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Full-time Output Control, EcoCute Employed to Boost Renewable Energy Ratio in Island

Urgent need for measures against corrosion of mounting systems

2019/05/13 22:17
Kenji Kaneko, Nikkei BP Intelligence Group, CleanTech Labo
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Solar power to shortly reach 'maximum capacity for grid connection'

Miyako Island in Okinawa Prefecture, Japan, is located almost in the middle between the main island of Okinawa and Taiwan, roughly 2,000km from Tokyo and 300km from Naha. The 204.5km2 island is a little smaller than Osaka City and has a population of slightly more than 55,000 people. Most of them live in the urban Hirara district.

Miyako is a flat island with no major rivers. It is formed from a raised coral reef. Sugar cane and other crops are grown on the island by pumping up the rainwater pooling in a dam constructed underground (Fig. 1). Although the island is warm throughout the year reflecting the subtropical climate, its natural environment is severe as it is easily affected by typhoons and drought.

Fig. 1: Sugar cane is the major crop of Miyako. Groundwater pooling in an "underground dam" is pumped up to tanks on hills and used to water sugar cane and other crops. (source: Nikkei BP)

The maximum demand for electric power is about 60MW in summe, while the minimum demand during the light-load period in the daytime is about 22MW in winter. Power generation facilities on the island are diesel engine, gas turbine and renewable energy-based power generators with a rated output of 60.5MW, 15MW and about 30MW, respectively.

Of the 30MW renewable energy-based power generation, wind power, a mega- (large-scale) solar power plant directly run by The Okinawa Electric Power Co Inc (Okiden) and solar systems set up by other consumers account for 4.8MW, 4MW and roughly 20MW, respectively (Fig. 2). The maximum grid capacity (capacity reserved for 30-day output restriction) for solar power on the island is set at about 24MW while applications have already been filed for further grid connections of about 17MW. Based on these circumstances, output control (output restriction) is expected to begin in the near future.

Fig. 2: The 4MW-output mega-solar plant directly run by Okiden was constructed as part of a national verification project. (source: Okiden)

Aiming for 'renewable energy ratio of 90%'

In Miyako, large-scale solar power projects with an output of 50kW or more can no longer apply for grid connection due to their impact on short-wave irregularity of electric power grids. In addition, if the grid connection exceeds the "capacity reserved for 30-day output restriction," even solar projects with an output of less than 50kW to be connected with a low-voltage grid will be required to accept unlimited output control without compensation. In fact, it has become difficult to develop new solar power plants under the current circumstances.

In March 2019, however, Miyakojima City announced its goals to further increase solar power generation on the island to 128MW in 2030 and 208MW in 2050.

These goals were set as measures to achieve an "energy self-sufficiency rate" of 22.5% in 2030 and 48.85% in 2050, which were advocated in the "Declaration of Eco Island Miyakojima 2.0" (Fig. 3). The island aims to achieve a "renewable energy-based power ratio of 55.1% and 91.9%" by adopting solar power equivalent to 128MW and 208MW as well as wind power equivalent to 6.9MW and 36.9MW in 2030 and 2050, respectively.

Fig. 3: Miyakojima City's self-sufficiency goals for primary energy (source: Miyakojima City)

These goals for solar power are two to three times more than the peak demand (approximately 60MW) at this moment. Is such a large-volume adoption possible while securing the profitability of solar power generation?