New Hampshire, USA — Nearly one month after Typhoon Haiyan ravaged the Philippines, affecting more than 12 million people and killing almost 6,000, many residents are still sitting in the dark. The Superstorm not only decimated the islands’ transmission systems, it knocked out one of its main power sources — geothermal.
An aerial shot of the province of Leyte shows the extent of damage brought by Super Typhoon Haiyan in Leyte province, the Philippines, on Sunday, Nov. 10, 2013. Credit: Bloomberg.
Clustered on the hardest hit island of Leyte, geothermal plants were a sitting duck for Haiyan’s harshest wrath. All five plants located on the island, totaling more than 600 megawatts (MW) of capacity, were incapacitated immediately following the storm. But in the weeks that followed, two plants were able to start putting some power back onto the grid, and revealed that the type of technology used may make a life-changing difference.
“What happened in the Philippines is interesting,” said Nir Wolfe, vice president of sales and business development at Ormat Technologies. Rather than comment on the distinctions between coal, gas and geothermal plants, Wolfe suggested that observers “note the differences in the technology of the [geothermal] power plants.”
The Philippines sits on a cauldron of geothermal resources, otherwise known as the Ring of Fire. It is a geologic region containing nearly 400 volcanoes that extends in a horseshoe shape from the bottom tip of South America, up along the Pacific coast through North America, and looping back through Asia and down to New Zealand.
This environmental zone means that the Philippines ranks second in the world behind the U.S. for the most geothermal development, with more than 1,900 MW of capacity. Much of this growth took place in the 1990’s to curb the nation’s reliance on oil.
Traditional vs. Binary
Since the island sits on resources that can reach more than 600 degrees Fahrenheit, geothermal developers were able to build traditional steam turbine systems. In dry-steam systems, developers drill a production well to access geothermal fluids directly from underneath the earth’s surface. These fluids travel up the well and push through a turbine as steam, which produces electricity. The fluid is then replaced into the ground via a reinjection well.
Flash-steam plants are very similar, but the fluid is pumped at a very high pressure into a flash tank, which is held at a lower pressure. The difference in pressure causes the fluid to “flash” and create steam, which drives a turbine to create electricity. Traditional plants typically use water-based cooling towers to prevent over-heating.
Binary geothermal systems are able to produce electricity from much lower-temperature fluid. This is possible due to the use of a “working fluid,” which has a much lower boiling point than the traditional resource. Geothermal water travels up an injection well and back down into the earth in a closed loop. However, when the fluid reaches the surface it travels through a heat exchanger. Inside this exchanger, the geothermal water heats up the working fluid. The working fluid then turns into a gas, which drives the turbine and ultimately produces electricity. Binary plants typically use air-based cooling towers.
A Binary Advantage?
The two geothermal plants that are already producing electricity in the Philippines, the 132-MW Upper Mahaio and 39.2-MW Leyte Optimization, are both binary plants, while the remaining three plants use a traditional stream-turbine design. According to the Energy Development Corportation (EDC), which owns and operates the plants, the majority of the damage affected the cooling towers. Since water-based cooling towers are at a much higher elevation than air-cooled, they faced the brunt of the storm.
“Somehow the binary systems survived the disaster a little bit better. Maybe because they are a little bit more rugged. Maybe because they are a bit more low profile and can better withstand high winds,” said Wolfe. “It is an advantage that we see with low-profile power plants worldwide — they are very reliable for electricity generation, grid connection, and maybe even for withstanding weather conditions.”
Binary systems are likely more robust in high winds due to their design, agreed Halley Dickey, director of geothermal business development at TAS Energy, although he noted that “hurricane-force winds are tough no matter how you look at it — requiring very stout design.”
Not only are air-cooled binary systems lower-profile, they also can be activated and deactivated in phases, according to Wolfe. For this reason, both binary plants in the Philippines were able to start feeding 57 MW of capacity to the grid even though they were not fully operational.
Binary plants are brought online in much smaller phases than traditional plants — typically in 5, 10, 15 or 20-MW increments, explained Dickey, whereas traditional plants are brought online in large 50 to 100 plus-MW segments.
“[Binary plants] are able to be deployed quicker and in phases much more easily than traditional steam,” said Dickey. “Because of scale, traditional plants are designed as big as possible, making it a major undertaking.” It may also be more difficult to get larger segments online after damages like those brought on by Typhoon Haiyan.
The EDC hopes to bring at least 147 MW back online by the end of December, but predicts it will take up to one year to reach full operation.