Only Nuclear Power Can Be Trusted in the Heatwave... If Not Added, We Would Have Feared a Blackout

Despite Record Peak Power Demand on the 22nd... Power Reserve Margin at 11.1%
Supply Capacity Exceeds Demand Increase

Restart of Two Nuclear Reactors Raises Reserve Margin by 2.7%P
Minimal Peak Contribution from Renewable Energy

Solar Power 1.4% · Wind Power 0.3% Only

On the 21st, marking Jungbok (중복) in the solar terms and the peak of scorching heat, commuters hurried their steps at Gwanghwamun Intersection in Jongno-gu, Seoul. / Photo by Moon Honam munonam@

[Sejong=Asia Economy Reporter Joo Sang-don] Despite the record-breaking peak power usage amid the heatwave, the power reserve margin remains above 10%. The power reserve margin indicates the supply capacity relative to power demand, and it is generally considered stable when above 10%. Recent restarts of two nuclear power plants have raised the reserve margin by more than 2 percentage points. Meanwhile, the peak-time contribution rate of solar power, one of the renewable energy sources, was only 1.4% of the total power generation.

According to the Korea Power Exchange on the 23rd, the peak power demand on the previous day was 89,958 MW at 6 p.m., an increase of 1,021 MW compared to the day before (88,937 MW). This marks the second consecutive day of record-breaking peak power demand this summer.

Despite the surge in power demand, the power reserve margin stood at 11.1%, exceeding 10%. This is because the supply capacity increased more than the demand growth. On the 13th, when the supply-demand situation was tightest this summer with a reserve margin of 10.1%, the supply capacity was 95,966 MW, but on the 22nd, it rose by 3,989 MW to 99,955 MW. During the same period, the increase in peak power demand was smaller at 2,786 MW.

The increase in supply capacity is largely due to the recent addition of two nuclear reactors to power production. Korea Hydro & Nuclear Power received approval from the Nuclear Safety and Security Commission to restart Shin-Wolsong Unit 1 on the 16th and began supplying power from the 18th. It has been operating at full capacity since the 21st. Shin-Kori Unit 4 started supplying power on the 21st and has been operating normally since the 22nd. The operation of Shin-Wolsong Unit 1 (1,000 MW) and Shin-Kori Unit 4 (1,400 MW) increased supply capacity by a total of 2,400 MW. Without these two reactors, the supply capacity on the 22nd would have decreased from 99,955 MW to 97,555 MW. Consequently, the supply reserve would drop from 9,997 MW to 7,597 MW. Dividing this figure by the previous day's peak power demand of 89,958 MW results in a reserve margin falling to 8.4%.

Professor Jung Dong-wook of the Department of Energy Systems Engineering at Chung-Ang University said, "Shin-Kori Unit 4, which was shut down due to a fire in the turbine auxiliary equipment, was brought online earlier in response to the surge in summer power demand, and Shin-Wolsong Unit 1 was restarted as scheduled following its regular inspection." He added, "Although there are claims that the current power supply concerns are not due to the nuclear phase-out policy, the fact remains that the available power generation capacity has decreased compared to the original plan."

Although the power reserve margin has been maintained at 11-12% despite the ongoing heatwaves, concerns about power supply and demand have not been fully resolved. On the 23rd, most regions nationwide are expected to experience heatwaves with daytime highs exceeding 35 degrees Celsius. Some inland western areas are forecasted to reach daytime highs above 38 degrees. The Korea Meteorological Administration predicts daytime highs of 37 degrees on the 24th and 36 degrees on the 25th.

Among the three nuclear reactors scheduled for sequential restart by the government, Wolseong Unit 3, which has not yet started supplying power, is expected to begin normal operation in the early hours of the 24th. Its operation will increase supply capacity by 600 MW. Although Wolseong Unit 3 has a capacity of 700 MW, it typically operates at around 80% output due to its heavy water reactor characteristics. Wolseong Unit 3 and its twin, Unit 4, currently operate at about 84% capacity, producing 605 MW. If power demand increases further before Wolseong Unit 3 begins full operation, the power supply situation could become tighter than it is now.

While the Moon Jae-in administration pursued an energy transition policy focused on nuclear and coal phase-out and increased renewable energy, most power during peak hours is still supplied by coal, liquefied natural gas (LNG), and nuclear power. According to data on "Power Generation by Source during Peak Hours" submitted by the Korea Power Exchange to Yoon Young-seok, a member of the People Power Party, the share of solar and wind power in total generation during peak hours from the 1st to the 15th of this month was only 1.7%. Solar power accounted for 1.4%, and wind power for 0.3%. Although solar and wind power capacity accounts for 14% of the total, their contribution to power generation during the summer peak hours when demand surges is minimal.

The same was true in previous winters and summers. From January 1 to 14 this year, solar power accounted for only 0.4% of generation during peak demand hours. Particularly in last summer, solar power's share during peak hours was 0.8% in July and 1.8% in August. Heavy snowfall covers solar panels, and rapid temperature changes reduce solar power generation efficiency. Solar power generation efficiency typically decreases when temperatures rise above 25 degrees Celsius due to module overheating.

On the other hand, during the first half of this month, coal accounted for 38.1% and LNG for 34.2% of total power generation, meaning fossil fuel generation accounted for 72.3% of power production. Nuclear power's share was 21.2%.