Challenge of long total cable length overcome

At many solar power plants, PV inverters are set up in the middle of arrays (a unit of panel installation) where some space is left vacant for them. In such a layout, no combiner boxes are set up very far from PV inverters, resulting in the shortest total length of cables between PV inverters and combiner boxes. As the total cable length gets shorter, both construction material cost and power transmission loss decrease and system efficiency increases as a result.

At "narrow and long mega-solar plants," however, such a layout is not possible. Although the six substations are positioned almost evenly in the 10km plant site, the total cable length cannot help but be long because of the large number of combiner boxes set up far from PV inverters. As a result, material cost rises and drags down the system efficiency in principle.

At the SGET Chiba New Town Mega Solar Power Plant under construction, there are electric poles at regular intervals beside the fence on the north side of arrays, and overhead cables are extended between the poles. On the ground under the cables, resin cable tubes have been laid. Electric cables from combiner boxes to PV inverters and 22kV extra-high-voltage cables from substations to the main substation are laid in the tubes and hung from the electric poles, respectively (Fig. 5).

Fig. 5: Generated power is transmitted to the main substation at 22kV extra-high voltage via overhead cables. (source: Nikkei BP)

Numerous cable tubes laid over one another along the base of the fence help you realize how long the total cable length is (Fig. 6). According to Toshiba, however, this did not lower system efficiency and increase cost so much that the plant's business performance would be affected, and the company compensated for the long cables by arranging the overall design.

Fig. 6: Cable tubes were laid between combiner boxes and PV inverters. (source: Nikkei BP)