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Unexplored Geothermal Potential May Offer Solution to Renewables' Reliability Problem

Courtesy Hawaii County Civil Defense

Hawaii is largely relying on solar panels and battery storage to achieve its 100 percent renewable electricity goal. But geothermal power offers the possibility of carbon-free energy without the inconsistency of solar and wind.

Currently, geothermal is not generating any electricity in Hawaii. Puna Geothermal Venture, the state’s only geothermal power plant, closed in 2018 after a near miss with a lava flow from nearby Kilauea Volcano.  

Prior to its closing, PGV supplied 31 percent of Hawaii Island’s electricity demand. The plant’s operator says it plans to reopen by the end of 2019.

Geothermal energy has only modest representation in for Hawaii’s energy portfolio. In 2018, prior to PGV’s closure, it supplied less than 4 percent of Hawaii’s total electricity production. Plans for the future include a modest increase in geothermal, but solar remains the dominant source.

But researchers at the University of Hawaii point out that most of the state has not been explored for geothermal potential, a process not unlike surveying for oil deposits.

Research recently presented by graduate student Ted Brennis with the Hawaii Groundwater and Geothermal Resources Center indicates that where resources are available, geothermal is competitive with wind and solar on both cost and land use.

He told HPR that Puna Geothermal Venture produces around 1 megawatt of power per acre of land it occupies, far more efficient than its renewable competitors.

“Solar resources generally occupy 5 to 10 acres per installed megawatt. Wind resources fluctuate between 30 and 100 acres per megawatt.”

Geothermal other main advantage is that it can provide what is called baseload capacity, the minimum amount of power needed to be on the grid at any given time.

While solar and wind output fluctuates seasonally and throughout the day, generation from geothermal can be adjusted in the same way a fossil fuel plant can increase or decrease output.

However, there are drawbacks. Surveying for geothermal resources can be costly and time consuming, with no guarantee suitable conditions will be found. Generating power from naturally hot water requires invasive drilling, and sometimes the use of hazardous chemicals.

Blowouts are also a possibility, in which hydrothermal fluids like sulfur dioxide and hydrogen sulfide are unexpectedly released into the atmosphere. Puna Geothermal venture experienced such an incident in 1991.

But Brennis cautions that “no renewable resource is perfect.” He points out that solar panels require the industrial scale mining of quartz, often sourced from open pit mines, and the use of hazardous industrial chemicals in the manufacturing process. Each 2 megawatt wind turbine needs around 700 tons of concrete, a major source of carbon emissions.

So can geothermal be a viable competitor to solar and wind father away from the active Kilauea Volcano? Brennis says that scientists believe the rest of Hawaii Island and Maui have strong potential for geothermal, but no one is really sure.

“That’s the key. We need to better characterize the potential across the rest of the state so we can plan effectively.”

Correction: The original version of this story stated that Puna Geothermal Venture supplied 25 percent of Hawaii Island's power. The actual value was 31 percent.

Ryan Finnerty was a producer on Hawaii Public Radio's local public affairs talkshow The Conversation.
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