Rechargeable Batteries Help Stabilize Solar Plant Output (page 3)
Results by smoothing output fluctuations, scheduled operation
Fig. 3: PV inverters and secondary batteries are all housed in buildings to prevent salt damage. The PV inverters are products of Toshiba Mitsubishi-Electric Industrial Systems (TMEIC) and the secondary batteries are products of NDK Insulators (NAS cells) and Toshiba (Li-ion cells).
Output load achieved as predicted the previous day
Subject 3 is the verification of "scheduled operation" of solar power generation. Scheduled operation indicates predicting and planning the output load (hourly changes) in solar power generation on the previous day based on weather forecasts and realizing the predicted output load by filling in the gaps with the actual output through secondary battery charging and discharging. If this could be realized, solar power generation, which is a variable power supply, can be positioned as a stable, programmed power supply like a diesel engine.
An example of the scheduled operation can be found in Fig. 7. As shown in this figure, the programs perfectly met the results with the gaps between the solar power generation programs on the previous day and the results of the day offset by the secondary battery charging and discharging.
Subject 4 is the verification of optimum secondary battery control using a simulated grid; this verification is now under way. Making the most of the load equipment to simulate 100 houses, this verification project’s key feature, cases of offsetting the fluctuations in solar power output using the secondary batteries installed in each home and substation are being compared and verified to determine the optimal installation spots for the secondary batteries when a large volume of solar power generation facilities are set up in a grid.
While collaborating with Okinawa Electric Power’s verification project, Miyakojima City announced "Declaration of Eco Island Miyakojima" and established goals to decrease its resource/energy dependency outside the island and cut its CO2 emissions by 70% by 2050. The pillars of this declaration include the introduction of large-volume reusable energy, energy saving and demand management.
As one of these specific approaches, the "Islandwide EMS (energy management system)" project was launched in alliance with Toshiba Corp and others in October 2013. Visualizing the energy use status at 200 homes and 25 offices, Miyakojima City will explore the possibility of energy-saving services and approach power use in accordance with the amount of solar and wind power supply.
With the verification project to control the demand side added to the secondary battery-based verification project by Okinawa Electric Power, expertise on maintaining power quality by quickly balancing supply and demand is likely to be acquired.