Economics

A critical, though not often discussed economic component of supercritical geothermal energy, at least indirectly, in terms of cost is corrosion resistance of metal component parts for a sealed, supercritical system.  ZGE has been following R & D regarding the corrosion response of various materials within a supercritical water (SCW) environment for some time.  Of recent note, we refer you to a Science Direct article citing Annals of Nuclear Energy, Volume 127, pages 351 – 363, dated May 2019 entitled Resistance of Candidate Cladding Material for Supercritical Water Reactor, summarizing studies conducted at Shanghai Jiao Tong University.  This work concerns corrosion test results for candidate materials such as ferritic/martensitic (F/M) steel, austenitic stainless steel, alumina-forming austenitic (AFA) stainless steel and oxide dispersion strengthened (ODS) steel.  Results suggest high Cr content austenitic stainless steel, proper Cr content AFA stainless steel, and ODS steel are promising cladding materials for SCW conditions as they each demonstrate satisfactory corrosion resistance up to 650°C.  Note this research as cited, relates to water reactors specifically, but applies directly to our geothermal work as well.

ZGE is developing a 10-year cash flow proforma for interested parties.  This conservative proforma is based on a new 409 MW plant and will be available in December 2020.

ZGE conceptual estimates suggest the capital cost for a new 409 MW, sealed, supercritical, geothermal well field and power plant in a geothermally active area to be approximately $640 million.  Assuming Operation and Maintenance expenses of $0.01/kWh, the cost of power from such a plant would be ± $0.025/kWh.   At 20% margin this power could be sold for ± $0.03/kWh.

Note that deep drilling costs vary per geographic location.  This estimate for a 409 MW plant assumes 15 wells (heat exchange cylinders) drilled at 8,000 vertical meters each.  Worksheet production and cost calculations are predicated on maintaining very high temperature conditions in the pressurized Exchange Chamber at all times for maximal power production, though the ZGE Closed System can operate cost competitively at lower temperatures and pressures.

Note that 8,000 m  – 12,000 m is the expected maximum range for economically feasible drilling depths to be found in geothermally favorable areas such as Central Arizona, Northern California, Northern Nevada, Southeastern Oregon, Southeastern Idaho, Northwestern Utah, West-Central Colorado and Northwestern Wyoming.  Note the Yellowstone National Park area is off-limits for geothermal energy harvesting.  {Favorable equates to higher subsurface temperatures at relatively shallow drilling depths.  Please refer to the NREL Map provided below.}  Note that many tectonically active areas experience magma intrusions where temperatures of 500°C to 600°C are reached at depths as shallow as ± 5,000 meters.

Please give us a call if you have questions, would like additional information or are just curious about closed supercritical production of steam for electricity generation.

Deep Ocean Vent
(Photo from Photo Bucket)

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Map by NREL.

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Geothermal Energy potential exists in some surprising places, even in ZGE’s home-state of Arizona. A 1978 report entitled Potential Geothermal Energy in Arizona by W.R. Hahman, Sr., D.H. White, and David Wolf states the Curie Point across much of central Arizona can be found at depths of 5km – 10km at a temperature of 575°C. The Curie Point, named after Pierre Curie, is the temperature above which magnetic materials lose their permanent magnetic properties, though these properties can usually be replaced by induced magnetism.