RENEWABLE ENERGY IN JAPAN (SMALL- TO MEDIUM-SCALE HYDROELECTRIC POWER, WAVE POWER, OCEAN THERMAL ENERFY, BIOMASS ENERGY AND GEOTHERMAL ENERGY)

Our last issue (June) introduced solar thermal, photovoltaic and wind power in Japan. This month we continue on the theme of renewable energy in Japan.http://www.japanfs.org/en/newsletter/200306.html

(4) Small- to medium-scale hydroelectric power

Hydroelectric power is Japan's largest energy resource. Potential hydropower generation is estimated theoretically at around 270 billion KWh per year. About 2,700 sites with potential hydropower resources remain undeveloped, which could provide 50 billion kWh per year with a maximum output of 13 million kW, according to the fifth Hydroelectric Power Generation Potential Survey conducted by the Ministry of International Trade and Industry (now the Ministry of Economy, Trade and Industry).

When the hydropower plants under operation and construction are added, potential water power in Japan totals 4,100 sites, 135 billion kWh, and 33 million kW, respectively. This means that in view of maximum output, about 60 percent of Japan's potential hydropower resources have already been developed during the country's nearly century-old history of hydroelectric development. The remaining 40 percent are still unused.

Because sites that can be easily developed have been already developed, small- to medium-scale hydroelectric power generation tends to be well-suited for the remaining sites. For reference, the Ministry estimates undeveloped potential hydropower at around 12 million kW. In this context, the Water Power Plan for a New Century has been proposed, to construct small- to medium-scale hydropower plants of capacity below 10,000 kW with a construction cost less than 3 million yen (about U.S.$25,000) per kilowatt at some 1,000 sites, generating collectively 5.5 million kW by 2010.

If micro-hydropower plants of capacity below 100 kW are included in this context, the total potential will increase by some 20 percent.

(5) Wave Power and Ocean Thermal Energy

Japan has a total coastline of 32,000 km, with estimated wave energy of 1.4 billion kW at peak times. A conservative view indicates that the usable portions of the coastline add up to only about 160 km. Even in this case, an annual average wave energy of 3.9 million kW would be available, generating an annual average of 1.3 million kW electricity.

Currently, the installation of wave power plants is rather costly, at about 5 million yen (U.S.$42,000) per kilowatt, leading to an overall production cost at 40 yen (33.3 U.S. cents) per kilowatt hour. Nevertheless, small-scale wave-power generators built into buoys, lighthouses, and light beacons have already been operational for special purposes.

Ocean thermal energy conversion (OTEC) is a technology that converts solar radiation to electric power by using the ocean's thermal gradient between cold deep water and warm surface water. In tropical and subtropical regions, ocean temperatures are 27-30 and 7-8 degrees Celsius in the surface and at the depth of 500 meters, respectively. A temperature gradient of this magnitude is sufficient for power generation.

The major problem with OTEC is its heavy consumption of power for pumping water, resulting in a net electrical power output at only about 15 percent of the generated power after subtracting the power needed to run the system. This gives an estimated cost of 19-23 yen (15.8-19.2 U.S. cents) per kilowatt hour.

It is estimated that at least 30 million kW of electricity could be generated by OTEC within Japan's exclusive economic zones, 200 nautical miles from the coast.

(6) Biomass Energy

According to a report from Japan's Science and Technology Agency, domestic biomass resources currently total about 1.5 billion tonnes, 94 percent of which come from forestland. Taking only timber in the tree trunk into account, domestic forest growth amounted to around 90 million cubic meters in 1995. One third of this resource, if used for biomass energy generation, is estimated to mean a supply of 20.7 to 31.1 billion kWh of electricity annually. This is equivalent to about 3 percent of Japan's total electricity supply.

(7) Geothermal Energy

Japan is a volcanic country with 200 geothermal zones containing 65 volcanoes. Geothermal power, thus, offers great potential as a domestic energy source. However, the scale of geothermal power in practice is still small and limited to resources at relatively shallow sites -- 2,000 meters below the earth's surface. Geothermal power plants constructed in Japan so far generate only 550,000 kW in total.

In June 1992, the government thoroughly revised its long-term energy outlook, aiming to develop 1 million kW of geothermal power by fiscal 2000 and 3.5 million kW by 2010.

Geothermal energy development in Japan has some disadvantages, however. Since fluid from the underground is mainly hot water, a steam turbine is likely to wear out quickly, affecting its efficiency. Having to dig two wells each, one for geothermal fluid supply and the other for its return, to put harmful substances in the hot water back in the soil is another factor pushing up the cost of geothermal energy development.

The Ministry of Economy, Trade and Industry has been developing binary cycle power generation, which uses two kinds of fluids such as a CFC substitute and isobutane in combination, to explore geothermal resources and to improve power generation efficiency. The ministry has also been studying hot dry rock power generation to produce steam and hot water by injecting water from above the ground into hot dry rocks underground.

We have reported "renewable energy in Japan" in the last issue and this issue. In Japan, development and utilization of renewable energy has been gaining momentum. With information from JFS, please keep updated.

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