Photovoltaics (PV)
Photovoltaics (PV) are semiconductor devices that convert sunlight directly into electricity, providing a renewable energy solution for a variety of applications. Comprised of individual solar cells, PV systems can charge batteries, power electrical loads, and even supply energy back to the grid, making them a versatile option for both residential and commercial use. The term "photovoltaic" derives from the Greek word for light and the name of Italian physicist Alessandro Volta, who contributed to the field of electricity. The technology began to take shape in the 19th century, with significant advancements leading to the development of modern solar cells in the mid-20th century.
PV systems can be integrated into buildings or installed as standalone units, typically in rooftop or ground-mounted configurations. They are often connected to the electrical utility grid, allowing users to benefit from metering arrangements like net metering or feed-in tariffs. The global market for PV has seen dramatic growth, driven by technological advancements and decreasing costs, with countries like Germany, China, and Japan leading in installations.
While PV technology offers many benefits, including minimal pollution and high reliability, there are environmental concerns associated with manufacturing and installation. As interest in sustainable energy continues to rise, understanding the mechanics, applications, and impacts of photovoltaics remains crucial for informed decision-making.
Photovoltaics (PV)
Summary: Solar cells, semiconductor devices that convert sunlight into direct-current electricity, are called photovoltaics. Groups of these cells can be used to charge batteries and power electrical loads to operate appliances and even return power to the electrical utility grid.
Photovoltaics (PV), or solar cells, are semiconductor devices that convert solar energy into direct-current (DC) electricity. Groups of PV cells are electrically configured into modules and arrays, which can be used to charge batteries or power a variety of electrical loads. With the appropriate power-conversion equipment, PV systems can produce alternating current (AC) compatible with conventional appliances and can operate in parallel to, and interconnected with, the electrical utility grid. This has made PV technology a strongly promoted renewable energy option across the world.
History
The word photovoltaic comes from the Greek word phos, meaning “light,” and the English word volt, derived from the name of Italian physicist Alessandro Volta (1745–1827), who was a pioneer in the field of electricity. The photovoltaic effect is the basic physical process through which a solar cell converts sunlight into electricity: briefly, photons of light collide with electrons, knocking them into higher states of energy. French physicist Alexandre-Edmond Becquerel (1820–91) first recognized the photovoltaic effect in 1839.
Credit for building the first solar cell is given to American inventor Charles Fritts (1850–1903). In 1883, Fritts coated the semiconductor selenium with a very thin layer of gold, thus creating a device that was about 1 percent efficient. Five years later, Russian physicist and Moscow University professor Aleksandr Grigorievich Stoletov (1839–96) built the first cell based on the photoelectric effect discovered by Heinrich Hertz (1857–94). The photoelectric effect occurs under the right circumstances when light is used to push electrons, freeing them from the surface of a solid. Albert Einstein (1879–1955) finally explained the photoelectric effect in 1905, for which he received the Nobel Prize in Physics in 1921. In 1946, Russell Ohl (1898–1987) patented the modern solar cell, having discovered it while working on a series of advances that would lead to the transistor.
The modern age of solar PV technology arrived in 1954, when Bell Laboratories discovered that silicon doped with certain impurities is very sensitive to light. This first solar PV module was mostly a curiosity, since it was too expensive to have widespread applications. The first practical use for PVs was in the space industry. The Soviets employed a solar array as early as May 15, 1957, when they launched the Sputnik 3 satellite. Throughout the 1960s, the technology was employed to power other orbiting satellites and spacecraft.
As PV technology advanced through space programs, its reliability was established, and costs began to decline. During the energy crisis of the 1970s, PV technology gained recognition as a source of power for nonspace applications. Improvements in manufacturing, performance, and quality of PV modules helped open up a number of opportunities for powering remote terrestrial applications, including battery charging for navigational aids, signals, telecommunications equipment, and other critical low-power needs.
The Basics
Electricity is essentially a stream of moving electrons. A basic PV cell allows for the direct conversion of solar radiation into electricity at the atomic level. The photons in sunlight hit the semiconductor materials in a panel and are reflected, are absorbed, or pass right through. The absorbed photons knock free the electrons from their atoms, and one or more electric fields act to force the freed electrons to flow in a certain direction. This flow of electrons is an electrical current that can be drawn off for external use, such as a providing light.
PV systems may employ a variety of materials in their construction, displaying different efficiencies. The most prevalent materials are derived from crystalline silicon and include single- or monocrystalline silicon, multi- or polycrystalline silicon, and amorphous silicon. Monocrystalline cells produce the most electricity per unit area, and amorphous cells the least. Amorphous silicon is among a group of other materials (also including cadmium telluride and copper-indium-gallium selenide) that are used in thin-film PV technology, which in 2009 was expected to soon dominate the market, due to its promise of reducing material requirements and manufacturing costs of PV modules and systems. However, by the end of 2013, the global market share of thin-film modules had shrunk from 16 percent in 2009 to 10 percent, while other crystalline silicon modules represented about 90 percent of the market .
A traditional PV cell typically produces a small amount of power. In order to produce more power, PV cells are electrically interconnected and mounted in an environmentally protective support structure to form a panel or module. Modules are designed to supply electricity ranging in output from 10 to 300 watts (W). A number of modules can be wired together to form an array. Another way to increase power output is to move from a fixed-angle array (oriented and inclined according to its latitudinal location) to one that is mounted on a single- or dual-axis tracking device. These types of arrays follow the sun, capturing the most sunlight possible throughout the day.
Modern PV modules are a safe, reliable, low-maintenance source of electricity that produces no on-site pollution or emissions. They boast minimal failure rates and projected service lifetimes of twenty to thirty years. Most major manufacturers offer warranties of twenty-plus years for maintaining a relatively high percentage of the initial rated power output (up to 80 percent).
Renewable Energy Generation
The 1970s energy crisis prompted the development of PV systems designed for residential and commercial usage. These systems operate interconnected with or independent of the utility grid, and they can be connected with other energy sources and energy storage systems. A grid-tied PV array may be deployed as an electricity generator in a variety of ways. Two of the more prevalent options are rooftop and ground-mounted systems, although building-integrated photovoltaics (BIPV) are increasing in popularity. Rooftop PV systems are particularly ideal in urban settings (though they may also prove useful in some rural areas), whereas ground-mounted systems are favored by rural generators.
Grid-tied systems are primarily connected with one of two different types of metering arrangements, depending on the local utility. Net metering is a program through which a utility charges a consumer for its net consumption of electricity. If the consumer produces a net surplus of electricity over the course of a given billing cycle, the utility will either pay that amount back or credit the consumer’s next utility bill.
Consumers contracting into feed-in tariff programs use the second option. In this arrangement, a separate utility meter measures the electricity generated by the PV system. The utility pays the consumer for electricity that is generated at a different rate (a tariff) from that used for what is taken from the grid. For example, in 2009, the Canadian province of Ontario started offering twenty-year fixed-price contracts paying rooftop PV generators $0.802 for every kilowatt-hour (kW·h) produced from rooftop systems smaller than 10 kW.
The PV Market
Today, the majority of PV installations supply grid-tied power generation. By the end of 2013, twenty-three countries had on-grid PV capacities greater than 100 megawatts (MW), and seventeen had capacities greater than 1 gigawatt (GW); in 2014, three more countries achieved 1 GW capacity. (Off-grid PV generation is a smaller market, accounting for just 1 percent of the market in 2013, and is used for remote homes, boats, recreational vehicles, electric cars, telecommunications, and remote sensing and monitoring.) Between 2003 and 2013, cumulative global PV capacity increased at an annual average rate of 49 percent, leading to over 135 GW of installed capacity worldwide, plus another 40 GW added in 2014.
Driven by advances in technology and increases in manufacturing scale and sophistication, the cost of PVs has declined steadily since the first solar cells were manufactured. The International Energy Agency (IEA) reported in 2014 that the cost of PV modules had decreased to one-fifth of their price in 2008, while full systems had decreased to just over one-third of their 2008 cost. By 2013, the typical cost of a PV system in the United States was around US$3.3 per watt for utility-scale systems, US$4.5 per watt for commercial systems, and US$4.9 per watt for residential. (Prices were generally lower in China and in non-US Western countries, e.g., US$1.4–1.5/W in China, US$1.7–2.0/W in Australia, US$1.4–2.4/W in Germany). Government- and utility-backed incentive programs, such as net metering and feed-in tariffs targeting solar-generated electricity, have also supported the deployment of solar PV installations in many countries. Global leaders include Germany, Italy, China, Japan, and the United States, particularly California.
In 2013, China and Japan became primary global drivers of PV installations, adding about 11 GW and 7 GW of new capacity, respectively. However, Germany remained the country with the greatest total capacity, with 38.2 GW installed by the end of 2014, compared to 28.2 GW in China, the first runner-up.
PV technology is also experiencing growing demand in the developing countries of Africa, Asia, and Latin America as they purchase very small-scale, off-grid systems. Sales and total capacity of off-grid systems have increased steadily since the early 1980s. In many cases, these systems are already at price parity with fossil fuels.
Environmental Concerns
Some researchers have noted potential issues with PV technology. Production of components creates hazardous materials, which may be discarded instead of recycled. PV system manufacturing can affect air, land, and water, while installation may result in views people find unsightly. Furthermore, PV systems can have environmental effects on habitat and biodiversity.
Bibliography
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Knier, Gil. “How Do Photovoltaics Work?” NASA Science. NASA, 6 Apr. 2011. Web. 13 May 2016.
“Photovoltaic (PV) Systems.” Canada Mortgage and Housing Corporation. Canada Mortgage and Housing, 2010. Web. 13 May 2016.
REN21. Renewables 2015: Global Status Report. Paris: REN21 Secretariat, 2015. REN21. Web. 13 May 2016.
Zhang, Haiyan, et al. "Green or Not? Environmental Challenges from Photovoltaic Technology." Environmental Pollution, vol. 320, 2023, doi.org/10.1016/j.envpol.2023.121066. Accessed 6 Aug. 2024.