Visit to Plant

Rooftop Solar Plant Prevents Roof Damage From Typhoon (Part 1)

No power generation for 3 weeks due to heavy snow

2019/05/21 10:17
Shinichi Kato, Nikkei BP Intelligence Group, CleanTech Labo
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In Shiraicho, Kofu City, central Yamanashi Prefecture, Japan, a mega- (large-scale) solar power plant with 4,354 solar panels equivalent to roughly 1MW of output is located on the rooftop of a warehouse near Route 140 (Fuefuki Line) running from the Kofu Minami Exit on the Chuo Expressway in the direction of Isawa (Fig. 1).

Fig. 1: Located near Kofu Minami Exit (source: Saito Warehouse)

This power plant was constructed and named "Kai-no-kuni Mega Solar Station" by Saito Warehouse Co Ltd (Chofu City, Tokyo), which developed and runs this warehouse (See related article). The company considered its warehouse in Kofu City suitable for the power generation business.

Yamanashi Prefecture boasts the longest hours of sunshine in Japan, and there are no high-rise buildings that would block sunshine around the warehouse. Saito Warehouse also considered the business risk was minimal as long as a secure power generation system was set up, and it could easily continue the power selling business even after the FIT-based purchase period is over, selling power at a low rate to the tenant companies in the warehouse, for example.

The company says it is more wary than industry peers in its mainstay warehouse business about risks related to long-term reliability and damage. It adopted safer and more reliable facilities as much as possible even though initial investment slightly increased and secured more-than-enough load bearing capacity for the roofs where the solar panels were set up.

Such a stance has also generated unexpected benefits, leading to minimizing problems caused by natural disasters after power selling started.

To boost the load bearing capacity of the roofs, Saito Warehouse invested about three times the cost originally required. These costs came from the measures to meet the required load bearing capacity of about 14kg/m2, which some areas of the roofs could not realize after arraying solar panels equivalent to roughly 1MW on them.

The company secured the required load bearing capacity in these areas by reinforcing the roofs. Saito Warehouse could have realized the roof reinforcement just to meet the original load bearing requirements at about 1.5 million yen. However, considering further safety improvements to cope with unexpected circumstances, it eventually spent about 5 million yen, more than three times the 1.5 million yen, to reinforce the roofs.

Tess Engineering Co Ltd (Osaka City) provided engineering, procurement and construction (EPC) services. Solar panels of Kyocera Corp and PV inverters manufactured by Toshiba Mitsubishi-Electric Industrial Systems Corp (TMEIC) were adopted (Fig. 2). Both products were selected according to Saito Warehouse's policy to choose products of Japanese manufacturers with excellent long-term reliability, in particular.

Fig. 2: Kyocera solar panels (top), TMEIC PV inverters (bottom) (source: Nikkei BP)

Every year since power generation began in June 2013, the solar plant has generated about 10% more power than initially estimated in the business plan, even though it has been struck each year by problems affecting the power generation amount. The power generation amount outperformed the estimate by about 13% in 2017 and about 10% in 2018.

Compared with the annual power generation of about 1,190,000kWh estimated in the initial business plan, the actual amount ranged from 1,270,000 to 1,300,000kWh per year, with the total amount reaching 7,480,000kWh.