Large-scale Geothermal "Flash" Technology: The San Jacinto-Tizate geothermal project

For the latest example of a classic, large-scale geothermal power plant technology, one must travel all the way to Nicaragua. Using so-called “flash” technology, the San Jacinto-Tizate project is a perfect example of where a pressurized hot brine is “flashed” into turbine-worthy steam.

Nicaragua recently welcomed the completion of this new geothermal power plant, installed near León, not far from the country’s capital of Managua. The San Jacinto-Tizate plant contributes approximately 70 megawatts (MW) of additional electric generation capacity, amounting to a 10% increase in Nicaragua’s power-generation fleet. San Jacinto’s power output has the additional charms of being clean, sustainable, and highly reliable—it harvests energy from underground hydrothermal reservoirs, heated by Nicaragua’s lively volcanic underpinnings.
 
Nicaragua is located on the circumpacific “Ring of Fire,” the gigantic volcanic activity zone where many of the world’s geothermal power-generation resources are found. To fuel the San Jacinto-Tizate power plant, extremely hot brine found hundreds to thousands of meters below the surface is accessed by production wells. The resulting mix of steam and brine is separated, the steam is used to drive turbine-generator sets, and the spent brine and condensate are returned to the reservoir via a different set of injection wells.

Other geothermal generation technologies are also in use, including binary technology applied to lower-temperature resources, and dry steam technology used in some rare areas where wells deliver dry, turbine-quality steam. But, flash technology remains the worldwide, utility-scale geothermal generation workhorse. There are approximately 10,000 MW of geothermal generation capacity in place throughout the world, with additional capacity now being added rapidly in California, Africa, Indonesia, Mexico, Turkey, and the Philippines.

Boasting positive power
Whatever the technology used, a geothermal power plant is typically a significant and rewarding asset to its host grid and community. A geothermal power plant draws on the immense and implacable flow of heat from the earth’s hellish inner regions, and keeps producing around the clock and around the seasons, indifferent to night or day, wind or calm, cloud or tempest. Geothermal power plants typically boast annual availability of 90% and above.

In addition, geothermal plants are typically good neighbors, emitting little except for water vapor (if a wet cooling tower is employed), and small amounts of non-condensible gases contained in the steam from below. A geothermal plant complex has a small power-block footprint, connected to a network of above-ground pipes, which link the plant with production and injection wells.

In practice, another great charm of geothermal power generation—a highly salient charm in the case of the San Jacinto-Tizate plant—is that it can offset the use of higher-cost fuel sources and deliver power at a lower cost, insulated from the volatility of fuel-supply markets. This is a tremendous asset in many places in the world, such as Nicaragua, that might otherwise rely deeply on imported high-value fuels, such as distillates or LNG. The exploitation of geothermal energy for power production can also free up domestic high-value resources for higher-market applications or export markets.

Harnessing heat
Of course, there are challenges involved in harnessing the heat of the earth for utility-scale renewable power production. The initial stages of locating and developing a high-energy hydrothermal resource involve a respectable level of expense and risk, because the fuel asset is far underground and can only be inspected indirectly. The final test of candidate geothermal well sites, particularly in a pioneer field, involves drilling expensive wells to see if they’re producers. So, most pioneer reservoir development efforts budget for a certain number of sadder-but-wiser dry holes. (Drilling risk is much reduced in thoroughly known and explored fields, such as the Geysers and Imperial Valley fields in California.)

A geothermal power plant can typically produce power at a highly completive price per kilowatt-hour (kWh), reckoned over the project lifecycle. However, the financing profile of a geothermal project can be disconcerting to investors, since the entire lifecycle fuel supply (the geothermal reservoir and piping systems) must be capitalized right upfront. Moreover, geothermal resources typically change—in temperature, brine composition, and optimal well locations—over their lifecycle, guaranteeing additional intellectual stimulation for any owners and operators as a project advances in age.

A great undertaking
The finance and development road leading to the successful development of the San Jacinto-Tizate geothermal power plant was necessarily a long and cautious one, requiring preliminary resource development using pilot wells and an initial installation of proof-of-project backpressure steam generation units over more than a decade. A listing of all entities involved in the financing of the project required most of the capital letters in the Roman alphabet: NGOs, DBs, GMBHs, IMF, KFW, ETC. The developers and their advisors and bankers challenged themselves continually throughout the history of the project to design and develop a reliable renewable power plant that would repay its investors, and still generate electricity at rates advantageous to local ratepayers in Nicaragua.

Nicaragua is a country with great potential, but one that has encountered devastating calamities, including earthquakes, civil strife, and hurricanes. It’s one of the poorer nations in the Western Hemisphere, with GDP three orders of magnitude less than that of the United States.

One of the key contributors to economic growth anywhere is access to affordable energy. The San Jacinto-Tizate project, thanks to the efforts of principals in Nicaragua and supporters elsewhere, is a much-needed new contribution to the national life and economic health of the people of Nicaragua.


Power Engineers
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