Wakkanai Mega Solar Plant Pioneers Local Use of Solar Electricity (2)

2020/03/25 16:51
Kenji Kaneko, Nikkei BP Intelligence Group, CleanTech Labo
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Continued from Wakkanai Mega Solar Plant Pioneers Local Use of Solar Electricity (1)

Output fluctuations reduced by 'AC link'

The system configuration of the power plant is different from normal configurations. The mega solar power plant and the storage battery system are respectively connected to separate inverters. The DC currents from the solar power plant and the storage battery system are converted to AC currents, which are combined for transmission to the grid. This is called the "AC (alternate current) link" method.

As measures for short-term fluctuations, rapid fluctuations in output from the mega solar power plant are detected in real time and the charge/discharge from the storage battery is controlled to offset the fluctuations. For example, the storage battery is charged responding to rapid increases in the output, and the storage battery is discharged responding to rapid declines in the output to reduce fluctuations in the output of power transmitted to the grid.

This method is incorporated generally for system configuration of mega solar power plants and wind power plants equipped with storage batteries in Japan. The system incorporated in Wakkanai was one of the first among such systems.

In this system, the power transmitted to the ballpark and the park is output from the inverter connected to the storage battery. Inverters connected to storage batteries can be used to convert the current from both DC to AC and AC to DC, and they are normally equipped with an isolated operation function that allows operation independent from the grid. This is because many storage batteries are assumed to be used as emergency power sources.

Power transmission to the ballpark and the park was possible during the blackout after the earthquake because a sufficient amount of power was stored in the storage battery and the inverter for the storage battery had an isolated operation function (Fig. 9 & 10).

Fig. 9: "Wakkanai City Onuma Ballpark" viewed from Milk Road (source: Nikkei BP)

Fig. 10: Visitor center in "Hokkaido Soya Fureai Park" (Source: Nikkei BP)