Residential Photovoltaic Power System Monitoring

by the CADDET Japanese National Team


The Japanese government's goal for photovoltaic power is to have installed capacity of 400 MW by the year 2000. Japan's photovoltaics programme began in 1992, with subsidised systems installed in public buildings such as schools, community halls and museums. Since then, the government has been encouraging the use of photovoltaics by various measures, including legislating to allow people to sell excess power generated by their home photovoltaic systems.

The Project

Under the Residential Photovoltaic Power Generation Monitoring Project, the Japanese government grants half the cost of a photovoltaic system (up to a limit of 5 kW per system) installed in the home. In exchange, the owner must provide system data for monitoring.


Photovoltaic systems are not yet widely used, because the power they generate costs more than that supplied by electricity companies. Because they are not in widespread use, photovoltaic systems cannot attain economies of scale in manufacture, thus the cost remains high. The Monitoring Project aims to break this vicious circle by providing subsidies to users, thus reducing the cost and stimulating the market. By monitoring and analysing these subsidised systems, the Project will collect information to contribute to the development of even better, cheaper photovoltaic equipment. Data from the Project will also help in defining the law relating to the use of photovoltaics.
 Implementation of the Monitoring Project should also assist the development of a network of distributors for photovoltaics, who will take on the jobs of marketing, installing and servicing the growing market.

Data Reporting

In return for the subsidy, the photovoltaic system owner must report data for three years following the installation as shown in the Table.
 These data are submitted to the New Energy Foundation, which manages the entire Project from selection of applicants to analysing and reporting the results.
 In the Japanese fiscal year 1994, the Project was given a budget of JPY2 billion (where JPY is the Japanese yen). More than a thousand applications were received, and almost 600 were granted subsidies. A typical 3 kW system then cost around JPY6 million.
 Fiscal Year 1995 saw an increase in the budget to JPY3.3 billion. Photovoltaic suppliers increased their sales effort by cutting prices to about JPY4.5 million for a 3 kW system. As a result, applications to the Project in that year rose to 5, 432. Just over 1, 000 people were selected by lottery to receive the available grants.
 Most of the applications have been for systems between 3 kW and 4 kW in size. The range that attracted the next largest number of applicants was above 5 kW, which is outside the range for which the subsidy is to be granted. The largest system applied for was 9.29 kW and the smallest 1.02 kW.

Table: Monitoring Data Collected

Reporting period

Data required


Electricity purchased from utility.
Electricity sold to utility.
Electricity generated by the photovoltaic system.

Annually (Maintenance)

Details of malfunctions with durations of shutdowns.
Details and costs of any repairs carried out.

Annually (User experience)

Changes in awareness of energy savings. User satisfaction with cost-effectiveness, ease of use, size and appearance of the system.
Problems such as noise and vibration.
Other matters, including evaluation by neighbours and post-installed service.

Further Work

The Monitoring Project will continue in 1996, again increasing the number of photovoltaic systems to be subsidised. A number of other legislative measures are making conditions more favourable to the use of photovoltaic systems. However, to attain more widespread use of photovoltaics and the self-sustaining growth of the industry, prices of equipment and services must come down further. The Japanese government is therefore urging manufacturers of photovoltaic systems and associated equipment, as well as distributors and the housing industry to redouble their efforts to stimulate growth in the photovoltaics marketplace.

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.

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