Continued from 40MWh Battery System Starts Operation in Fukushima (1)
Insufficient thermal power lowering margin
The main purpose of the large-capacity storage battery system is "to improve the supply/demand balance through the introduction of a large amount of solar power." The "insufficient thermal power lowering margin" observed around noon (when the load is low and the solar power output reaches its maximum) will be a problem when a large amount of solar power is connected to the power grid.
The grid operator maintains the supply/demand balance by lowering the output of thermal power responding to the increase in the solar power output. However, thermal power plants cannot be shut down completely. Thermal power plants have to be prepared for the need to increase the output in a short time because the solar power output could drop suddenly due to rapid weather changes. If the operation is stopped, it will take a long time to start up, and, therefore, the output is reduced to the minimum partial load for stable operation.
Even if the output from thermal power plants that the producer owns is reduced to this level, if solar power output continues to increase further, the "insufficient thermal power lowering margin" will occur, and the supply will exceed the demand.
In the event of such situation, the supply/demand balance will be maintained by operating hydroelectric power plants (pumping up). If excess power still remains after this operation, actions are taken according to the following operation rules and in this order: (1) Reduce the output from thermal power sources other than Tohoku Electric Power Co Inc, (2) Supply power to areas outside the Tohoku region via grid cables, (3) Reduce power generation from biomass mono-fuel power generation facilities and (4) Reduce output from biomass power generation facilities using local resources. If the supply still exceeds the demand, the solar power output is reduced (Fig. 8).
In the process to reduce solar power output, charging of the large-capacity 40MWh storage battery system at the Minami-Soma Substation plays a role identical to that of pumping-up generator operation. The company estimated the effect of the battery system in expansion of the solar power connectable amount (frame of access for 30 days, etc) at 50MW.
The effect of the supply/demand balance improvement by the storage batteries extends to the entire Tohoku region. However, the expanded connection frame was strategically allotted this time as a policy decision to areas in Fukushima Prefecture where evacuation orders were lifted.