Geothermal Power Generation via Unused Heat from Hot Springs

Overview

Every day, approximately 15,000 tons of hot springs water at a temperature of 100°C flow out from 27 sources at Obama Onsen, one of the tourist destinations in Unzen City, Nagasaki. However, approx. 70% of the hot springs water is unused and is disposed of into Tachibana Gulf, where a magma chamber is said to exist at the bottom of the sea.

In 2013, General Incorporated Association Obama Onsen Energy, in which local residents participate, built Obama Onsen Binary Cycle Power Station with a subsidy from Japan’s Ministry of the Environment for the purpose of effectively utilizing unused hot springs water and expanding the use of natural energy. After a three-year trial period, SymEnergy, a domestic Japanese company, started operating the power plant to supply electricity for approximately 149 households. Furthermore, as the power plant has been selected as one of the tourist sites for the Obama Eco Tour, it has now become a tourist attraction.

In the process, however, the local government’s plans were suspended due to residents’ opposition to binary-cycle power generation involving the drilling of hot springs. With Unzen City drawing on this experience, in 2021, for any developers planning to construct a geothermal power plant, an ordinance came into effect requiring that the consent of residents be obtained. Then, in 2023, the city announced that it is aiming to become a zero-carbon city by 2050 and is working to expand renewable forms of energy, including geothermal power generation.

Successful outcomes

• Electricity sales have amounted to approx. 790,000 kWh annually, creating sales of approx. 31.6 million yen. The electricity provides for approx. 149 average households.
• The CO2 reduction is equivalent to 888 t-CO2 per year.
• In total, 2,437 people (178 groups) visited the site from across Japan and overseas in 2013.

The first step toward carbon neutrality via geothermal power generation and enriching the local area

Unzen City, with a population of about 41,200 people, is located on the Shimabara Peninsula and features a beautiful sea with rich marine resources. The steamy volcanic landscape is designated as a national park, while the fault landforms are designated as a geopark.

In the 1980s, Japan’s New Energy and Industrial Technology Development Organization (NEDO) conducted the first geothermal development survey in the former Obama Town (now Unzen City), but continued surveys were suspended due to strong opposition from residents. About 20 years later, in 2004, the town was approved as a special zone for renewable energy by the national government and applied to the prefectural government for a permit to drill hot springs in order to introduce geothermal binary-cycle power generation. However, the local government’s plan was not realized due to opposition from the Association to Protect Hot Springs, a group of hot spring business owners and residents concerned about depletion of the water source and pollution. The main reasons for not being able to build consensus involved the corporate and municipal initiative to promote the project and inadequate consultation with the local community.

A turning point came in 2010. Unzen City, where the hot springs are located, and Nagasaki University’s Faculty of Environmental Science collaborated to propose a demonstration experiment of binary-cycle power generation using existing hot springs without drilling. At that time, drawing from the lessons learned from the past, a council (General Incorporated Association Obama Onsen Energy) was established with local residents as the main body, and the geothermal power generation project was realized under the leadership of local residents.

Mr. Hiroshi SASAKI of the New Energy Promotion Team, Environmental Policy Division of Unzen City said: “We spent sufficient time in discussion with residents. The project differed from past projects in that it was not premised on commercialization but rather conveyed the intention to demonstrate what we can achieve by using the source of the hot springs already owned by the city. The hot springs business owners also wanted to make use of the unused hot springs heat.”

During the three-year trial period, the amount of electricity generated by the facilities, the effect of reducing CO₂ emissions, and business feasibility were verified. However, it was discovered that components in the hot springs water adhered to pipes and heat exchangers, making them as hard as concrete and greatly reducing power generation efficiency. Research continued, and countermeasures for hot springs scaling were in place by the time when management was handed over to a private company; however, a complete solution is yet to be found.

Japan has limited energy resources, and its energy self-sufficiency rate is low, at 11.3% (2020). Unzen City is also losing approximately 3.7 billion yen (2015) in energy costs to outside the local area, and the municipal government intends to promote the local production for local consumption of energy by utilizing geothermal and other natural energy sources. In 2021, the city enacted an ordinance on the protection and utilization of geothermal resources. In addition, the research & development of low-cost compact geothermal binary-cycle power generators will be conducted so that local companies, such as hot springs and accommodations businesses, can generate their own electricity by utilizing existing hot springs, and methods will be explored to reuse hot springs water used at the power plant as a heat source for bathing and aquaculture. In the future, the goal is to start a power generation business that can return profits from geothermal power sales to the local community by providing for the welfare of residents (e.g., support for school lunch expenses).

Obama Onsen Binary Cycle Power Station

Unzen City and SymEnergy
http://obamaonsen-pj.jp/

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