Popular hot springs in Japan co-exist with binary geothermal power plants

Japanese people love Onsen, or hot springs, to relax and feel rejuvenated in naturally heated, spring water, which is rich in minerals. Hot springs are located in mountains, next to rivers, near oceans, and basically everywhere due to the abundance of active volcanoes present in Japan. In fact, there are 27,405 identified hot spring wells and over 21,000 combined hot spring spas and inns, according to 2014 data published by the nation’s Ministry of Environment.

Over 126 million people visit Onsens annually, spending considerable amount of money at spas, hotels, restaurants, and shops at hot springs. Because of the significant economic activities related to tourism, local communities didn’t think that Onsen business and geothermal power plants could co-exist.

Show right: Yumura Hot Springs in Hyogo prefecture, Credit: The Town of Shinonsen

They were concerned that deployment of geothermal power plants would change the quality and compositions of spring water, which contains a lot of organic matter that is known to provide health and beauty benefits. Most importantly, the community feared that geothermal power plants would dry up their precious spring water wells. Their concerns were eliminated when binary geothermal power plants were introduced.

Nation’s First Binary System Installed at an Evacuation Site

Yumura Onsen in Shinonsen town, Hyogo prefecture, installed two 20 kW (a total of 40 kW) binary geothermal power plants at Yakushiyu, a day spa, which also is a state designated evacuation site where people in the community can assemble in the case of emergencies or disasters.

“Onsen” Binary Geothermal Systems (2 x 20 kW), Credit: The Town of Shinonsen

Binary geothermal power plants, or “Onsen” Binary plants, use chemical fluids known as a second liquid (e.g., Isobutene and n-Pentane) that boils at a lower temperature than water. Hot spring water passes through a heat exchanger and heats up the second liquid in a closed loop. Heat from the geothermal water causes the secondary fluid to flash to vapor, which then drives the turbines, and subsequently the generators. The vapor is condensed back to liquid and begins the cycle again. Because this is a closed-loop system, virtually nothing is emitted to the atmosphere.

One advantage of Onsen binary systems is to be able to operate with lower temperature waters at around 100 degrees Celsius (C) (212 degrees Fahrenheit (F)).

“Since we didn’t plan to make steam or flash cycle geothermal plants – which require very high temperature geothermal fluids – we didn’t need to find and dig new wells,” Kaoru Taniguchi, a worker at Department of Local Deployment, Town of Shinonsen, said. “We just installed a geothermal system at a spa where abundant hot water existed.”

At Yumura Onsen, when geothermal water enters into the binary system, the temperature is around 90 degrees C (194 degrees F) and after water gives away heat to the second liquid, water temperature goes down to 65 degrees C (149 degrees F). The hot spring water, which never comes into direct contact with the second liquid, is then used at spas for tourists and later injected back into the ground to be reheated.

Simplified diagram of a “Onsen” binary geothermal plant at Yumura Onsen, Credit: The Town of Shinonsen

“At the very beginning, some community members worried that we would lose our spring water,” Taniguchi said. “We explained that we don’t lose water. To generate electricity, we only lose some heat from spring water, which is already available at the ground surface. Once they understood that we don’t dig new wells and draw extra water from the underground, we got their blessings.” Last year, the system generated about 140 MWh of electricity, out of which about 72 MWh is used at Yakushiyu spa and charge an energy storage (10 kW).

Revitalizing the Onsen community after the Fukushima Disasters

Tsuchiyu, a hot springs community, near Fukushima city, Fukushima prefecture, completed a 400 kW binary geothermal plant in November. “Our hot springs used to attract 230,000 visitors a year,” Katsuichi Kato, president of Genki Up Tsuchiyu Company, said. “After the Fukushima nuclear melt-down followed by tsunami disasters in March 2011, we lost significant numbers of tourists and five out of 16 inns became out of business. Among those who remain in business, we pondered how to revitalize our community and we chose renewable energy.”

Genki Up Tsuchiyu is organized by members of the Tsuchiyu Onsen Cooperative.

400-kW Onsen Binary Geothermal Power Plant at Tsuchiyu, Fukushima Prefecture, Credit: Genki Up Tsuchiyu Company

Prior to the development, he assured his cooperative members that the amount, quality and temperature of the hot springs would not change. “Since we could use the existing wells, instead of finding and drilling a new one, the project posed a very low risk for us,” Kato said. The company chose Nevada-based Ormat Technologies to develop the plant. “When we started planning [the plant] four years ago, Ormat had extensive knowledge and experience of developing binary geothermal power plants, while here in Japan companies were still conducting field tests with their systems,” Kato said.

The Tsuchiyu Onsen Binary possesses a unique feature in order to take advantage of the natural resources that exist in the community: two types of water. Geothermal water from the existing well has temperatures of around 100 degrees C (212 degrees F). The water is used to heat n-Pentane, a secondary liquid, which is vaporized to turn the turbines. In order to cool and condense the secondary liquid, cold water from a nearby lake in the mountain is drawn into the system. The temperature of the mountain water is about 10 degrees C (50 degrees F).

Cool mountain water is used as a coolant for the geothermal power plant at Tsuchiyu Hot Springs in Fukushima Prefecture, Credit: Genki Up Tsuchiyu Company

After the generation cycle, the temperature of the hot spring water is reduced by 30 degrees C to about 70 degrees C (158 degrees F) while the temperature of the mountain water goes up by 10 degrees C to about 20 degrees C (68 degrees F). The hot spring water and mountain water are then mixed together to use at nearby spas for visitors. Genki Up Tsuchiyu is currently considering the use of the subsequent recycled mountain water for fish farming or greenhouse fruit cultivation.

The National Government to Increase its Support for Geothermal

Although Japan has the world's third largest geothermal reserves, the nation has only installed about 530 MW of geothermal power capacity. The nation launched the feed-in tariff (FIT) program in 2012 to increase the deployment of renewable energy, including geothermal power, however, only 10 MW of geothermal power has been developed during the last three years, compared to about 22 GW of solar photovoltaic (PV).

To increase the deployment of geothermal power, the national government has recently created a special entity called the Japan Oil, Gas and Metals National Corporation (JOGMEC). JOGMEC provided the first loan guarantees to the Onsen Binary at Tsuchiyu hot springs. The total project cost of the plant was 700 million yen ($5.7 million). The company received a subsidy of 100 million yen ($812,000) from the Ministry of Economy, Trade and industry (METI) and received a loan guarantee on the remaining 600 million yen from JOGMEC.

“Since we didn’t have any collateral, [the loan guarantee from JOGME] helped us to secure commercial loans,” Kato said. The company also utilizes the FIT. All electricity generated from the binary system, except for electricity consumed to operate the condenser, is sold to its local utility company, Tohoku Electric Power Co., at a rate of 40 yen/kWh ($0.32/kWh) for 15 years. Kato said the company will try to pay off the loan as soon as possible with the revenue generated by the FIT and start re-directing the proceeds to rebuild and revitalize the town. He also has a vision to make the town powered by 100 percent renewable energy, which is aligned with the goal created by Fukushima prefecture (100 percent renewable by 2040).

Binary geothermal power technology allows communities to re-utilize existing hot spring wells, and since they can be deployed in small scale, they can be used as distribution generations to support local sustainability. Under the nation’s new energy policy for 2030, between 1.4 GW and 1.55 GW worth of geothermal energy is planned to be deployed.

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