PGV provides power for some 30,000 Big Island homes and businesses, using steam produced deep in the East Rift Zone of the volcano to power the company's turbines in Pohoiki.

To generate that same electricity from a traditional oil-fired power plant, the state would have to import an additional 400,000 barrels of oil each year. PGV is the state's second-largest single renewable energy producer, after O'ahu's garbage-burning H-Power plant.

In these times of sky-high oil prices and instability in the Middle East, that might look like slam-dunk justification for quickly expanding geothermal production, but it isn't that simple.

PGV obtained government approvals six years ago to double its production from 30 megawatts to 60 megawatts, but the company still hasn't installed the equipment necessary to produce the extra power. A megawatt is enough power to run about 1,000 homes.

Hawaii Electric Light Co. President Warren Lee said HELCO probably won't need another 25 megawatts from PGV until about 2020 because HELCO has a comfortable margin of extra generation capacity.

Part of the reason HELCO won't need more power from PGV sooner is that HELCO and independent power producer Hamakua Energy Partners added modern and highly efficient new generators in Keahole and Hamakua during the past seven years.

HELCO also has plans to boost power production still more at Keahole in 2009 by installing new equipment to generate another 18 megawatts from waste heat generated by the company's new diesel turbines, Lee said.

That is why the infamous Big Island rolling blackouts of the early 1990s, when demand for power outstripped HELCO's ability to generate electricity, are a fading memory.

But the new petroleum-fired plants also mean HELCO won't need another large block of geothermal power for many years to come, and HELCO is Puna Geothermal Venture's only customer.

"We wouldn't just go up to 60 megawatts if there's no need for it," said Barry Mizuno, PGV's former general manager and financial manager, and now a consultant for the company. "We need a market for the electricity that we generate."

HELCO has been negotiating off and on for years with PGV for a modest boost of about eight additional megawatts of geothermal power, but it isn't clear when a contract for the additional power might be finalized.

Lee said whether the utility buys more power from PGV will depend on the price and whether PGV is reliable.

PGV has had difficulty in recent years just delivering the 30 megawatts it is required to provide under its existing contract, and recently the company has produced an average of only about 25 megawatts, Lee said.

Plant Manager Mike Kaleikini said PGV, which is owned by Ormat Technologies Inc., has been having problems since the middle of last year, but expects to be back to full production in April.

The most recent work included clearing out obstructions in two production wells used to extract the superheated water and steam from underground, and crews also repaired the walls of an injection well, which is used to pump fluid into the ground after it has been used to produce electricity.

PGV also redrilled a fourth well to convert it from an injection well to an extraction well, part of $32 million in upgrades to the plant since it was purchased by Ormat Technologies in 2004.

Serious discussions with HELCO over PGV's plan to produce more power were put on hold when the plant began to have problems last year, Kaleikini said. He said he doesn't expect serious talks to resume until power production is back up.

"It's a reasonable thing, and that's what we need to do," he said. "We need to honor our existing contract before we can ask for more."

Lee pointed out that even when HELCO might need significant amounts of additional power in about 2020, there is no guarantee that PGV will be the supplier. The state Public Utilities Commission will require that prospective providers competitively bid for the right to deliver that power, Lee said.

Other uses for geothermal power besides selling it to the operator of the Big Island power grid have been investigated, but those uses probably are years off.

State and utility officials studied the idea of laying undersea cable to move electricity from geothermal sources under the Big Island to the much larger electrical market on O'ahu, but laying the cable proved to be too expensive for the plan to work.

More recently, there has been interest in the idea of using geothermal power to produce hydrogen, which would then be used for other types of power generation, or as a transportation fuel, said Maurice Kaya, chief technology officer for the state Department of Business, Economic Development and Tourism.

Kaya said the state has been working with the federal Department of Energy to investigate that possibility, although widespread commercial use of hydrogen for energy is generally regarded as a decade or more off.

"While it has not been as visible, we've not lost our enthusiasm for the potential for geothermal energy on the Big Island," Kaya said.

Reach Kevin Dayton at kdayton@honoluluadvertiser.com.