State to harness idle solar farm for fresh water

A state-owned technology park on Hawaii island, with help from a federal grant aimed at advancing technology to make nonpotable water drinkable, has found a way to repurpose an abandoned $20 million solar farm.

The Natural Energy Laboratory of Hawaii Authority in Kona recently won a $1.9 million U.S. Department of Energy grant to fund a proposal to turn seawater into fresh water more cheaply using unconventional solar panels.

NELHA, a state entity, plans to connect the idle solar farm of a now defunct former tenant to a planned desalination plant designed to remove salt from seawater under low pressure, known as forward osmosis, as opposed to the traditional reverse osmosis process, which requires high pressure and is more costly and energy intensive.

Under the proposal, seawater superheated by the solar array will be pulled through advanced polymer membranes at relatively low pressure.

The advantage, according to NELHA Executive Director Gregory Barbour, is that this system uses less energy and therefore costs less. It also doesn’t require electrical power, which allows such systems to work in places without electrical grid infrastructure.

“It is an exciting project perfectly suited for NELHA, which has a mission to be a demonstration site for sustainable technologies,” he said.

NELHA said it expects to desalinate water at a cost that’s 40 percent less than current state-of-the-art technology, where electricity can account for up to half of a desalination plant’s operating expenses.

The project will produce fresh water for NELHA tenant Cyanotech Corp., a company that grows microalgae in ponds and makes nutritional supplements.

Other partners in the project are California­-based water purification firm Trevi Systems Inc. and local freshwater think tank Hawaii First Water LLC.

The system is designed to produce 130,000 gallons of fresh water daily and will test the energy efficiency and durability of forward osmosis filter membranes from Trevi.

If the project succeeds, it could be scaled up as a new commercial technology, according to the Department of Energy.

The endeavor, dubbed the Hawaii SunShot Desal Project, is one of 14 proposals recently funded by the federal agency, which awarded a total of $21 million to projects in 11 states to advance desalination technology.

Under the Hawaii grant award, NELHA and its partners expect to contribute $2.3 million toward the project — $1.3 million from Trevi, $800,000 from NELHA and $200,000 from Cyanotech.

Barbour said winning the award is important for desalination technology and allows the state to make use of a failed $20 million system that was privately financed but also received state tax credits.

The system was built in 2009 by an affiliate of Sopogy Inc., a Honolulu-based firm that created a system using polished aluminum dishes to concentrate sunlight and make electricity.

Sopogy’s innovative system heated mineral oil or other heat-transferring liquids up to 500 degrees. This liquid would be circulated to create vapor for turning a turbine and generating electricity before being returned to the polished mirrors.

At NELHA, Sopogy installed 1,000 of its half-­barrel-shaped dishes on 4 acres to provide steam and hot water to some companies at the tech park while sending excess heat to turbines for electricity generation.

Sopogy said the electrical production piece of its solar farm could power the equivalent of about 250 homes and eliminate 2,000 barrels of imported oil annually. It was the biggest test of Sopogy’s technology at the time, and promised to pave the way for bigger applications using the system that the company said was about twice as efficient as standard solar panels.

However, Sopogy’s tech park system never performed to its full potential. Later, advances and price reductions in traditional solar panels upended Sopogy’s position, and the company folded in 2014. NELHA assumed ownership of the solar facilities after Sopogy defaulted on its lease.