MAT-20037-XA121 Solve Problems with Math 2…
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Competency
In this project, you will demonstrate your mastery of the following competency:
Solve prac!cal problems using basic mathema!cal calcula!ons
Scenario
You work for OneEarth, an environmental consul!ng company that specializes in building condi!on assessments,
contaminated site remedia!on, and energy audits. Founded by an environmentally concerned ci!zen 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 exper!se in achieving this goal. Knowing of your desires to diversify your experience and professional por"olio,
:
your manager, Claire DeAir, has consented for you to join the team working with SNHU. You’re responsible for
crea!ng a technical report based on an analysis of the data the onsite team has collected over the last few weeks to
determine the cost-effec!veness of SNHU adop!ng solar energy.
Direc!ons
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 Suppor!ng Materials sec!on, you will conduct a series of calcula!ons. With those calcula!ons, 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 calcula!ons and
determina!ons:
A calcula!on of the total electricity output of a solar panel system in kilowa"s hours (kWh)
Use the following steps as a guide to making this calcula!on:
How many panels fit on the roof, assuming the building is rectangular? (To make this determina!on,
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 direc!on and mul!ply
to obtain the required number of panels.)
What are the dimensions of the building’s roof in meters?
What are the dimensions of each solar panel in cen!meters? (To convert from inches to cen!meters,
mul!ply the dimensions in inches by 2.54 and do not round un!l the last step of the calcula!on.) Find
the number of meters for each dimension.
How many panels will fit on the roof in each direc!on? Round down to the nearest panel. When
calcula!ng 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 adop!ng a solar panel system that
covers the en!re roof based on the average monthly sunlight? (1kW = 1000W, and 1 hour of sunlight
produces 400 wa$s per panel)
How many kW per hour of sunlight could be produced per solar panel? Per en!re system (based on
how many panels could fit on the roof)?
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 likely average amount of kWh produced per panel based on the average amount of
sunlight per month? Per year? Round to the nearest hundredth kWh.
What is the total amount of kWh that is produced by the en!re solar panel system per month based
on the average monthly sunlight? Per year?
A calcula!on of the difference between the current electricity usage of the building and the electricity
:
generated by a solar panel system in kilowa" hours and in dollars
generated by a solar panel system in kilowa" hours and in dollars
Use the following steps as a guide to making this calcula!on:
How much electricity does the building use on average annually?
What is the es!mated total amount of kWh produced by the en!re solar panel system on this building per
year, based on the average monthly sunlight for the area?
Based on the average cost of electricity in the area, about how much is the annual electricity cost for the
SNHU building?
Is the amount of electricity generated by the solar array sufficient to cover SNHU’s yearly electricity
usage?
If not, what is the remaining energy needed in kW? How much would this cost in dollars? In other
words, what is the remaining u!lity bill?
If the energy generated is more than the energy needed to run the building, how much addi!onal
savings is there for energy that can be channeled to other buildings on campus or sold back to the
energy company?
A determina!on of the likelihood of receiving a damaged panel
SNHU expressed some concerns about receiving damaged solar panels from the manufacturer. You would like
to be transparent and address these concerns by illustra!ng 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 defec!ve.
How many panels fit on the roof?
What is the probability or likelihood that SNHU will receive a damaged solar panel, based on the number
of panels it would be purchasing?
A determina!on of how long it would take to pay back the cost of buying the system in years
Use the following steps as a guide to making this calcula!on—you can assume there will not be any required
maintenance during the first 10 years:
What would be the upfront cost to purchase and install the solar panel system?
How much does each panel cost? How much does the en!re system cost?
How much does installa!on cost?
What are the government incen!ves? How does that affect the cost?
What is the remaining u!lity cost, if there is one?
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 !me in years should take into account all
:
energy savings, not just those for the building on which the solar array is installed.
energy savings, not just those for the building on which the solar array is installed.
A determina!on of whether there is a cost savings over 10 years for leasing the solar panel system
Use the following steps as a guide to making this calcula!on:
What is the total cost without solar for 10 years, in dollars?
What is the total cost with solar for 10 years, in dollars?
How much does it cost to rent the en!re solar panel system?
What is the total remaining u!lity bill for 10 years?
What are the 10-year savings? (Cost Without Solar for 10 Years - (Cost of Solar Panel Rental for 10 Years +
Remaining U!lity Bills for 10 Years) = Total 10-Year Saving)
A recommenda!on for whether SNHU should install solar energy panels on its buildings based on your
calcula!ons
An explana!on of whether SNHU should invest in a solar energy system by purchasing it upfront or by leasing
it (Base your response on your calcula!ons.)
What to Submit
Every project has a deliverable or deliverables, which are the files that must be submi$ed before your project can be
assessed. For this project, you must submit the following:
Technical Report (1,000–1,500 words)
Using the data provided in the SNHU Site Data document in the Suppor!ng Materials sec!on, you will conduct a
series of calcula!ons. Your computa!ons will inform your recommenda!ons. First, you will determine whether or not
SNHU should adopt solar panels. Then, you will explain whether or not SNHU should purchase or lease a solar panel
system. Specifically, you will reference and incorporate the energy output of a solar panel system, the difference
between current usage and the energy generated by the system, the likelihood of a damaged panel, the costs to pay
for the system, and any savings for leasing a panel. Your proposi!on should be informed and supported by your
calcula!ons. You can include visual and graphical elements in your report to illustrate your proposi!ons.
Suppor!ng Materials
The following resource(s) may help support your work on the project:
Cita!on Help
Need help ci!ng your sources? Use the CfA Cita!on Guide and Cita!on Maker.
SNHU Site Data
This document contains the data that OneEarth’s onsite team has collected over the last few weeks to determine the
cost-effec!veness of SNHU adop!ng solar energy.
:
Informa!on on Solar Energy
Informa!on on Solar Energy
Website: All About Solar Energy
Use this resource to learn more about everything you would need to know about solar energy.
Reading: Solar Energy
In this Shapiro Library resource, you can explore solar energy.
Reflect in ePor!olio
Download
Print
Open with docReader
Ac"vity Details
Task: View this topic
:
Read all about your project here. This includes the project scenario, direc!ons for
comple!ng the project, a list of what you will need to submit, and suppor!ng materials
that may help you complete the project.
Building
Location
Manchester, New Hampshire 03101
United States of America
Building Roof Dimensions: 60 m x 30 m
Roof Assessment of the Building
The engineering team has inspected the roof and determined:
There are no obstructions on the roof; therefore, the panels can be placed close together.
The building is structurally sound and can hold more than 15 kg per square meter of weight.
Expected Hours of Sunlight in Manchester, NH (by Month)
January
February
March
April
May
June
163
168
214
227
267
287
July
August
September
October
November
December
301
277
237
206
143
142
Electricity Usage for the Building
Average Electricity Usage (kWh) Annually: 271,253 kWh
National Average Cost of Electricity: $0.165 per kWh
Note: This is a projection of the building’s energy use over the next 10 years based on the assumption that there
will not be a drastic increase or decrease during that period.
Solar Panels
Size and Weight: 80 in x 40 in x 2 in; 50 lbs
Watts: 400
Amps: 9.86A
Volts: 40.6 DC
Cost: $560.00 per panel
Purchasing a Solar Panel System for the Building:
Installation: $0.75 per watt
Incentives: If you purchase the system upfront, you will receive a 30% discount on the total cost of the
panels and the installation.
Leasing / PPA a Solar Panel System for the Building
Upfront Cost: $0.00
Monthly Payment (Including Savings): $97.00 per panel
Remaining Utility Bill: $20/month
Duration: 20 years
Incentives: Assume that SNHU does not qualify for leasing incentives.
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Carbon Footprint.
Authors:
Droujkova, Maria
Source:
Salem Press Encyclopedia of Science, 2019. 3p.
Document Type:
Article
Subject Terms:
Ecological impact
Ecology
Environmental responsibility
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 he or she uses energy efficient light bulbs, whether he or
she shops for food at local stores, and what sort of technology he or she uses 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
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Accession
Number:
89404314
Database:
Research Starters
Carbon Footprint
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Fields of Study: Fields of Study: Algebra; Data Analysis and Probability; Measurement; Representations.
Summary: A carbon footprint is a mathematical calculation of a person’s or a community’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 he or she uses energy efficient light bulbs, whether he or she shops for food at local stores, and what sort of technology
he or she uses 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.
:
The notion of a carbon footprint is being considered in a wide range of areas, including the construction of low-impact homes, offices, and other
buildings. The design 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.
These are in turn related to the Navier–Stokes equations describing the motion of fluid substances, named for mathematicians Claude-Louis
Navier and George Stokes. The Navier–Stokes equations are also of interest to pure mathematics, since many of their mathematical properties
remain unproven at the beginning of the twenty-first century.
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 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.
A man rides a bicycle to work in
an effort to reduce his carbon
The food that people eat contributes to the carbon footprint if it is transported by motorized vehicles before
footprint. By David Dennis
being eaten. The movement of locavores (people who eat locally grown foods) aims to minimize the
Scotts Valley, CC BY-SA 2.0
carbon footprint of food. Also, different farming practices may contribute more or less to the carbon
(http://creativecommons.org/licenses/bysa/2.0), via Wikimedia
footprint of food.
Commons
The objects people use contribute to their carbon footprints. Recycling and reusing reduces the need for
landfills, waste processing, and waste removal, all of which have carbon footprints. There are individuals
and communities who avoid waste entirely; several countries, such as Japan, have plans to mandate zero-waste practices within the next few
decades.
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
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generally used to offset the cost to the environment.
Emissions trading is another mathematics-rich area 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.
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 emission 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 are relatively high costs involved in switching to wind 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, in the late 2000s, the average annual carbon footprint of a US citizen
was about 30 metric tons per year, and a Japanese citizen about 10 metric tons per year. 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 vary by country.
For example, the greatest item in the US carbon footprint is shelter (25%), with mobility being second (21%). In contrast, Canada’s greatest
item affecting carbon footprint is mobility (30%), and its second greatest is shared between shelter and service (18% 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.
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.
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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, 2019, 3p
Item: 89404314
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Solar Energy.
Authors:
Plitnik, George R., B.A., B.S., M.A., Ph.D.
Source:
Salem Press Encyclopedia of Science, 2018. 7p.
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
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Number:
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Database:
Research Starters
Solar Energy
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American Accent
Summary
Related Information
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.
Solar Power
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.
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
Solar Cell Panel: The solar cell
allow energy to be withdrawn when needed or fed into the grid when not
panel collects energy from the
necessary.
Energy Storage
Technologies
sun and can provide electric
energy. © EBSCO
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
Fuel Cell Technologies
stored. Also, active collection devices are constructed of expensive nonrenewable resources such as aluminum
and copper.
Hydroelectric Power
Plants
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
Hydrology and
Hydrogeology
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.
Wind Power
Technologies
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 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, solar water heating systems have grown
at an average annual rate of 20 percent, 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 southfacing 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 thermo-siphon, 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.
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
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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.
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 and insufficient economies of scale have
inhibited even lower costs for PV systems, but prices are projected to continue to drop as research raises the conversion efficiency of PV cells.
It is projected that by the year 2020, the cost of installed PV units will be half 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 by 2020, there will be 500,000 additional
installations and a cumulative world capacity of 1,500 gigawatts.
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. From 1995 to 2009, solar module costs per installed watt declined at 5 to 6 percent
annually, a trend projected to continue, 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, 550megawatt solar park in Charanka, India, which was the first of its kind in the country. was completed by the end of 2014. The 550-megawatt
facility in San Luis Obispo, California, called the Topaz Solar Farm, was also completed in 2014. The following year, Solar Star in Rosamond,
California, was complete and was at the time the world's largest solar farm with 1.7 million solar panels.
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
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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 6 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, air-conditioning, 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. As of 2012, the global capacity of these systems totaled 255 gigawatts, with China
being the greatest consumer at over 70 percent of that capacity. 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.
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.
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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 50-megawatt 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 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. 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.
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 10,000 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 decade 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.
Bibliography
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Hossain, Jahangir, and Apel Mahmud, eds. Large Scale Renewable Power Generation: Advances in Technologies for Generation,
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Kut, David, and Gerald Hare. Applied Solar Energy. 2nd ed. London: Butterworth, 1983. Print.
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Rathore, Mahesh, et al. "A Review of Solar Cookers." International Jour. of Modern Trends in Engineering 2349–9745 (2–4 July 2015): 1997–
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"Renewables Global Status Report." REN21. Renewable Energy Policy Network for the 21st Century, 6 June 2014. Web. 20 Aug. 2014.
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Solar Energy International. Photovoltaics: Design and Installation Manual. Gabriola Island: New Society, 2004. Print.
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Trabish, Herman K. "Solar Hot Water at Intersolar: Something Old, Something New Something Borrowed." Greentech Media. Greentech
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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, 2018, 7p
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