79MW Solar Plant Achieves Utilization Rate of 17.6% in Tohoku (page 5)
2x areal efficiency, 1.6x overloading by setting up more than 1MW per 1ha
'Failures fixed collectively'
That said, for panel replacement and other maintenance work in high positions, it is a challenge as the eight-row arrays as high as 2.7m require a lot of work and cost.
"Replacing defective panels and doing other maintenance work at the mega-solar plant would not increase cost so much if we collectively fix them no more than once or twice a year," said Sano, commenting on this point (Fig. 8).
The Watari Solar Power Plant tries to find failures at an early stage through remote control and data collection, adopting a string monitoring system of Sumitomo Electric Industries Ltd, for example.
"Although it is very important to swiftly understand where the failures are, cost efficiency is not good if we repair each failure every time we find one," Sano said. "Mega-solar operation requires a concept of running it without making too much effort even if there are some small failures and efficiently fixing multiple failures collectively."
Overloaded by '1.6x'
Adopting "eight-row arrays, installation angle of 10° and 1.4m space between the arrays" based on such an operational method, the Watari Solar Power Plant could set up panels equivalent to about 80MW on an approximately 75ha site. As a result, the overloading ratio rose to 1.61 times in comparison with the grid capacity of 49.3MW. This is an unusually high ratio in Japan where the ratio is 1.2 to 1.3 times at many mega-solar plants (Fig. 9).
The effect of "overload" to set up more solar panels than a grid capacity is generally said to "boost business performance by increasing power generation in the morning and evening even though power generation around noon on a sunny day is slightly reduced." The limited grid capacity can be effectively used as the graph of alternating power generation (power sales) per day is a "trapezium," and the utilization factors of PV inverters and grid facilities improve.
However, "If the overloading ratio were about 1.2 to 1.3 times, the power generation of solar panels would scarcely exceed grid capacity even at noon on a sunny day," Sano said, based on his experience in mega-solar operation thus far. "To boost utilization factors through peak cut effects, setting up more panels and boosting the overloading ratio to 1.3 times or more is necessary."