Environmental Drawbacks of Renewable Energy: Real or Exaggerated?
Heidi Anderson, Energy Analyst at Frost & Sullivan
Contents
Hydroelectric Power
Biopower
Geothermal Power
Wind Power
Solar Power
Weighing the Benefits against the Risks
Long considered a novel concept, renewable energy technologies are finally becoming a mainstream energy option. Deregulation has opened the door to competition and new power generation options are becoming entrenched in the North American electricity infrastructure. There are a number of renewable power options available, some still developing and others in commercial production. Renewable energy includes, but is not limited to, wind, solar, biopower, geothermal and small hydropower. Along the path to full competition, renewable energy has encountered numerous barriers including legislative inadequacies, high production costs and powerful fossil fuel lobbies. Perhaps the most unusual opposition, however, comes from those groups, including environmental ones, that claim renewable energy has detrimental effects on the environment.
This is not to suggest that any one group is denouncing all of renewable energy as environmentally bereft. Rather, separate claims have been made and scientific studies conducted regarding specific technologies. Renewable energy has always been seen as one of the answers to the pollution caused by fossil fuel-based power. Now some technologies have come under attack for creating the very environmental harm that they were supposed to prevent. The question remains: Whether or not the opposition is unfounded?
Hydroelectric Power (Back to top)
Hydroelectric power is one of the nation's oldest sources of renewable power. Its classification as renewable, however, has come under attack and as a source of renewable power generation, it is often overlooked. Many state renewable standards call for the development of non-hydroelectric power and most definitions of renewable energy do not include large hydropower (systems greater than 15 or 30 MW, depending on the source). Additionally, new constraints imposed on hydropower operation have led to more stringent trends in re-licensing, resulting in a loss of capacity.
It is true that the environmental effects caused by a hydroelectric system can be extensive. However, it is important to note that every project is different. The environmental effects examined below are analyzed in a broad context and it should not be assumed that every hydropower facility has similar impacts. Differences between reservoir-based systems and run-of-the-river projects, as well as differences between each individual facility, make it impossible to generalize on the environmental impacts of hydroelectric power. It is also important to note that not every dam produces electricity. In the United States, for example, only three percent of more than 75,000 dams are used for power production.
Changes to the Ecosystem
A number of changes to the ecosystem result from the use of a reservoir-based hydroelectric system. These include stratification, supersaturation, changing water levels, and sedimentation.
Stratification can occur when the rate of a river slows due to a dam and colder, oxygen-depleted water sinks to the bottom due to its higher density. The resulting layering effect puts the coldest water on the bottom and the warmest on top. If the water released to produce electricity is from the lower levels, the oxygen-depleted water can change the downstream habitat.
Two phenomena unique to a reservoir-based hydroelectric system are supersaturation and sedimentation. Supersaturation occurs when air that is trapped in water spilled over a dam hits the pool on the other side and creates turbulence. Since the air is composed primarily of nitrogen, the level of nitrogen dissolved in water can increase significantly, causing supersaturation. The excess nitrogen levels in the water can be transferred into the tissues of fish and other aquatic creatures. If fish swim from a nitrogen-saturated area into a lower pressure area, injury and death can result (a similar condition to "the bends" that can occur in scuba diving). Sedimentation occurs when sediments that are typically suspended in water collect behind a physical barrier such as a dam. The nature of sedimentary buildup can vary based on the project, but two harmful changes to the ecosystem can result. First, downstream habitats can decline because the sediments no longer provide inorganic or organic nutrients. Second, when sediment builds up behind a dam more organisms feed on the nutrients available. This increased population uses oxygen and can deplete the reservoir supply.
One of the more harmful effects of a hydroelectric storage project is the changing water levels that can result. A dam can raise the water level several hundred feet (effectively burying the current ecosystem) and, if the reservoir is used to provide "power peaking" electricity, the water level can be raised and lowered frequently. If this occurs, it is difficult for the surrounding habitat to reach equilibrium and for vegetation to be reestablished.
Changes to Aquatic Habitat
The greatest impacts of a hydroelectric project are found in fish populations and, more specifically, salmon populations (since the majority of hydro projects are located in the Northwest where salmon populations are greatest). Some of the most common impacts regarding fish and hydroelectric projects are listed below:
- Contact with turbines or the dam itself can cause injury or death to fish and when they are exited to a small area they are subject to predators. Fish passage rates, however, are generally better than 90 percent.
- As mentioned earlier, supersaturation conditions can create elevated nitrogen levels in fish populations, which can cause death.
- A dam is a physical barrier to salmon migrations. Although a number of "fishways" exist to aid upstream migration, they are not always foolproof. Since salmon do not feed during the voyage back to their spawning grounds, a loss of time and energy can be critical.
There is no doubt that hydroelectric systems can have a significant effect on the environment (although not all do). Proponents of hydropower point to atmospheric emissions that are avoided by the use of hydro facilities. According to 1997 figures issued by the National Hydropower Association, hydropower avoided the release of 83 million tons of carbon, 2 million tons of sulfur dioxide, and 1.3 million tons of nitrogen oxides. A recent study released by the World Commission on Dams, however, found that some hydroelectric systems release more greenhouse gases into the atmosphere than do coal-fired power generation. Decaying vegetation trapped in stagnant water produces methane, which is 20 times more potent as a greenhouse gas than carbon dioxide. The report is far from inclusive, however, as it only looks at four countries and analyzes emissions data that varies widely from site to site. However, it does offer the possibility that hydroelectricity may not be justified in its claim that it prevents global warming.
Biopower (Back to top)
The environmental considerations involved in the use of biomass-based power are second only to hydropower. Biopower is created by the combustion of biomass and biomass-derived fuels, making air pollution a valid concern. Also of concern is the impact biomass use has on the agriculture and forestry industries.
Air Pollution
Anytime a fuel source is combusted to produce electricity, air pollutants can result. Conventional biomass plants have emissions similar to coal-fired power plants except that there are only trace amounts of sulfur dioxide and toxic metals produced. The biggest concern over conventional biomass combustion is particulate emissions which must be controlled with special devices. Newer technologies, such as gasifier/combustion plants, will generate significantly lower emissions (more comparable to natural gas).
A benefit of combusting biomass fuel over fossil fuels is that it has the potential to greatly reduce greenhouse gas emissions. Although combusting biomass releases carbon dioxide, the amount released is very near to the amount required to grow biomass. It is a sustainable cycle that results in a net release of carbon dioxide.
Agriculture and Forestry Concerns
Biopower has the potential to be both beneficial and detrimental to both agriculture and forestry. Dedicated agricultural feedstocks cultivated solely for use in electricity generation can be a boon to farmers. Crops grown specifically for energy purposes can be grown in underutilized land and be a stabilizing factor in areas prone to erosion. Large-scale energy farming, however, could be detrimental both in terms of land use and the chemicals necessary to produce crops. Monitoring of development and use would be necessary to ensure that cultivating crops for energy does not create more harm than it prevents.
Byproducts from forestry have long provided a basis for biomass power generation. Increasing the amount of wood used for energy could be both positive and negative. It could result in more careful management of the resources used in forest products development. It could also, under the excuse of "green" power development, contribute to undesirable exploitation of commercial forests. As with the growth of energy crops, controls and standards will need to be established to ensure that abuses do not occur.
Geothermal Power (Back to top)
Air Quality Concerns
Any air quality concerns regarding the use of geothermal power stem from flashed-steam plants. Binary systems do not allow steam to separate and, because they are closed-loop systems, there is no chance that byproducts from geothermal steam will enter the atmosphere.
Carbon dioxide is the dominant noncondensible gas produced when steam separates from water in flashed-steam geothermal systems. However, CO2 emissions from a geothermal power plant are only a fraction of what is produced for the same output of electricity for power plants that use hydrocarbons. In 1991 figures, the average carbon dioxide emissions from a coal plant were 990 kg per MWh of electricity produced and 540 kg for a natural gas plant. In comparison, a geothermal flashed-steam plant produced 0.48 kg per MWh of electricity produced.
Another concern regarding geothermal plants is hydrogen sulfide emissions because they are detectable by humans at concentrations of less than 1 ppm in air. In early geothermal development H2S was a concern but it was also one of the first major research efforts in the National Geothermal Program. Processes have now been developed that remove more than 99.9 percent of hydrogen sulfide emissions, an acceptable amount according to conventional air quality standards.
Geothermal plants also emit some sulfur but in levels far below that of a coal-based plant. Unlike fossil fuel plants, geothermal power production does not involve high combustion pressures, eliminating the release of nitrogen oxide emissions.
Water Quality Concerns
Although water quality concerns regarding geothermal power production are natural, they are essentially unfounded. In the United States, the only geothermal water that is allowed to flow into lakes and streams is lower-temperature water that is of drinking quality. All other applications must inject the water back into the reservoir. Both production and injection wells are lined to prevent the introduction of geothermal water into surrounding freshwater aquifers.
Wind Power (Back to top)
As renewable energy technologies go, wind power is fairly environmentally benign. It produces no air or water pollution and involves no toxic substances. However, there are some objections to its development. Land use and avian mortality are the two biggest concerns.
Land Use
The amount of land required to sustain a wind project can be misunderstood. Many early studies considered the entire area upon which wind turbines were placed as occupied (the actual turbines as well as the space between them). In actuality, however, the land surrounding wind turbines can be used for other purposes or left in its natural state. Some of the biggest developments in California are situated on grazing lands with no disruption to the cattle who feed there. The greatest potential for future development is in the Great Plains; sufficient quantities of wind and extensive farming areas provide the perfect setting for multiple wind turbines.
Avian Mortality
Avian mortality became a concern because of the relatively high number of bird deaths surrounding California's Altamont Pass, one of the largest wind development areas. There have only been a few studies conducted regarding the association between birds and multiple wind turbines. These limited results seem to indicate that avian mortality is a site-specific problem and that a bird colliding with a wind turbine is not a common occurrence.
Wind system manufacturers have already taken steps to limit the number of birds killed around wind turbines. For example, one of the suspected problems at Altamont Pass is that the "lattice" towers supporting the turbines make an ideal perch for birds. Tubular towers greatly reduce this opportunity and are becoming the preferred choice in the development of new projects.
Although avian mortality is a valid concern, the number of birds killed due to wind turbines is not astronomical. A two-year study of the Altamont Pass project reported 182 dead birds. By comparison, a study at a single coal-fired power plant recorded approximately 3,000 bird deaths in a single evening.
Solar Power (Back to top)
The primary environmental concerns surrounding solar power relates to how they are manufactured and installed. There are no environmental effects caused by the operation of solar power.
Manufacturing and Installation Issues
The materials used in solar manufacturing are often hazardous. Arsenic and cadmium are common materials used in solar production facilities as is silicon, which can create problems if it is inhaled. However, the dangers faced by working with hazardous materials in the solar industry are fairly routine hazards in an industrial society and can be mitigated by careful regulation.
Most solar installations are small-scale, dispersed applications. They generally utilize unused portions of buildings, such as roofs, or take advantage of the design of the building for use as a collector. For large-scale solar installations, approximately one square kilometer is required for every 20 to 60 megawatts of power produced. This amount of land use, however, is not unusual for utility-scale power plants. The same amount or more is required per unit of energy in a coal-based power plant, especially when the land required for strip mining is taken into account.
Weighing the Benefits against the Risks (Back to top)
While detractors of renewable energies point to real drawbacks, a weighing of the energy options indicates these drawbacks are nearly insignificant when weighed against the major problems and issues surrounding conventional energies.
External costs from fossil fuel-based electricity generation are extensive. Pollution has been linked to human health costs, higher health insurance rates, missed work and even death. Not to mention environmental concerns created by acid rain and global warming.
Electricity generation accounts for 36 percent of primary energy consumption in the United States and 35 percent of total carbon dioxide emissions. The predominant source of emissions from the electric utility industry is coal (89 percent), but coal consumption (and, consequently, emissions) is offset by the use of non-fossil fuel sources and natural gas. A typical 500 MW coal plant burns 1.4 million tons of coal and produces 3.5 billion kilowatt-hours of electricity. It also produces the following:
- 10,000 tons of sulfur dioxide
- 10,200 tons of nitrogen oxide
- 3.7 million tons of carbon dioxide
- 720 tons of carbon monoxide
- assorted toxic heavy metals including mercury, arsenic, lead and cadmium
In conclusion, while drawbacks to renewable energies no doubt exist, policymakers and industry leaders must maintain a balanced perspective if the United States is to develop reasonably priced, environmentally safe electricity for all its citizens and businesses.
(For a comprehensive view of the North American Renewable Energy Market please contact Rolf Gatlin at 210.348.1017 or rgatlin@frost.com and reference Frost & Sullivan report #7233-14).