Geothermal energy is heat energy derived from earth’s core and is a “renewable resource” as defined by the Pacific Northwest Electric Power Planning and Conservation Act of 1980 and The National Energy Policy Act of 1992; estimated by the U.S. Geothermal Industry for the Renewable Energy Task Force (1997) as “equivalent to 42 million megawatts of power”. Geothermal Energy, earth’s core energy, competently mined and shared, is completely renewable and 100% sustainable for the millions of years we imagine earth’s core will remain hot.
Potential for extracting and utilizing thermal energy found beneath earth’s lithospheric crust and mantle, sometimes referred to as “heat mining”; for direct use or generation of electricity is a subject of significant interest. If historic extraction challenges are overcome employing innovative technology, heat mining can efficiently, more cost effectively and safely employed, in which case, geothermal resources represent a nearly inexhaustible source of non-fossil fuel-non-CO2 emitting, non-nuclear waste producing, non-polluting fuel. The term heat mining is usually constrained in context of harvesting earth’s heat at a maximum extraction rate not exceeding earth’s localized ability to replenish the heat, therefore never depleting the source.
It should be noted that many if not most other so-called “green” or “clean” alternative technologies have practical limitations in terms of availability, efficiency and unit cost. Electrically powered vehicles for example, currently require recharging via electricity generated by fossil or nuclear fuel powered generating facilities. Pollution is not eliminated and if employed on a large-scale, demand will drive the cost of electricity to unreasonable levels given current technological limitations. Hybrid vehicles, able to independently produce their own electricity using natural gas, gasoline or diesel fuel also contribute to pollution. These electric vehicles have a bright future, but their potential can’t be realized until we develop new, more viable technologies for electricity generation.
We see large scale implementation of solar collector farms and wind turbine fields, at significant cost and low efficiency levels exerting their own environmental impacts, at this point not fully determined. Many, if not most people don’t care to see large solar farms or wind turbines near their homes, particularly when the wind turbines aren’t maintained and produce nothing. Additionally, there is daily unreliability in that wind doesn’t always blow and the sun doesn’t always shine. Hydrogen powered vehicles are an exciting alternative, but at present, the large volume of fuel storage required per vehicle and lack of refueling stations makes them impractical.
Natural gas-powered vehicles are a good stop gap, but natural gas is not renewable, costs rise over time and emissions contribute to so-called greenhouse gases. A vehicular fueling distribution network must also be created for natural gas refueling as it doesn’t presently exist. Ethanol fuels on any large scale are an environmental and economic disaster worse than gasoline or diesel fuel. Ethanol production is causing food shortages and food cost increases, which worsen as ethanol production is increased. Ethanol, by the time it’s harvested, refined and used contributes more greenhouse emissions to our atmosphere than gasoline or diesel fuel, while simultaneously increasing food costs. It’s a non-starter.
Historically, utilization of geothermal energy in North America goes back about 10,000 years – roughly coincident with the first agricultural revolution beginning about 12,000 years ago. Paleo-Indians were known to use geothermal hot springs for warmth, cooking and cleaning by direct use. More recently geothermal energy has been utilized for many things such as food processing, producing electricity or for heating buildings, streets and sidewalks.
Regarding electricity generation, the first sizable geothermal electricity generating plant, a dry-steam plant was constructed in Larderello, Italy in 1904 and is still operational today. The first U.S. commercial geothermal power plant, called “The Geysers” in northern California began operation in the1960’s. The Geysers geothermal system today, is the largest single, renewable energy source in the world.
The United States currently adds about 3,000 megawatts of electricity to the national grid annually via geothermal means; a small portion of annual U.S. electricity production. Uncertainty regarding availability, renew-ability and cost of conventional fossil fuels along with potential thermal and environmental pollution, in conjunction with national security concerns, makes electricity production using geothermal heat an attractive alternative. The geothermal option has not, unfortunately, been without its own issues and costs.
Generally speaking, the temperature of earth’s crust (lithosphere) increases with depth at an average rate of 3°C per 100 meters of depth, though in most locations this ratio doesn’t hold until depths sufficient to stabilize temperatures have been obtained. In Iceland for example, this depth seems to be about 3,500 meters. Harnessing this heat energy at useful temperatures, say higher than 150°C under normal crust conditions requires drilling to great depth at investment costs rendering it economically undesirable. There are, however, geographic regions having pronounced geologic, or more importantly, geothermal anomalies, providing access to usefully high temperatures at relatively shallow depth. Heat energy can be mined in these areas at significantly reduced cost if done in an appropriate and safe manner. Iceland is one such location, where the Iceland Deep Drilling Project (IDDP) was initiated at the 2000 World Geothermal Congress. IDDP drilling is taking place along a rifted plate margin on a mid-ocean ridge; these ridges being geothermally productive areas.
Now serving as a modern-day example, Iceland’s Deep Drilling Project (IDDP-1), harvests 30 kg/s heated geothermal brine at 330 °C, 165 bars yielding 20 MW of power per geothermal well. In electrical energy terms, this is 20 MWh (20,000kWh) of electricity provided every 60 minutes per well. More interestingly, Iceland’s deep drilling project (IDDP-2), in January 2017 drilled in 168 days at Reykjanes, in southwestern Iceland, to a depth of 4,659 meters, reaching a temperature of 426 °C, 340 bars. Production testing will not be complete until sometime in 2018. Iceland’s work is exciting because properties of water reach a singularity at water’s critical temperature of 374 °C, 221 bars, where aqueous fluid is no longer a liquid nor a gas and has no boundary layer. This allows fine tuning of temperature and pressure for turbine related equipment rendering plant operations more easily controlled and efficient. More significantly, aqueous fluids maintained above critical temperatures can provide more than five times the power producing potential of the same fluid at 225 °C. You may recall, water boils at 100 °C (212 °F) near sea level, so these temperatures are very hot. IDDP’s modeling suggests a supercritical geothermal well may provide ten times the power output of today’s conventional geothermal wells.
Employing current relevant art forms, geothermal heat energy is typically extracted by pumping hot brine directly from an underground geothermal reservoir in hot dry rock (HDR), by pumping extraneous water under high pressure through the hot rock creating or augmenting a below ground reservoir. This involves fully opening existing rock fractures to maximize permeable flow; or may involve fracturing the rock (fracking), creating additional cracks, making it more permeable should the existing rock not be in a sufficiently fractured condition. Water is pumped into the below ground reservoir through a supply or injection well. Hot water or steam is removed from the underground reservoir through a return well and used to drive a turbine, which drives a generator producing electricity. Water is heated by the geothermal source as it passes through the fractured hot rock reservoir from the injection supply well to the return well. This system is currently employed in Iceland and other locations throughout the world. The innovative, closed Z Group geothermal system by the way, eliminates the need for such fracking.
Anyway, for today’s geothermal systems via the return well, heated water is pumped or in the case of steam may rise convectively to the surface where its useful thermal energy is used directly or can be converted to electrical energy. After using, the water may be re-circulated back to the reservoir to mine more heat or may be wasted. These fluids can be used for direct heating of structures, for food processing or more frequently for the generation of electricity using steam turbines employing what is known as the Rankine Cycle. Depending primarily on available temperature the type of electric generating plant may be a flash, dry steam or binary plant. Both Larderello, Italy and the Geysers in California are rare dry steam fields. In a dry steam field, steam, not fluid shoots up the well and powers the turbines.
What are some of the issues? Many patents have been issued over the years addressing toxicity and corrosiveness of geothermal brines, which are damaging to mechanical equipment, piping, etc. These patents, considered as a group, clearly demonstrate the types of difficulties encountered in attempting to mine geothermal heat energy using insitu or augmented brines. As mentioned above geologic formations yielding high temperature rock and/or fluids at shallow depths are economically attractive candidates for heat mining. Unfortunately, many, if not most of these formations are found in tectonically active locations, some of which experience significant faulting along with earthquake activity and in the case of active volcanoes, may experience flows of molten igneous material (magma) or airborne ash and debris. Applying geothermal technology inappropriately within such a tectonically active area can be unsafe and from an investment standpoint must be characterized as high risk. Careful selection of safe geothermally productive sites is therefore critical to the future exploitation of geothermal energy in any form.
A second issue in various locations is legal. Some geothermally active formations are located within scenic areas or even within national parks like Yellowstone National Park. These areas are inviolate. For example, per the Geothermal Steam Act of 1970 and as amended in 1988 “certain lands, including lands within units of the National Park System are closed to federal geothermal leasing”.
Another significant issue involves direct use of geothermal fluids as is typical today. These below ground geothermal fluids; sometimes called brines due to their high mineral content can contain other potential contaminants such as sulfur, boron and arsenic. Such fluid can be highly corrosive and direct use thereof can be damaging to equipment, obviously increasing operation and maintenance costs. This has resulted in several new patents over the years directly related to improving equipment usability and reliability as well as to developing processes for removing contaminants prior to use and/or after using. The direct use of brines pumped from geothermal reservoirs is costly from an anti-corrosion standpoint, but perhaps more so by limitations of “renewability”, which in some ways becomes the most significant issue regarding future investment in geothermal energy. Underground brine reservoirs can be depleted just as ground water can.
Underground geothermal reservoirs are renewable if rain continues to fall above ground and the earth’s core remains hot. There are, however, serious limitations on the rate at which these insitu brines can be removed from the reservoir and replenished. If geothermal brine is removed from the reservoir at rates higher than that at which the aquifer can recharge itself; fluid levels within the reservoir will drop over time, resulting in a necessary increase in pumping cost at the least and in the worst case, diminishment of the resource for useful purposes.
The situation described above has occurred at The Geysers in California over the last two decades resulting in less fluid being pumped and less electricity being produced. The Geyser circumstance was largely resolved by the world’s first wastewater-to-electricity system (Southeast Geysers Effluent Pipeline), which conveys water from Clear Lake and wastewater effluent from Lake County, both of which are used to replenish the Geysers underground geothermal reservoir(s), increasing electric production capacity. The Geyser’s situation was dealt with at significant expense via conveyance from an outside water source located many miles away to replenish reservoir levels using injection wells.
As touched on previously, another relevant art form fractures the hot dry rock if not sufficiently permeable and pumps water down into the rock fractures under high pressure to be heated, then extracted. This process has been successful, but raises serious questions regarding potential long term environmental effects of artificially injecting large quantities of water into what has historically been dry rock strata. Such systems are employed in Iceland and have been in use for a long period of time both in generation of electricity and for direct use in heating and food processing. Additionally, some researchers believe hydraulic fracturing, sometimes called fracking may stimulate earthquake activity in tectonically sensitive areas.
The list of problems historically associated with using and harvesting geothermal energy sources is not particularly long. It is none-the-less a serious list posing rather costly solutions.
In determining whether a geothermal electric generating plant should be built and in determining the size of plant to be built; a cost-benefit analysis must be performed. A major component of this analysis is estimated future revenue generated through sales of electricity produced both to pay back initial capital investment as well as providing a reasonable dividend to shareholders. Uncertainty regarding future reservoir levels means uncertainty regarding future electricity production, meaning uncertainty regarding future revenue streams, meaning increasing investment risk. This increased risk is significant as capital investments required are substantial.
One last complication regarding direct use of geothermal brines is environmental. Vaporization of insitu geothermal fluids employed to drive a steam turbine and subsequent condensation back to liquid tends to bring contaminants out of solution. Direct discharge of untreated brine back into the reservoir or to a local river or lake can result in chemical pollution. Treatment of this brine is an additional cost.
Direct discharge of un-cooled geothermal brines to a lake or river can result in thermal pollution. This is serious as an increase as small as 4°C within a water course can be fatal to fish and harmful to aquatic plants. Some geothermal electricity generating plants reinject treated brine back into the underground reservoir. Some plants cool and waste treated brine to a local water course. In either case, both treatment and cooling of vast quantities of geothermal fluid add significantly to the cost of electricity production by currently applied geothermal technologies. Added cost is added financial risk.
Given uncertainties of maintaining underground reservoir levels and high costs of recharging diminishing reservoir levels with pumped surface water; it would reduce both investment and power supply risks significantly if there were a way to by-pass or eliminate direct use of geothermal brines altogether.
As you may have already guessed, Z Group Energy has developed such a system and that system was patented in February 2013 as U.S. Patent #8,381,523 B2. The Z Group system is a closed, geothermal system eliminating all use of insitu, corrosive or toxic geothermal brines, eliminates any need for fracking and emissions from which, are nothing more than H2O, that is water. Our patent is entitled GEOTHERMAL ELECTRICITY PRODUCTION METHODS AND GEOTHERMAL ENERGY COLLECTION SYSTEMS. We’ll delve into that system in later posts.
If you have questions regarding the Z Group Energy system, I can be contacted at: firstname.lastname@example.org. You can also message me on any page of our website; comment on our Facebook Page; or comment on our YouTube Channel – Z Group Energy. Thank you so much for your interest in this important industry.
 Ronald DiPippo, “Chapter 11 – Larderello Dry-Steam Power Plants, Tuscany, Italy,” in Geothermal Power Plants (Third Edition) (Boston: Butterworth-Heinemann, 2012), 249–68, doi:10.1016/B978-0-08-098206-9.00011-7.
 “About Geothermal Energy | Calpine Corporation,” accessed July 22, 2017, http://www.geysers.com/geothermal.aspx.
 John, “Geothermal Investments | Off The Grid News,” accessed July 22, 2017, http://www.offthegridnews.com/grid-threats/geothermal-investments/.
 “International Geothermal Association: The World Geothermal Congress,” accessed July 22, 2017, https://www.geothermal-energy.org/conferences_events/the_world_geothermal_congress.html.
 A-to-Z Guide to Thermodynamics, Heat and Mass Transfer, and Fluids Engineering: AtoZ (Begellhouse, 2006).
 “The Water Story | Calpine Corporation,” accessed July 22, 2017, http://www.geysers.com/water.aspx.