Koyo Electric: Obama Onsen Binary Power Station

Infrastructure |
Binary Type Geothermal Power Generation
Facility Overview

About The Facility

It is a binary power generation using hot spring heat.At the Obama hot spring in Obama-machi, Unzen city, Nagasaki prefecture where this power plant is located, Obama Hot Spring Energy corporation has mainly led this project through collaboration with local officials such as hot spring ryokan, related administrative organizations such as prefecture / city, and institutions such as university / enterprise etc. It has been committed to community development and community creation by taking advantage of hot spring power generation such as cooperation with environmental education and Geopark tourism.

This power plant, after hot spring power generation demonstration project of the Ministry of the Environment over a three year period of fiscal 2013 from fiscal 2011. Koyo Electric purchase in June 2014, is what has been done to improve the construction of high efficiency. As the engineering company of hot spring binary power generation, we overall produce from the selection of a generator that is commensurate with the scale of the source, the various applications and design and construction, maintenance, up to finance.

Since April 2013, "Obama Onsen Geo-tour" planned by Obama hot spring tourism Association, it has been possible not only to see this power generation during city walk but also listen to the lecture including the story of the regional consensus in specialized course.

How We Work

In this power station, a power generation project using a binary power generation system capable of generating power even with low heat of around 100 degrees is being carried out. Binary power generation is a system that evaporates a medium with low boiling point such as Freon and turns the turbine, so it has the feature that it does not require deep excavation like ordinary geothermal power generation.

In addition, since the temperature of hot spring water is lowered by electricity generation, it can be used in heat utilization projects such as hot spring farming and large outdoor bath with secondary hot spring water.
After purchasing this power station, Koyo Electric conducts renovation work to improve business profitability and increase power generation efficiency, such as countermeasures to make hot spring scale less likely to adhere to piping, measures to reduce the in-house electric power consumption, etc. In particular, seawater cooling in hot spring binary power generation is the first case in Japan.

Contents of the Tour

1. Tour Type: Industrial Tour

2. Tour Contents:

  • Itinerary:
    • Introduction of the history of Obama Onsen Binary Power Generation plant.(50minutes)

    • Learn about the obstacle about hot-springs mineral deposits and the solutions to deal with it. (20minutes)

    • Learn the mechanism of power generation and overview of the facility, visit the facility such as the heat exchanger. (20 minutes)

    • Get to know more about this power plant.(20minutes)

  • Acceptance Conditions:

    • Opening Time:Weekday

    • Start Time:9AM or 3PM

    • Tour Time Required:120min

    • Price :3,000 yen per person(20 people above -10%)

      • If you stay at the Obama Onsen, the price will be 2,000 yen per person.

      • Material fee is included into the tour price

  • Meeting Spot::

    • Unzen E-Canledge Communication center

Visit Us

We develop the energy creation business with the idea of " energy resources are those of the land " in power development business.

We are working on the development of various renewable energy aiming for "local production of energy from the energy" and "small-scale distributed energy society".

We look forward to your visit.

Make an inquiry to visit the facility by clicking the button above.
Obama Onsen Binary Power Station
Where We Are
Obamacho Marina, Unzen, Nagasaki Prefecture 854-0517
Facility Owner Profile
Facility Owner Name
Koyo Electric Co.
3 Chome-7-14 Sumiyoshimiyamachi, Higashinada-ku, Kōbe-shi, Hyōgo-ken 658-0053
Capital Amount
Main Business
Energy Creation (Solar power generation business etc), Energy Trade Area (Trade in electricity etc), Energy Saving Area (Energy conservation support service etc)
Tel: +81-7-8851-8819
Accepted Languages
  • Japanese

Binary Type Geothermal Power Generation

Energy > Energy Conversion > Geothermal to Electric > Steam Power by Ground Geothermal > Binary Type


It is a method of pumping hot water using a liquid such as ammonia or pentane / flon which boiling points are lower than water and evaporating the liquid by using a heat exchanger to generate electricity. The binary system can generate electricity by utilizing already existing hot springs, and it is possible to secondary use of hot water once used.

Current Situation

It is practically used in some countries such as the United States and the Philippines. In Japan, a demonstration test of 2,000 kW binary power plant at Hatchobaru started in 2003. In recent years, binary power generation which utilizes existing hot springs has attracted attention. There is great expectation for some reasons; low development risks and its exploring and drilling costs, possibility of coexisting with existing hot springs. Demonstration operation of binary power generation utilizing hot spring heat (project of Ministry of the Environment) was carried out for about one year from April 2013 to March 2014, and now the power distribution project using fixed price purchase system is started.

In Use
To use and apply technologies commercially or publicly on the assumption of economic establishment and sustainable operation mainly by companies.
Readiness Technologies Readiness Levels for the DOE
Actual application of technology is in its final form – Technology proven through successful operations.

Technology Scheme

Using a production well (steam well), extract the geothermal fluid from the deep underground geothermal reservoir. The geothermal fluid is used to steam the low boiling point medium by a preheater and an evaporator. This medium vapor turns the turbine and generates electricity. The medium vapor after power generation is returned to the liquid by the condenser, guided to the preheater, and reused for power generation. The geothermal fluid which has finished heating the low boiling point medium is led to the reduction well and returned to the deep underground.

Merit & Strength

1. Operation at low temperature

  • It is possible to generate power even with a heat source at 150 ° C or lower. Fluorocarbon alternatives are often used as low boiling point medium, and its boiling point is about 15 °C so even hot water of 100 degrees or less can be boiled.

2. Ease of introduction

  • Since it can generate electricity at low temperature, operation such as conventional geothermal power generation or deep excavation are not necessary. Therefore it can be introduced at a relatively low cost and in a short period of time.

Demerit & Weakness

1. Necessity of heating source

  • Since a liquid such as ammonia or pentane / flon low boiling point than water is used as a heating source, access to them is necessary.
(*) Deloitte Analysis section is provided by Deloitte Tohmatsu Consulting Exponential experts to serve helpful information on the subjects discussed. This section content describes generic information related to a technology, product, system or service developed or in use at the facility mentioned at the top. The same description may apply to several facilities.
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Koyo Electric: Obama Onsen Binary Power Station
Infrastructure |
Binary Type Geothermal Power Generation
Make an inquiry to visit the facility by clicking the button above.
Obama Onsen Binary Power Station