Geothermal electricity generation does involve a small amount of geothermal pollution in that the steam coming up from below ground carries some toxic gases, but in most plants these gases, as well as the steam, are condensed and reinjected into the ground so the effect on the environment is negligible. There are no CO2 emissions from geothermal energy so it is a much better source of electricity than coal or natural gas or nuclear (or even large-scale hydro generation which requires the flooding of large areas of land).

Geothermal electricity generation does involve a small amount of geothermal pollution in that the steam coming up from below ground carries some toxic gases, but in most plants these gases, as well as the steam, are condensed and reinjected into the ground so the effect on the environment is negligible. There are no CO2 emissions from geothermal energy so it is a much better source of electricity than coal or natural gas or nuclear (or even large-scale hydro generation which requires

Geothermal electricity generation does involve a small amount of geothermal pollution in that the steam coming up from below ground carries some toxic gases, but in most plants these gases, as well as the steam, are condensed and reinjected into the ground so the effect on the environment is negligible. There are no CO2 emissions from geothermal energy so it is a much better source of electricity than coal or natural gas or nuclear (or even large-scale hydro generation which requires the flooding of large areas of land).

The big problem is that there are not many places where you can build a geothermal power station. You need hot rocks of a suitable type, at a depth where we can drill down to them. The type of rock above is also important, it must be of a type that we can easily drill through. Sometimes a geothermal site may "run out of steam", perhaps for decades. Hazardous gases and minerals may come up from underground, and can be difficult to safely dispose of.

A price on carbon, such as that which would exist under a GHG cap-and-trade program, would raise the cost of electricity produced from fossil fuels relative to the cost of electricity from renewable sources, such as geothermal energy, and other lower-carbon technologies.

Unlike a coal or Natural Gas plant, geothermal facilities do not need to purchase fuel to generate electricity

The constant temperature of the Earth creates underground sources of heat, hot water and steam which become fuel to produce geothermal energy. People have used various forms of geothermal energy for hundreds of years; modern technology accesses these underground reservoirs, steam deposits and hot air by drilling, and then using the heat or hot water directly or using it to create power. Geothermal energy represents an enormous, underused power source that provides clean, renewable energy in virtually unlimited supply.

The initial costs of geothermal energy are high -- wells can cost $1 to $4 million each to drill, and installation of a home geothermal pump system can run as much as $30,000 [sources: REPP, Consumer Energy Center]. However, a home geothermal energy pump can cut energy bills by 30 to 40 percent and will pay for itself within 5 to 10 years [source: Consumer Energy Center].

Advantages: Geothermal energy cost is extremely low compared to many other energy sources. It has low pollution compared to fossil fuels and nuclear energy. Geothermal energy is a renewable energy source. Almost no environmental impact when using geothermal heat from nuclear decay. Geothermal heat pump systems can reduce your energy use storing heat from the summer/sun and makes use of it in the night and winter. Low maintenance systems.

Disadvantages: The most important disadvantage is absolutely the geological problem.  The heat source is mostly close to volcanic activity of some sort. Chemicals are byproducts of the production electricity with hot ground water. Some geothermal plants use a lot of water and it needs to go somewhere its after use. Some of the poluting chemicals in that water and steam are sulfur, mercury, hydrogen sulfide, arsenic, ammonia. Earth is a changing creature.  A drilled hole in the ground could supply thousands of homes heat and one earthquake could change that in a second.  It can also change gradually over time. Location, location, location.  That is certainly true of geothermal energy.  It cannot be transported over vast distances.  If used to heat up houses or for hot tap water it is only the quality of the pipe that delivers the water that determines how far it can go and if it will be of any use when it arrives. If the heat is used for electrical production it helps to have plants close so the energy loss is not too great. 

Corrosion is a big problem.  Composition of the chemicals can vary but it is always a problem.  It is among other the reason they need to heat up clean water to use and do not use it directly in to heating of houses.  In cases it has been used directly it causes pipes to corrode. In nuclear heating rock the rock cools down over few decades and hundreds of years are needed to get initial heating back.  Power stations of that sort are therefore not considered as profitable. Geothermal Heat pump systems do have high installation cost. Some areas run out of water or run low on ground water during seasonal dry spells. Less water means less heat and less energy to produce. Some drilling sites are too hot to handle.  Yea. Drillers have actually tried and tried some holes and they just can’t get the needed equipment in because the holes shoot it out like guns.   With workers running to stay alive while steel rains down on them. 

Geothermal energy has been used for thousands of years in some countries for cooking and heating. It is simply power derived from the Earth's internal heat.This thermal energy is contained in the rock and fluids beneath Earth's crust. It can be found from shallow ground to several miles below the surface, and even farther down to the extremely hot molten rock called magma.These underground reservoirs of steam and hot water can be tapped to generate electricity or to heat and cool buildings directly.A geothermal heat pump system can take advantage of the constant temperature of the upper ten feet (three meters) of the Earth's surface to heat a home in the winter, while extracting heat from the building and transferring it back to the relatively cooler ground in the summer

There are three types of geothermal power plants: dry steam, flash, and binary. Dry steam, the oldest geothermal technology, takes steam out of fractures in the ground and uses it to directly drive a turbine. Flash plants pull deep, high-pressure hot water into cooler, low-pressure water. The steam that results from this process is used to drive the turbine. In binary plants, the hot water is passed by a secondary fluid with a much lower boiling point than water. This causes the secondary fluid to turn to vapor, which then drives a turbine. Most geothermal power plants in the future will be binary plants.