. Cooking: Solar ovens use sunlight for cooking, drying and pasteurization. These appliances are divided into three main categories: box ovens, panel ovens and reflective ovens. Water purification: With the solar distillation process, drinking water can be produced from salty or bad-tasting water. Arab chemists of the 16th century first achieved this technology. Then a larger scale solar distillation project began in 1872 in Las Salinas, Chile. Architecture: Sunlight has influenced building design since the beginning of the history of architecture. The advanced methods of solar architecture and urban planning were first used by the Greeks and Chinese, who built their buildings facing south to maximize the use of light and heat.

In new solar design methods, computer modeling is used and solar heating, lighting and ventilation systems are presented in an integrated package. Active solar equipment such as pumps, fans and replaceable windows can complement the passive design and improve the overall performance of the system. Agriculture and horticulture. The agriculture and horticulture industry seeks to optimize the received solar energy and increase the productivity of the units. Methods such as timed cycles, row orientation, alternating height between rows and combinations of plant species can help develop crop yields. In some places, farmers use fruit walls to maximize solar energy absorption. These walls increase the speed of fruit ripening by keeping them warm. The initial walls were built perpendicular to the ground and towards the south; But over time, sloping walls were used to better absorb sunlight. In addition to breeding, solar energy also plays a role in other agricultural applications such as pumping water, drying crops, hatching and drying agricultural fertilizers. Greenhouses also convert sunlight into heat. In this situation, it is possible to grow many products naturally. Transportation: One of the goals of engineers since the 1980s has been the development of solar cars. Some vehicles use solar panels to provide emergency power, including air conditioning to cool the interior of the car, thus reducing fuel consumption. Fuel production: Solar chemical processes use solar energy to carry out chemical reactions. These processes can convert the sun’s energy into transportable and storable fuels. Solar chemical reactions can be divided into two types: thermochemical and photochemical. Since the 1970s, hydrogen production technologies have been a major part of solar energy research.

Prominent solar power plants in the world

In June 2017, China and India were recognized as leaders in the development of large-scale solar energy projects. Energy demand in the United States is increasing despite the recession thanks to government financial incentives and increasing public environmental concerns. Although the largest power plants are located outside the United States; But two power plants are under construction in California and New Mexico.

Tanger power plant in China, the largest solar power plant in the world

The construction of these two power plants can reduce the dominance of Europe on the solar energy market and create a balance. Among the large and vast power plants in the world, the following can be mentioned: 1. India’s Kamuti solar power plant, with a power output of 648 megawatts The facility in Kamuti, Tamil Nadu has an approximate capacity of 648 MW and covers approximately 10 km. 2. Longjiaxia Dam Solar Park (China) This solar park is one of the latest large-scale solar energy projects. 300 hectares of solar panels have been installed in a solar farm in the city of Cixi in the eastern province of Zhijiang. This farm is expected to produce 220 gigawatts of electricity in a year, this amount can provide the energy needed for almost 100,000 households. 3. Kurnool Ultra Mega Solar Park of India (900 MW) Providing 900 MW of solar power capacity, this park ranks higher than the 648 MW plant in Tamil Nadu and the Topaz plant (with a capacity of 550 MW) in California. 4. China’s Datong Solar Power Plant (1000 MW) China’s Datong power plant will be the largest solar power plant in the world after completion. According to government statistics, from July 2016 to January 2017, Datong produced a total of 870 megawatts of electricity, equivalent to more than 120 million watts per month. 5. Tanger China Solar Park (1500 MW) The 1547 MW solar power plant in Zhongyi is the world’s largest solar power plant, which is also known as the Solar Wall of China. The Tanger Desert is a natural and barren area that covers 36,700 km and the solar power plant occupies 1,200 km of this area (3.2% of the total area).

Prominent solar power plants in Iran

Iran is one of the countries with high potential in the field of solar energy, despite having 300 sunny days out of the total of 365 days a year in more than two-thirds of its area and an average radiation of 4.5 to 5.5 kilowatt hours per square meter per day. According to studies conducted by the German Aerospace Center (DLR), it is possible to install more than 60,000 megawatts of solar thermal power plants in an area of more than 2,000 square kilometers.

According to the report of the Ministry of Energy, a summary of the activities carried out in the solar field is as follows: 1. Construction of the Shiraz linear parabolic solar thermal power plant with a capacity of 250 kW up to the stage of steam production and conducting research in the field of manufacturing technology and mold testing related to the collector mirror of the Shiraz power plant, glass bending and the production of parabolic mirrors, creating scientific and technical potential and training skilled experts for design and the construction and operation of large solar power plants in the future and the construction of control systems and software for controlling solar collectors in solar thermal power plants regarding solar thermal power plants 2. Photovoltaic electricity supply to villages (electricity to 358 rural households) with a total capacity of 386 kilowatts 3. Design, installation and operation of a photovoltaic power plant with a nominal capacity of 97 kilowatts in the Sarkvir region of Semnan 4. Design, installation and commissioning of a photovoltaic power plant with a nominal capacity of 30 kW connected to the grid in Taleghan 5. Design, installation and commissioning of a photovoltaic power plant with a nominal capacity of 5 kW in the Darbid region of Yazd 6. Study and research to master the design and manufacturing technology of solar stirling dish (in progress) 7. Conducting potential measurements and preparing the solar atlas of the country and laying the groundwork for the preparation of Iran’s solar radiation potential maps with the German Space Agency (DLR). 8. Designing, building and installing various types of solar power systems such as photovoltaic street lights, water pumps for agricultural purposes, equipping a border area, tunnel lighting with the help of photovoltaic systems 9. Study and fabrication of ohmic junctions for thin film silicon solar cells 10. Designing, compilation of technical knowledge and construction of inverter (inverter) connected to the grid with a power of 5 kW and also inverter connected to the grid without a transformer with a power of 1.5 kW 11. Studies on recognition, technical and economic feasibility of application and design of hybrid renewable energy systems (wind-diesel-photovoltaic-biomass and solar) in Iran 12. Construction of a solar park at Taleghan New Energy site 13. Conceptual design of Shiraz solar hybrid power plant in order to increase the capacity of 500 kW using advanced linear parabolic collectors (in progress) 14. Study of various solar water desalination technologies 15. Evaluating the behavior of consumers of solar energy systems (water heaters and stoves) in Armardeh forest area 16. Designing and manufacturing a 5 ton solar refrigeration device using the solar solid desiccant method Previously, in 2010, Yazd Solar Combined Cycle Power Plant was known as the eighth largest solar power plant in the world. It was the first time that a power plant used the combination of solar energy and natural gas in the world. This power plant was built with the knowledge of Iranian experts and its total capacity reached 308 megawatts at the time of operation and under ISO conditions. According to Tasnim’s report, on September 29 last year, the Ministry of Energy reached an agreement with the English Corex company to build a 600 megawatt solar power plant. This power plant, if completed and built, will be known as the sixth largest solar power plant in the world.

Advantages and disadvantages of solar energy

With the growing threat of climate change from excessive carbon emissions, many countries are looking for clean energy alternatives to their traditional fossil fuels. Among all energy alternatives, solar energy has been the most expensive. However, considering the pros and cons and the 80% drop in the price of solar panels in the last five years, solar energy has a bright future. Among the benefits of this energy, the following can be mentioned: Solar energy is a sustainable alternative to fossil fuels. Although fossil fuels have an expiration date; But the sun’s energy will be available for at least a few billion years. In addition, every day 73,000 terawatts of solar energy reaches the earth’s surface, which is 10,000 times more than the daily energy consumption of the entire world. To use this huge energy source, it is only necessary to implement the necessary technology. The impact of solar energy on the environment is much less compared to fossil fuels. This energy does not emit greenhouse gas because the technology does not require the combustion of fuel. Although solar thermal power plants (CSP) are relatively suboptimal due to water consumption and based on the type of technology used, using the right technology can increase efficiency, for example photovoltaic solar cells (PV) do not need water to produce electricity.

Energy independence

Since sunlight is abundant in most countries of the world, it can turn any country into a potential energy producer and reduce countries’ dependence on energy, and on the other hand, increase their security. Solar energy does not only increase security and independence at the national level; But on a smaller scale, for example, by installing solar panels on the roofs of houses, it is possible to provide the electricity needed by every household.

Disadvantages

One of the biggest problems with solar technology is that it only produces energy when the sun is shining. This means that energy supply may be disrupted at night or on cloudy days. This wouldn’t be a problem if there were low-cost ways to store energy, since long periods of sunshine could produce the excess energy. For example, Germany, one of the pioneers of solar technology, is currently working on the development of energy storage to solve this problem.

Land damage

One of the concerns of solar energy is damage to the land, erosion and loss of wildlife. Although solar PV systems can be installed on fixed sites, large PV systems may require 3.5 to 10 acres of land to produce each megawatt of electricity, and CSP facilities may require 4 to 16.5 acres of land to produce the same host. To solve this problem, facilities can be installed in low quality areas or along roads and highways.

Lack of materials

Some solar technologies require rare materials in their production. However, this is a problem with PV technology, not CSP technology. For example, many rare and rare materials are by-products of other processes and are not directly extracted from the mine. The recycling of PV materials and the resulting advances in nanotechnology increase the efficiency of solar cells and help increase power supply, but perhaps finding alternatives with more abundance can play a major role in solving this problem. Although solar technology has its drawbacks and is expensive in some markets, it is a very good alternative to fossil fuels. Cost problems can be solved by future technological advances in increasing efficiency and storage capacity. Considering the potential benefits of harvesting heat and sunlight, the motivation for future development of solar energy will be high. Source: Zomit