Artificial Geothermal Energy

Natural geothermal energy, also known as hydrothermal energy, starts with water underground trapped in holes or cracks in rocks. The water and rocks, heated by the earth’s mantle or radioactive minerals in the rock, becomes steam. This steam is released by drilling, drives turbines in generators, and thereby creates electricity for homes and other facilities. It’s termed “natural” as nature provides the hot rocks, the connected holes or cracks, and the water. Enhanced, or engineered geothermal systems, on the other hand, start with hot rocks and add the water and / or the cracks and connections. Thus, all geothermal electricity has the same sources, the difference being the role of nature vs. engineers. Engineered geothermal systems presents some unique benefits; specifically, they:

• Are no longer dependent on what nature can provide in terms of water temperature or the quantity of water,
• Have no geographic limitations and the effects on availability of natural sources, and
• Have designed efficiencies beyond those available from nature.

A Geothermal Power Plant

Engineered geothermal systems are built into hot, deep rocks. Wells 2 to 6 miles deep are drilled into the rocks where the temperature ranges between 160 degrees F and 600 degrees F. Water is then forced into the cracks in the rock using high pressure pumps. The power plant itself is on the surface, consisting of injection and production wells:

• Cold water is pumped down the injection wells.
• The water becomes heated as it percolates through the cracks in the hot rock.
• Once heated, it rises by its own heat or by the pressure from incoming water up the production well.
• The hot water becomes steam which drives the turbines.
• Cooling towers cool the water and recycle it back into the injection wells.

Virtually any location can be used to build an engineered geothermal system as hot rock is prevalent throughout the world. The best sites are where the hot rock is most stressed and nearest the surface.

The Risks of Artificial Geothermal Energy

The construction underground produces controllable risks:

• Vibrations at the surface, equivalent to a small earthquake underground, can happen during fracturing. By planting seismometers around the rocks to be fractured, there is ample opportunity to turn off the water should it become necessary.
• Large earthquakes can occur, but typically only if the developers put the system near a big fault. Use of regional maps indicating where these faults lie and the measurement of seismicity at all sites prior to pumping water generally preclude such an event.
• Water usage can be a huge issue as over 2 million gallons is required to open the cracked rock and once a rock is unsealed, it draws on nearby reservoirs, significantly lowering the water table. By adding millions more gallons of water at the surface, water that can be reused, this can be prevented from happening.
• As a result of water circulating through the hot rock and picking up arsenic or other poisonous substances, contaminants are produced which can leak at the surface or into the underground freshwater. By keeping the circulating water contained, engineers are able to keep these substances contained.

Benefits of Artificial Geothermal Energy

Whether natural or engineered, geothermal power has economic and environmental benefits.

• Since the earth is always hot and radiating heat, in contrast to wind power or solar power, it can supply electricity around the clock.
• Geothermal and natural geothermal power is renewable as it does not deplete the earth’s heat. Sites can wear out as the rock between the pairs of wells will get cold. But, by drilling new wells nearby, the supply of hot water remains.
• The power plants are clean. Depending on the design, they emit little if any gas into the environment; and the circulating water remains in the pipe, boiling another fluid to turn the turbines.
• The footprint is relatively small at 80,000 square feet per MW. This compares favorably to solar panels which require over 710,000 square feet per MW, coal plants at 430,500 square feet per MW, and a nuclear plant at 107,500 square feet per MW.
• Since the resource is on home soil and unlimited the cost of imports is not a factor; and unlike nuclear power, the byproducts of geothermal cannot be used to develop weapons. The net effect is geothermal power offers security.

Engineered geothermal will work anywhere since it only requires hot rock and the variable in finding hot rock is how deep to dig.

The Economics of Artificial Geothermal Energy

Two questions persist in considering the feasibility of engineered geothermal systems, namely:

• How fast will these systems pay for themselves, and
• What will this do to the cost of power?

The major expense in installing one of these systems lies in the drilling of wells, One 2.5 mile well, considered middle-range, costs about $5 million. If one must dig deeper, even 20 percent, the drilling cost escalates to $20 million per well, a four-fold increase in cost. Once these wells are drilled, the costs to operate the system are relatively low. Typically, an engineered geothermal power plant will produce 1 to 50 MW of electricity, considerably less than the 2,000 MW that a coal-fired plant will supply.

Investors can benefit, receiving around 18 percent of the investment they made in building underground parts of the system. This annual recovery is similar to the anticipated return from an oil or natural gas field.

Consumers can benefit as well. Though everyone acknowledges that the first engineered geothermal systems are inefficient and result in the cost of electricity between 18 and 75 cents per kWh, the maturing technology indicates that the cost of engineered geothermal energy will drop to 4 to 9 cents per kWh, well below today’s  cost of electricity from coal.

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