PV-powered rest house opens in Japan
by the CADDET Japanese National Team

A village which enjoys some of the sunniest conditions in Japan has installed a 30 kWp PV power generation system at its hot spring rest house. The system, constructed as a field test facility and expected to generate some 34,000 kWh/year, has been operating successfully for several years.

Akeno-mura hot spring rest house


Akeno-mura, a farming village about 120 km west of Tokyo, is one of the sunniest places in Japan. It has a high proportion of clear days, over 2,700 hours of sunshine a year and a more than 62% chance of sunshine.

When the old village office was rebuilt several years ago, the village planned to install a PV system in the new building as a field test facility supported by the New Energy and Industrial Technology Development Organisation (NEDO). However, since NEDO had just supported the installation of a large 95 kWp PV test system at a golf course in the same prefecture, the village project was abandoned because financial assistance was not available.

Then, the village discovered a 45.1C mineral hot spring, and a rest house was constructed to use this hot water, which is pumped up at a flow rate of 100 litres/min. Plans were once again made to build a PV system. This time, NEDO granted a subsidy and the PV test facility was installed.

The system

The rest house is a reinforced concrete construction, built about 720 m above sea level on a south-facing slope. The PV array is mounted on the semi-circular roof, which is inclined nearly due south at an angle of 22. By using the roof structure to house the PV modules, considerable cost savings were made on materials and installation of the mounting frames. From a distance, the PV array appears to be integrated with the roof. The design is very eye-catching, arousing interest in PV power generation among visitors to the rest house.

The PV array uses single-crystal silicon PV modules supplied by Showa Shell Sekiyu KK. Each module has a 12.6% conversion efficiency and a maximum output of 70 kWp (1 kW/m2, AM 1.5, cell temperature 25C), weighs 7 kg and measures 1,290 x 430 x 35 mm. The array has 434 modules arranged in 31 parallel lines, each consisting of 14 modules connected in series. The total area of the array is 260 m2 and its maximum output is 30.38 kWp.

The PV system is connected to a Tokyo Electric Power Company distribution line through a 30 kW capacity inverter. The inverter, manufactured by Japan Storage Battery Company, has an efficiency of 90% or more and converts 300 V dc power generated by the array into 200 V ac power. It also has an independent operating function, so that if the power supply from the public grid fails, the inverter supplies dc power directly to the rest house as an emergency back-up.


Total investment in the PV system was about JPY 57 million (where JPY is the Japanese yen), including the cost of monitoring instruments. These measure data such as the amount of power generated, the PV power's voltage and current, the amount of solar radiation, and temperatures. Also included are the outdoor electronic display boards which continuously show the intensity of solar radiation, the output of the PV system and the power received from the public grid. Two thirds of the total sum was subsidised by NEDO.


Electricity generated by the PV system, together with that supplied from the public grid, is used mainly to power the pumps for the hot spring, and to operate the lighting and air-conditioning systems in the rest house. Under favourable weather conditions, the PV system can generate about 34,000 kWh/year of electricity - about 11% of the rest house's total annual power consumption.

The graph (above) shows the performance of the PV system for a one year period from April 1997 to March 1998. Owing to mechanical trouble, the instrumentation system could not provide data for the periods 1-25 April and 27 May-18 June 1997. With these exceptions, the PV system generated 2,600-3,900 kWh/month of electricity, fulfilling expectations. The rest house uses considerable amounts of power to maintain the facilities, even on the one day each week when it is closed, so the PV system rarely exports electricity to the public grid.

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.