Six firms come up with proposals after Chiba Prefecture's public call

Chiba Prefecture decided to leverage this site for a mega-solar plant, publicly recruited constructors and operators and selected Sparx Green Energy & Technology Co Ltd (SGET, Minato-ku, Tokyo) from six applicants.

The project cost totals approximately ¥4.4 billion (approx US$39.5 million), and a purchase price at ¥32/kWh has been approved. The annual rent to pay Chiba Prefecture is ¥180/m2.

Construction started in April 2016, and operation is slated to start in July 2017. As of February 2017, roughly 50% of the construction had been completed. The constructor had installed almost all the solar panels and started building PV inverters and other substation facilities as well as the main substation facilities for connection with the grid of Tokyo Electric Power Co Holdings Inc (Fig. 3). The plant plans to start receiving power by the end of April and enter a test operation phase after that.

Fig. 3: Gantry (gate style) iron tower of the main substation facilities being constructed (source: Nikkei BP)

Toshiba Corp provided engineering, procurement and construction (EPC) services while Toshiba's solar panels (60 cells, 270W/unit) and Toshiba Mitsubishi-Electric Industrial Systems Corp's (TMEIC) PV inverters (750kW product) were adopted.

Extra high-voltage power at 22kV transmitted to substations via overhead cables

When completed, this will be Japan's longest mega-solar plant running about 10km from Muzai, Shiroi City, to Wakahagi, Inzai City.

"Narrow and long mega-solar plants" face such large-scale challenges as the long total cable length from combiner boxes, in which panel wires are bundled, to PV inverters and how efficiently a lot of solar panels can be positioned and set up on narrow and long sites.

At the SGET Chiba New Town Mega Solar Power Plant, "substations," where electric current is collected from panels and boosted to 22kV, are set up at six locations. Direct current (DC) is first transmitted from solar panels to combiner boxes by each string (a DC circuit of panels), then passed on to PV inverters at substations after combining several string circuits in series, converted to alternate current (AC) and boosted before being relayed to the main substation (Fig. 4).

Fig. 4: Generated power is boosted to 22kV at six substations. Toshiba solar panels and TMEIC PV inverters were adopted. (source: Nikkei BP)