In this chapter, we’ll review Unit 6 of the AP Environmental Science Course, Energy Resources and Consumption. According to the College Board, about 10–15% of the test is based directly on the ideas covered in this chapter. If you are unfamiliar with a topic presented here, consult your textbook for more in-depth information.

Unlike the essential elements we discussed in earlier chapters, energy flows on a one-way path through the atmosphere, hydrosphere, and biosphere, and is essential for living organisms in many of its forms.

• At the most fundamental level, energy is defined as the capacity to do work. There are three types of energy: potential energy is energy at rest—it’s stored energy—while kinetic energy is energy in motion. You might recall from your physics class that potential energy can be converted to kinetic energy.

• The third type of energy is radiant energy—for example, sunlight—and it is the only form of energy that can travel through empty space.

• Two terms that describe the movement of energy around the Earth are convection, which is the transfer of heat by the movement of the heated matter, and conduction, which is the transfer of energy through matter from particle to particle.

• Keep in mind that different energy sources are capable of storing types of energy that differ in quality. For example, both wood and coal will burn to produce heat, but coal produces more heat because it contains higher energy quality.

• Net energy yield refers to the comparison between the energy cost of extraction, processing, and transportation and the amount of useful energy derived from the fuel.

UNITS OF ENERGY

Energy Units: joule (J), calorie (cal), British thermal unit (BTU), and kilowatt hour (kWh), which is a measure of watts × time

Power Units: watt (W) and horsepower (hp)

Remember, watts are equal to volts × amperage. You should also be intimately familiar with the First and Second Laws of Thermodynamics, so let’s review those before we move on—and make sure you memorize them before test day!

What About Natural Gas?

Currently, natural gas is used for heating homes and cooking. It can also be burned to generate electricity. Some power plants are designed to switch between oil and natural gas fuels depending on the cost.

• The engines of cars and trucks can be modified to burn natural gas instead of gasoline. There is a landfill operator in the state of New Jersey who tested a process of trapping methane from a landfill, liquefying it, and then using the liquid methane to power the trucks that bring garbage to the landfill.

• Because of its simple molecular structure, natural gas produces only carbon dioxide and water when it burns. It does not produce the oxides of nitrogen and sulfur associated with burning coal or oil. Before you get really excited about natural gas, you should be aware of its dangers.

• In an uncontrolled release (like a leak), it can cause violent explosions. It is also more difficult to transport than coal or oil. Because a tank can hold a small amount of gas, producers liquefy it by putting the gas under high pressure (Liquefied Natural Gas).

• This process requires energy. Natural gas can also be transported by pipes. However, pipes carry the risk of leaks and explosions, and some habitats are damaged during the building of the pipe system.

RENEWABLE ENERGY

• One interesting fuel that’s recently been developed is called gasohol, a type of synfuel. Gasohol is a gasoline extender made from a mixture of 90 percent gasoline and 10 percent ethanol, which is often obtained by fermenting agricultural crops or crop wastes.

• So, as you can see, it is partly derived from organic substrate. Gasohol has higher octane than gasoline and burns more slowly, coolly, and completely, thus resulting in reduced emissions of some pollutants. Despite those advantages, it also vaporizes more readily than gasoline, and has the potential to aggravate ozone pollution in warm weather.

• Ethanol and, similarly, methanol from organic sources are surface carbons and therefore add no net carbon to the atmosphere. However, because ethanol is carbon-based, carbon dioxide is released during its combustion.

• Ethanol-based gasohol is also expensive and energy-intensive to produce—one bushel of corn produces only two and a half gallons of ethanol.

There are other problems associated with dams that you need to know about. One of them is silting. As water sits behind the dam, the normal sediments it carries have time to sink to the bottom. This puts additional weight on the structure and means that dams have to be built strong enough to hold back the many tons of sediment.

Solar Energy

Passive solar energy collection is the use of building materials, building placement, and design to passively collect solar energy (such as through windows) that can be used to keep a building warm or cool. On the other hand, active collection is the use of devices, such as solar panels, that collect, focus, transport, or store solar energy.

• Solar panels absorb solar energy and pass on the energy to tubes in which water is circulating; this heated water can be stored for later use. Direct collection of solar energy via photovoltaic cells (PV cells) produces electricity, which is then stored in batteries.

• When sunlight hits the PV cells, electrons are energized and can flow freely, producing an electric current. After this, one of two things can happen.

• If the home or building is connected to a regional electric grid, the energy produced is fed into the grid; this results in the electricity meter on the building actually spinning backward! Homeowners who have installed solar panels receive a credit against further charges from their electricity providers when the energy that they’ve fed into the grid exceeds the amount of energy the household uses.

• If the home or building is not connected to the local electric grid, the energy stored can be stored in batteries to be utilized later. While the use of solar energy produces no air pollutants, the production of photovoltaic cells does require the use of fossil fuels.

• The advantages of solar panels are that photovoltaic cells use no moving parts, require little maintenance, and are silent. However, not every location receives enough sunlight to make solar panels worthwhile. Also, the initial financial outlay for solar power is significant, although money is saved when the home is disconnected from the regional grid.

• Additionally, some states (such as New Jersey) give homeowners financial assistance for the installation of solar systems in their homes. Eventually, new technology should significantly lower the cost of solar systems.

• While many PV cells are installed on rooftops or in backyards to power individual homes and businesses, larger arrays of PV cells can generate more power for commercial or industrial use. The desert is a particularly profitable place to locate such an array given the abundance of sunshine. However, large solar energy farms do have the potential to negatively impact desert ecosystems.

Wind Energy

Wind energy is the fastest growing alternative energy source, and modern wind turbines are usually placed in groups called wind farms or parks. In the United States, the largest of these wind farms is located in Altamont Pass, California; this farm has several thousand wind turbines.

• Wind-generated power has been increasing at a rate of more than 30 percent per year and is projected to supply a full 20 percent of the world’s energy needs by 2030. Although, in the United States, wind farms are predominately in California and Texas at this time, many locations have enough prevailing winds to make production of electricity from wind power feasible.

• Wind farms can also be located offshore in the ocean, and although they’re currently only located near to shore, in the future they may be placed on floating docks in deep water.

• At this time, wind power is more costly than using fossil fuels because of the initial outlay of capital that must be invested in order to build the windmills; windmills are also considered by many to be annoyingly loud and unattractive.

• However, perhaps the biggest problem with this type of renewable energy source is that alternate energy sources must be in place for times when there is no wind.

• In the 1990s, one other public concern about the use of wind turbines was that birds would be cut up and killed by the blades, but now we know that as long as wind farms are not located in the middle of migration routes, only one or two birds per turbine per year are killed—and this is far fewer than the number of birds killed by other types of towers. Finally, one tremendous advantage of using wind energy is that it produces no harmful emissions.

Other Sources of Energy

There are two other less widespread renewable energy sources: tidal movement in the ocean (tidal power) and hydrogen cells. You should be somewhat familiar with both of these energy sources for the exam.

Ocean Tides

The tidal movements of ocean water can be tapped and used as a source of energy. To harvest tidal energy, dams are erected across outlets of tidal basins.

• Incoming tides are sluiced through the dam, and the outgoing tides pass through the dam, turning turbines and generating electricity. Recently, ocean dams have been developed that allow energy to be harnessed from both the outgoing and incoming tides.

• At this time, there is a tidal power plant installed in the East River in New York, NY. It harnesses enough power to power 10,000 homes.

• There are many different designs of ocean tide power plants in the idea stages. One of these involves having waves push into a chamber of air; the compressed air is then forced through a small hole at the turbine, and turns the turbine as it is released.

• An experimental prototype of this design has been installed off the coast of Scotland and is nicknamed the LIMPET (Land-Installed-Marine-Powered Energy Transformer).

Hydrogen Cells

Hydrogen is obtained from fossil fuels by a process called reforming. Hydrogen is very difficult to store and not very energy dense, but hydrogen fuel cells are considered by many to be the best, cleanest, and safest fuel source.

• Free hydrogen is not found on Earth, but it can be released through the process of electrolysis, in which hydrogen atoms are stripped from water, leaving the oxygen atom.

• Hydrogen can also be obtained from organic molecules, but the use of organic sources can release pollutants—as can the process of electrolysis if a fossil fuel, such as natural gas or coal, is used to drive the process. However, once the free hydrogen is released, it can be stored and then used to generate electricity through the reverse reaction of electrolysis.

• One of the major benefits of the use of hydrogen fuel cells is that the only waste from the fuel cell is steam—water vapor. This technology has been used for decades in spacecrafts, but the high cost of the fuel cell and lack of hydrogen fuel stations has limited the technology to just a few test programs.

• The United States Department of Energy estimates that hydrogen fuel cells large enough to power light trucks and cars in the United States will require the production of 150 megatons of hydrogen per year (in 2004, only nine megatons of hydrogen were produced).

• In order for hydrogen to become a truly viable option as a renewable energy source, an inexpensive and efficient way to produce hydrogen from nonfossil fuel sources must be developed. One of the most promising techniques for this involves the use of photovoltaic cells to harvest sunlight and then power the splitting of the water molecule.

ENERGY CONSERVATION: A FINAL NOTE

When we discuss energy conservation, we are basically referring to the practice of reducing our use of fossil fuels and reducing the impact we have on the environment as we produce and use energy. One important form of energy conservation is the use of alternative fuel cars. They are gaining in popularity and acceptance. Battery electric vehicles (BEVs) are slowly becoming more commonplace.

• These vehicles run on battery power alone and can be charged with electric power. Their downsides include the pollution from the production and disposal of the batteries, expense, and the relative dearth of charging stations.

• A more popular alternative is the hybrid-electric vehicle. Hybrid vehicles are built with two motors: one electric and one gasoline powered.

• The electric motor powers the car from 0 to about 35 miles per hour. Above 35 mph, the gasoline engine starts and helps to power the car. At highway speeds, both the electric and gas motors operate. The cars are designed so that when the brakes are applied, some of the energy is transferred from the brakes to recharge the electric motor’s battery.

• Not only do these cars have good gas mileage, but they also produce far less CO2 pollution than traditional gas-powered vehicles. Several carmakers also make models that use propane or natural gas as fuels, although these are not as common as hybrids.

• These generate only CO2 and water as emissions, and they get good gas mileage. A problem is the lack of refueling stations, although devices are available that allow refueling from home. Cars can also be retrofitted with natural gas fuel tanks, so the driver can choose between gasoline or methane fuel.

-Another type of alternative fuel is used cooking oils.

• The oils used in deep-fat fryers can be filtered and then burned in diesel-fueled cars, trucks, and buses. After starting the engine on pure diesel fuel, the driver switches to the biofuel to drive.

• At the end of the trip, the driver runs on pure diesel fuel again for a few minutes before shutting off the engine.

Another front on which steps are being taken to increase energy conservation is building design.

• Designers are rediscovering and modernizing techniques like passive solar heating, using thermal mass to regulate temperatures, and incorporating photovoltaic cells and smart regulation technology to reduce the amount of energy used from the grid in heating, cooling, lighting, and other energy use.

• While offices, factories, and other commercial buildings are a prime target of conservation efforts, these ideas can be implemented on a smaller scale in individual homes as well.

• Residential energy consumers can adjust thermostats to reduce the use of heat and air conditioning, conserve water, use energy-efficient appliances, and use conservation in their landscaping.

• It has been argued that finding new fossil fuel sources would serve the same purpose as would reducing our current use of fossil fuels. However, this is not true—this statement does not take into consideration the fact that our use of fossil fuels has numerous negative effects on the environment.

• Additionally, in the long term it will not help us much to conserve fossil fuel resources— simply because these are not renewable energy sources—so they will eventually be depleted. Therefore, if we are to have dependable, long-term, renewable sources of energy, we must continue to develop, implement, and improve upon current renewable technology and methods.

On the legislative front, the United States has adapted the CAFE, or Corporate Average Fuel Economy, standards. These standards set mile-per-gallon standards for a fleet of cars. The goal of these standards is to reduce energy consumption by increasing the fuel economy of cars and light trucks.

• Review the CAFE standards described on this page. Finally, do not forget the role of mass transit in reducing pollution. Buses and trains can move many more people than cars.

• When the amount of pollution made by the vehicle is divided by all the passengers it is carrying, the bus or train generates far less pollution per person than a car. In order to determine whether or not a resource should be used, citizens, governments, and businesses engage in a process called cost-benefit analysis.

• Costs and benefits can be either tangible (measurable), or intangible (immeasurable). Consider a corporation interested in clearing a forest for wood.

• The benefits are jobs and lumber (both tangible), while the costs are the loss of beauty and recreation opportunity (intangible), decreased biodiversity, and carbon dioxide removal (tangible).