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Output Stabilization Technology for Mega Solar Systems

Controlling renewable energy output using storage cells

Since the start of the Feed-in Tariff Scheme (FIT) for renewable energy in 2012, entries into the power generation business from outside the industry are increasing, which has called into question the ideal state of operation and maintenance of power systems. For example, an issue with power generation that uses such renewable energy sources as solar and wind is to generate and supply electricity depending on power demand, as there are significant fluctuations in output due to changes in weather conditions. Losing the balance of power supply and demand causes frequency disturbances, which can lead to power system problems as well as faulty operation of equipment and devices in factories and households.
With this background, there has been attention on a system that is capable of adjusting the power supply demand balance through storage cells. For instance, the system works to charge the excess of electricity in a storage cell when the amount of power supply (power generation) exceeds the demand (consumption), and to discharge electricity from a storage cell when the amount of supply falls short of the demand. Our strength lies in the highaccuracy control technology for such charging and discharging of storage cells. As one example of applying this technology, this article covers the Hidaka Kuratomi Solar Power Plant (9 MW) in the town of Hidaka, Hokkaido, which started its operation in April this year.

Photovoltaic power system configuration

Satisfying the needs of both utility companies and power producers to realize unprecedentedly high-accuracy control

Compared with other areas in Japan, Hokkaido has a large proportion of renewable energy out of the maximum demand. Operating a photovoltaic power plant requires high-accuracy output control capable of accommodating power output fluctuations. While the general rate of output change in a certain period (or the output change rate) is about 10% per 10 minutes, Hokkaido Electric Power Co., Inc. required a rate of within 1% per minute, a high level of demand anywhere in the world.
Increasing the storage cell’s capacity facilitates the achievement of the output change rate target but does not reduce the investment cost, as desired by customers (power producers). For that reason, we were assigned the challenge of reducing the cell’s capacity while realizing the desired output change rate.
To meet these strict conditions, we created a control model for Hokkaido Electric Power Co., Inc. by utilizing our past achievements in storage cell control with wind power generation facilities, where we have led the industry in continued demonstration and actual operation.

R&D results ① Achieved a globally high output change rate of 1% per minute or less ② Storage cell’s capacity reduced by about 20% compared to conventional products (of other companies)

Using this model, we analyzed one year of power generation data from another photovoltaic power plant second-by-second to adjust the control parameters. This research and development took two years, but as a result, we were able to meet Hokkaido Electric Power Co., Inc.’s output change rate requirement and successfully reduce the storage cell’s capacity by about 20% compared to a conventional product (of another company). After actual verification, the development was completed in the first half of 2016. This technology is making significant contributions to our landing orders for the seven photovoltaic power systems with a total scale of 150 MW (as of September 2017).

Voices of developers

High control technology for added value in business

In addition to the photovoltaic power generation that became widespread with the introduction of the Feed-in Tariff Scheme, Japan also has high expectations for wind power generation. We will shorten the development period by feeding back the high control technology developed with photovoltaic power and using it for wind power generation as well. We also intend to work together with the operations department to expand our competitive solution business overseas, including Southeast Asia, by using the control technology as added value.

Advanced Algorithm Research Department, System Technology Research Center, Advanced Technology Laboratory, Corporate R&D Headquarters

The article and the affiliations are at the time of coverage.