Physics 100

Lecture 20

Solar Photovoltaic Energy

April 11, 2018

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Written Quiz – Chapters 8-9

Timer applet

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The Electromagnetic Spectrum

Electromagnetic waves carry energy

Waves are characterized by wavelength,

frequency, and speed

Speed c is constant, so higher frequency

f corresponds to lower wavelength l

f cl

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The

Electromagnetic

Spectrum

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Photons

Electromagnetic waves come in little bundles

of energy called photons.

The higher the frequency (bluer the light) the

greater the energy.

The photons that are sufficiently energetic are

absorbed by solar cells to create electricity.

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photon constant frequencyE

Rank the energies of visible, radio, and

ultraviolet photons, from least to greatest.

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A. radio < visible < ultraviolet

B. visible < radio < ultraviolet

C. ultraviolet < visible < radio

D. radio < ultraviolet < visible

About Semiconductors

Semiconductors are often doped with impurities

P-type has too few bonding electrons

N-type has too many bonding electrons

A p-n junction forms the core of a working

photovoltaic cell. It gives the charges energy.

A photon striking the junction forms an

electron-hole pair, but the electron and hole are

forced in different directions, creating an

electrical current.

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A semiconductor

lattice

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n-typep-type

The

Photovoltaic

Effect

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Photovoltaic cells

Three kinds:

• Single-crystal

• Polycrystalline

• Amorphous

More info: http://www.eere.energy.gov/basics/renewable_energy/pv_cell_materials.html

Photo credits: http://www.eepe.murdoch.edu.au/resources/info/Tech/pv/index.html

Durable, reliable

Energy is intermittent

Expensive – 3 to 4 year

payback

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Solar Photovoltaic

Facts

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SEIA Solar Industry Data

The U.S. in 2015 has over

22,700 MW of installed solar

PV capacity, enough to

power more than 4.6 million

average American

households

Since the beginning of 2010,

the average cost of a PV

system has dropped by more

than 45 percent, and by an

even greater amount for

utility-scale projects.

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Right here at UWSP

There is a large solar

photovoltaic panel at the

Noel Center for the Fine

Arts. The energy it

produces is used to light

a section of the inner

courtyard area.

More information about campus

energy production and usage can

be found at the UWSP Office of

Sustainability.

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What does it mean to say the efficiency

of a solar cell is 15%?

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A. 15% of the incident voltage becomes

current

B. 15% of the cell’s electrons become

holes

C. 15% of the incident light energy

becomes electrical energy

D. 15% of the input energy becomes light

energy

Storing solar energy

Intermittent solar and wind energies must

be stored for round-the-clock use.

Besides charging a battery (pp. 382-384, 397),

electrical energy can be stored by

pumping water (pp.386, 398), compressing

air, or converting it to the kinetic energy of

a rotating flywheel by means of a motor

(p. 398). Let’s explore the latter idea…

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A flywheel’s energy in J is given by

0.15[ω(rpm)]2. What power is needed

to spin rotor to 6000 rpm in 2.0 min?

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A. 450 W

B. 7.5 W

C. 3.0 kW

D. 45 kW

A flywheel’s energy in J is given by

0.15[ω(rpm)]2. What power is needed

to spin rotor to 6000 rpm in 2.0 min?

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A. 450 W

B. 7.5 W

C. 3.0 kW

D. 45 kW

2

2

0.15

0.15 6000 rpm J45,000 J/s

2.0 min 60 s/min

45 kW

WP

t t

P

Suppose the motor/flywheel system

is 88% efficient. What electrical

solar power must be supplied?

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A. 51 kW

B. 40 kW

C. 8.8 kW

D. 197 kW

Suppose the motor/flywheel system

is 88% efficient. What electrical

solar power must be supplied?

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A. 51 kW

B. 40 kW

C. 8.8 kW

D. 197 kW

out

solar

outsolar

45 kW 51 kW

0.88

Pe

P

PP

e

If a solar array is 24% efficient and

the insolation is 700 W/m2, what

array area is required?

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A. 0.0175 m2

B. 304 m2

C. 29.1 m2

D. 168 m2

If a solar array is 24% efficient and

the insolation is 700 W/m2, what

array area is required?

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A. 0.0175 m2

B. 304 m2

C. 29.1 m2

D. 168 m2

solar

solar

2

2

51,136 W

0.24 700 W/m

304 m or about 57 ft 57 ft

P IA

PA

I

Photovoltaic power plants

Solar Star California (579 MW, world’s largest in 2015)

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Photo credit: SunPower

Photo credit: Clean Technica and photo link

List of largest photovoltaic power stations

Photovoltaic power plants

Cestas Solar Farm France (300 MW, largest in Europe)

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Photo credit: PV magazine

Photo credit: PVTech

Photovoltaic power plants

Sarnia Solar Project, Canada (80 MW)

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Right here in Wisconsin

A 2.0-MW solar field built for Dairyland Power Cooperative in Medford, WI.

(Photo: Courtesy of Renew Wisconsin) USA Today article

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Right here in Wisconsin:

A 100-MW solar photovoltaic project is

planned (to open in 2021)

The Point Beach Solar Energy Center in Two Rivers, WI will be modeled

after the North Star Solar Project in North Branch, MN, the largest in the

Midwest. (Photo: Courtesy of D. E. Shaw Renewable Investments) Web site

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