A total of 44 trades were completed by the close of trading, with the East Area Peakload Electricity contracts being the most active, which covers supplies for the Tokyo area at peak times, TOCOM said.
Twenty-three trades were completed over four contract months, with the most active being the contract for September settlement, which settled at 13.51 yen (12.5 U.S. cents) per kilowatt hour (kWh) after opening at 13 yen.
The spot price index for base load supplies traded on the Japan Electric Power Exchange for Sept. 18 delivery closed at 8.37 yen/kWh.
On TOCOM, the 44 transactions included 20 off-floor trades. No trades were registered for West Area Peakload Electricity contracts, which cover the Kansai area in western Japan, the second main economic region of Japan after Tokyo.
The futures started trading three and a half years after the government pushed through the biggest shake-up in the country's electricity sector following the 2011 Fukushima disaster.
Since those 2016 changes, around 600 companies have registered to join a market still dominated by Tokyo Electric Power and nine other regional utilities.
But most new entrants need to source power for their customers from JEPX, where volumes more than quadrupled while prices fluctuated sharply, especially in summer and winter.
About 30 firms can currently trade electricity futures on the exchange and 8 brokers handle transactions, TOCOM has said.
(Reporting by Yuka Obayashi and Aaron Sheldrick; editing by David Evans)