سه شنبه ۲۷ شهریور ۰۳ | ۱۷:۵۴ ۷ بازديد
C H A P T E R 1
Introduction to
Renewable Energy
1-1 WHY RENEWABLE ENERGY?
To meet its energy needs, the world community currently depends heavily on fossil fuels
that are nonrenewable and unfriendly to the environment. Table 1-1 presents total world
delivered energy consumption based on end-use sector and fuel type. Breakdown of each
fuel by sector and each sector by fuel is also provided. As shown in Fig. 1-1, more than half
of the global energy is used by the industrial sector (54.6%), followed by the transportation
sector with 25.6 percent, the residential sector with 12.7 percent, and the commercial sector
with 7.1 percent (EIA, 2018). Energy use is expected to increase worldwide, driven mainly
by industry, but this will mostly take place in developing countries with strong economic
growth.
Total global energy supply in 2017 was 589 Quad Btu, which is equivalent to 5.6 × 1017 kJ.
Fossil fuels accounted for 82.7 percent (27.1% coal, 33.4% oil, 22.2% natural gas) of this
total energy production. Renewable energy (including hydroelectric power), which is envi-
ronment-friendly and can be harvested indefinitely, was responsible for 12.7 percent of the
total energy supply globally. Nuclear power supplied the remaining 4.6 percent of the total
energy supply (Fig. 1-2) (EIA, 2018).
In 2015, total electricity generation in the world was 24,255 TWh (or 24.255 × 1012 kWh
since 1 TWh = 1 billion kWh = 109 kWh). Fossil fuels accounted for 66.3 percent of total
electricity generation in the world with 39.3 percent for coal, 22.9 percent for natural gas,
and 4.1 percent for oil. Renewable energy (including hydroelectric power) and nuclear
power were responsible for 23.1 percent and 10.6 percent of global electricity generation,
respectively (Fig. 1-3). A total of 5603 TWh (or 5.603 × 1012 kWh) of renewable electricity
was generated that year (IEA, 2017).
Total installed capacity of electricity in the United States in 2016 was 1074 GW, and
the U.S. power plants generated 4077 TWh (4.077 × 1012 kWh) of electricity that year.
Figure 1-4 shows the percentages of electricity generation in the United States by the fuel
type and source. Approximately 83.9 percent of electricity was generated by coal, natural
gas, and nuclear power plants. The remaining 16.1 percent was generated mostly by renew-
able sources including hydro (6.5%) and wind (5.5%). The remaining generation was due to
biomass, solar, and geothermal (EIA, 2018).
A comparison of U.S. electricity production data to global electricity generation data
shows that the share of renewable electricity in the United States is considerably less than
that in the world. Therefore, great potential exists to increase the share of renewables in
TABLE 1-1 Total World Delivered Energy Consumption by End-Use Sector and Fuel in 2017 (EIA, 2018)
All values are in Quad Btu (quadrillion Btu). (1 quadrillion Btu = 1 × 1015 Btu = 0.95 × 1015 kJ)
Fuel Total Electricity Residential Commercial Industrial Transportation
All End-Use
Sectors
Oil* 196.7 6.7 8.5 3.9 69.7 106.7 188.8
Natural gas 130.7 44.0 20.6 8.8 53.2 4.1 86.6
Coal 159.8 90.5 4.3 1.6 63.5 0.0 69.4
Nuclear 26.9 26.9 — — — — —
Electricity — — 21.0 16.8 35.1 1.6 74.5†
Renewables 74.9 55.5 1.3 0.2 17.9 — 19.4
Total 589.0 223.6† 55.7 31.3 239.4 112.4 438.8
*The values given for oil also include other nonpetroleum liquid fuels such as ethanol, biodiesel, coal-to-liquids,
natural gas liquids, and liquid hydrogen.
†The difference between the total energy value of fuel consumption to produce electricity (223.6 Quad Btu) and the
actual amount of electricity consumed by all end-use sectors (74.5 Quad Btu) is equal to the energy lost during the
production of electricity, which is equal to 223.6 - 74.5 = 149.1 Quad Btu. As a result, the difference between the totals
in the second and last column is also equal to 589.0 - 438.8 = 150.2 Quad Btu, which is very close to 149.1 Quad Btu.
Transportation,
25.6%
Residential,
12.7%
Commercial,
7.1%
Industrial,
54.6%
Figure 1-1 Percentages of global
energy use by end-use sectors in
2017 (EIA, 2018).
Nuclear,
4.6%
Coal,
27.1%
Natural gas,
22.2%
Oil,
33.4%
Renewables,
12.7%
Figure 1-2 Percentages of total world
primary energy supply by fuel in 2017
(EIA, 2018).
the U.S. energy mixture. In 2000, only nine percent of electricity came from renewables,
and EIA (2018) projections indicate that the renewables will constitute 18 percent of elec-
tricity generation by 2040. Coal- and nuclear-based electricity generations are expected to
decrease in the coming years, but natural gas electricity generation is expected to increase
due to additional shale gas reserves.
Renewable electricity generation by source in the United States is given in Fig. 1-5.
Total generation by renewables was about 640 billion kWh in 2017. This is projected to
increase above 1600 billion kWh by the year 2050. Renewable electricity generation in 2017
is dominated by hydropower and wind, but solar electricity increased at the highest rate
among all energy sources. Solar electricity is estimated to take the greatest share by the
year 2050, followed by wind, hydropower, and geothermal. Other renewables represented
in Fig. 1-5 are due mostly to biomass electricity production by the means of MSW/LFG
(municipal solid waste/land fill gas) (EIA, 2018).
Renewables are currently the fastest-growing energy source in the world. Depletion
and emission concerns over fossil fuel use and increasing government incentives can cause
even higher growth in the use of renewables in the coming decades. The fastest-growing
Oil,
4.1%
Renewable,
7.1%
Hydro,
16.0%
Nuclear,
10.6%
Natural gas,
22.9%
Coal,
39.3%
Figure 1-3 Percentages of global electricity generation by fuel type and source
in 2015. Total electricity generation = 24,255 TWh (IEA, 2017).
Hydro,
6.5%
Other,
2.6%
Biomass,
1.5%
Coal,
30.4%
Nuclear,
19.7%
Natural gas,
33.8%
Wind,
5.5%
Figure 1-4 Percentages of electricity generation by fuel type and source in the
United States in 2016 (EIA, 2018).
renewable sources are solar and wind. The installed wind capacity has increased from
18 GW in 2000 to 539 GW by the end of 2017. The solar power capacity has increased
by 97 GW in 2017 bringing the global capacity to over 400 GW. The installed capacity
of hydropower exceeds 1250 GW worldwide. Hydroelectric, geothermal, and wind power
generation technologies are able to compete with fossil fuel–based electricity generation
economically, but solar electricity generation is still expensive. However, steady decreases
in solar electricity cost combined with increased government incentives are likely to help
wider use of solar electricity in the coming years.
EXAMPLE 1-1 In Table 1-1, the total energy consumption by different energy sources is given to be 589.0 Quad Btu
while the total energy use by all end-use sectors is 438.8 Quad Btu. Explain the difference between
these two values. Using the data in Table 1-1, calculate the total amount of energy lost during the
production of electricity by all energy sources. Also, calculate the amount of electricity produced in
kWh and the overall thermal efficiency of electricity production by all energy sources.
SOLUTION The difference between the total energy value of fuel consumption to produce electricity
(223.6 Quad Btu, third column, last row) and the actual amount of electricity consumed by all end-use
sectors (74.5 Quad Btu, last column, fifth row) is equal to the energy lost during the production and
distribution of electricity, which is equal to
Energy lost = 223.6 − 74.5 = 149.1 Quad Btu
The difference between the totals in the second and last column is equal to
Energy lost = 589.0 − 438.8 = 150.2 Quad Btu
which is very close to the value of 149.1 Quad Btu.
The amount of electricity produced is expressed in kWh as
21.83 trillion kWh
Electricity produced (74.5 10 Btu) 1 kJ
0.94782 Btu
1 kWh
3600 kJ
21.83 10 kWh
15
12
= ×
= × =
An Analysis of World
Energy Consumption
1800
1600
1400
1200
1000
800
600
400
200
0
2017
History Projections
Solar PV
Wind
Geothermal
hydroelectric
other
2010 2020 2030 2040 2050
Figure 1-5 Renewable electricity
generation by source in the United
States, in billion kWh (EIA, 2018).
The thermal efficiency of a power plant is defined as the power produced divided by the energy
consumed. According to the data in Table 1-1, 223.6 Quad Btu of energy is consumed in all power
plants worldwide, and 74.5 Quad Btu of electricity is produced. The overall thermal efficiency of
producing electricity is then
33.3%
Electricity produced
Energy consumed
74.5 10 Btu
223.6 10 Btu 0.333th,overall
15
15
η = = ×
× = =
That is, about 67 percent of energy is lost during the conversion of energy sources (coal, oil, natural
gas, renewable) into electricity. ▲
EXAMPLE 1-2 Ton of oil equivalent (toe) is an amount of energy unit commonly used to express large amounts of
energy. It represents the amount of energy released by burning 1 ton (1000 kg) of crude oil. One toe
is taken equal to 41.868 GJ, sometimes rounded to 42 GJ. The power plants in the United States gen-
erated 4.05 × 109 MWh of electricity in a year. According to the data in Table 1-1, 74.5 Quad Btu of
electricity is produced. Express these values in the toe unit. Also, determine the percentage of global
electricity generation that occurred in the United States.
SOLUTION Noting that 1 MWh = 1000 kWh, 1 kWh = 3600 kJ, 1 GJ = 1 × 106 kJ, and 1 toe = 41.868 GJ,
we express electricity generation in the United States in toe, as follows:
Electricity generation (in U.S.) (4.05 10 MWh) 1000 kWh
1 MWh
3600 kJ
1 kWh
1 GJ
1 10 kJ
1 toe
41.868 GJ
9
6
3.48 10 toe8
( )= ×
×
= ×
Noting that 1 Quad = 1 × 1015 Btu and 1 toe = 41.868 GJ, we express global electricity generation in
toe, as follows:
Electricity generation (world) (74.5 Quad) 1 10 Btu
1 Quad
1.055 kJ
1 Btu
1 GJ
1 10 kJ
1 toe
41.868 GJ
15
6
1.88 10 toe9
= ×
×
= ×
The percentage of global electricity generation that occurred in the United States is determined to be
18.5%Percent generation in U.S. Electricity generation (U.S.)
Electricity generation (world)
3.48 10 toe
1.88 10 toe 0.185
8
9= = ×
× = =
That is, 348 million toe of electricity is generated in the United States and 1.88 billion toe of electricity
is generated in the world. The U.S. electricity generation represents 18.5 percent of global generation.
Note that toe unit is not normally used to express the amount of electricity. Instead some multiples of
kWh such as MWh, GWh, and TWh are used. ▲
Consequences of Fossil Fuel Combustion
Fossil fuels have been powering industrial development and the amenities of modern life
since the 1700s, but this has not been without undesirable side effects. Pollutants emitted
during the combustion of fossil fuels are responsible for smog, acid rain, and numerous
other adverse effects on the environment. Environmental pollution has reached such high
levels that it has become a serious threat to vegetation, wildlife, and human health. Air pol-
lution has been the cause of numerous health problems including asthma and cancer. But
this fossil fuel–based economy is not sustainable since the estimated life of known reserves
is limited. Therefore, the switch to renewable energy sources is inevitable.
Ton of Oil Equivalent
(toe) Unit
Carbon dioxide (CO2) is the primary greenhouse gas that contributes to global
warming. Global climate change is widely regarded as due to the excessive use of fossil
fuels such as coal, petroleum products, and natural gas in electric power generation, trans-
portation, buildings, and manufacturing, and it has been a concern in recent decades. The
concentration of CO2 in the atmosphere as of 2019 is about 410 ppm (or 0.41%). This is
20 percent higher than the level a century ago. Various scientific reports indicate that the
earth has already warmed about 0.5°C during the last century, and it is estimated that the
earth’s temperature will rise another 2°C by the year 2100. A rise of this magnitude is feared
to cause severe changes in weather patterns with storms and heavy rains and flooding at
some parts and drought in others, major floods due to the melting of ice at the poles, loss
of wetlands and coastal areas due to rising sea levels, variations in water supply, changes in
the ecosystem due to the inability of some animal and plant species to adjust to the changes,
increases in epidemic diseases due to the warmer temperatures, and adverse side effects on
human health and socioeconomic conditions in some areas.
The combustion of fossil fuels produces the following undesirable emissions (Fig. 1-6):
• CO2, primary greenhouse gas: contributes to global warming
• Nitrogen oxides (NOx) and hydrocarbons (HC): cause smog
• Carbon monoxide (CO): toxic
• Sulfur dioxide (SO2): causes acid rain
• Particulate matter (PM): causes adverse health effects
Notice from this emissions list that CO2 is different from the other emissions in that
CO2 is a greenhouse gas and a natural product of fossil fuel combustion while other emis-
sions are harmful air pollutants.
The concern over the depletion of fossil fuels and pollutant and greenhouse emissions
associated with their combustion can be tackled by essentially two methods:
1. Using renewable energy sources such as solar, wind, hydroelectric, biomass, and
geothermal to replace fossil fuels.
2. Implementing energy efficiency practices in all aspects of energy production, dis-
tribution, and consumption so that less fuel is used while obtaining the same use-
ful output.
Energy efficiency is to reduce energy use to the minimum level, but to do so without
reducing the standard of living, production quality, and profitability. Energy efficiency is an
expression for the most effective use of energy resources, and it results in energy conserva-
tion. Energy efficiency can only reduce fossil fuel use while renewable energy can directly
replace it.
Figure 1-6 Effects of undesirable
emissions from the combustion
of fossil fuels.
FOSSIL FUEL EMISSIONS
CO2 ⇒ global warming
NOx and HC ⇒ smog
CO ⇒ toxic
SO2 ⇒ acid rain
PM ⇒ adverse health effects
Renewable Energy Sources
The main renewable energy sources include solar, wind, hydro, biomass, and geothermal
(Fig. 1-7). Energy sources from the ocean, including ocean thermal energy conversion
(OTEC), wave, and tidal, are also renewable sources, but they are currently not economical
and the technologies are still in the experimental and developmental stage.
An energy source is called renewable if it can be renewed and sustained without any
depletion and any significant effect on the environment. It is also called an alternative,
sustainable, or green energy source (Fig. 1-8). Fossil fuels such as coal, oil, and natural gas,
on the other hand, are not renewable, and they are depleted by use. They also emit harmful
pollutants and greenhouse gases.
The best-known renewable source is solar energy. Although solar energy is sufficient
to meet the entire energy needs of the world, currently it is not used as extensively as fos-
sil fuels because of the low concentration of solar energy on earth and the relatively high
Figure 1-8 Renewable energies such as solar water collectors are called green energy since they emit
no pollutants or greenhouse gases.
Figure 1-7 The switch from fossil
fuels to renewable energy sources
is inevitable.
RENEWABLE ENERGY
SOURCES
Solar
Wind
Hydro
Geothermal
Biomass
Ocean (OTEC, wave, tidal)
capital cost of harnessing it. The conversion of kinetic energy of wind into electricity via
wind turbines represents wind energy, and it is one of the fastest-growing renewables as
wind turbines are being installed all over the world. The collection of river water in large
dams at some elevation and then directing the collected water into a hydraulic turbine is
the common method of converting water energy into electricity. Hydro or water energy
represents the greatest amount of renewable electricity production, an
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