Hawaii’s Big Island is setting an example for the world with its hydrothermal energy capturing operations. As we know, there’s an incredible volume of heat and lava under the state’s islands’ surfaces, and it’s this clean, naturally occurring energy that’s being harvested to generate renewable electricity.
Despite setbacks due to a month-long eruption of the Kīlauea Volcano that almost swallowed some of the geothermal plants around its base, operations are back on track. One energy company in particular, Puna Geothermal Venture (PGV), has been leading the pack in the sector for decades and showing others how it’s done.
Hawaii offers limitless geothermal energy to power its population
Hydrothermal energy and geothermal energy are two terms for the same thing: heat that exists beneath the surface of the Earth. This is a renewable resource that can be harvested for electricity generation by feeding water into a well system deep underground, where it’s heated and returned to the surface.
In some cases, steam or water (“brine”) already exists in hydrothermal reservoirs, where it can be tapped by drilling. These reservoirs typically occur in regions where tectonic plates meet or in areas of high volcanic activity. This is why Hawaii is the ideal place to source its electricity “fuel” from its naturally occurring subsurface heat.
PGV is at the top of its hydrothermal game after 30 years of energy operations
PGV has been operating on Hawaii’s Big Island since 1993 when geothermal mining was still a relatively new way to generate clean electricity. This makes the company one of the most experienced in the solar power industry in the world, and not even a volcanic eruption in its site of operations could shut it down.
PGV targets steam and brine in hydrothermal reservoirs that are created by superheated subsurface magma and the process involves two cycles.
The 1st cycle
In the first, the steam that’s harvested from a production well is passed through a separator to extract it from the brine. The steam then enters a geothermal combined cycle and turns a turbine at Level I, which produces electricity, before undergoing a vaporizing process.
The steam still has further to go, being directed to another turbine at Level II where even more electricity is generated. The next stop is the condenser, where the steam is converted back into a liquid state. Non-condensable gases are directed to what’s called an abatement system, and the rest of the condensed liquid is returned to the ground via an injection well.
The 2nd cycle
The next cycle of processes sees the brine collected from the initial separator undergoing a binary cycle where it’s vaporized and turned into steam. This steam powers another turbine to generate electricity and is then sent back to the condenser. The condensate is once again sent back underground via an injection well and non-condensable gases go to the abatement system.
The injection pipes used to send the liquid back beneath the surface are lined with a sleeve of liquid nitrogen, which ensures that the brine doesn’t intrude into the groundwater. These pipes extend 3,000 feet underground, which is a significant distance below the water table.
PGV operations were almost wiped out by a volcano
In May 2018, a month-long eruption of the Kīlauea Volcano began that saw around one billion cubic yards of lava cover the landscape and destroy about 700 homes. The landscape was irreversibly altered and PGV’s electricity plant, which is situated on a small hill, was completely surrounded by lava.
The facility escaped unscathed, but all roads to the site, several wells, and transmission lines were overrun. Fortunately, before the lava reached the wells, the company had sealed them with iron plugs, ensuring that no lava intruded into the shafts.
It took many months of recovery efforts, but PGV was able to salvage all of its wells except one, and regained operational status in November 2020. The plant is still serving as a model for other parts of the world looking to harness the power of underground heat to produce renewable electricity. The US Department of Energy is also realizing the potential of geothermal energy and doing what it can to facilitate development in the sector.