Chapter 12 questions Renewable Energy

Describe current policy for renewable energy and energy efficiency as an outcome of recent government programs.

-average fuel economy standards to 54.5 mpg for cars by 2025 -tax credits increase efficiency in homes -encourage waste-energy recovery -hybrid cars.

Where is wind power being harvested, and what is the future potential for wind farms?

At wind farms. Wind power is an affordable, efficient and abundant source of domestic electricity. It's pollution-free and cost-competitive with energy from new coal- and gas-fired power plants in many regions.

How does a PV system work, and what are some present applications of such cells?

Each cell consists of two very thin layers of semiconductor material separated by a junction layer. The lower layer has atoms with single electrons in their outer orbital that are easily lost. The upper layer has atoms lacking electrons in their outer orbital; these atoms readily gain electrons. The kinetic energy of light photons striking the two layer "sandwich" dislodges electrons form the lower layer, creating a current that can flow through a motor or some other electrical device and back to the upper side. Thus, with no moving parts, solar cells convert light energy directly to electrical power, with an efficiency of 15-20%. PV cells a already in common use in pocket calculators, watches, and numerous toys. Panels of PV cells provide power for rural homes, irrigation pumps, traffic signals, radio transmitters, lighthouses, offshore oil-drilling platforms, Earth-orbiting satellites, and other installations that are distant from power lines.

What is the potential for developing more hydroelectric power in North America versus developing countries, and what would be the environmental impacts of such development?

Ecological disruption (i.e. downstream: sediments at dam, fish migration halted; in reservoirs: flooding, sediment retention, pollution) Disruption of people, loss of cultural resources, risk of failure, high rates of evaporative losses.

How much solar energy is available, and what happens when it is used? What are some problems with harnessing solar energy?

Full sunlight can deliver about 700 watts per square meters to Earth's surface when the Sun is directly overhead. At that rate, the Sun can deliver 700 MW of to an area of 390 square miles. The Sun delivers 10,000 times the energy used by humans. If humans were to capture and obtain useful work from solar energy, it would still be converted into heat and lost in accordance with the Second Law of Thermodynamics. The overall energy balance would not change. The main problem with using solar energy is one of taking a diffuse and intermittent source and concentrating it into an amount and form, such as fuel and energy, that can used to provide heat and run vehicles, appliances, and other machinery. Also overcoming such obstacles must be cost effective.

Why is it important for renewable energy sources to replace fossil fuels? What are the prospects for getting it done?

The salient reason is global climate change. Clearly the manufacture of wind turbines, PV panels, transmission lines, concentrated solar power plants, electric vehicles, recharging stations, and so on would have to take place in a relatively short period of time and this would require massive government support. Another barrier to accomplishing this transition is the way in which government subsidies.

What is geothermal energy, and what are two ways is it being harnessed?

There are springs that yield hot, almost boiling, water. Natural steam vents and other thermal features are also found in the area. They occur where the hot, molten rock of Earth's interior is close enough to the surface to heat ground water, particularly in volcanic regions. Using such naturally heated water or steam to heat buildings or drive turbogenerators is the basis of geothermal energy. Enhanced geothermal systems and Geothermal heat pump.

Describe two concentrated solar power systems, how they work, and their potential for providing power.

Wind power is the age-old concept that has proved most practical with wind-driven propeller blades. The propeller shaft is geared directly to a generator. Wind farms are now producing pollution-free, sustainable power for around 5 cents per kilowatt-hour that is competitive with the rates of traditional sources. -generate solar power by using mirrors to concentrate a large area of sunlight into a small area.