Hydrothermal energy, which is also known as conventional geothermal energy, is formed “when water is heated in the earth” and “hot water or steam is trapped in porous and fractured rocks beneath a layer of relatively impermeable caprock,” according to the Department of Energy’s Office of Energy Efficiency & Renewable Energy. This results in what is known as a “hydrothermal reservoir” where the hot water or steam can be tapped by drilling and then brought to the surface to generate electricity. Hydrothermal reservoirs typically occur where tectonic plates meet or in areas of high volcanic activity.
The Puna Geothermal Venture (PGV), which has been in operation on the Big Island of Hawai’i since 1993, harnesses the steam from hydrothermal reservoirs heated by underground magma. Geothermal electricity generation at PGV involves two cycles. In one of the cycles, the steam is harvested from a production well and passes through a separator, where the steam is separated from the brine. The steam is then directed through a geothermal combined cycle, where it initially turns a turbine at level I, thus generating electricity, and then passes through a vaporizer system. The steam is then directed from this vaporizer system to a second turbine at level II, where it generates more electricity, and then passes upward into a condenser where the steam is returned to a liquid state. The non-condensable gasses in the steam are sent to a so-called abatement system and the rest of the condensate is injected back into the ground via an injection well.
Meanwhile, the second of the two cycles involves directing the brine from the initial separator on the system through a binary cycle, where it is turned into steam in a vaporizer, directed to a turbine, and used to generate electricity before being sent to the condenser. The resulting condensate is then reinjected via an injection well and any non-condensable gasses are sent to the abatement system. I recently had the pleasure of touring the facility, where Plant Manager Jordan Hara explained that each “injection pipe is lined with a sleeve filled with nitrogen to prevent brine intrusion into the groundwater.” These sleeves extend down 3000 feet, which is “a good distance beyond the water table,” said Hara.
According to Mike Kaleikini, vice president of Community Affairs, PGV “has a contract with Hawaiian Electric to provide 38 megawatts of clean, renewable, geothermal energy.” To put that into perspective, one megawatt of electricity is enough to power about 800 to 1,000 homes. “Since 1993,” said Kaleikini, “the amount of renewable energy that … has been delivered by PGV has displaced the need to burn over 141 million gallons of oil.” However, the PGV plant was nearly destroyed by a months-long eruption of the nearby Kīlauea Volcano, which began in early May 2018. The dramatic eruption ultimately produced about one billion cubic yards of lava that altered the landscape and destroyed about 700 homes. The geothermal electricity plant, which is located on an elevated knoll, “found itself surrounded entirely by lava,” according to Kaleikini. Although the facility itself was largely untouched, several of the wells and transmission lines were compromised and all roads to the facility were blocked by lava. Fortunately, the company was able to protect nearly all of the wells with “cast iron bridge plugs” to protect them against lava intrusion, according to Drew Spake, a project geologist at the site.
After many months of painstaking recovery efforts, PGV was able to bring all but one of its wells back online and regained operational status in November of 2020. According to Kaleikini, Hawaii’s “Public Utilities Commission, the PUC, conditionally approved an amended and restated power purchase agreement” in March of 2022. “The agreement will allow PGV to decommission the existing, older generating units and replace them with three, more modern generating units … and the best part of it is that the three new units that are replacing the twelve older units will be able to generate 8 more megawatts with the same amount of geothermal resource that we are using today for the 38 megawatts.” These efforts are intended to help Hawai’i achieve its goal “to be on 100% renewable energy by 2045,” said Kaleikini.
Geothermal energy uses about 1 to 8 acres per megawatt hour generated, while coal uses about 19 acres per megawatt. According to Hara, “Geothermal also uses only about 1% of the land required for solar and 3% of the land required for wind power.” When asked why geothermal makes so much sense in Hawai’i, Hara responded: “Not only do we have an awesome geothermal resource here but … [geothermal] requires a smaller physical footprint compared to other energy sources, which is critical on an island where land is so limited and expensive.”
Visit punageothermalproject.com to learn more.
Trey Gerfers serves as general manager of the Presidio County Underground Water Conservation District. A San Antonio native, he has lived in Marfa since 2013 and can be reached at tgerfers@pcuwcd.org.