Parameter

Geothermal

Wind

Coal

Air Emissions

Key Airborne Contaminants:

Values in lb/Mwh

Sulfur Dioxide: 0-0.35

Nitrogen Oxide: 0

Particulates: 0

Carbon Dioxide: 0-88.8

Scrubbers reduce air emissions but produce a watery sludge high in sulfur and vanadium, a heavy metal that can be toxic in high concentrations. Additional sludge is generated when hydrothermal steam is condensed, causing the dissolved solids to precipitate out. This sludge is generally high in silica compounds, chlorides, arsenic, mercury, nickel, and other toxic heavy metals. One costly method of waste disposal involves drying it as thoroughly as possible and shipping it to licensed hazardous waste sites. Research under way at Brookhaven National Laboratory in New York points to the possibility of treating these wastes with microbes designed to recover commercially valuable metals while rendering the waste nontoxic.

Usually the best disposal method is to inject liquid wastes or redissolved solids back into a porous stratum of a geothermal well.

This technique is especially important at geopressured power plants because of the sheer volume of wastes they produce each day. Wastes must be injected well below fresh water aquifers to make certain that there is no communication between the usable water and waste-water strata. Leaks in the well casing at shallow depths must also be prevented.

None

Sulfur Dioxide: 13 - 19.39

Nitrogen Oxides: 4.31 - 6

Particulates: 2.23

Mercury

Carbon Dioxide: 2191 – 2249

Mining, cleaning, and transporting coal to the power plant generate additional emissions. For example, methane, a potent greenhouse gas that is trapped in the coal, is often vented during these processes to increase safety.

Hydrogen Sulfide (H2S) (see SO2, above, for impacts and comparative information):

Hydrogen sulfide is now routinely abated at geothermal power plants, resulting in the conversion of over 99.9 percent of the hydrogen sulfide from geothermal noncondensable gases into elemental sulfur, which can then be used as a non-hazardous soil amendment and fertilizer feedstock. Since 1976, hydrogen sulfide emissions have declined from 1,900 lbs/hr to 200 lbs/hr or less, although geothermal power production has increased from 500 megawatts (MW) to over 2,000 MW

None

Not considered a coal issue.

Mercury:

Although mercury is not present in every geothermal resource, where it is present, mercury abatement equipment typically reduces emissions by 90 percent or more. The comparatively .highest. mercury emitters, two facilities at The Geysers in California, release mercury at levels that do not trigger any health risk analyses under strict California regulations.

None

Significant previously unregulated issue. In 1999, an estimated 47.8 tons of mercury were released from coal plants annually. In total, 117.3 tons were released, including 11 other major source categories.

Noise Pollution:

Normal geothermal power plant operation typically produces less noise than the equivalent produced .near leaves rustling from breeze,. according to common sound level standards, and thus is not considered an issue of concern.

Said to affect some people

Generally not an issue.

Water Use :

Geothermal plants use 5 gallons of freshwater per megawatt hour, while binary air-cooled plants use no fresh water.

None

Large quantities of water are frequently needed to remove impurities from coal at the mine. In addition, coal-fired power plants use large quantities of water for producing steam and for cooling. When coal-fired power plants remove water from a lake or river, fish and other aquatic life can be affected, as well as animals and people who depend on these aquatic resources. Water taken from a river or wells is released from cooling towers or back to the river.

Water Discharges and Quality:

Geothermal fluids used for electricity are injected back into geothermal reservoirs using wells with thick casing to prevent cross-contamination of brines with groundwater systems. They are not released into surface waterways. At The Geysers facility, 11 million gallons of treated wastewater from Santa Rosa are pumped daily for injection into the geothermal reservoir. Injection reduces surface water pollution and increases geothermal reservoir resilience.

None

Pollutants build up in the water used in the power plant boiler and cooling system. If the water used in the power plant is discharged to a lake or river, the pollutants in the water can harm fish and plants. Further, if rain falls on coal stored in piles outside the power plant, the water that runs off these piles can flush heavy metals from the coal, such as arsenic and lead, into nearby bodies of water. Coal mining can also contaminate bodies of water with heavy metals when the water used to clean the coal is discharged back into the environment. This discharge usually requires a permit and is monitored.

Water for power plant must be demineralized for use in the boiler.

River water or well water used for condenser may have biocide added.

Avian and Bat fatalities:

None

Measureable. Raptor kills of more concern.

None

Visual Pollution:

Generally these plants are more spread out and use smaller stacks and cooling towers, if needed.

Measureable. Considered significant by some.

Cooling towers, when used, can be an issue.

Solid Waste

Arsenic and silica are the major solid wastes.

None

Solid waste (bottom ash), about 10%, is composed primarily of metal oxides and alkali.

Solid waste is also created at coal mines when coal is cleaned and at power plants when air pollutants (flyash) are removed from the stack gas. Much of this waste is deposited in landfills and abandoned mines, although some amounts are now being recycled into useful products, such as cement and building materials.

Reserves:

US annual coal consumption in 2003 was about 1.1 billion tons. US Coal reserves are about 268 billion tons, of which 43 percent are in surface mines. The three major coal-producing states are Wyoming, West Virginia, and Kentucky.

Mining

Mining, cleaning, and transporting coal to the power plant generate additional emissions. For example, methane , a potent greenhouse gas that is trapped in the coal, is often vented during these processes to increase safety.

Land Use :

404 square meters of land per gigawatt hour

Subsidence : Subsidence, or the slow, downward sinking of land, may be linked to geothermal reservoir pressure decline. Injection technology, employed at all geothermal sites in the United States, is an effective mitigating technique.

Induced Seismicity : While earthquake activity, or seismicity, is a natural phenomenon, geothermal production and injection operations have at times resulted in low-magnitude events known as microearthquakes.. These events typically cannot be detected by humans, and are often monitored voluntarily by geothermal companies.

1007.252 (direct)- 115834 (total) square meters per gigawatt hour

Assume 34% capacity factor, Conversion from Direct: 0.74 acres/Mw

Total: 85.25 acres/Mw

Subsidence : Not a wind issue

Induced Seismicity : Not a wind issue

3632 square meters per gigawatt hour.

Subsidence : Has occurred in coal mines.

Induced Seismicity : Not a coal issue.

Hundreds of millions of songbirds and other species