Accuracy higher than gas turbines
Q: The output of the mega solar power plant is controlled by each of the PV inverters. Was the high-accuracy output control at an interval of four seconds realized because of the high-performance PV inverters?
Morjaria: Correct. Mega solar plants at present are capable of reducing the load on the grid to which they are connected and offering services for stabilization following the improvement in PV inverter functions, which was realized by the progress of power electronics. PV inverters and the system that integrally controls groups of multiple PV inverters are the key technologies.
In fact, the accuracy of grid stabilization by power electronics actually has reached a level higher than that achieved by turbine generators, which were conventionally used for stable grid operation.
The actual output of the mega solar power plant responding to AGC command values reached an accuracy of 87 to 93% in the validation project. The accuracy is roughly 40% in steam turbines and 63% in gas turbines, according to data. It was confirmed that the accuracy of grid stabilization by mega solar power plants is higher by 24 to 30 points, compared with gas turbines (Fig. 4).
Instantaneous response is higher when the output is controlled by power electronics, using digital semiconductors, compared with turbine generators that turn several thousand times per minute.
Q: At this validation, the output increase/reduction within a range of 30MW was realized by reserving 10% (30MW) of the mega solar equipment capacity for grid stabilization services. If this method is incorporated, however, the equipment use rate in the power sale business drops.
Morjaria: You are right. The reserved 30MW is not sold and is counted as the "cost." However, if the services are provided in the future and are paid for, the power will become the income source.
At present, the cost is lower compared with a case where storage batteries are introduced to realize the same function. We think it is likely that the cost for offering grid stabilization services will be lower when this method is incorporated, compared with gas turbines that are used to realize the same functions and accuracy.
For offering grid stabilization services using gas turbines, fuel is consumed to increase the output. For output from mega solar power plants, fuel is not needed and the marginal cost is zero. In addition, if the output from gas turbines is increased or reduced repeatedly at an interval of seconds, abrasion and deterioration of turbine blades and so forth are accelerated, which will be reflected in the cost. If PV inverters and power electronics are used, abrasion and deterioration seldom occur.
In other words, we estimate that the "grid stabilization services using mega solar power plants" feature higher cost competitiveness, compared with existing competing technologies.