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| ES&E Publisher Tom Davey, checks out a solar powered car designed by Queen's University engineering students. |
By Heidi Anderson, Energy Analyst,
Frost &
Sullivan, San Jose, California
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.
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| ES&E Publisher Tom Davey, checks out a solar powered car designed by Queen's University engineering students. |
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.
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
Hydroelectric power is one of North America'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. 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 eco-system 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 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. Downstream habitats can decline because the sediments no longer provide inorganic or organic nutrients. 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 re-established.
Changes to Aquatic Habitat
The greatest impacts of a hydroelectric project are found in fish populations and, more specifically, salmon populations:
Recent Findings
Proponents of hydropower point to atmospheric emissions that are avoided by the use of hydro facilities. According to 1997 figures issued by the US National Hydropower Association, hydropower avoided the release of 83 million tons of carbon, 2 million tons of sulphur 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
The environmental considerations involved in the use of biomass-based power are second only to hydropower. Bio-power 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 sulphur 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.
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 under-utilized land and be a stabilizing factor in areas prone to erosion.
GEOTHERMAL POWER
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 by-products 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. 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.
Water Quality Concerns
Although water quality concerns regarding geothermal power production are natural, they are essentially unfounded.
WIND POWER
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.
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
The primary environmental concerns surrounding solar power relate 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 used, 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 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 kilometre 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
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.
Electricity generation accounts for 36 percent of primary energy consumption in the United States and 35 percent of total carbon dioxide emissions. 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:
In conclusion, while drawbacks to renewable energies no doubt exist, policymakers and industry leaders must maintain a balanced perspective if reasonably priced, environmentally safe electricity is to be developed.
This article was abridged from Environmental Science & Engineering magazine, which also contains many more articles not posted on our Web Site. See our home page on how to order your subscription. We regret we can only accept orders from Canada and the United States