Puna Geothermal Venture
Power Generation
Plant technician Taylor Sumida monitoring field equipment.
Geothermal energy is a top source of renewable energy, better than solar or wind. When the wind doesn’t blow and the sun doesn’t shine, the heat from the volcano continues to produce a steady flow of power.
The heat from Earth’s core continuously flows outward. When temperatures and pressures become high enough, some of the surrounding rock melts, becoming magma. Because it is lighter, the magma rises, moving slowly up toward Earth’s crust, carrying with it the heat from below.
Sometimes the hot magma reaches the surface, where we know it as lava. Kilauea Volcano on the Big Island of Hawaii, for example, has been actively spewing lava since the 1980s. Most often the magma remains below Earth’s crust, heating nearby rock, rainwater and seawater that has seeped deep into the earth. Some of this hot water travels back up through faults and cracks and reaches Earth’s surface as hot springs or geysers. Most of it stays deep underground, trapped in cracks and porous rock. This natural collection of hot water is called a geothermal reservoir.
Once geothermal waters reach the surface, the steam is sent to the power plant and used to drive generators to produce electricity, and the brine and gases are re-injected back into the injection zone below the water table. Combined, Puna Geothermal Venture’s five production wells normally produce an average of two million pounds of geothermal fluid per hour. Like wells in other volcanic regions (Indonesia, Philippines and Iceland), PGV’s wells are considered prolific in comparison to other types of geothermal wells in the industry.
There are three types of power-generating plants: dry steam, flash steam and binary cycle. Dry steam plants, first used in Italy more than 100 years ago, route the steam directly to a power plant to produce electricity. Dry steam plants are used in places such as The Geysers in California, where steam is close to the surface. Flash steam power plants cause the fluid to rapidly vaporize, driving turbines that in turn drive a generator. Binary-cycle plants are similar and the most advanced. Their closed-loop circulation system means that no excess gases or fluids reach the open air. PGV’s power plant utilizes the closed-loop binary system.