What happens during a solar site survey in Japan
A step-by-step account of what a survey covers and what the written report can include
A site survey is the starting point for any rooftop installation, and it is also the most useful step for an owner who is still deciding whether solar makes sense for the property. This note explains what a survey looks at and what a written report can include.
Roof assessment: pitch, orientation and condition
The first thing to assess is the roof itself. Pitch and orientation determine how much sunlight the panels receive through the year. In most of Japan a south-facing roof at a moderate pitch, roughly 20 to 30 degrees, is close to ideal. East- or west-facing roofs produce less but are sometimes viable, depending on when the household uses its power.
The condition of the roof covering matters too. Panels are mounted on rails fixed to the roof structure, and the roof has to be in good enough shape to carry the mounting hardware for the life of the system. Concerns about the roof should go into the report, and the load-bearing and waterproofing questions belong to the people who design and fit the mounting.
Shading measurement
Shading is the most common reason a roof that looks suitable from the street turns out to be less productive than expected. A survey maps the shading at the proposed panel positions, taking in neighbouring buildings, chimneys, aerials and trees, using observation on site and, where useful, a shading tool.
That shading data feeds into the yield estimate. It helps to see the estimate month by month, not only as an annual average, because low winter sun can be blocked by objects that never touch the panels in summer.
Electrical panel and connection point
The existing distribution board has to be inspected to confirm that it can take the solar connection and, if storage is planned, the battery interface. Older boards sometimes need upgrading before a system can be connected safely, and the report should say so if that applies.
The survey also identifies a practical place for the inverter: sheltered, ventilated and reachable for future maintenance.
The written report
After the visit, a written report can set out the roof assessment, the shading picture, a month-by-month yield estimate, a suggested system configuration and any issues found. The findings stay with you whether or not you go on to an installation. Estimates in the report are estimates, not guarantees of output or savings.
The survey report does not contain a price. A quote is a separate document, prepared once the panel and inverter specifications are settled and the current FIT rate and any subsidies have been checked against official sources. Whether a survey is charged is stated in writing before any visit is booked.
If you have questions about what a survey involves before asking for one, the FAQ covers the most common points. You can also write to us from the contact page.