Physics 100

Lecture 19

Solar Thermal Energy

April 9, 2018

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Class Quiz Ch. 8-9: Which of the following is the

most important factor in understanding

the “carbon cycle” of the Earth?

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A. Absorption of carbon by

plants

B. Absorption of carbon by

the ocean

C. Production of carbon by

plants

D. Production of carbon by

polar glaciers

A. Absorption of carbon by plants

B. Absorption of carbon by the ocean

C. Production of carbon by plants

D. Production of carbon by polar glaciers

Class Quiz Ch. 8-9: Which of the following is the

most important factor in understanding

the “carbon cycle” of the Earth?

See pp. 287-288

of the text.

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Reminder of the hazards of

carbon-based energy

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Citation: Physics Today 69, 11, 48 (2016); full articleEach row of the diagram represents a carbon reservoir, with the amount of carbon

in each reservoir in 1870 shown in the middle column in petagrams (1 Pg = 1015 g).

The boxes and arrows to the left and right depict the carbon budget16 in petagrams

for the period 1870–2014.

Some good news

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https://www.eia.gov/todayinenergy/detail.php?id=30712

Alternatives to fossil fuel energy

Nuclear energy

• No emissions, but

safety and waste

disposal problems

Renewable energy

• Solar thermal

• Solar electric

• Wind

• Biomass

• Geothermal

• Nuclear fusion

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Renewable energy overview

7 www.eia.gov/totalenergy/data/monthly/pdf/sec1_6.pdf

see also www.eia.gov/totalenergy/data/monthly/

Renewable energy trends

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https://www.eia.gov/outlooks/steo/report/renew_co2.cfm?src=Environment-b1

2013 2014 2015 E 2016 2017 2018 P 2019 P

Geothermal 0.214 0.222 0.226 0.210 0.212 0.227 0.229

Hydropowera 2.562 2.469 2.257 2.472 2.772 2.594 2.542

Solar 0.305 0.427 0.522 0.570 0.770 0.904 1.069

Waste Biomass 0.496 0.488 0.494 0.503 0.484 0.492 0.496

Wind 1.596 1.729 1.765 2.113 2.367 2.454 2.642

Wood Biomass 2.170 2.214 2.041 2.153 2.172 2.154 2.158

Electricity Subtotalb 7.343 7.549 7.305 8.006 8.754 8.795 9.102

Biomass-based Diesel 0.205 0.198 0.222 0.291 0.279 0.325 0.361

Ethanol 1.090 1.107 1.141 1.182 1.189 1.218 1.223

Biofuels Subtotal 1.295 1.305 1.363 1.473 1.467 1.535 1.584

Otherc 0.801 0.817 0.823 0.832

Total 8.638 8.854 8.668 10.279 11.054 11.154 11.519

Doubling time:

3.24 y

7.01 y

The Solar Constant

S = 1354 W / m2

Fluctuates from 1321 (in July) to 1412 W / m2

(in January) due to slight change in distance

from Sun

Seasons are due to tilt of the Earth’s axis

relative to orbital plane, not the variation in

the solar constant

Includes infrared, visible, and ultraviolet light

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Insolation

The amount of solar radiation that

reaches the Earth’s surface is called

insolation (incident solar radiation)

(not to be confused with insulation, a material

that impedes thermal conduction)

Insolation is affected by many factors…

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Atmospheric absorption

The surface never gets more than 1050 W/m2

(on a clear day) due to atmospheric absorption

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Energy Balance for the Earth

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On average (including

cloudy days), only 50%

of solar radiation

reaches the Earth’s

surface.

Figure 6.4

page 156

A closer look

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Atmosphere:+217% −217% = 0% net

Earth’s surface:+163% −160% = 3% net(in reality this is very

close to zero, the

numbers were rounded)

+48%

+23%

+33% +113%

−23%

−60%

−29% −105%

+8%+21%

+29% +105%−119%

−33%−8%

The tilt of the Earth’s Axis

Changes how much sunlight is received

by a location on the Earth throughout the

year

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Seasonal change to insolation

The Sun’s angle above

the horizon changes

with the seasons

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The sun doesn’t shine all day

Stevens Point gets about 1250 Btu/ft2/d

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Map of average solar insolation

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10

12

12

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2224

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10

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12<10

10-12

12-14

14-16

16-18

18-20

20-22

22-24

24-26

26-28

>28

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Stevens Point gets about 1250 Btu/ft2/d of

insolation. Convert this number to kWh/m2/d

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A. 0.253 kWh/m2/d

B. 1.25 kWh/m2/d

C. 3.94 kWh/m2/d

D. 236 kWh/m2/d

Stevens Point gets about 1250 Btu/ft2/d of

insolation. Convert this number to kWh/m2/d

2 2

2 6 2

2

1250 Btu 1055 J 1 kWh 3.28 ft

ft d 1 Btu 3.6 10 J 1 m

kWh3.94

m d

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How much water can you heat from 20ºC to

50ºC per day using a 10 m2, 50% efficient solar

collector in Stevens Point, on average?

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A. 2260 kg

B. 565 kg

C. 150 kg

D. 3.94 kg

How much water can you heat from 20ºC to

50ºC per day using a 10 m2, 50% efficient solar

collector in Stevens Point, on average?

2

solar 2

67

7

kWh0.50 3.94 10 m 19.7 kWh/d

m d

kWh 3.6 10 J19.7 7.09 10 J/d

d 1 kWh

7.09 10 J/d565 kg

4190 J/kg °C 30°C

P IA

Qm

c T

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about 147 gallons!

Solar Thermal Facts

Water heating is the most common

application for solar energy

Domestic hot water (DHW) systems are

being sold with a 5% annual growth (14 year

doubling time)

95% of solar heaters are for swimming pools,

only 5% for DHW

About two-thirds of a household’s DHW load

can be economically met by solar

EIA web site

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Solar Thermal Facts

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Estimated 35,464 new DHW

systems installed in 2010,

and 29,540 pool systems

Total US capacity is over 815

MWTh (megawatts thermal

equivalent)

Today there are an estimated

790,000 solar pool heating

systems installed in the U.S.,

more than any other solar

technology application.

SEIA Solar Industry Data graphs from 2013 report

Batch water heater

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Flat-plate collector

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US Solar Energy Year in Review 2008

Flat-plate collector

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US Solar Energy Year in Review 2008

Right Here at UWSP

There is a solar water heating system on the roof of many residence halls and the HEC

Energy production used to be tracked on the web. There is a document about performance history of the HEC system and the eventual removal of the HEC panels in July 2016.

The UWSP Sustainabilitysite has some additionalinformation

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Solar Space Heating

Three components:

• Insulation

• Solar collection

• Thermal storage

Can reduce heating

costs up to 80%

Not as popular due

to costs.

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Compare 2008 installations: 139 MWTh hot water,

762 MWTh pool heating, 21 MWTh space heating

US Solar Market Insight SEIA Solar Heating & Cooling

Approximately what maximum percentage

of the 40,000 Btu/h home heating needs

can be met by a 700 ft2, 50% efficient

collector if the insolation is 1700 Btu/ft2/d?

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A. 25%

B. 35%

C. 60%

D. 75%

Approximately what maximum percentage

of the 40,000 Btu/h home heating needs

can be met by a 700 ft2, 50% efficient

collector if the insolation is 1700 Btu/ft2/d?

2

solar 2

solar

Btu h40,000 24 960,000 Btu/d

h d

Btu1700 700 ft 0.50 595,000 Btu/d

ft d

595100 62%

960

Q

E

E

Q

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Concrete has a density of 2400 kg/m3

and

a specific heat of 750 J/kg/oC. What

volume of concrete can store as much

heat as 10 m3

of water (42 MJ/oC)?

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A. 4.29 m3

B. 12.1 m3

C. 18.5 m3

D. 23.3 m3

Concrete has a density of 2400 kg/m3

and

a specific heat of 750 J/kg/oC. What

volume of concrete can store as much

heat as 10 m3

of water (42 MJ/oC)?

A. 4.29 m3

B. 12.1 m3

C. 18.5 m3

D. 23.3 m3

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6

3

3

and density

solve for :

42 10 J/ C

2400 kg/m 750 J kg C

23.3 m or about 12.7 tons of concrete!

mQ mc T

V

Qmc V c V

T

Q TV

c

National Solar Thermal Test

Facility – Albuquerque, NM

Can generate

about 1.5 MW

of electricity

Used for

research and

development

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Solar Energy Generating Systems (SEGS)

Second largest solar

energy facility in the

world, with 354 MW

installed capacity

(California Mojave

Desert)

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Entire image courtesy Wikipedia

Aerial view showing portions of four of the five SEGS III–VII plants located at Kramer Junction

Ivanpah Solar Electric Generating System

Commissioned 2014

CA Mojave desert

Currently world’s

largest solar

thermal facility

at 392 MW

List of worldwide

solar thermal

power stations

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