Homework Help: Social Studies: World Issues: Power Sources

Cons about renewable and nonrenewable power sources.

Hydropower

Other than manufacture of machinery and materials and construction of facilities, hydroelectric power does not produce any emissions. Creation of large reservoirs may also present recreational opportunities, but the impacts often outweigh the benefits. Development and operation of hydroelectric plants cause extensive environmental damage, including changes to natural river flows, degraded water quality, blocking of seasonal fish migration, impacts to fisheries, and widespread ecosystem damage from flooding large areas of land. For this reason, some experts do not consider large hydropower a renewable energy resource and question it as a viable option for our energy future. Large hydropower is not considered renewable energy in the context of "Green-e" renewable energy verification and certification. It is unfortunate that 24 percent of current U.S. energy supply comes from large hydropower, considering its environmental effects. In many cases this technology is the same as large hydropower except for the scale of operation. A small hydro system called "flume diversion" involves diversion of some water flow from a stream or river, using it for power generation, and then returning it to the river's flow. "Run-of-the-river," another type of small hydro system, uses the energy in the river's flow to turn the turbine and generate electricity; no water is diverted from the river or stream. Although their smaller scale does reduce some environmental impacts inherent to large hydro, small hydro facilities block fish migration, reduce productivity of fisheries, degrade water quality, and diminish some recreational opportunities. Many environmentalists and recreationists are justifiably concerned about small hydro having "renewable" status despite these impacts. Solar Thermal

Parabolic troughs or mirror arrays focus sunlight onto a contained working fluid, usually a special oil or molten salt. The superheated fluid is then routed to a boiler and the steam is used in turbines to generate electricity. Like PV arrays, solar thermal systems are modular. They can be sized to meet any power requirement and modified to meet changing energy needs. Solar thermal systems produce relatively few environmental impacts, mostly from manufacture of modules and construction materials, and from equipment used during assembly of large systems. Solar thermal systems are very land-intensive and have inherent aesthetic impacts similar to those of PV arrays. Some systems can reach heights of over 200 meters, which may be another aesthetic effect and a cause of public opposition.

Geothermal

This is another energy resource not exempt from environmental harms. One concern is the potential contamination of groundwater with sulfides and other pollutants if well casings are not done properly. In addition, carbon dioxide (a greenhouse gas) and hydrogen sulfide (distinguished by its "rotten egg" odor) are released by geothermal plants despite the absence of fuel burning processes. Finally, many geothermal reservoirs are located in sensitive and pristine wilderness areas that should not be disturbed.

Wind

One environmental concern about wind power is bird mortality. Turbine blades normally spin at high speeds and are difficult to see. Birds that drift into turbine blades are killed instantly in most cases and raptors such as the golden eagle (a federally protected species) are especially vulnerable. Proposed solutions to this problem include changing the tower design to eliminate beams used as perches, painting the turbine blades in colors and patterns to visually emphasize their presence, and reducing the populations of the raptors' prey by changing or removing vegetation. (Changing vegetation types and enhancing turbine visibility are mitigations aimed at reducing bird mortality, but these activities are likely to cause other problems.) Locally, researchers at UC Santa Cruz have chosen Altamont Pass as the subject of an investigation into the avian mortality issue.

Natural gas

At present, demand for natural gas, especially from the industrial and electric power generation sectors, is growing at a faster rate than that which supply can meet. When used near the site of its production, natural gas is inexpensive to produce, but the process needed to compress and liquefy it is costly and energy-inefficient, and natural gas cannot easily and efficiently travel or overseas without being compressed or liquefied. Because this issue has arisen relatively recently, prices for natural gas have gone up at a faster rate than was predicted. Another issue of concern is the high flammability potential of natural gas and the frequent leaks occurring in natural gas pipelines.

Petroleum

As with all other fossil fuels, petroleum exists in finite supply, and world oil demand is following a trajectory that may outpace existing stocks in the coming decades and drive high prices and fuel shortages. Furthermore, many of the oil-rich countries supplying petroleum to the United States are politically unstable or have used their status as oil providers to artificially raise prices, and in the recent past America has been subject to inconsistent pricing trends because of this instability. Since September 11th, 2001, focus on imports has intensified. In addition to the above concerns surrounding supply, petroleum contains many toxic components and even after refining releases large quantities of air pollutants when combusted. Air pollutants include particulate matter (PM) in the forms of soot and ash, sulfur oxides (SOx), and nitrogen oxides (NOx), which cause environmental damage in the form of acid rain and health problems such as asthma and lung disease. Petroleum is also toxic if leaked into surface or groundwater supplies: for example, in 1989 the Exxon Valdez oil spill killed millions of animals and plants along the Alaskan coastline, and even now the area is not entirely free of oil contamination. Oil spills typically cause major damage by releasing a large amount of oil into a concentrated area, but far more oil leaks into water supplies each year from improper disposal of used motor oil. Another petroleum-related difficulty is storage: petroleum is an inherently unstable fuel that breaks down into sludge over time. Storage tanks can easily leach oil into groundwater, and contaminants such as water and other non-oil substances frequently become mixed with stored petroleum and impair its energy efficiency.

Coal

Though gasification removes air pollutants more efficiently than scrubbers, the process is very expensive, and the technology is not sufficiently developed at this time to commence gasification on a substantial and economically viable scale. However, this may soon change, as coal gasification becomes one of the United States' top research priorities.

Homework Help: Social Studies: World Issues

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