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You work for OneEarth, an environmental consulting company that specializes in building condition assessments, contaminated site remediation, and energy audits. Founded by an environmentally concerned citizen in 2010, OneEarth has emerged as the highest-quality and most comprehensive environmental services company in the region.
Southern New Hampshire University (SNHU), a private nonprofit university located in Manchester, New Hampshire, in the United States, is dedicated to reducing its carbon footprint. SNHU has approached OneEarth for its assistance and expertise in achieving this goal. Knowing of your desires to diversify your experience and professional portfolio, your manager, Claire DeAir, has consented for you to join the team working with SNHU. You’re responsible for creating a technical report based on an analysis of the data the onsite team has collected over the last few weeks to determine the cost-effectiveness of SNHU adopting solar energy.
Directions
You’ve been asked to recommend whether or not SNHU should install solar energy panels on one of its buildings in Manchester, New Hampshire, to reduce the university’s carbon footprint. Using the data in the SNHU Site Data document in the Supporting Materials section, you will conduct a series of calculations. With those calculations, you will create a technical report for SNHU that explains whether the university should invest in solar energy by purchasing the system or by leasing. Your technical report should include the following calculations and determinations:
A calculation of the total electricity output of a solar panel system in kilowatts hours (kWh)Use the following steps as a guide to making this calculation:
How many panels fit on the roof, assuming the building is rectangular? (To make this determination, determine the number of panels that can fit along one side, and the number of rows of panels that can fit along the opposite side. Round down to the nearest whole number of panels in each direction and multiply to obtain the required number of panels.)
What are the dimensions of the building’s roof in meters?
How many panels will fit on the roof in each direction? Round down to the nearest panel. When calculating the number of panels, be sure that when you change from length to width on the roof, you also change from length to width on the panels.
Find the area of the panels in meters to make sure that the area of the panels is less than the area of the roof.
What is the total amount of electricity that could be produced by adopting a solar panel system that covers the entire roof based on the average monthly sunlight? (1kW = 1000W, and 1 hour of sunlight produces 400 watts per panel)
How many hours of sunlight are expected on average per month? Calculate the average hours based on the monthly data provided. Round down to the nearest tenth of an hour.
What is the total amount of kWh that is produced by the entire solar panel system per month based on the average monthly sunlight? Per year?
A calculation of the difference between the current electricity usage of the building and the electricity generated by a solar panel system in kilowatt hours and in dollarsUse the following steps as a guide to making this calculation:
How much electricity does the building use on average annually?
Is the amount of electricity generated by the solar array sufficient to cover SNHU’s yearly electricity usage?
If the energy generated is more than the energy needed to run the building, how much additional savings is there for energy that can be channeled to other buildings on campus or sold back to the energy company?
A determination of the likelihood of receiving a damaged panelSNHU expressed some concerns about receiving damaged solar panels from the manufacturer. You would like to be transparent and address these concerns by illustrating the likelihood of a damaged panel based on the size of the system SNHU would be purchasing.The manufacturer has reported that since solar panels are complex and evolving technology, 1 out of every 1,000 manufactured solar panels is defective.
How many panels fit on the roof?
A determination of how long it would take to pay back the cost of buying the system in yearsUse the following steps as a guide to making this calculation—you can assume there will not be any required maintenance during the first 10 years:
How much does each panel cost? How much does the entire system cost?
What are the government incentives? How does that affect the cost?
How much will your solar panels save SNHU per year?
How long would it take to pay back the cost of purchasing the solar panel system in years? (Years = Cost to Purchase and Install Solar Panel System / Savings Per Year) The time in years should take into account all energy savings, not just those for the building on which the solar array is installed.
A determination of whether there is a cost savings over 10 years for leasing the solar panel systemUse the following steps as a guide to making this calculation:
What is the total cost with solar for 10 years, in dollars?
What is the total remaining utility bill for 10 years?
A recommendation for whether SNHU should install solar energy panels on its buildings based on your calculations
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Record: 1
Title: Carbon Footprint.
Authors: Droujkova, Maria
Source: Salem Press Encyclopedia of Science, 2022. 3p.
Document Type: Biography
Subject Terms: Ecology
Environmental responsibility
Ecological impact
Abstract: Carbon footprint is intended to be a measure of the ecological impact of
people or events. It is a calculation of total emission of greenhouse
gases, typically carbon dioxide, and is often stated in units of tons per
year. There is no universal mathematical method or agreed-upon set of
variables that are used to calculate carbon footprint, though scientists
and mathematicians estimate carbon footprints for individuals,
companies, and nations. Many calculators are available on the internet
that take into account factors like the number of miles a person drives or
flies, whether or not they use energy efficient light bulbs, whether they
shop for food at local stores, and what sort of technology they use for
electrical power. Some variables are direct, such as the carbon dioxide
released by a person driving a car, while others are indirect and focus on
the entire life cycle of products, such as the fuel used to produce the
vegetables that a person buys at the grocery store and disposal of
packaging waste.
Full Text Word Count: 1642
Accession Number: 89404314
Database: Research Starters
Carbon Footprint
Summary: A carbon footprint is a mathematical calculation of an entity’s total emission of greenhouse gases
per year.
Carbon footprint is intended to be a measure of the ecological impact of people or events. It is a calculation of
total emission of greenhouse gases, typically carbon dioxide, and is often stated in units of tons per year. There
is no universal mathematical method or agreed-upon set of variables that are used to calculate carbon
footprint, though scientists and mathematicians estimate carbon footprints for individuals, companies, and
nations. Many calculators are available on the internet that take into account factors like the number of miles a
person drives or flies, whether or not they use energy efficient light bulbs, whether they shop for food at local
stores, and what sort of technology they use for electrical power. Some variables are direct, such as the carbon
dioxide released by a person driving a car, while others are indirect and focus on the entire life cycle of
products, such as the fuel used to produce the vegetables that a person buys at the grocery store and disposal
of packaging waste.
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The notion of a carbon footprint has been considered in a wide range of areas, including the construction of
low-impact homes, offices, and other buildings. Designs must take into account not only the future impact of the
building in terms of carbon emissions, but carbon-related production costs for the materials, labor, and energy
used to build it. Mathematical modeling and optimization helps engineers and architects create efficient, useful,
and sometimes even beautiful structures while reducing the overall carbon footprint. Mathematicians are also
involved in the design of technology that is more energy efficient, as well as methods that allow individuals and
businesses to convert to electronic documents and transactions rather than using paper. These methods
include using improved communication technology, faster computer networks, improved methods for digital file
sharing and online collaboration, and security protocols for digital signatures and financial transactions.
Manufacturers are increasingly being urged and even required to examine their practices, since manufacturing
processes produce both greenhouse gasses from factory smokestacks and waste heat. Mathematicians and
scientists are working on ways to recycle much of this heat for power generation. One proposed device
combines a loop heat pipe, which is a passive system for moving heat from a source to another system, often
over long distances, with a Tesla turbine. Patented by scientist and inventor Nikola Tesla, a Tesla turbine is
driven by the boundary layer effect rather than fluid passing over blades as in conventional turbines. It is
sometimes called a Prandtl layer turbine after Ludwig Prandtl, a scientist who worked extensively in developing
the mathematics of aerodynamics and is credited with identifying the boundary layer.
A man rides a bicycle to work in
an effort to reduce his carbon
footprint. By David Dennis Scotts
Valley, CC BY-SA 2.0
(http://creativecommons.org/licens
sa/2.0), via Wikimedia Commons
Carbon Footprints of People
A calculation of the carbon footprints of different aspects of people’s lives, and then the aggregate for a year, is
always an estimate. For example, different towns use different methods for generating electricity. Entering data
for an electric bill allows for a rough estimate of the household’s carbon footprint, but not exact numbers, which
would depend on the electricity generating methods. Houses contribute to carbon footprints through their
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building costs, heating and cooling, water filtration, repair, and maintenance—all of which use products with
carbon footprints.
Travel is another major contributor to peoples’ carbon footprints. Daily commutes and longer trips with any
motorized transportation contribute to carbon dioxide emissions. When computing carbon footprints, fuel
production and storage costs have to be taken into consideration.
The food that people eat can contributes to the carbon footprint, especially if it is transported by motorized
vehicles before being eaten. The movement of locavores (people who eat only locally grown foods) aims to
minimize the carbon footprint of food. Also, different farming practices may contribute more or less to the
carbon footprint of food.
The objects people use every day contribute to their carbon footprints. Recycling and reusing reduces the need
for landfills, waste processing, and waste removal, all of which have substantial carbon footprints. There are
individuals and communities who attempt to avoid waste as much as possible in order to reduce their overall
environmental impact. However, even activities that do not create physical waste, such as internet use, can be
calculated to have both direct and indirect carbon footprints.
Economy and Policy
There are two main strategies for addressing carbon footprints. The first strategy is to lower the carbon footprint
by modifying individual behaviors, such as traveling by bike, eating locally, and recycling. The second strategy
is to perform activities with negative carbon footprints, such as planting trees, to match carbon footprints of
other activities.
Some companies incorporate activities that offset the carbon footprint of their main production into their
business plans, either lowering their profit margins or passing the cost to their customers. There are economic
laws and proposals that attempt to integrate carbon footprint considerations into the economy, usually through
taxes on use of fuel, energy, or emissions. Carbon dioxide emissions, in economic terms, are a negative
externality (a negative effect on a party not directly involved in the economic transaction). Money collected
through carbon taxes is generally used to offset the cost to the environment.
Emissions trading (or carbon trading) is another method of dealing with carbon footprints economically.
Governments can sell emission permits to the highest-bidding companies, matching their carbon footprints, and
capping the total emission permits sold. This method allows prices of permits to fluctuate with demand, in
contrast with carbon taxes in which prices are fixed and the quantities of emissions can change. Economists
model the resulting behaviors, and advise policymakers based on the models’ outcomes.
Marginal Abatement Cost Curve
“Marginal cost” is an economic term that means the change of cost that happens when one more unit of
product is made, or unit of service performed. For physical objects, the curve is often U-shaped. The first units
produced are very costly because their cost production involves setting up the necessary infrastructure. As
more units are produced, and the infrastructure is reused, the price goes down until the quantities of production
reach such levels that the logistic difficulties drive the price per additional units higher again.
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A marginal abatement curve shows the cost of reducing emissions by one more unit. These curves are usually
graphed in percents. For example, such a curve can be a straight line, with the cost of eliminating the first few
percent of emissions being zero or even negative. This happens because it can be done by changing practices
within existing economic infrastructures, such as cheap smart switches into the residential sector’s lighting
grids. Additional lowering of the carbon footprint, however, requires deeper and costlier changes to the way of
life. For example, there have historically been relatively high costs involved in switching to wind power and
solar power, or switching to the use of crop rotations that do not require high-carbon fertilizers.
Country by Country
The average carbon footprint of citizens varies by country. For example, by the late 2010s, the per capita
annual carbon footprint in US was about 15 metric tons (the highest in the world), while in India it was about 1.5
metric tons, according to the World Economic Forum. However, these calculations are extremely complicated
because of global trade. For example, many developed countries “export” or “outsource” their carbon emissions
to developing countries. Products imported from developing countries account for anywhere from a tenth to a
half of the carbon footprints of developed nations.
International calculations indicate a strong correlation between the average carbon footprint of a country’s
citizen and the average per capita consumption. The higher the consumption rates, the higher the average
carbon footprint.
The categories used for calculation for countries are similar to those used for individuals and include
construction, shelter, food, clothing, manufactured products, services, transportation, and trade. The ratios of
these items to one another in the carbon footprints can vary by country. For example, at least one study found
that the greatest item in the US carbon footprint was shelter (25 percent), with mobility being second (21
percent); in contrast, Canada’s greatest item affecting carbon footprint was mobility (30 percent), and its
second greatest was shared between shelter and service (18 percent each).
Studies have also been conducted to determine whether population density directly correlates with the carbon
footprint of an area. The nuances revealed through such studies continue to stress the significance of the
theory regarding the need for more thorough and flexible approaches to reducing carbon emissions.
Bibliography
Berners-Lee, Mike. How Bad Are Bananas? The Carbon Footprint of Everything. Greystone Books, 2011.
Bewicke, Henry. “Chart of the Day: These Countries Have the Largest Carbon Footprints.” World Economic
Forum, 2 Jan. 2019, www.weforum.org/agenda/2019/01/chart-of-the-day-these-countries-have-the-largestcarbon-footprints/. Accessed 23 Dec. 2021.
“Carbon Footprint Calculator.” United States Environmental Protection Agency, www3.epa.gov/carbon-footprintcalculator/. Accessed 23 Dec. 2021.
“Carbon Footprint Factsheet.” Center for Sustainable Systems, University of Michigan, 2021,
https://css.umich.edu/factsheets/carbon-footprint-factsheet. Accessed 23 Dec. 2021.
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Dickerson, Kelly. “These Maps Show Which Areas of the Country Have the Biggest Carbon Footprints.”
Business Insider, 11 Feb. 2014, www.businessinsider.com/carbon-footprint-maps-2014-1. Accessed 21 Feb.
2017.
Goleman, Daniel. Ecological Intelligence: How Knowing the Hidden Impacts of What We Buy Can Change
Everything. Broadway Books, 2009.
Muthu, Subramanian Senthilkannan, editor. The Carbon Footprint Handbook. CRC Press, 2016.
Zubelzu, Sergio, and Roberto Álvarez Fernández. Carbon Footprint and Urban Planning: Incorporating
Methodologies to Assess the Influence of the Urban Master Plan on the Carbon Footprint of the City. Springer,
2016.
Copyright of Salem Press Encyclopedia of Science is the property of Salem Press. The copyright in an
individual article may be maintained by the author in certain cases. Content may not be copied or emailed to
multiple sites or posted to a listserv without the copyright holder’s express written permission. However, users
may print, download, or email articles for individual use.
Source: Salem Press Encyclopedia of Science, 2022, 3p
Item: 89404314
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Record: 1
Title: Solar Energy.
Authors: Plitnik, George R., B.A., B.S., M.A., Ph.D.
Source: Salem Press Encyclopedia of Science, 2022. 3p.
Document Type: Article
Subject Terms: Solar energy
Abstract: Solar energy is light from the sun that has been converted into heat
energy or electricity. The three most common conversion methods are
passive systems, which collect and store solar energy without the use of
any other source of energy and using few or no moving parts; active
systems, which collect and store energy by employing electric energy;
and photovoltaic systems (PV), which convert sunlight into electricity.
Both passive and active systems use glass to admit sunlight and prevent
heat from escaping and mass to store the heat collected. The four types
of passive systems are direct gain, indirect gain, attached gain, and
thermosyphon. Active systems either collect sunlight directly on flat
surfaces or use parabolic reflectors to achieve high temperatures by
focusing the light. Either air or water may be used to transfer the heat
from the collector to storage.
Full Text Word Count: 4592
Accession Number: 89250581
Database: Research Starters
Solar Energy
Summary
Solar energy is the energy from the sun that is captured and used to heat homes or provide electricity. The
three main types of solar energy systems are passive, in which solar energy is stored without using any other
energy source; active, in which electricity is used to capture the sun’s energy; and photovoltaic, which directly
converts sunlight into electricity. Although solar energy is free in that costs are not involved in generating it, it is
not constant and must be captured and stored. Also, the systems used to capture solar power remain
expensive.
Definition and Basic Principles
Solar energy is light from the sun that has been converted into heat energy or electricity. The three most
common conversion methods are passive systems, which collect and store solar energy without the use of any
other source of energy and using few or no moving parts; active systems, which collect and store energy by
employing electric energy; and photovoltaic systems (PV), which convert sunlight into electricity. Both passive
and active systems use glass to admit sunlight and prevent heat from escaping and mass to store the heat
collected. The four types of passive systems are direct gain, indirect gain, attached gain, and thermosyphon.
Active systems either collect sunlight directly on flat surfaces or use parabolic reflectors to achieve high
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temperatures by focusing the light. Either air or water may be used to transfer the heat from the collector to
storage.
Solar Cell Panel: The solar cell
panel collects energy from the
sun and can provide electric
energy. © EBSCO
PV systems use arrays of photocells to transform solar radiation directly into DC (direct current) electricity. The
photocells, typically semiconducting silicon crystals, act as insulators until illuminated by radiant energy. The
material then conducts electricity, effectively making each cell a small battery. By connecting photocells into
large modular arrays, sufficient electric energy can be generated to power homes or, when sufficient modules
are present, to produce electricity for a centralized power plant. Small PV systems may use battery storage or
tie into the electric grid to allow energy to be withdrawn when needed or fed into the grid when not necessary.
Although solar energy is free energy in that there is no cost to generate it, it has several disadvantages. It is
diffuse and intermittent, and it must be stored. Also, active collection devices are constructed of expensive
nonrenewable resources such as aluminum and copper.
Background and History
Solar energy has always provided, directly or indirectly, virtually all of humanity’s energy. Ancient Greek homes
were oriented toward the south, and early Chinese architecture incorporated solar design to heat interior
spaces. By the first century BCE, Rome had added clear glass windows to Greek solar designs to trap the
heat, thus creating the first true passive solar design. The sun was also used to heat water entering the huge
public baths indigenous to Roman society.
After the fall of Rome, solar architecture was forgotten until the sixteenth century, when greenhouses were
used to grow exotic fruits and vegetables in northern Europe. By the eighteenth century, large glass windows
enabled the construction of better greenhouses, which evolved in the nineteenth century into ostentatious
conservatories for displaying exotic plants.
Active systems that focused sunlight to produce high temperatures were developed in the nineteenth century.
Domestic hot water systems were first built and marketed in the early twentieth century. By mid-century, active
systems using air to heat homes appeared, but their acceptance was limited because of their high costs.
Photovoltaics (PV) trace their origin to the late 1880s when Charles Fritts (1850–1903) developed a solar
electric cell using germanium crystals, but commercial development stagnated until the 1950s when Bell
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Laboratories produced a viable but costly silicon-based system to power remote communication devices. The
National Aeronautics and Space Administration (NASA), needing lightweight reliable energy sources for its
nascent space program, adapted these PV systems for its first satellites, launched in the late 1950s.
In the 1970s, because of the oil embargoes and rise in fuel prices, solar energy began to capture the interest of
the public. However, the decline in oil prices in the 1980s produced a drop in the interest in solar power. Since
the mid-1990s, the market in solar water heating systems have grown at a rapid rate. Industry estimates
suggest the market will grow at a rate of 6.7 percent from 2021 to 2026, rendering solar water heating the most
widely deployed solar technology of the early twenty-first century.
How It Works
Although less than half of the solar radiation that reaches the Earth is available for human use (some is
absorbed by the atmosphere, land, and oceans, and some is radiated back to space), this amount is prodigious
enough to provide for all human energy needs if it could be efficiently captured. Because solar radiation is
dilute and noncontinuous, large collector areas are necessary, and storage devices must be integrated.
Photovoltaic systems convert radiation directly into electricity, and solar thermal units collect energy for interior
spaces or water heating. Passive systems convert sunlight directly into interior space heating, and active
heating systems require electricity to power pumps or fans. Active systems may be subdivided into those that
use flat-panel stationary collectors and those that focus incoming solar rays to achieve temperatures high
enough to create steam.
Photovoltaic.Photovoltaic cells transform solar radiation directly into electricity. The cells consist of two types
of silicon crystals in which bound electrons are energized into a conducting state when irradiated by light. The
freed electrons cross the junction between the two crystals more easily in one direction than the other, thus
creating negative and positive surfaces, the basis of a battery. This photobattery provides direct current (DC)
electricity. The brighter the irradiating light, the greater the current. By connecting large arrays of such cells, a
solar module, which typically can provide 170 watts per square meter of surface area at 14 percent efficiency,
is created.
Solar panels that are used to power homes and businesses are typically made from modules holding about
forty cells. A typical house requires an array of ten to twenty solar panels to provide sufficient power. The
panels are mounted at a fixed angle facing south, or they can be mounted on a tracking device that follows the
sun, allowing them to maximize solar energy capture. For large electric facility or industrial applications,
hundreds of solar arrays are interconnected to form a large utility-scale photovoltaic system.
Passive Solar Heating. Passive solar heating systems use south-facing glass windows to collect solar energy
and a room’s interior mass to store energy and regulate temperature swings. The three main types of passive
systems are direct, indirect, and attached gain. Direct-gain systems incorporate ample interior mass for
storage, and indirect-gain systems require a massive wall positioned directly behind the south-facing glass.
Attached-gain systems consist of a greenhouse, accessible to the house, attached to an exterior southern wall.
When the greenhouse is warm, the doors can be opened to heat the house. A fourth system, the thermosiphon, uses flat-plate collectors to heat water and a storage tank located above the collector top. Heated water
rises by natural convection into the storage tank, creating a siphon effect that keeps the fluid circulating.
Because no electricity is used, this constitutes a passive system.
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A well-designed passive system, in addition to double-paned south-facing glass and interior mass, includes
movable insulation to cover the windows at night, overhangs above the windows to keep out the summer sun,
and sufficient house insulation to minimize heat loss.
In direct-gain systems, the thermal mass, incorporated into a floor or wall, is typically brick, tile, or concrete.
The mass must be sized to the total area of south-facing glass—the greater the area of glass, the greater the
mass required to prevent overheating the room. Indirect gain systems use a massive wall of brick or barrels of
water located in proximity to the south-facing glass. The outside-facing surface of the mass is painted black to
effectuate solar gain stored in the mass. The heat is released through vents into the interior living space by
natural convection; at night, the vents are closed, preventing convective heat loss, while the mass radiates heat
into the interior space.
Attached gain, or greenhouse, systems are usually entirely glass with concrete or soil serving as the mass.
When properly designed, an attached greenhouse can be used to provide food as well as heat during the
winter. A different application of passive solar is the thermal chimney ventilation system, consisting of an interior
vertical shaft vented to the exterior. When the chimney warms, the enclosed air is heated, causing an updraft
that draws air through the building.
Active Solar Heating. Active solar heating systems transfer a sun-heated fluid (air or water) from an exterior
south-facing collector to the point of use or to a storage facility. In air systems, the storage facility is a bed of
rocks, and in water systems, tanks of water.
In addition to the collector and storage feature, active systems include a pump or fan to circulate the fluid and a
differential thermostat that regulates fluid flow to those times when the collector is at least 10 degrees
Fahrenheit hotter than the storage facility. Active systems may be used to heat interior space or to produce
domestic hot water. The circulating fluid for domestic hot-water systems is always water, and the storage unit is
a water tank. Space heating units may circulate either air or water, but air systems are more common.
Solar flat-plate collectors consist of a rectangular box containing a black metallic plate covered by nonreflecting
tempered glass. In water systems, tubes to conduct water are soldered to the plate, and in air systems, small
channels direct the air. When the sun strikes the black surface, light is changed into heat, which is transferred
to the fluid moving across the heated surface. For maximum efficiency, collectors should be oriented directly
south and set at an angle (from horizontal) equal to the local latitude (for domestic hot-water systems) or
latitude plus 10 degrees (for space heating systems).
Both space heating and domestic hot-water systems use water mixed with propylene glycol antifreeze as the
circulating fluid, propelled by a pump. Heat from the fluid is transferred to the hot-water storage tank through a
heat exchanger, to be used for domestic hot water or as preheated fluid for hydronic baseboard heating
systems.
When air is used as the working fluid, excess heat is stored either in smooth rocks or in a phase-change
material. Rock storage consists of a 280-cubic-foot bin of 1-inch-diameter smooth rocks weighing 7 tons. When
the collector is warmer than the house, a fan pumps the air directly from the collectors into the house. When
heat is not required, air is directed through the rock bin, transferring the heat into the rocks. At night, air from
the house can be circulated through the rocks to reclaim the stored heat.
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Focusing Collectors. Concentrated sunlight is realized in one of two ways: troughs of parabolic mirrors that
focus sunlight to an oil-filled tube positioned along the focal line, or huge assemblies of mirrors that reflect
sunlight from a large area to a small central receiver. Either method may be used in a solar thermal power
plant, where the concentrated radiation is used to produce high-temperature steam that drives a turbine to
create electricity. A solar furnace is a type of focusing collector employing parabolic curved mirrors to
concentrate sunlight to a focal point to generate extremely high temperatures.
Applications and Products
Photovoltaic Systems. Because PV cell arrays are expensive, the cost of the electricity produced in
photovoltaic systems has traditionally exceeded the cost of fossil fuel electricity. Since the mid 1970s, however,
the cost has consistently decreased so that by 2014, the cost per kilowatt of photovoltaic electricity was
comparable to fossil fuel costs. Low market penetration, new technology, and insufficient economies of scale
have inhibited even lower costs for PV systems, and prices have continued to drop as research raises the
conversion efficiency of PV cells. By 2020, the cost of energy for PV solar was 82 percent less than the 2010
cost. As one of the most rapidly growing alternate energy sources with production doubling every two years
since about the 1980s, it is projected that solar installations will continue to increase and the cumulative world
capacity will continue to rise. In 2019 the global solar capacity had risen to 580 gigawatts (GW). Following two
years of record growth in solar energy, installed global solar capacity reached 971GW by the end of 2021.
Based on estimates, the global solar capacity topped 1000GW—1 terawatt (TW)—in 2022.
Although individual household PV modules are more expensive per kilowatt than large centralized PV power
plants, individual units become cost competitive when distribution costs are eliminated. Between 2010 and
2019, solar module costs fell dramatically by 90 percent—a trend that continued into the 2020s, particularly in
regions with ample sunlight, expensive fossil fuel electricity, and government incentives.
Traditionally solar cells have been made from pure crystalline silicon doped with boron or phosphorus. The
manufacturing process is not inexpensive, and the conversion efficiency rarely exceeds 15 percent. Research
on using amorphous silicon has led to less expensive PV cells but these cells have considerably lower
efficiencies of less than 6 percent. Nevertheless, PV laminates composed of thin nonreflective layers of
amorphous silicon photocells coated on flexible plastic have been made into roofing material. With such panels,
a dual function is served: Roofs are weather-protected with material that generates electricity whenever the sun
shines. Because PV modules have no moving parts and low maintenance, these systems are projected to last
at least thirty years, the typical lifetime of quality roofing shingles. If the excess energy is stored in rechargeable
batteries, it would be possible for homeowners to eliminate their reliance on the grid. Alternately, if the PV
system is integrated with the grid, the need for a large bank of storage batteries is eliminated. Excess electricity
is sent back into the grid for credit, and the grid provides for nighttime or cloudy weather requirements.
Worldwide, the trend through the 2000s has been toward ever larger scale centralized PV power stations, as
typified by the large-scale, 550-megawatt solar park in Charanka, India, which was the first of its kind in the
country, completed in 2012 and later expanded. The 550-megawatt facility in San Luis Obispo, California,
called the Topaz Solar Farm, was completed in 2014. The following year, Solar Star in Rosamond, California,
was complete and was at the time the world’s largest solar plant with 1.7 million solar panels. By 2021, Solar
Star had fallen to seventh on the list of world’s largest solar farms. Topping that list was the Noor Complex
Solar Power Plant, in the Sahara Desert in Morocco. Upon its com-pletion in 2020, the Noor Complex had a
solar capacity of 580 megawatts.
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Since batteries are not practical as a backup supply in large-scale applications, storage is achieved using
excess energy to pump water from a lower elevation reservoir to a higher one; the energy is reclaimed by
releasing the water through a hydroelectric generator. By judiciously pairing PV systems with wind energy and
biogas generators, a twenty-four-hour supply of renewable electricity can be virtually guaranteed. Such a
system has been successfully pilot tested by the Institute for Solar Energy Supply Technology at the University
of Kassel, Germany.
Passive Solar Heating.Daylighting systems collect and disperse sunlight into interior spaces using skylights,
clerestory windows, and light tubes. Physiological and psychological benefits accrue when natural lighting
replaces artificial, and the necessity of summer air-conditioning to eliminate waste heat from incandescent
bulbs is reduced. Properly implemented systems can reduce lighting related energy consumption by 25
percent.
Integrated passive systems that combine solar heating, ventilation, and lighting, tailored to the local climate,
create well-lit spaces maintaining a comfortable temperature with minimal use of fossil fuel energy. For
agriculture, greenhouses have been superseded by less expensive tunnels of polyvinyl covering rows of crops
to support winter growth.
Another application, still in the experimental stage, is the solar pond, a pool of saturated saltwater at least six
feet deep that collects and stores solar energy. The concentration of salt increases with depth, preventing
convection currents and allowing the temperature to increase with depth. An experimental pond near the Dead
Sea was able to achieve temperatures approaching 200 degrees Fahrenheit at its bottom layer. When used to
drive a heat engine to produce electricity, the overall efficiency was 2 percent.
Solar cookers use solar radiation for cooking, drying, and pasteurization. The simplest solar cooker consists of
an insulated container with a transparent cover that can achieve temperatures as high as 300 degrees
Fahrenheit. More elaborate cookers, using focusing mirrors, can achieve temperatures of 600 degrees
Fahrenheit in direct sunlight.
Active Solar Heating. Solar thermal technologies can be used for water heating, space heating, airconditioning, and process heating. The most common types of solar water heaters are glazed flat-plate
collectors, evacuated tube collectors to achieve higher temperatures, and unglazed flat-plate collectors used to
heat swimming pools. By 2018, the global capacity of these systems totaled 482 gigawatts, with China being
the greatest consumer by far, installing a total of over 330 gigawatts of solar water heating. Over 90 percent of
homes in Israel and Cyprus use solar domestic hot-water systems, while in the United States and Australia, the
main application is as heaters for swimming pools.
Solar distillation, operating by passive, active, or hybrid modes, is used to make saltwater or brackish water
potable. Water for household use or storage may be easily disinfected by exposing water-filled bottles to
sunlight for several hours. More than 2 million people in developing countries disinfect their daily drinking water
by this method. In small-scale sewage treatment plants, solar radiation is an effective means of treating
wastewater in stabilization ponds without employing chemicals or using electricity.
Phase-change materials, such as Glauber’s salt (sodium sulfate decahydrate), store energy by transforming
from solid to liquid at a temperature of about 85 degrees Fahrenheit. Heat from the sun is absorbed by melting
the salt; when the temperature drops below the melting point, the salt resolidifies, releasing the stored heat.
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Concentrating Collectors. Hybrid solar lighting systems use sun-tracking focusing mirrors and optical fiber
transmission to provide interior lighting. Typically half of the incident sunlight can be transmitted to rooms,
where it replaces or supplements conventional lighting.
The Solar Kitchen, located in Auroville, India, uses a stationary spherical reflector to focus light to a linear
receiver, perpendicular to the sphere’s interior surface, where steam, used for kitchen process heat, is
produced.
A solar concentrating device developed by Wolfgang Scheffler in 1986 produces temperatures between 850
and 1,200 degrees Fahrenheit at a fixed focal point by means of flexible parabolic dishes that track the sun’s
diurnal motion and adjust curvature seasonally. By 2008, more than 2,000 large Scheffler cookers had been
built, most used for cooking meals. The world’s largest system, in Rajasthan, India, can cook up to 35,000
meals daily.
Another application, developed by Sandia National Laboratories, combines high temperatures from focusing
collectors with a catalyst to decompose carbon dioxide into oxygen and carbon monoxide. The carbon
monoxide can then be reacted with hydrogen to produce hydrocarbon fuels.
In the United States, the first commercial concentrating system, Solar Total Energy Project (STEP), was
developed in Shenandoah, Georgia. This system was developed as part of the National Solar Thermal Energy
Program that was instituted in the 1970 during the oil crisis, and STEP was jointly financed by Georgia Power
and the US Department of Energy. In Southern California, a system of parabolic trough collectors heats oil in
tubes along the focal line. The heated oil is used to produce steam to power a generator.
Central receivers, or power towers, use an extended assembly of moveable sun-tracking mirrors to reflect
sunlight to a small region on top of a tower, where temperatures between 1,000 and 2,700 degrees Fahrenheit
provide the motive power to produce electricity. The first large-scale demonstration facility, constructed in
southern California in 1982, was a 10-megawatt plant, later increased to 200 megawatts, at a cost competitive
with fossil fuel plants. Shortly after this plant proved its feasibility, additional commercial units in the 30- to 50megawatt range were constructed in the southwestern United States, Spain, Italy, Egypt, and Morocco. By the
end of 2013, several new large thermal solar generating stations became operational in the United States,
which more than doubled the generating capacity. Abengoa’s Solana plant, which was constructed in Arizona,
produces 250 megawatts of energy, and Bright Source in California’s Mohave Desert produces over 390
megawatts. More large-scale additions were completed in 2015 and 2016, and in 2014, Iraq successfully
experimented with several versions of small-scale power towers with the goal of collecting and redirecting solar
energy to produce steam for power generators. Thermal storage is provided by molten nitrate salts pumped
from a cold reservoir to a hot reservoir by excess solar energy. The stored energy is used to produce
superheated steam for the electric generation system when the tanks are emptied. The high-temperature
storage increases the efficiency of electrical conversion, making these systems competitive with coal-burning
plants.
The world’s largest solar furnace, constructed in 1970 in the French Pyrenees mountains, where annual
sunlight exceeds three hundred days, consists of an array of 63 flat moveable mirrors that reflect sunlight into a
huge curved mirror. The mirror, covering one entire side of a multistoried building, consists of 9,600 curved
glass reflectors totaling an area of 20,000 square feet. This mirror focuses the light onto an area of about 1
square foot, where the 1,000 kilowatts of power delivered creates a temperature in excess of 5,400 degrees
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Fahrenheit. Furnaces of this type are primarily used for research in the high-temperature properties of metal
oxides or in exposing materials to intense thermal shock.
Careers and Course Work
By the middle of the twenty-first century, solar power is likely to be the dominant global energy resource;
consequently, numerous new career opportunities await those with technological interests and skills. One of the
fastest-growing jobs in the country, in fact, is solar PV installers; according to the US Bureau of Labor Statistics,
employment of PV installers was expected to grow by more than 50 percent between 2019 and 2029. The
median 2021 salary for a PV installer was $47,670 per year. If a student finds that their college or university
does not offer an undergraduate major in solar energy, those wanting to enter the field can major or minor in
electrical engineering, mechanical engineering, or physics. To obtain a job as a PV installer, a course in
photovoltaic systems at a technical school or community college, or other experience in the construction
industry, may be all that is necessary.
The Research Laboratory of the University of Central Florida (Cocoa), in addition to researching PV materials,
conducts solar thermal systems testing. Other US research programs are found at Georgia Institute of
Technology, North Carolina State University, and the Universities of Wisconsin, Texas, Delaware, Oregon, and
Arizona.
Social Context and Future Prospects
Every day, the Earth receives ten thousand times more energy from the sun than humans consume from fossil
fuels. As fossil fuels are depleted and the pollution produced by them becomes increasingly problematic,
sustainable alternate energies, with the sun as a major provider, will become the planet’s viable energy future.
The increased use of solar energy will require two economic shifts, supply and demand. First, the pressure to
shift to clean, renewable energy supplies is mandated by the increased costs to society of continued reliance
on polluting nonrenewable fuels. Second, a move away from large centralized power plants to increased
reliance on smaller locally generated energy providers is anticipated. Several indirect benefits of the world’s
transition to a solar economy include the creation of wealth in underdeveloped countries rich in solar resources,
improved homeland security through reductions in energy imports, reduced pollution and lessened effects on
the global climate, and the ready availability of potable water through desalination plants.
During the first decades of the twenty-first century, it became apparent that several crises were converging. As
the world’s population increases, obtaining the basic necessities of life, such as food and water, becomes
progressively more problematic for underdeveloped nations. At the same time, the global demand for energy is
accelerating as fossil fuel resources are being depleted and global warming threatens ultimately to render
Earth uninhabitable. Arguably, the best course for humanity is to convert to sustainable food production and
energy use. Solar energy, in all its myriad forms, is uniquely positioned to accomplish this transition, if people
have the fortitude to endure temporary deprivation so as to ultimately abide harmoniously with the natural
environment.
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