The Okinawa Electric Power Company, Incorporated (OEPC)
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R & D Information
The business circumstances of the electric power industry is becoming increasingly challenging due to a variety of laws and measures, such as the Kyoto Protocol and Special Measures Law Concerning the Use of New Energy by Electric Utilities (also referred to as the "RPS Law") to prevent against global warming in order to reduce CO2 emissions and increase the use of renewable energy. OEPC is conducting various studies aimed at finding effective solutions to these urgent issues.
Utilizing renewable energy sources
Although such renewable energy sources as wind and solar power have disadvantages in energy density and therefore generating cost, they are "clean" forms of energy that do not contribute to global warming through the release of CO2; and are thus coming under growing scrutiny as answers to society's energy needs. In April 2003, the RPS Law came into force in Japan, imposing an obligation on electricity retailers to use a certain amount of electricity from new energy according to the amount of their retailing electricity. OEPC is committed to the development and adoption of renewable forms of energy such as solar and wind power. As Of the end of March 2009, the Company has a total capacity of 18,158kW(including small hydroelectric generators) of renewable energy throughout the prefecture including remote islands.
Verification of introduction of off-grid renewable energy systems for remote islands
1. Power Generating Facilities on Miyako Island
2. The Principle of Solar Cells, and the Types and Characteristics of the Panel
Solar cells are made of the semiconductor junctions of n-type silicon and p-type in general.
Positive charges and negative charges appear when sunlight hits the semiconductor.
Positive charges move to p-type, negative charges move to the n-type, so electromotive force is developed.
And electricity will be flown between the electrodes by connecting to loads. Weather conditions would swing solar power output greatly, this fluctuated output could impact on power quality such as voltage and frequency deviations
Solar power output decreases with increasing temperature of the module in general. The decrease rate in thin-film output will be low even if the temperature is increased in comparison with polycrystalline modules.
3. Typhoon-Resistant Design for Solar Panels
- Since the site is in a typhoon-frequented zone, the PV panel supports were designed with a reference wind velocity of 46 m/sec. (considering a max. instantaneous wind velocity 73 m/sec).
- The installed PV panel inclination is 5 degrees, to protect the facility from strong winds and to minimize the installation area.
- To avoid salt attack,the PV panel supports were coated with heavy-duty salt-resistant paint.
4. Features of NAS Battery(Sodium-Sulfur Battery)
The NAS Battery is a secondary battery with sodium and sulfur electrodes. Large capacity batteries of this type also have been made. The NAS Battery is free of self-discharge, featuring high energy density and high efficiency, small size. It should be noted, however, that it is necessary to maintain specified temperatures in the inner cell by a heater, since sodium and sulfur are used in liquid phase.
Response performance of the NAS Battery The NAS Battery excellent in response performance can absorb abrupt fluctuations of PV output that cannot be compensated by a thermal generator.
5. The Principle of the Power System Frequency
For stable supply of electricity, there is a need from time to time we adjust the supply and demand equally to maintain nominal frequency (60Hz) constant. In order to do that, we need to fine-tune the output of generators sensitively. If the supply is less than demand, the frequency would decrease if the supply is greater than the demand to reverse, then the frequency would increase.
Unless the balance between supply and demand is constant, frequency would be fluctuated.
As a result, power supply would be ceased as huge frequency deviation could affect the quality of the product such as factories.
The output powers of renewable energy such as solars and wind turbines are changeable greatly, these fluctuated output could impact on power quality such as voltage and frequency deviations.
We’re demonstrating test of systematic stabilization measures using a storage batteries to mitigate their unstable power quality.
6. Features of the Simulated Power Distribution System
7. Description of the Demonstration Researc
a. Validation of the output fluctuation control effect(storage battery + PV)
-Validate the control effect for smoothing abrupt PV output fluctuations, and determine the required capacity of storage battery.
b. Validation of the frequency fluctuation control effect(storage battery + PV + (existing wind Turbine))
-Validate the frequency stabilizing function of the combination of PV and storing battery (device for actively supporting frequency control), with the frequency control of the existing power source, and determine the required capacity of storage battery.
c. Validation of the PV scheduled operation(storage battery + PV)
-Study the prediction technique of PV output, and prepare the generation plan based on the predicted PV output and remaining power in the storage battery, for systematic output operation according to the plan.
-Determine the required capacity of storage battery and its operation.
d. Validation of optimum control layers in the simulated distribution line
-In the simulated distribution line, validate the optimum control layers of storage batteries and PV equipment linked to the line.
8. Demonstration Research Schedule
Biomass energy
OEPC conducted research on the use of woody biomass made out of construction and demolition waste, which, in Okinawa Prefecture, was mostly incinerated without being used effectively. Having confirmed that the biomass was perfectly usable based on the result of field tests conducted from June 2007 to October 2008 at the coal-fired Gushikawa thermal power station, we built a biomass distribution facility at the station, and on March 25, 2010, we started burning the biomass pellet (mixed with coal by three percent in weight). The successful utilization of the "carbon neutral" biomass fuel has enabled us to reduce CO2 emissions, curb our coal consumption, and make effective use of an untapped energy source.