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Seafront Solar Plant Withstands Wind, Wave, Ground Subsidence (page 2)

'Overload' helps PV inverters work at maximum efficiency around noon

2014/04/28 13:40
Shinichi Kato, Nikkei BP CleanTech Institute
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This is a common method in the building construction and real estate industries. In terms of this scale, the total return on investment is reportedly more efficient with the funds raised through each company's credit as a joint venture rather than structuring project financing.

In project financing, the cash in advance, known as the "upfront fee," the commission paid when a loan is made, is said to reach hundreds of millions of yen. Considering this cash payment in advance, legal and other payments as well as the cost for SPC operation, the return on investment is lowered unless the project financing extends to a quite large scale.

Connection with special high voltage grid within Oita Works

Compared with other areas in Kyushu, where many mega-solar power plants have been constructed, the concentration is exceptionally high in Oita Prefecture. As a result, during grid connection talks, some electric power companies have requested a restricted amount of power connection and cost provision.

At this mega-solar power plant, however, Mitsui said there were few such restrictions. This is because Kyushu Electric Power had established a large-volume grid at a special high voltage (66,000V) for the industrial site aimed at concentrating heavy industries that use a considerable amount of electricity.

Given the special high voltage grid that runs across the site (Fig. 3 & 4) in front of MES Oita Works, the capital investment for grid connection was reportedly no more than about ¥15 million.

When connecting a mega-solar power plant, "power factor control" to prevent the grid voltage from rising is almost always requested in grid connection talks. However, there was no power factor control set at "Mitsui Engineering & Shipbuilding/Mitsui Fudosan Oita Solar Power Plant."

Attention paid to impact of moisture on amount of power generation

Toko Electrical Construction Co Ltd provided the engineering, procurement and construction (EPC) services as well as operation and maintenance. Mitsubishi Electric Corp's solar panel and Toshiba Mitsubishi-Electric Industrial Systems Corp's (TMEIC) PV inverter were adopted.

A total of 65,058 261W model solar panels (17MW-equivalent), roughly 1.2 times the PV inverters' rated output of 14MW, were installed.

Setting up solar panels with more output than the PV inverters' rated output is a method called "overload." It has the benefit that it can increase the amount of power generated by adding the output of solar panels in consideration of the decline in the amount of power generation due to overall system losses and less sunshine on a cloudy day or in the morning and late afternoon. The method increases uptime rate of PV inverters.

The overload ratio of 1.2x is the typical ratio used at mega-solar power plants that have plenty of room for panels. Considering system losses, the generated power is said to hardly outperform the rated output of PV inverters.

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