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Geothermal power builds up head of steam

TOKYO -- Anyone who has enjoyed Japan's countless hot springs knows the country has geothermal resources -- steam that can be used to drive a turbine and generate electricity.   

Yanaizu-Nishiyama geothermal power plant (Courtesy of Mitsui Mining and Smelting)

     Japan has the world's third-largest reserves of such power, the latent potential to produce around 23 million kilowatts of geothermal electricity. Research and development efforts are underway that aim to more than double Japan's geothermal resources. New technology, such as injecting water underground to increase the amount of steam produced, could help make that a reality.

Squeeze harder

At the Yanaizu-Nishiyama geothermal power plant in Yanaizu, Fukushima Prefecture, researchers are pumping water deep underground to see whether they can coax more steam out.     

     Tohoku Electric Power handles electricity generation at the plant, while Mitsui Mining and Smelting subsidiary Okuaizu Geothermal provides the steam. The plant began operating in 1995 and initially produced around 65,000kW, but the volume of steam has fallen and output has recently dropped to just one-third the previous level. The falloff may be occurring because the plant is drawing hot water from underground faster than it is replenished.

     To produce geothermal power, one needs a supply of subterranean water and a heat source. The hot water and steam accumulate in a stratum known as a storage layer, before being guided to the surface and used to spin turbines. Rainwater and other surface water that seeps into the ground collects and "recharges" the supply of groundwater, a process that can take months or years. If this recharging is too slow, the supply of groundwater declines and the amount of steam produced diminishes as well.

     The aim of the experiments is to artificially increase the water supply so that the volume of steam is restored. One of the new technologies being used is called a recharge-type enhanced geothermal system, or EGS.

     Commissioned by the Japan Oil, Gas and Metals National Corp., Okuaizu Geothermal has teamed up with the National Institute of Advanced Industrial Science and Technology and Geothermal Energy Research & Development, a joint venture involving a number of companies working on geothermal power. This is the first full-scale groundwater recharging project in Japan.

Magnificent magma

A number of projects are taking place in Japan and elsewhere to develop new geothermal technologies. In June, Japan's New Energy and Industrial Technology Development Organization held a workshop to discuss the latest developments.

     A more aggressive approach to improving the storage layer of geothermal resources is called capacity-enhancement EGS. This technique injects water into the ground at high pressure, crushing some of the subsurface rock. This improves water flow and widens fragmented storage layers.

     Hot, dry rock power generation relies on creating an artificial storage layer. Deep underground, temperatures are high, but water is not always present. This technique pumps water into these dry areas at high pressure, fracturing the rock and allowing steam to collect in an artificial storage layer.

     There are two types of power generation possible using hot, dry rock, depending on the geological formation. Places with shallow rock that fractures easily are called brittle regions, while areas where the rock becomes soft at high temperatures deeper underground are called ductile regions.

     Another promising area of study is supercritical geothermal power generation -- which taps geothermal resources deeper down, near the layer of molten rock or magma -- and magma power generation, which uses the magma's heat directly.

Power on tap

According to NEDO, Japan could generate 23.7 million kilowatts of electricity using the country's conventional geothermal resources, but if power generation using hot dry rock in brittle regions becomes possible, that would add another 29 million kilowatts of capacity, more than doubling the total. The increase would be even greater if ductile regions and supercritical power generation are added, though it is unclear by how much.

     So far, Japan has barely scratched the surface of its geothermal potential. The country produces a mere 520,000kW of geothermal power using conventional techniques. EGS and other technologies will foster greater use of these resources and will put new puff into steam beds that are diminishing.

     "We have reached the stage where we must establish good technology -- with industry, government and academia coming together as a single technology organization," said Akira Yabe, unit director at NEDO's Technology Strategy Center, at the recent workshop. "There are still not a lot of players in this field. We want many to rapidly enter."

     Participants at the workshop discussed potential problems such as a loss of heat due to pumping water underground, and the possibility of touching off earthquakes. It will take time to fully develop Japan's geothermal resources. Researchers and engineers will be hoping the good ideas continue to bubble forth.

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