ENV330

Chapter 16

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· Core Case Study Saving Energy and Money

· 16.1 A New Energy Transition

· 16.1a Establishing New Energy Priorities

· 16.2 Reducing Energy Waste

· 16.2a We Waste a Lot of Energy and Money

· 16.2b Improving Energy Efficiency in Industries and Utilities

· 16.2c Building a Smarter and More Energy-Efficient Electrical Grid

· 16.2d Making Transportation More Energy-Efficient

· 16.2e Switching to Energy-Efficient Vehicles

· 16.2f Buildings That Save Energy and Money

· 16.2g Air Conditioning and Climate Change

· 16.h Saving Energy and Money in Existing Buildings

· 16.2i Why Are We Wasting So Much Energy and Money?

· 16.2j Relying More on Renewable Energy

· 16.3 Solar Energy

· 16.3a Heating Buildings and Water with Solar Energy

· 16.3b Cooling Buildings Naturally

· 16.3c Concentrating Sunlight to Produce High-Temperature Heat and Electricity

· 16.3d Using Solar Cells to Produce Electricity

· 16.4 Wind Energy

· 16.4a Using Wind to Produce Electricity

· 16.5 Geothermal Energy

· 16.5a Tapping into the Earth’s Internal Heat

· 16.6 Biomass Energy

· 16.6a Producing Energy by Burning Solid Biomass

· 16.6b Using Liquid Biofuels to Power Vehicles

· 16.7 Hydropower

· 16.7a Producing Electricity from Falling and Flowing Water

· 16.8 Hydrogen

· 16.8a Will Hydrogen Save Us?

· 16.9 A More Sustainable Energy Future

· 16.9a Shifting to a New Energy Economy

· Tying It All Together Saving Energy and Money and Reducing Our Environmental Impact

· Chapter Review

· Critical Thinking

· Doing Environmental Science

· Data Analysis

16.1aEstablishing New Energy Priorities

Shifting to new energy resources is not new. The world has shifted from primary dependence on wood to coal, then from coal to oil, and then to our current dependence on a mixture of oil, natural gas, and coal as new technologies made these three energy resources more available and affordable. Each of these shifts in key energy resources took about 50 to 60 years. Making an energy shift involves making an enormous investment in scientific research, engineering, research, technology, and infrastructure to develop and spread the use of new energy resources.

Currently, the world gets 85% of its commercial energy, and the United States gets 80% of its commercial energy from three carbon-containing fossil fuels—oil, coal, and natural gas ( Figure 15.2 ). These energy resources have supported tremendous economic growth and improved the lives of many people.

However, many people are awakening to the fact that burning fossil fuels, especially coal, plays an important role in three of the world’s most serious environmental problems: air pollution, climate change, and ocean acidification. Fossil fuels are affordable because their market prices do not include these and other harmful health and environmental effects. In addition, they have been receiving government (taxpayer) subsides for decades, even though they are well-established and profitable businesses.

According to many scientists, energy experts, and energy economists, over the next 50 to 60 years and beyond, we need to and can make a new energy transition by

1. improving energy efficiency and reducing energy waste;

2. decreasing our dependence on nonrenewable fossil fuels;

3. relying more on a mix of renewable energy from the sun, wind, the earth’s interior heat (geothermal energy), and hydropower to produce most of the world’s electricity;

4. developing modern smart electrical grids to distribute electricity produced from renewable and nonrenewable energy resources; and

5. shifting to much greater dependence on electric cars, buses, scooters, and other vehicles with batteries that are recharged by electricity produced by solar cells and wind turbines.

Energy researchers and analysts point out that it is both technologically and economically feasible to make a transition toward getting most of our electricity from the sun and wind over the next 50-60 years. It would also be a way to implement the solar energy principle of sustainability globally.

This restructuring of the global energy system and economy over the next 50 to 60 years and beyond will save money, create profitable business and investment opportunities, and provide jobs. For example, building and installing solar cells and wind turbines (on land and at sea) will create thousands of jobs. It will also save lives by sharply reducing air pollution and by helping keep climate change and ocean acidification from spiraling out of control and creating ecological and economic chaos. Finally, it will increase our positive environmental impact, and pass the world on to future generations in better shape than we found it, in keeping with the ethical principle of sustainability.

This energy shift is being driven by the availability of perpetual supplies of clean and increasingly cheaper solar and wind energy throughout the world. Advances in solar cell and wind turbine technology have been steadily reducing the cost of using wind and solar energy to produce electricity. This is in contrast to fossil fuels, which are dependent on finite supplies that are not widely distributed, are controlled by a few countries, and are subject to fluctuating prices based on supply and demand.

In this new technology-driven energy economy, an increasing percentage of the world’s electricity will be produced locally from available sun and wind and regionally from solar cell power plants and wind farms. It will be transmitted to consumers through modern, interactive, smart electrical grids. Homeowners and businesses with solar panels on their land or their roofs (or roof coverings that contain solar cells) will be able to heat and cool their homes and businesses, run electrical devices, charge hybrid or electric cars, and sell the excess electricity they produce. The United States will benefit economically, because making such a market-based shift will set off an explosion of innovations in energy efficiency, renewable energy, and battery technology that will create millions of jobs. Old energy technologies would be replaced by cleaner and cheaper new energy technologies. According to economists, this is how creative capitalism works.

Like any major societal change, this shift will not be easy. However, to many analysts the current and long-term harmful environmental, health, and economic benefits of making this shift far outweigh any temporary harmful effects this shift might cause.

This shift is underway and gaining momentum as the cost of electricity produced from the sun and wind continues its rapid fall and investors see a way to make money on two of the world’s fastest growing businesses. Germany, Sweden, and Denmark have made significant progress in this energy resource transition.

Costa Rica is a global leader in this transition, as well as in reforestation ( Chapter 10   Core Case Study ). It gets none of its electricity from burning coal and more than 90% of its electricity from renewable resources—hydropower, geothermal energy, and wind and solar power. Costa Rica’s National Decarbonization Plan calls for having electric passenger trains in service by 2022 and having nearly a third of its buses running on electricity by 2035. It also envisions nearly all of its cars and buses running on electricity by 2050, supported by battery recharging stations throughout the country. If this ambitious plan succeeds, it will show the world how a small country can make a transition to a new and more sustainable energy system.

The United States has yet to commit to making the new energy shift. The reasons are complex, but this is partly because of more than four decades of opposition by politically and economically powerful fossil fuel and electric utility companies. The only question is whether we have the political and ethical will to make this vitally important economic and environmental transition.

16.2aWe Waste a Lot of Energy and Money

Improving energy efficiency and wasting less energy are key strategies in using energy more sustainability. Energy efficiency is a measure of how much useful work we can get from each unit of energy. Improving energy efficiency means using less energy to provide the same amount of work. We can do this by using more energy-efficient cars, heating and cooling systems, light bulbs (such as LED bulbs), appliances, computers, and industrial processes.

43%

Percentage of energy used in the United States that is unnecessarily wasted.

No energy-using device operates at 100% efficiency because some energy is always lost to the environment as low-quality heat, as required by the second law of thermodynamics (see  Chapter 2 ). About 84% of all commercial energy used in the United States is wasted ( Figure 16.2 ). About 41% of this energy unavoidably ends up as low-quality waste heat in the environment because of the degradation of energy quality imposed by the second law of thermodynamics. The other 43% is wasted unnecessarily, mostly due to the inefficiency of industrial motors, motor vehicles, power plants, light bulbs, and numerous other devices. This wasted energy is the country’s largest untapped source of energy. Reducing this huge waste of energy would save consumers money and reduce our harmful environmental impact from energy use. According to energy experts, the United States has more potential for improving energy efficiency than any other country.

Figure 16.2

Flow of commercial energy through the U.S. economy. Only 16% of the country’s high-quality energy ends up performing useful tasks.

Critical Thinking:

1. What are two examples of unnecessary energy waste?

(Compiled by the authors using data from U.S. Department of Energy.)

Another reason for our costly and wasteful use of energy is that many people live and work in poorly insulated, leaky houses and buildings that require excessive heating during cold weather and excessive cooling during hot weather (see  Figure 16.1 ). In addition, about 75% of Americans who commute to work do this mostly alone in energy-inefficient vehicles, and only 5% rely on more energy-efficient mass transit.

A major way in which we waste energy and money is through heavy reliance on widely used energy-inefficient technologies. One example is data centers, which process all online information (such as data on social media sites) and provide cloud-based data storage for users. These data centers–some of them as big as two football fields–require huge amounts of energy to operate and to cool because of the massive heat thrown off by their rows and rows of servers. Typically, these centers use only 10% of the electrical energy they consume. The other 90% is lost as waste heat. These data centers run 24 hours a day at their maximum capacities, regardless of the demand. Some data companies are reducing their environmental impact by getting the electricity they use mostly or totally from solar and wind energy.

Another example of energy waste is internal combustion engine, which propels most motor vehicles. It wastes about 75% of the high-quality energy in its gasoline fuel. Thus, only about 25% of the money people spend on gasoline provides them with transportation. The other 75% pays for waste heat released into the atmosphere.

We could cut much of this energy waste by changing our behavior.  Energy conservation  means reducing or eliminating the unnecessary waste of energy. If you ride your bicycle to school or work rather than driving a car, you are practicing energy conservation. Another way to waste less energy and money is to turn off lights and electronic devices when you are finished using them.

Improving energy efficiency and conserving energy have numerous economic, health, and environmental benefits ( Figure 16.3 ). To most energy analysts, they are the quickest, cleanest, and usually the cheapest ways to provide more energy, reduce pollution and environmental degradation, and slow climate change and ocean acidification.

Figure 16.3

Improving energy efficiency and conserving energy can have important benefits.

Critical Thinking:

1. Which two of these benefits do you think are the most important? Why?

Top: Dmitry Raikin/ Shutterstock.com. Center: V. J. Matthew/ Shutterstock.com. Bottom: andrea lehmkuhl/ Shutterstock.com.

Utility companies and industries can save energy by using  cogeneration  to produce two useful forms of energy from the same fuel source. For example, the steam used for generating electricity in a power or industrial plant can be captured and used again to heat the plant or other nearby buildings. The energy efficiency of cogeneration systems is 60–80%, compared to 25–35% for coal-fired and nuclear power plants. Denmark uses cogeneration to produce 38% of its electricity compared to 12% in the United States.

Inefficient motors account for 60% of the electricity used in U.S. industry. Industries can save energy and money by using more energy-efficient variable-speed electric motors that run at the minimum speed needed for each job. In contrast, standard electric motors run at full speed with their output throttled to match the task. This is somewhat like using one foot to push the gas pedal to the floorboard of your car and putting your other foot on the brake pedal to control its speed.

Recycling materials such as steel and other metals can save energy and money in industry. For example, producing steel from recycled scrap iron uses 75% less high-quality energy than does producing steel from virgin iron ore and emits 40% less . Industries can also save energy by using energy-efficient LED lighting; installing smart meters to monitor energy use; and shutting off computers, printers, and nonessential lights when they are not being used.

One way to include more of these hidden costs in the market price is through higher gasoline taxes—an application of the full-cost pricing principle of sustainability. However, higher gas taxes are politically unpopular, especially in the United States. Some analysts call for increasing U.S. gasoline taxes and reducing payroll and income taxes to offset any additional financial burden to consumers. Another way for governments to encourage higher energy efficiency in transportation is to give consumers significant tax breaks or other economic incentives to encourage them to buy more fuel-efficient vehicles.

Here are ways to reduce energy use in existing buildings and to cut energy waste and save money on electricity, heating, and cooling bills (see  Core Case Study ):

· Conduct an energy audit to detect air leaks ( Figure 16.1 ).

· Insulate the building and plug air leaks.

· Use energy-efficient (double- or triple-pane) windows.

· Seal leaky heating and cooling ducts in attics and unheated basements.

· Heat interior spaces more efficiently. In order, the most energy-efficient ways to heat indoor space are superinsulation (including plugging leaks); a geothermal heat pump that transfers heat stored from underground into a home; passive solar heating; a high-efficiency, conventional heat pump (in warm climates only); and a high-efficiency natural gas furnace.

Figure 16.8  lists ways in which individuals can cut energy use and save money in their homes.

Figure 16.8

Individuals matter: People can save energy and money where they live and reduce their harmful environmental impact.

16.2iWhy Are We Wasting So Much Energy and Money?

Considering its impressive array of economic and environmental benefits (Figure 16.3), why is there so little emphasis on reducing energy waste by improving energy efficiency and conserving energy? One reason is that energy resources such as fossil fuels and nuclear power are artificially cheap. This is primarily because of the government subsidies and tax breaks they receive and because their market prices do not include the harmful environmental and health costs of producing and using them. This distortion of the energy marketplace violates the full-cost pricing principle of sustainability.

Another reason for continuing energy waste is that governments do not provide significant government tax breaks, rebates, low-interest and long-term loans, and other economic incentives for individuals and businesses to invest in improving energy efficiency. A third reason is that most governments and utility companies have not put a high priority on educating the public about the environmental and economic advantages of improving energy efficiency and conserving energy.

Some critics say an emphasis on improving energy efficiency does not work because of the rebound effect in which some people tend to use more energy when they buy energy-efficient devices. For example, some people who buy a more efficient car tend to drive more, which offsets some of their energy and money savings and their reduced environmental impact.

Instead of downplaying efforts to improve energy efficiency, energy experts call for a major program to educate people about the rebound effect and its waste of money and long-lasting harmful health and environmental effects.

16.2jRelying More on Renewable Energy

In addition to reducing energy waste, we can make greater use of renewable energy from the sun, wind, flowing water, biomass, and heat from the earth’s interior (geothermal energy). The lesson from one of nature’s three scientific principles of sustainability is to rely mostly on solar energy. Most forms of renewable energy can be traced to the sun, because wind, flowing water, and biomass would not exist, were it not for solar energy. Another form of renewable energy is geothermal energy, or heat from the earth’s interior. All of these sources of renewable energy are constantly replenished at no cost to us.

In 2018, renewable energy, mostly solar and wind energy, provided about 8.4% the world’s electricity and 8.2% of U.S. electricity, according to BP. Studies by the IEA and the United Nations Environment Programme, project that with increased and consistent government backing in the form of research and development funds, subsidies and tax breaks, renewable energy from the sun and wind could provide as much as 50% of the world’s electricity by 2050. The U.S. National Renewable Energy Laboratory (NREL) projects that, with a crash program, the United States could get as much as 50% of its electricity from renewable energy sources—mostly wind and solar—by 2050. In 2017, jobs in solar and wind power were growing 12 times faster than the rest of the U.S. economy, according to a report from the nonprofit Environmental Defense Fund. In 2017, renewable energy provided about 786,000 jobs in the United States, 1.2 million in Europe, and 3.8 million in China, according to the Renewable Energy Agency.

According to the IEA, solar and wind are the world’s fastest-growing energy resources and nuclear energy is the slowest (Figure 15.24). China has the world’s largest installed capacity for electricity from wind power and solar cells. It plans to become the largest user and seller of wind turbines and solar cells, which are projected to be two of the world’s fastest growing businesses over the next few decades. China’s goal is to greatly expand its production of electricity from renewable wind, sun, and flowing water (hydropower) to help reduce its use of coal and the resulting outdoor air pollution that kills about 1.2 million of its citizens each year.

If renewable energy is so great, why does it provide only 11% of the world’s energy (Figure 15.2, left) and 12% of the energy used in the United States (Figure 15.2, right)? There are several reasons.

First, people tend to think that solar and wind energy are too diffuse, too intermittent and unreliable, and too expensive to use on a large scale. However, these perceptions are out of date. In the United States, solar and wind energy have become cheaper sources of electricity than coal and nuclear power and are equal to or cheaper than natural gas in some areas. Use of back-up storage systems for wind and solar power—including lithium-ion, zinc-air, and sodium-sulfur rechargeable battery systems is projected to increase tenfold in the next few years. The use of a new nationwide smart electrical grid could also help make solar and wind energy reliable sources of electricity by shifting electricity among different source locations to even out the power supply regionally and nationally.

One of the problems with direct solar energy is that it is dispersed.  Solar thermal systems , also known as concentrated solar power (CSP), use different methods to collect and concentrate solar energy to boil water and produce steam for generating electricity. These systems can be used in deserts and other open areas with ample sunlight.

One such system uses rows of curved mirrors, called parabolic troughs, to collect and concentrate sunlight. Each trough focuses incoming sunlight on a pipe that runs through its center and is filled with synthetic oil (Figure 16.13). Solar energy heats this oil to a temperature high enough to boil water and produce steam that spins a turbine to generate electricity.

Figure 16.13

Solar thermal power: This solar power plant in California’s Mojave Desert uses curved (parabolic) solar collectors to concentrate solar energy for producing electricity.

National Renewable Energy Laboratory

Another solar thermal system (Figure 16.14) uses an array of computer-controlled mirrors to track the sun and focus its energy on a central power tower. The concentrated heat is used to boil water and produce steam that drives turbines to produce electricity. The heat produced by either of these systems can also be used to melt a type of salt stored in a large insulated container. The heat stored in this molten salt backup system can be released as needed to produce electricity at night or on cloudy days.

Figure 16.14

Solar thermal power: In this system in California an array of mirrors tracks the sun and focuses reflected sunlight on a central receiver to boil the water for producing electricity.

Sandia National Laboratories/National Renewable Energy Laboratory

Some analysts see solar thermal power as a growing and important source of the world’s electricity. However, because solar thermal systems have a low net energy, they require large government subsidies or tax breaks to be competitive in the marketplace. These systems also require large volumes of cooling water for condensing the steam back to water and for washing the surfaces of the mirrors and parabolic troughs. However, they are usually built in sunny, arid desert areas where water is scarce. Figure 16.15 summarizes the major advantages and disadvantages of using these solar thermal systems.

Figure 16.15

Using solar energy to generate high-temperature heat and electricity has advantages and disadvantages.

Critical Thinking:

1. Do the advantages outweigh the disadvantages? Why or why not?

Top: Sandia National Laboratories/National Renewable Energy Laboratory. Bottom: National Renewable Energy Laboratory.

We can also use concentrated solar energy on a smaller scale. In some sunny areas, people use inexpensive solar cookers to focus and concentrate sunlight for boiling and sterilizing water (Figure 16.16, left) and cooking food (Figure 16.16, right). Solar cookers can replace wood and charcoal fires and reduce indoor air pollution, a major health hazard in less-developed nations. They also help reduce deforestation by decreasing the need for firewood and charcoal made from firewood.

Figure 16.16

Solutions: Solar cooker (left) in Costa Rica and simple solar oven (right).

chriss73/ Shutterstock.com; M. Cornelius/ Shutterstock.com

We can convert solar energy directly into electrical energy using  photovoltaic (PV) cells , commonly called  solar cells . Most solar cells are thin transparent wafers of purified silicon (Si) or polycrystalline silicon with trace amounts of metals that allow them to produce electricity when sunlight strikes them. Solar cells are wired together in a panel and many panels can be connected to produce electricity for a house or a large solar power plant (Figure 16.17). Such systems can be connected to electrical grids or to batteries that store the electrical energy until it is needed. Large solar-cell power plants are operating in Germany, Spain, Portugal, South Korea, China, and the southeastern United States. In 2017, factories in China produced more than two-thirds of the world’s solar cell panels.

Figure 16.17

Solar cell power plant: Huge arrays of solar cells can be connected to produce electricity.

Ollyy/ Shutterstock.com

Arrays of solar cells can be mounted on rooftops or incorporated into almost any type of roofing material. Nanotechnology and other emerging technologies will likely allow the manufacturing of solar cells in paper-thin, rigid or flexible sheets that can be printed like newspapers and attached to or embedded in other surfaces such as outdoor walls, windows, drapes, and clothing (to recharge batteries in mobile phones and other personal electronic devices). Figure 16.18 shows a solar cell village in Germany. Solar power providers in several countries are putting floating arrays of solar cell panels on the surfaces of lakes, reservoirs, ponds, and canals. In 2017, China developed the world’s largest floating solar farm on a lake. Engineers are developing dirt and water-repellent coatings to keep solar panels and collectors clean without having to use water. GREEN CAREER: Solar-cell technology

Figure 16.18

Solar cell village in Germany.

iStock.com/schmidt-z

Nearly 1.3 billion people, most of them in rural villages in less developed countries are not connected to an electrical grid. A growing number of these people are using rooftop solar panels (Figure 16.19) to power energy-efficient LED lamps that can replace costly and inefficient kerosene lamps that pollute indoor air. Expanding off-grid solar-cell systems to additional rural villages will help hundreds of millions of people lift themselves out of poverty and reduce their exposure to deadly indoor air pollution.

Figure 16.19

Solutions: A solar cell panel provides electricity for lighting this hut in rural West Bengal, India. In 2017, solar cells produced 6.3% of India’s electricity.

Jim Welc/National Renewable Energy Laboratory

India has more than 300 million mostly rural poor people who are not connected to an electrical grid. Private entrepreneurs in India and Africa are setting up stand-alone solar-powered microgrids where a centralized group of solar cell panels are connected by cable to a few dozen homes and local businesses. Customers use cell phones to connect to village smart meters and purchase a certain amount of electricity. The smart meters cut off the power when a user’s payment runs out.

Solar cells have no moving parts, need no water for cooling, and operate safely and quietly. They do not emit greenhouse gases or other air pollutants, but they are not a carbon-free option because fossil fuels are used to produce and transport the panels. However, the emissions per unit of electricity produced are much smaller than those generated by using fossil fuels and nuclear power to produce electricity. Conventional solar cells also contain toxic materials that must be recovered when the cells wear out after 20–25 years of use, or when they are replaced by new systems.

One problem with current solar cells is their low energy efficiency. They typically convert only about 20% of the incoming solar energy into electricity, although their efficiency is rapidly improving. In 2014, researchers at Germany’s Fraunhofer Institute for Solar Energy Systems developed a solar cell with an efficiency of 45%—compared to an efficiency of 35% for fossil fuel and nuclear electric power plants. They are working to scale up this prototype cell for commercial use. Figure 16.20 lists the major advantages and disadvantages of using solar cells to produce electricity.

Figure 16.20

Using solar cells to produce electricity has advantages and disadvantages.

Critical Thinking:

1. Do the advantages outweigh the disadvantages? Why or why not?

Top: Martin D. Vonka/ Shutterstock.com. Bottom: pedrosala/ Shutterstock.com.

Some communities and neighborhoods are using community solar or shared solar systems to provide electricity for individuals who rent or live in condominiums, or whose access to sunlight is blocked by buildings or trees. Customers buy the power from a centrally located small solar cell power plant. The power is delivered by the local utility and customers share deductions on their monthly bills for any excess power the project sells back to the grid.

We can convert solar energy directly into electrical energy using  photovoltaic (PV) cells , commonly called  solar cells . Most solar cells are thin transparent wafers of purified silicon (Si) or polycrystalline silicon with trace amounts of metals that allow them to produce electricity when sunlight strikes them. Solar cells are wired together in a panel and many panels can be connected to produce electricity for a house or a large solar power plant (Figure 16.17). Such systems can be connected to electrical grids or to batteries that store the electrical energy until it is needed. Large solar-cell power plants are operating in Germany, Spain, Portugal, South Korea, China, and the southeastern United States. In 2017, factories in China produced more than two-thirds of the world’s solar cell panels.

Figure 16.17

Solar cell power plant: Huge arrays of solar cells can be connected to produce electricity.

Ollyy/ Shutterstock.com

Arrays of solar cells can be mounted on rooftops or incorporated into almost any type of roofing material. Nanotechnology and other emerging technologies will likely allow the manufacturing of solar cells in paper-thin, rigid or flexible sheets that can be printed like newspapers and attached to or embedded in other surfaces such as outdoor walls, windows, drapes, and clothing (to recharge batteries in mobile phones and other personal electronic devices). Figure 16.18 shows a solar cell village in Germany. Solar power providers in several countries are putting floating arrays of solar cell panels on the surfaces of lakes, reservoirs, ponds, and canals. In 2017, China developed the world’s largest floating solar farm on a lake. Engineers are developing dirt and water-repellent coatings to keep solar panels and collectors clean without having to use water. GREEN CAREER: Solar-cell technology

Figure 16.18

Solar cell village in Germany.

iStock.com/schmidt-z

Nearly 1.3 billion people, most of them in rural villages in less developed countries are not connected to an electrical grid. A growing number of these people are using rooftop solar panels (Figure 16.19) to power energy-efficient LED lamps that can replace costly and inefficient kerosene lamps that pollute indoor air. Expanding off-grid solar-cell systems to additional rural villages will help hundreds of millions of people lift themselves out of poverty and reduce their exposure to deadly indoor air pollution.

Figure 16.19

Solutions: A solar cell panel provides electricity for lighting this hut in rural West Bengal, India. In 2017, solar cells produced 6.3% of India’s electricity.

Jim Welc/National Renewable Energy Laboratory

India has more than 300 million mostly rural poor people who are not connected to an electrical grid. Private entrepreneurs in India and Africa are setting up stand-alone solar-powered microgrids where a centralized group of solar cell panels are connected by cable to a few dozen homes and local businesses. Customers use cell phones to connect to village smart meters and purchase a certain amount of electricity. The smart meters cut off the power when a user’s payment runs out.

Solar cells have no moving parts, need no water for cooling, and operate safely and quietly. They do not emit greenhouse gases or other air pollutants, but they are not a carbon-free option because fossil fuels are used to produce and transport the panels. However, the emissions per unit of electricity produced are much smaller than those generated by using fossil fuels and nuclear power to produce electricity. Conventional solar cells also contain toxic materials that must be recovered when the cells wear out after 20–25 years of use, or when they are replaced by new systems.

One problem with current solar cells is their low energy efficiency. They typically convert only about 20% of the incoming solar energy into electricity, although their efficiency is rapidly improving. In 2014, researchers at Germany’s Fraunhofer Institute for Solar Energy Systems developed a solar cell with an efficiency of 45%—compared to an efficiency of 35% for fossil fuel and nuclear electric power plants. They are working to scale up this prototype cell for commercial use. Figure 16.20 lists the major advantages and disadvantages of using solar cells to produce electricity.

Figure 16.20

Using solar cells to produce electricity has advantages and disadvantages.

Critical Thinking:

1. Do the advantages outweigh the disadvantages? Why or why not?

Top: Martin D. Vonka/ Shutterstock.com. Bottom: pedrosala/ Shutterstock.com.

Some businesses and homeowners are spreading the cost of rooftop solar power systems over decades by including them in their mortgages. Others are leasing solar-cell systems from companies that install and maintain them.

Some communities and neighborhoods are using community solar or shared solar systems to provide electricity for individuals who rent or live in condominiums, or whose access to sunlight is blocked by buildings or trees. Customers buy the power from a centrally located small solar cell power plant. The power is delivered by the local utility and customers share deductions on their monthly bills for any excess power the project sells back to the grid.

Use of solar cells is the world’s fastest growing way of producing electricity. Between 2001 and 2018, the cost per watt of electricity produced by solar cells fell by 80%. Producing electricity from solar cells is expected to grow because solar energy is unlimited and available throughout the world. It is also a technology, not a fuel such as coal or natural gas, the prices of which are controlled by available supplies. Prices for solar cell systems are likely to continue dropping because of technological advances, mass production, and decreased installation costs. In 2018, California had half of the country’s rooftop solar cell installations and a quarter of U.S. solar-energy jobs.

Solar cells cannot produce electricity at night, and storing energy in large batteries for use at night and on cloudy days is expensive. However, researchers at Ohio State University have developed a solar cell panel with a built-in battery that is 25% less expensive and 20% more efficient than conventional batteries. If it can be mass-produced, this invention could revolutionize the use of solar energy to produce electricity. GREEN CAREER: Solar-cell technology

Learning from Nature

A rainforest butterfly species called the glasswing, with its transparent wings, provided the inspiration for a cost-effective coating for solar panels that allows the panels to absorb more light and generate electricity more efficiently.

If pushed hard and supported by government subsidies equivalent to or greater than fossil fuel subsidies, solar energy could supply as much as 23% of U.S. electricity by 2050, according to projections by the NREL. After 2050, solar electricity is likely to become one of the top sources of electricity for the United States and much of the world. If this happens, it will represent a global application of the solar energy principle of sustainability.

16.5aTapping into the Earth’s Internal Heat

Geothermal energy  is heat stored in soil, underground rocks, and fluids in the earth’s mantle. It is used to heat and cool buildings and to heat water to produce electricity. Geothermal energy is available around the clock but is practical only at sites with high enough concentrations of underground heat.

A geothermal heat pump system (Figure 16.24) can heat and cool a house almost anywhere in the world. This system makes use of the temperature difference between the earth’s surface and underground at a depth of 3–6 meters (10–20 feet), where the temperature typically is  year-round. In winter, a closed loop of buried pipes circulates a fluid, which extracts heat from the ground and carries it to a heat pump, which transfers the heat to a home’s heat distribution system. In summer, this system works in reverse, removing heat from a home’s interior and storing it below ground.

Figure 16.24

Natural capital: A geothermal heat pump system can heat or cool a house almost anywhere.

According to the EPA, a geothermal heat pump system is the most energy-efficient, reliable, environmentally clean, and cost-effective way to heat or cool a space. Installation costs can be high but are recouped within 3 to 5 years, after which these systems save energy and money for their owners. Initial costs can be added to a home mortgage to spread the financial burden over two or more decades.

Engineers have also learned how to tap into deeper, more concentrated hydrothermal reservoirs of geothermal energy (Figure 16.25). Wells are drilled into the reservoirs to extract their dry steam (with a low water content), wet steam (with a high water content), or hot water. The steam or hot water can be used to heat homes and buildings, provide hot water, grow vegetables in greenhouses, raise fish in aquaculture ponds, and spin turbines to produce electricity.

Figure 16.25

Power plants can produce electricity from heat extracted from underground geothermal reservoirs. The photo shows a geothermal power plant in Iceland that produces electricity and heats a nearby spa called the Blue Lagoon.

Richard Nowitz/National Geographic Image Collection

Drilling geothermal wells, like drilling oil and natural gas wells, is expensive and requires a major investment. It is also a risky investment because drilling projects do not always succeed in tapping into concentrated deposits of geothermal energy. Once a successful deposit is found, it can supply geothermal energy for heat or to produce electricity around the clock, as long as heat is not removed from the deposit faster than the earth replaces it—usually at a slow rate. When this happens, geothermal energy becomes a nonrenewable resource.

Geothermal energy generates electricity in 24 countries and provides heat in 70 countries. The United States is the world’s largest producer of geothermal electricity from hydrothermal reservoirs, most of it in California, Nevada, Utah, and Hawaii. Figure 16.26 is a map of the best geothermal energy sites in the continental United States. The U.S. Geothermal Energy Association (GEO) estimates that 90% of the available geothermal energy for producing electricity in the United States and 60% of the potential supply in California has not been tapped.

Figure 16.26

Potential geothermal energy resources in the continental United States.

(Compiled by the authors using data from U.S. Department of Energy and U.S. Geological Survey)

Iceland gets almost all of its electricity from renewable hydroelectric (72%) and geothermal (25%) power plants (Figure 16.25, photo) and about 90% of its demand for heat and hot water from geothermal energy. In Peru, a National Geographic Explorer is carrying out research to develop that country’s geothermal resources (Individuals Matter 16.1).

Individuals Matter 16.1

Andrés Ruzo—Geothermal Energy Sleuth and National Geographic Explorer

Courtesy of Andrés Ruzo

Andrés Ruzo is a geophysicist with a passion to learn about geothermal energy and to show how this renewable and clean energy source can help us solve some of the world’s energy problems. As a boy, he spent summers on the family farm in Nicaragua. Because the farm rests on top of the Casita Volcano, he was able to experience firsthand the power of the earth’s heat.

As an undergraduate student at Southern Methodist University (SMU) in Dallas, Texas (USA), because of his boyhood experience, he took a course in volcanology. The course awakened his passion for geology along with a desire to learn more about the earth’s heat as a source of energy. This led him to pursue a PhD in geophysics at SMU’s Geothermal Laboratory.

Beginning in 2009, he has been gathering data across Peru to develop the country’s first detailed heat flow map—which will help identify areas of geothermal energy potential. His fieldwork involves lowering temperature-measuring equipment down into oil, gas, mining, or water wells. Much of this work was done in the Talara Desert in northwestern Peru, where surface temperatures can exceed ‍. These data illustrate how thermal energy flows through the upper crust of the earth, and highlights areas where earth’s heat can potentially be tapped as a source of energy.

Ruzo believes that geothermal energy is a “sleeping giant” that, if properly harnessed, can be an important renewable source of heat and electricity. He says that his goal in life is “to be a force of positive change in the world.”

Another source of geothermal energy is hot, dry rock found 5 kilometers or more (3 miles or more) underground almost everywhere. Water can be injected through deep wells drilled into this rock. Some of the water absorbs the underground heat and becomes steam that is brought to the surface and used to spin turbines to generate electricity. According to the U.S. Geological Survey, tapping just 2% of this source of geothermal energy in the United States could produce more than 2,000 times the amount of electricity currently used in the country. The limiting factor is its high cost, which could be brought down by more research and improved technology. GREEN CAREER: Geothermal engineer

Figure 16.27 lists the major advantages and disadvantages of using geothermal energy. The biggest factors limiting the widespread use of geothermal energy are the lack of hydrothermal sites with concentrations of heat high enough to make it affordable and the high cost of drilling the wells and building the plants.

Figure 16.27

Using geothermal energy for space heating and for producing electricity or high-temperature heat for industrial processes has advantages and disadvantages.

Critical Thinking:

1. Do you think the advantages outweigh the disadvantages? Why or why not?

Photo: N. Minton/ Shutterstock.com

In addition, burning wood and other forms of biomass produces  and other pollutants such as fine particulates in smoke.  Figure 16.28  lists the major advantages and disadvantages of burning solid biomass as a fuel.

Figure 16.28

Burning solid biomass as a fuel has advantages and disadvantages.

Critical Thinking:

1. Do the advantages outweigh the disadvantages? Why or why not?

Top: Fir4ik/ Shutterstock.com. Bottom: Eppic/ Dreamstime.com.

Biomass can also be converted into liquid biofuels for use in motor vehicles. The two most common liquid biofuels are ethanol (ethyl alcohol produced from plants and plant wastes) and biodiesel (produced from vegetable oils). The three biggest biofuel producers are, in order, the United States (producing ethanol from corn), Brazil (producing ethanol from sugarcane residues), and the European Union (producing biodiesel from vegetable oils).

Ecologist David Tilman ( Individuals Matter 12.1 ) estimates that the net energy of cellulosic ethanol is about five times that of corn-based ethanol. However, producing cellulosic ethanol is not yet affordable, and growing switchgrass or miscanthus requires even more land than does growing corn. More research is also needed to determine possible environmental impacts.

In Malaysia and Indonesia, large areas of tropical rain forests are being cleared and replaced with plantations of oil palm trees ( Figure 10.4 ), which produce a fruit that contains palm oil. After the oil is extracted, about a third of it is exported to Europe to make biodiesel fuel and the rest goes into processed food and cosmetics. The clearing and burning of tropical forests to make space for these palm oil plantations eliminates the vital biodiversity of the forests. It also adds  to the atmosphere, and the resulting plantations remove far less  than do the forests they replace.

In a United Nations report on bioenergy, and in another study by R. Zahn and his colleagues, scientists warned that large-scale biofuel crop farming could reduce biodiversity by eliminating more forests, grasslands, and wetlands and increasing soil degradation and erosion. It would also lead to higher food prices if it becomes more profitable to grow corn for biofuel rather than for feeding livestock and people.

Figure 16.29  compares the advantages and disadvantages of using biodiesel and ethanol liquid biofuels.

Figure 16.29

Ethanol and biodiesel biofuels have advantages and disadvantages.

Critical Thinking:

1. Do the advantages outweigh the disadvantages? Why or why not?

16.7aProducing Electricity from Falling and Flowing Water

Hydropower  is any technology that uses the kinetic energy of flowing and falling water to produce electricity. This renewable energy resource is an indirect form of solar energy because it depends on heat from the sun evaporating surface water as part of the earth’s solar-powered water cycle (Figure 3.19).

The most common way to harness hydropower is to build a high dam across a large river to create a reservoir (see Chapter 13 opening photo). Some of the water stored in the reservoir is allowed to flow through large pipes at controlled rates, turning blades on a turbine that produces electricity (see Figure 13.15), which is distributed by the electrical grid.

Hydropower is the world’s most widely used renewable energy resource. In 2017, it produced about 17% of the world’s electricity according to the IEA. In 2017, the world’s top four producers and consumers of hydropower were, in order, China, Canada, Brazil, and the United States. In 2017, hydropower supplied about 7.5% of the electricity used in the United States and about half of the electricity used on the West Coast, mostly in Washington and California.

According to the United Nations, only 13% of the world’s potential for hydropower has been developed. Countries with the greatest potential include China, India, and several countries in South America and Central Africa. China, with the world’s largest hydropower output, plans to more than double its output during the next decade and is building or funding more than 200 hydropower dams around the world.

Hydropower is the least expensive renewable energy resource. Once a dam is up and running, its source of energy—flowing water—is free and is annually renewed by snow and rainfall unless climate change reduces the water flow in some areas with existing hydropower plants. Despite their potential, some analysts expect that the use of large-scale hydropower plants will fall slowly over the next several decades, as many existing reservoirs fill with silt and become useless faster than new systems are built.

There is also growing concern over emissions of methane, a potent greenhouse gas, from the decomposition of submerged vegetation in hydropower plant reservoirs, especially in warm climates. Scientists at Brazil’s National Institute for Space Research estimate that the world’s largest dams altogether are the single largest human-caused source of climate-changing methane. The electricity output of hydropower plants may also drop if atmospheric temperatures continue to rise and melt mountain glaciers that are a primary source of water for these plants.

It is unlikely that large new hydroelectric dams will be built in the United States because most of the best sites already have dams and because of the high cost of building new dams. In addition, there is growing controversy over the harmful effects of interrupting river flows. However, the turbines at many existing U.S. hydropower dams could be modernized and upgraded to increase their output of electricity. Figure 16.30 lists the major advantages and disadvantages of using large-scale hydropower plants to produce electricity.

Figure 16.30

Using large dam and reservoir systems to produce electricity has advantages and disadvantages.

Critical Thinking:

1. Do the advantages outweigh the disadvantages? Why or why not?

Photo: Andrew Zarivny/ Shutterstock.com

Some scientists say that the fuel of the future is hydrogen gas . Most of their research has been focused on using fuel cells ( Figure 16.31 ) that combine  and oxygen gas  to produce electricity while emitting nonpolluting water vapor  into the atmosphere.

Figure 16.31

A fuel cell takes in hydrogen gas and separates the hydrogen atoms’ electrons from their protons. The electrons flow through wires to provide electricity, while the protons pass through a membrane and combine with oxygen gas to form water vapor. Note that this process is the reverse of electrolysis, the process of passing electricity through water to produce hydrogen fuel.

Widespread use of hydrogen as a fuel for running motor vehicles, heating buildings, and producing electricity would eliminate most of the outdoor air pollution that comes from burning fossil fuels. It would also greatly reduce climate change and ocean acidification, because its use does not increase  emissions as long as the  is not produced with the use of fossil fuels or nuclear power.

Turning hydrogen into a major fuel source is a challenge for several reasons. First, there is hardly any hydrogen gas  in the earth’s atmosphere.  can be produced by heating water or passing electricity through it; by stripping it from the methane  found in natural gas and from gasoline molecules; and through a chemical reaction involving coal, oxygen, and steam. Second, hydrogen has a negative net energy because it takes more high-quality energy to produce  using these methods than we get by burning it.

Third, although fuel cells are the best way to use , current versions of fuel cells are expensive. However, progress in the development of nanotechnology (see  Science Focus 14.1 ) and mass production could lead to less expensive fuel cells.

Fourth, whether or not a hydrogen-based energy system produces less  and outdoor air pollution than a fossil fuel system depends on how the  fuel is produced. Electricity from coal-burning and nuclear power plants can be used to decompose water into  and . However, this approach does not avoid the harmful environmental effects associated with using coal and the nuclear fuel cycle. Research indicates that making  from coal or stripping it from methane or gasoline adds much more  to the atmosphere per unit of heat generated than does burning the coal or methane directly.

Hydrogen’s negative net energy is a serious limitation. It means that this fuel will have to be heavily subsidized in order for it to compete in the open marketplace. However, this could change. Chemist Daniel Nocera has been learning from nature by studying how a leaf uses photosynthesis to produce the chemical energy used by plants and he has developed an “artificial leaf.” This credit-card-sized silicon wafer produces  and  when placed in a glass of tap water and exposed to sunlight. The hydrogen can be extracted and used to power fuel cells. Scaling up this or similar processes to produce large amounts of  at an affordable price with an acceptable net energy over the next several decades could represent a tipping point for use of solar energy and hydrogen fuel. Doing so would help implement the solar energy principle of sustainability on a global scale.

Figure 16.32  lists the major advantages and disadvantages of using hydrogen as an energy resource. GREEN CAREER: Fuel cell technology

Figure 16.32

Using hydrogen as a fuel for vehicles and for providing heat and electricity has advantages and disadvantages.

Critical Thinking:

1. Do the advantages outweigh the disadvantages? Why or why not?

Photo: LovelaceMedia/ Shutterstock.com

According to its proponents, a major shift to a new set of energy resources over the next 50 to 60 years (see Section 16.1) would have numerous environmental, health, and economic benefits.

China (which uses 20% of the world’s energy) and the United States (which uses 19% of the world’s energy) are the key players in making this shift. China has a long way to go in reducing its heavy dependence on coal and leads the world in climate-changing  emissions. However, it has launched efforts to make its economy more energy efficient, build a modern smart electrical grid, and install solar hot water heaters on a large scale. China is also building wind farms and solar power plants, supporting research on better batteries and solar and wind technologies, and building and selling all-electric cars. It is also making money by producing and selling more wind turbines and solar cell panels than any other country.

The United States is also making efforts to shift to a new energy economy. However, it is falling behind China’s efforts and those of countries such as Germany, Sweden, and Denmark. This is mostly because of more than 40 years of successful efforts by powerful fossil fuel and electric utility companies to stop or slow down this energy shift because it threatens their profits.

This energy and economic transition is underway and is accelerating because market forces increasingly drive it. This is the result of the rapidly falling prices of electricity produced by the sun and wind and new energy technologies. Investors are moving rapidly into clean energy technologies. According to many scientists and energy economists, the shift to a new energy economy could be further accelerated if citizens, the leaders of emerging renewable energy companies, and energy investors demanded the following from their elected officials:

We have the creativity, wealth, and most of the technology to make the transition to a safer, more energy-efficient, and cleaner energy economy within your lifetime. With such a shift, we would greatly increase our beneficial environmental impact. Figure 16.33 lists ways in which you can take part in the transition toward such a future.

Figure 16.33

Individuals matter: You can make a shift in your own life toward using energy more sustainably.

Critical Thinking:

1. Which three of these measures do you think are the most important ones to take? Why? Which of these steps have you already taken and which do you plan to take?

Big Ideas

· To make our economies more sustainable, we need to reduce our use of fossil fuels, especially coal, and greatly increase energy efficiency, reduce energy waste, and use a mix of renewable energy resources, especially the sun and wind.

· Making this energy shift will have important economic and environmental benefits.

· Making the transition to a more sustainable energy future will require including the harmful environmental and health costs of all energy resources in their market prices, taxing carbon emissions, and greatly increasing government subsidies and research and development for improving energy efficiency and developing renewable energy resources.

· Tying It All TogetherSaving Energy and Money and Reducing Our Environmental Impact

·

· LianeM/ Shutterstock.com

· In the Core Case Study, we learned that by wasting energy, we waste money and increase our harmful environmental impact. The world and the United States waste so much energy that reducing this waste by increasing energy efficiency and saving energy is the quickest, cleanest, and usually the cheapest way to provide more energy. In doing so, we would also reduce pollution and environmental degradation and slow climate change and ocean acidification.

· Over the next 50 to 60 years, we could choose to rely less on fossil fuels, especially coal, and more on increasing energy efficiency and using a mix of solar, wind, and other renewable energy resources. Making this energy shift would have enormous economic, environmental, and health benefits.

· Relying more on energy from the sun and wind helps us to implement the solar energy principle of sustainability. It also follows the chemical cycling principle of sustainability by reducing our excess inputs of  into the atmosphere, which disrupt the earth’s carbon cycle and cause ocean acidification when the ocean removes some of this excess  from the atmosphere. This energy shift also mimics the earth’s biodiversity principle of sustainability by reducing the environmental degradation that degrades biodiversity.

· Making this shift will require implementing the full-cost pricing principle of sustainability by including the harmful health and environmental costs of energy resources in their market prices. It will also require compromise and trade-offs in the political arena, in keeping with the win-win principle of sustainability. By making this energy shift, we would also be implementing the ethical principle of sustainability, which calls for us to leave the earth’s life support system in as good as or better than it is now.

· Tying It All TogetherSaving Energy and Money and Reducing Our Environmental Impact

·

· LianeM/ Shutterstock.com

· In the Core Case Study, we learned that by wasting energy, we waste money and increase our harmful environmental impact. The world and the United States waste so much energy that reducing this waste by increasing energy efficiency and saving energy is the quickest, cleanest, and usually the cheapest way to provide more energy. In doing so, we would also reduce pollution and environmental degradation and slow climate change and ocean acidification.

· Over the next 50 to 60 years, we could choose to rely less on fossil fuels, especially coal, and more on increasing energy efficiency and using a mix of solar, wind, and other renewable energy resources. Making this energy shift would have enormous economic, environmental, and health benefits.

· Relying more on energy from the sun and wind helps us to implement the solar energy principle of sustainability. It also follows the chemical cycling principle of sustainability by reducing our excess inputs of  into the atmosphere, which disrupt the earth’s carbon cycle and cause ocean acidification when the ocean removes some of this excess  from the atmosphere. This energy shift also mimics the earth’s biodiversity principle of sustainability by reducing the environmental degradation that degrades biodiversity.

· Making this shift will require implementing the full-cost pricing principle of sustainability by including the harmful health and environmental costs of energy resources in their market prices. It will also require compromise and trade-offs in the political arena, in keeping with the win-win principle of sustainability. By making this energy shift, we would also be implementing the ethical principle of sustainability, which calls for us to leave the earth’s life support system in as good as or better than it is now.

· Data Analysis

· Study the table below and then answer the questions that follow it by filling in the blank columns in the table.