PV-powered water quality system in Japan
by the CADDET Japanese National Team

Large-scale photovoltaic (PV) power generation facilities have been installed on the shore of a reservoir in Japan and on a platform floating on the surface. They are being used in a 4-year project to study a PV-powered water quality preservation (algae collection) system and PV power generation on the reservoir.


Ogochi Reservoir, with an effective storage capacity of 185.4 million m3, was completed in 1957 to make the water supply to Tokyo more reliable. Fostering and maintaining the forests in the area and preserving water quality in the reservoir is the responsibility of the Bureau of Waterworks, which has made considerable efforts to protect the environment. However, some algae has appeared in the upper reaches of the reservoir, although the water quality is still maintained. The Bureau is investigating methods of preventing algal growth and, as part of this project, has installed large-scale PV facilities on the shore and the surface of the reservoir. During a 4-year period from April 1999 to March 2003 the Bureau will:

  • assess the function and performance of a PV power generation system on the surface of
  • the reservoir;
  • verify algae removal by a PV-powered water quality preservation system;
  • investigate the operation of a PV-powered boat for algae transportation.

The PV installations are also designed to supply power to temporary emergency shelters.

Onshore PV system

With an output of 125 kWp, the onshore solar cell array consists of 1,008 panels (each 120 x 80 cm), has a total area of about 970 m2 and doubles as a roof for a car park in front of the Oku-tama Museum. The electricity it generates is used to charge the battery which powers the solar boat. The system is also interconnected with the public power supply to the museum, which uses the surplus electricity. Annual power generation by the PV system is estimated at some 125,000 kWh.

Surface PV system

The water quality preservation plant and a 28 kWp PV power generation system are installed on a floating platform in the reservoir. This system is expected to generate 25,000 kWh/year of electricity.

The water quality preservation plant is independently powered by this floating PV system. The plant draws algae and water from the lake by two vortex flow jet pumps through a filtration and de-watering processes. It can collect 6.7 kg/hour of algae with a water content of 8.5%.

Solar boat

The solar boat carries the dewatered algae from the floating platform to a base on the shore. With a displacement of 17 tons and a passenger capacity of 20, it is powered by PV panels (1.2 kWp in total) mounted on its roof and side, and an on-board battery which is charged by the onshore PV installation. The boat can operate for about five hours per charge.

Although, at present, PV systems have been used as an auxiliary power source in some ships, this solar boat is deemed to be the first in practical use in Japan which is solely propelled by clean energy from PV power generation. The boat has no emissions and produces less noise than a diesel-powered boat.

Emergency power supply

When power supply from the public grid is cut off in the event of a disaster, such as a large earthquake, the PV facilities at Ogochi Reservoir will be used as emergency power sources for two temporary shelters in the area. These emergency power sources are expected to supply 1.8 kW of power to provide lighting for the two shelters for 12 hours.


Construction of the research facilities at Ogochi Reservoir cost JPY 500 million (where JPY is the Japanese yen). Of this, half of the installation cost related to PV power generation was subsidised from the “Financial Support Programme Promoting the Installation of Energy Supply Facilities in Harmony with the Environment” of the Agency of Natural Resources and Energy, Ministry of International Trade and Industry. In addition, Fuji Electric Co and the Bureau of Environment Protection of Tokyo are providing financial support.


The Tokyo Metropolitan Government has made a commitment to the United Nations Framework Convention on Climate Change to cut CO2 emissions in 2010 by 6% compared with 1990 levels. The PV power generation research project at Ogochi Reservoir will help in attaining this goal.

For more information contact the CADDET Japanese National Team in Tokyo.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors.  They do not necessarily reflect the official view of CADDET.

Enquiries concerning the Newsletter should be addressed to Pauline Toole, Editor, CADDET Centre for  Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, United Kingdom. Tel: +44 1235 432968, Fax: +44 1235 433595.