The solar PV is a power source that produces electricity from renewable sources, one obtained directly from solar radiation by a device semiconductor called photovoltaic cell. This type of energy is used mainly to produce electricity on a large scale through distribution networks, but also allows to feed countless applications and autonomous devices, as well as to supply mountain shelters or isolated homes from the electricity grid. Due to the growing demand for renewable energy, the manufacture of solar cells and photovoltaic installations has advanced considerably in recent years. They started mass production from 2000, when environmentalists Germans and Eurosolar organization secured funding for the creation of ten million solar roofs.
Photovoltaic energy does not emit any type of pollution during its operation, contributing to avoid the emission of greenhouse gases. Its main disadvantage is that its production depends on solar radiation, so if the cell is not aligned perpendicular to the Sun you lose between 10-25% of the incident energy. As a result, the use of solar trackers has been popularized in network connection plants to maximize energy production. Production is also affected by adverse weather conditions, such as lack of sun, clouds or dirt that is deposited on the panels. This implies that in order to guarantee the electricity supply it is necessary to supplement this energy with other manageable energy sources such as power stations based on the burning of fossil fuels, hydroelectric energy or nuclear energy.
Thanks to technological advances, sophistication and economy of scale, the cost of photovoltaic solar energy has been reduced steadily since the first commercial solar cells were built, increasing efficiency, and making The average cost of electricity generation is already competitive with conventional energy sources in a growing number of geographical regions, reaching network parity. Currently the cost of the electricity produced in solar installations is between $ 0.05-0.10 / kWh in Europe, China, India, South Africa and the United States. In 2015, new records were reached in projects in the United Arab Emirates (0.0584 $ / kWh), Peru (0.048 $ / kWh) and Mexico (0.048 $ / kWh). In May 2016, a solar auction in Dubai reached a price of 0.03 $ / kWh.
Applications of photovoltaic solar energy
The large-scale industrial production of photovoltaic panels took off in the 1980s, and among its many uses can be highlighted:
Telecommunications and signaling
Photovoltaic solar energy is ideal for telecommunications applications, including those found for example local stations telephony, antennas of Radio and Television, relay stations microwaves and other electronic communication links. This is due to the fact that, in most telecommunications applications, storage batteries are used and the electrical installation is normally carried out in direct current.(DC). On hilly and mountainous terrain, radio and television signals may be interfered with or reflected due to undulating terrain. In these locations, low power transmitters (LPT) are installed to receive and retransmit the signal among the local population.
Photovoltaic cells are also used to power emergency communication systems, for example on SOS (Emergency telephone) posts on roads, railway signaling, beacon for aeronautical protection, meteorological stations or monitoring systems for environmental and quality data. water.
The reduction in the energy consumption of the integrated circuits made possible in the late 1970s the use of solar cells as a source of electricity in calculators, such as the Royal Solar, Sharp EL-8026 or Teal Photon.
Also other fixed devices that use photovoltaic energy have seen their use increase in the last decades, in places where the cost of connection to the electrical network or the use of disposable batteries is prohibitively expensive. These applications include for example sunlamps, water pumps, parking meters, emergency telephones, trash compactors, signals temporary or permanent traffic loading stations or remote monitoring systems.
In isolated environments, where little electrical power is required and access to the network is difficult, photovoltaic panels are used as an economically viable alternative for decades. To understand the importance of this possibility, it is worth bearing in mind that approximately a quarter of the world population still does not have access to electric power.
In developing countries, many villages are located in remote areas, several kilometers from the nearest electricity grid. As a result, photovoltaic energy is increasingly being incorporated to provide power to homes or medical facilities in rural areas. For example, in remote parts of India a rural lighting program has provided lighting using LED lamps powered by solar energy to replace kerosene lamps. The price of solar lamps was approximately the same as the cost of supplying kerosene for a few months. Cubaand other Latin American countries are working to provide photovoltaic energy in areas far from the conventional electricity supply. These are areas in which the social and economic benefits for the local population offer an excellent reason to install photovoltaic panels, although normally this type of initiatives have been relegated to specific humanitarian efforts.
PV is also used to feed facilities pumping for irrigation, drinking water in rural areas and livestock water, or systems desalination of water.
Photovoltaic pumping systems (like those powered by wind power) are very useful where it is not possible to access the general electricity network or is a prohibitive price. Their cost is generally cheaper due to their lower operation and maintenance costs, and they have a lower environmental impact than pumping systems powered by internal combustion engines, which also have lower reliability.
The pumps used can be either alternating current (AC) or direct current (DC). Normally DC motors are used for small and medium applications up to 3kW of power, while for larger applications, AC motors are used coupled to an inverter that transforms the DC current from the photovoltaic panels for its use. This allows to dimension systems from 0.15 kW to more than 55 kW of power, which can be used to supply complex irrigation systems or water storage.
Hybrid solar-diesel systems
Due to the decrease in costs of photovoltaic solar energy, the use of hybrid solar-diesel systems is also expanding, combining this energy with diesel generators to produce electricity in a continuous and stable manner. These types of installations are normally equipped with auxiliary equipment, such as batteries and special control systems to achieve the stability of the system’s electrical supply at all times.
Due to its economic viability (the transport of diesel to the point of consumption is usually expensive) in many cases old generators are replaced by photovoltaic, while the new hybrid facilities are designed in such a way that they allow to use the solar resource whenever it is available, minimizing the use of generators, thus reducing the environmental impact of power generation in remote communities and facilities that are not connected to the electricity grid. An example of this are the companies mining, Whose operations are normally found in open fields, far from large population centers. In these cases, the combined use of photovoltaics allows to greatly reduce the dependence on diesel fuel, allowing savings of up to 70% in the cost of energy.
This type of systems can also be used in combination with other sources of renewable energy generation, such as wind power.
Transport and maritime navigation
Although photovoltaics is still not widely used to provide traction in transport, it is increasingly used to provide auxiliary power in ships and cars. Some vehicles are equipped with air conditioning powered by photovoltaic panels to limit the interior temperature on hot days, while other hybrid prototypes use them to recharge their batteries without the need to connect to the power grid. It has been amply demonstrated the practical ability to design and manufacture solar – powered vehicles and boats and aircraft, being considered the most viable road transport for photovoltaics.
The Solar Impulse is a project dedicated to the development of an airplane propelled solely by photovoltaic solar energy. The prototype can fly during the day propelled by the solar cells that cover its wings, at the same time that it charges the batteries that allow it to stay in the air during the night.
Solar energy is also commonly used in lighthouses, buoys and maritime navigation beacons, recreational vehicles, charging systems for the electric accumulators of ships, and cathodic protection systems. The recharging of electric vehicles is becoming increasingly important. 94
Photovoltaic integrated in buildings
Many photovoltaic installations are often located in buildings: they are usually located on an existing roof, or they are integrated into elements of the building’s own structure, such as skylights, skylights or facades.
Alternatively, a photovoltaic system can also be physically located separate from the building, but connected to the electrical installation thereof to provide power. In 2010, more than 80% of the 9000 MW of photovoltaics that Germany had in operation by then, had been installed on rooftops.
Building integrated photovoltaics (BIPV) is increasingly being incorporated as the main or secondary source of electrical energy in new domestic and industrial buildings, and even in other architectural elements, such as example bridges. Roof tiles with integrated photovoltaic cells are also quite common in this type of integration.
According to a study published in 2011, the use of thermal imaging has shown that solar panels, provided there is an open gap through which air can circulate between the panels and the roof, provide a passive cooling effect on buildings during the day and also help keep the heat accumulated during the night.
Photovoltaic connection to network
One of the main applications of photovoltaic solar energy more developed in recent years, consists of power plants connected to the grid for electricity supply, as well as photovoltaic self – consumption systems, generally of lower power, but also connected to the electricity grid.
A photovoltaic system, or solar PV system is a power system designed to supply usable solar power by means of photovoltaics. It consists of an arrangement of several components, including solar panels to absorb and directly convert sunlight into electricity, a solar inverter to change the electric current from DC to AC, as well as mounting, cabling and other electrical accessories. PV systems range from small, roof-top mounted or building-integrated systems with capacities from a few to several tens of kilowatts, to large utility-scale power stations of hundreds of megawatts. Nowadays, most PV systems are grid-connected, while stand-alone systems only account for a small portion of the market.
Rooftop and building integrated systems
Photovoltaic arrays are often associated with buildings: either integrated into them, mounted on them or mounted nearby on the ground. Rooftop PV systems are most often retrofitted into existing buildings, usually mounted on top of the existing roof structure or on the existing walls. Alternatively, an array can be located separately from the building but connected by cable to supply power for the building. Building-integrated photovoltaics (BIPV) are increasingly incorporated into the roof or walls of new domestic and industrial buildings as a principal or ancillary source of electrical power. Roof tiles with integrated PV cells are sometimes used as well. Provided there is an open gap in which air can circulate, rooftop mounted solar panels can provide a passive cooling effect on buildings during the day and also keep accumulated heat in at night. Typically, residential rooftop systems have small capacities of around 5–10 kW, while commercial rooftop systems often amount to several hundreds of kilowatts. Although rooftop systems are much smaller than ground-mounted utility-scale power plants, they account for most of the worldwide installed capacity.
Concentrator photovoltaics (CPV) is a photovoltaic technology that contrary to conventional flat-plate PV systems uses lenses and curved mirrors to focus sunlight onto small, but highly efficient, multi-junction (MJ) solar cells. In addition, CPV systems often use solar trackers and sometimes a cooling system to further increase their efficiency. Ongoing research and development is rapidly improving their competitiveness in the utility-scale segment and in areas of high solar insolation.
Photovoltaic thermal hybrid solar collector
Photovoltaic thermal hybrid solar collector (PVT) are systems that convert solar radiation into thermal and electrical energy. These systems combine a solar PV cell, which converts sunlight into electricity, with a solar thermal collector, which captures the remaining energy and removes waste heat from the PV module. The capture of both electricity and heat allow these devices to have higher exergy and thus be more overall energy efficient than solar PV or solar thermal alone.
Many utility-scale solar farms have been constructed all over the world. As of 2015, the 579-megawatt (MWAC) Solar Star is the world’s largest photovoltaic power station, followed by the Desert Sunlight Solar Farm and the Topaz Solar Farm, both with a capacity of 550 MWAC, constructed by US-company First Solar, using CdTe modules, a thin-film PV technology. All three power stations are located in the Californian desert. Many solar farms around the world are integrated with agriculture and some use innovative solar tracking systems that follow the sun’s daily path across the sky to generate more electricity than conventional fixed-mounted systems. There are no fuel costs or emissions during operation of the power stations.
Developing countries where many villages are often more than five kilometers away from grid power are increasingly using photovoltaics. In remote locations in India a rural lighting program has been providing solar powered LED lighting to replace kerosene lamps. The solar powered lamps were sold at about the cost of a few months’ supply of kerosene. Cuba is working to provide solar power for areas that are off grid. More complex applications of off-grid solar energy use include 3D printers. RepRap 3D printers have been solar powered with photovoltaic technology, which enables distributed manufacturing for sustainable development. These are areas where the social costs and benefits offer an excellent case for going solar, though the lack of profitability has relegated such endeavors to humanitarian efforts. However, in 1995 solar rural electrification projects had been found to be difficult to sustain due to unfavorable economics, lack of technical support, and a legacy of ulterior motives of north-to-south technology transfer.
Until a decade or so ago, PV was used frequently to power calculators and novelty devices. Improvements in integrated circuits and low power liquid crystal displays make it possible to power such devices for several years between battery changes, making PV use less common. In contrast, solar powered remote fixed devices have seen increasing use recently in locations where significant connection cost makes grid power prohibitively expensive. Such applications include solar lamps, water pumps, parking meters, emergency telephones, trash compactors, temporary traffic signs, charging stations, and remote guard posts and signals.
In May 2008, the Far Niente Winery in Oakville, CA pioneered the world’s first “floatovoltaic” system by installing 994 photovoltaic solar panels onto 130 pontoons and floating them on the winery’s irrigation pond. The floating system generates about 477 kW of peak output and when combined with an array of cells located adjacent to the pond is able to fully offset the winery’s electricity consumption. The primary benefit of a floatovoltaic system is that it avoids the need to sacrifice valuable land area that could be used for another purpose. In the case of the Far Niente Winery, the floating system saved three-quarters of an acre that would have been required for a land-based system. That land area can instead be used for agriculture. Another benefit of a floatovoltaic system is that the panels are kept at a lower temperature than they would be on land, leading to a higher efficiency of solar energy conversion. The floating panels also reduce the amount of water lost through evaporation and inhibit the growth of algae.
PV has traditionally been used for electric power in space. PV is rarely used to provide motive power in transport applications, but is being used increasingly to provide auxiliary power in boats and cars. Some automobiles are fitted with solar-powered air conditioning to limit interior temperatures on hot days. A self-contained solar vehicle would have limited power and utility, but a solar-charged electric vehicle allows use of solar power for transportation. Solar-powered cars, boats and airplanes have been demonstrated, with the most practical and likely of these being solar cars. The Swiss solar aircraft, Solar Impulse 2, achieved the longest non-stop solo flight in history and plan to make the first solar-powered aerial circumnavigation of the globe in 2015.
Telecommunication and signaling
Solar PV power is ideally suited for telecommunication applications such as local telephone exchange, radio and TV broadcasting, microwave and other forms of electronic communication links. This is because, in most telecommunication application, storage batteries are already in use and the electrical system is basically DC. In hilly and mountainous terrain, radio and TV signals may not reach as they get blocked or reflected back due to undulating terrain. At these locations, low power transmitters (LPT) are installed to receive and retransmit the signal for local population.
Solar panels on spacecraft are usually the sole source of power to run the sensors, active heating and cooling, and communications. A battery stores this energy for use when the solar panels are in shadow. In some, the power is also used for spacecraft propulsion—electric propulsion. Spacecraft were one of the earliest applications of photovoltaics, starting with the silicon solar cells used on the Vanguard 1 satellite, launched by the US in 1958. Since then, solar power has been used on missions ranging from the MESSENGER probe to Mercury, to as far out in the solar system as the Juno probe to Jupiter. The largest solar power system flown in space is the electrical system of the International Space Station. To increase the power generated per kilogram, typical spacecraft solar panels use high-cost, high-efficiency, and close-packed rectangular multi-junction solar cells made of gallium arsenide (GaAs) and other semiconductor materials.
Specialty Power Systems
Photovoltaics may also be incorporated as energy conversion devices for objects at elevated temperatures and with preferable radiative emissivities such as heterogeneous combustors.
The 122 PW of sunlight reaching the Earth’s surface is plentiful—almost 10,000 times more than the 13 TW equivalent of average power consumed in 2005 by humans. This abundance leads to the suggestion that it will not be long before solar energy will become the world’s primary energy source. Additionally, solar electric generation has the highest power density (global mean of 170 W/m2) among renewable energies.
Solar power is pollution-free during use, which enables it to cut down on pollution when it is substituted for other energy sources. For example, MIT estimated that 52,000 people per year die prematurely in the U.S. from coal-fired power plant pollution and all but one of these deaths could be prevented from using PV to replace coal. Production end-wastes and emissions are manageable using existing pollution controls. End-of-use recycling technologies are under development and policies are being produced that encourage recycling from producers.
PV installations can operate for 100 years or even more with little maintenance or intervention after their initial set-up, so after the initial capital cost of building any solar power plant, operating costs are extremely low compared to existing power technologies.
Grid-connected solar electricity can be used locally thus reducing transmission/distribution losses (transmission losses in the US were approximately 7.2% in 1995).
Compared to fossil and nuclear energy sources, very little research money has been invested in the development of solar cells, so there is considerable room for improvement. Nevertheless, experimental high efficiency solar cells already have efficiencies of over 40% in case of concentrating photovoltaic cells and efficiencies are rapidly rising while mass-production costs are rapidly falling.
In some states of the United States, much of the investment in a home-mounted system may be lost if the home-owner moves and the buyer puts less value on the system than the seller. The city of Berkeley developed an innovative financing method to remove this limitation, by adding a tax assessment that is transferred with the home to pay for the solar panels. Now known as PACE, Property Assessed Clean Energy, 30 U.S. states have duplicated this solution.
There is evidence, at least in California, that the presence of a home-mounted solar system can actually increase the value of a home. According to a paper published in April 2011 by the Ernest Orlando Lawrence Berkeley National Laboratory titled An Analysis of the Effects of Residential Photovoltaic Energy Systems on Home Sales Prices in California:
The research finds strong evidence that homes with PV systems in California have sold for a premium over comparable homes without PV systems. More specifically, estimates for average PV premiums range from approximately $3.9 to $6.4 per installed watt (DC) among a large number of different model specifications, with most models coalescing near $5.5/watt. That value corresponds to a premium of approximately $17,000 for a relatively new 3,100 watt PV system (the average size of PV systems in the study).
Impact on Electricity Network
With the increasing levels of rooftop photovoltaic systems, the energy flow becomes 2-way. When there is more local generation than consumption, electricity is exported to the grid. However, electricity network traditionally is not designed to deal with the 2- way energy transfer. Therefore, some technical issues may occur. For example, in Queensland Australia, there have been more than 30% of households with rooftop PV by the end of 2017. The famous Californian 2020 duck curve appears very often for a lot of communities from 2015 onwards. An over-voltage issue may come out as the electricity flows from these PV households back to the network. There are solutions to manage the over voltage issue, such as regulating PV inverter power factor, new voltage and energy control equipment at electricity distributor level, re-conductor the electricity wires, demand side management, etc. There are often limitations and costs related to these solutions.
Implication onto Electricity Bill Management and Energy Investment
There is no silver bullet in electricity or energy demand and bill management, because customers (sites) have different specific situations, e.g. different comfort/convenience needs, different electricity tariffs, or different usage patterns. Electricity tariff may have a few elements, such as daily access and metering charge, energy charge (based on kWh, MWh) or peak demand charge (e.g. a price for the highest 30min energy consumption in a month). PV is a promising option for reducing energy charge when electricity price is reasonably high and continuously increasing, such as in Australia and Germany. However, for sites with peak demand charge in place, PV may be less attractive if peak demands mostly occur in the late afternoon to early evening, for example residential communities. Overall, energy investment is largely an economical decision and it is better to make investment decisions based on systematical evaluation of options in operational improvement, energy efficiency, onsite generation and energy storage.
The environmental impact of silicon technology and thin-film technology are typical of semiconductor manufacturing, with the associated chemical and energy-intensive steps. The high-purity silicon production in silicon technology is decisive due to the high energy consumption and the amount of secondary substances. For 1 kg ultrapure silicon, up to 19 kg of secondary substances are produced. As ultrapure silicon is mostly produced by subcontractors, the selection of suppliers in terms of environmental aspects is crucial for the environmental performance of a module.
In thin-film technology, cleaning the process chambers is a sensitive issue. Here are partially the harmful substances nitrogen trifluoride and sulfur hexafluoride used. In the use of heavy metals such as CdTe technology is argued with a short energy payback time on the life-cycle basis.
In 2011, the Bavarian State Office for the Environment confirmed that CdTe solar modules pose no danger to humans and the environment in the event of a fire.
Due to the absolute freedom from emissions in operation, photovoltaics has very low external costs. If these are around 6 to 8 ct / kWh for power generation from coal and lignite, they are only about 1 ct / kWh for photovoltaic systems (year 2000). This is the conclusion of an expert opinion of the German Aerospace Center and the Fraunhofer Institute for Systems and Innovation Research. For comparison, the value of 0.18 ct / kWh of external costs for solar thermal power plants, which is also mentioned there, should be mentioned.
Greenhouse Gas Balance
Even if there is no operation even in CO 2e emissions are, then photovoltaic systems can not yet be present CO 2e produced, transported and assemble -free. Depending on the technology and location, the calculated CO 2e emissions of photovoltaic systems in 2013 amount to between 10.5 and 50 g CO 2e / kWh, with averages in the range of 35 to 45 g CO 2e / kWh. A recent study from 2015 found average values of 29.2 g / kWh. These emissions are caused by the combustion of fossil fuels, especially during the production of solar plants. With further expansion of renewable energies as part of the global transformation to sustainable energy sources, the greenhouse gas balance will thus improve automatically. Also decreasing emissions result from the technological learning curve. Historically, emissions have fallen by 14% per doubling of installed capacity (as of 2015).
After a comprehensive comparison of the Ruhr-University Bochum from 2007, the CO was 2e emissions in photovoltaics still at 50-100 g / kWh, and especially the modules used and the location were crucial. By comparison, it was 750-1200 g / kWh for coal -fired power plants, 400-550 g / kWh for CCGT gas power plants, 10-40 g / kWh for wind energy and hydropower, and 10-30 g / kWh for nuclear energy (without final disposal), and in solar thermal energy in Africa at 10-14 g / kWh.
The photovoltaic energy payback period is the period during which the photovoltaic system has delivered the same amount of energy needed throughout its life cycle; for manufacturing, transport, construction, operation and dismantling or recycling.
It is currently (as of 2013) between 0.75 and 3.5 years, depending on the location and photovoltaic technology used. CdTe modules performed best at 0.75-2.1 years, while amorphous silicon modules were 1.8-3.5 years above average. Mono- and multicrystalline systems as well as plants based on CIS were about 1.5 to 2.7 years old. The lifespan of the study was assumed to be 30 years for modules based on crystalline silicon cells and 20 to 25 years for thin-film modules, while the lifespan of the inverters was assumed to be 15 years. By 2020, an energy payback period of 0.5 years or less for southern European crystalline silicon plants is considered achievable.
When used in Germany, the energy needed to produce a photovoltaic system is recovered in solar cells in about two years. The harvest factor is at least 10 under typical German irradiation conditions, a further improvement is likely. The lifetime is estimated at 20 to 30 years. On the part of the manufacturers, the modules are usually given performance guarantees for 25 years. The energy-intensive part of solar cells can be reused 4 to 5 times.
PV systems are predominantly constructed on existing roofs and traffic areas, which does not lead to additional space requirements. Outdoor facilities in the form of solar parks take on the other hand, additional space to use, often already pre-contaminated areas such. B. conversion areas(from military, economic, traffic or residential use), areas along highways and railway lines (in 110 m strip), areas that are designated as a commercial or industrial area or sealed areas (formerly landfills, parking lots, etc.) are used. If photovoltaic systems are erected on agricultural land, which is currently not supported in Germany, competition for use may occur. However, it must be taken into account that solar parks have a much higher energy yield compared to bioenergy generation on the same area. Solar parks supply about 25 to 65 times as much electricity per unit area as energy crops.
Recycling PV Modules
So far, the only recycling plant (specialized pilot plant) for crystalline photovoltaic modules in Europe is in Freiberg, Saxony. The company Sunicon GmbH (formerly Solar Material), a subsidiary of SolarWorld, achieved a mass-based recycling rate for modules of an average of 75% in 2008 with a capacity of approx. 1200 tonnes per year. The amount of waste of PV modules in the EU in 2008 was 3,500 tonnes / year. Due to extensive automation, a capacity of approx. 20,000 tonnes per year is planned.
To build a voluntary, EU-wide, nationwide system for recycling, the solar industry founded a joint initiative in 2007, the Association PV CYCLE. An estimated 130,000 tonnes of obsolete modules per year are expected in the EU by 2030. As a reaction to the overall unsatisfactory development, since January 24, 2012, solar modules have also been subject to an amendment to the electronic waste directive. For the PV industry, the amendment stipulates that 85 percent of the solar modules sold must be collected and 80 percent recycled. By 2014, all EU-27 Member States should transpose the Regulation into national law. The aim is to make producers responsible for providing structures for recycling. The separation of the modules from other electrical appliances is preferred. Existing collection and recycling structures will also be expanded.
Source from Wikipedia