For four days from Monday, June 27 to Thursday, June 30, the supply-demand balance for electricity in the Tokyo area was tight. While the government issued a warning and called for power saving, TEPCO Power Grid (TEPCO PG), the grid operator in the Tokyo area, secured supply capacity by pumped hydro and electricity imports from other areas. During the daytime when demand increased, solar power generation covered more than 20% of demand making up for the shortfall in supply capacity. The highest supply-demand rate (demand/supply) remained at 96%, below the 97% level at which power outages could occur.
The tight supply-demand situation was avoided by combining multiple means, such as pumped hydro and electricity imports, in addition to energy saving and demand response. The importance of a flexible power system that can adjust supply to meet demand was obvious. There are calls for the restart of nuclear power plants to expand supply capacity, but this is not an effective solution. On the one hand the output of nuclear power plants is not flexibly adjusted in Japan categorizing as a baseload power source, on the other hand there are concerns about unreliability of the aging facilities. The best course of action is to quickly move forward with expanding batteries and taking other effective measures to increase the flexibility of the power system.
Peak in the Morning covered by Solar, Pumped Hydro in the Evening
According to the supply-demand data published by TEPCO PG, the tightest situation was expected to occur between 16:00 and 17:00 on the four days (Table 1). However, it peaked between 9:00 and 10:00 or 8:00 and 9:00 in the morning.
Table1. Forecast and Actual of Peak Supply-Demand in the Tokyo Area (June 27-July1)
In areas where solar power generation is widely installed, daytime supply increases significantly on sunny days, while electricity demand is high in the morning and evening in summer and winter due to air conditioning and other factors. As a result, supply and demand may become tight in the morning and evening when the solar power generation is low. In particular, the evening is the most important time to watch as solar power generation decreases while demand remains high. This is the main reason why TEPCO PG expected the peak supply-demand from 16:00 to 17:00.
On Wednesday, June 29, when the peak supply-demand was forecasted to reach 100%, the measures TEPCO PG implemented to alleviate the peak can be clearly seen (Table 2). From midnight to morning, when demand is low, the company used surplus power to increase the amount of water for pumped hydro and generated power mainly in the evening. In addition, power supply from other areas through inter-regional interconnections was also increased in the evening. The supply-demand rate from 16:00 to 17:00 was down to 90%. The widespread call for power saving through warning signals by the government as well as the demand response program for industrial consumers had a significant effect in alleviating the tight supply and demand in the evening.
Talbe2．Demand and Supply for 24 Hours on June 29 in the Tokyo Area
It should be noted that solar power also made a significant contribution. In fact, at 9:00-10:00, when the actual supply-demand peaked, 24% of demand was covered by solar, and 9% even at 16:00-17:00, far exceeding the supply by hydro. In addition, there is a considerable amount of solar power generated and consumed onsite by households and factories, helping to reduce demand. Further expansion of solar power generation in the future will be an effective countermeasure to mitigate the tight supply-demand issue. Some have suggested that solar power is the cause of the tight supply-demand, but this view is incorrect. Solar power plays a major role in supplying electricity.
Problem of Dependence on Aging Thermal and Nuclear Power Plants
Rather, the aging thermal power plants had caused problems. JERA (thermal power generation company of TEPCO and Chubu Electric Power) scheduled to resume operation the unit 5 of the Anegasaki Thermal Power Plant (fuel: LNG, capacity: 600 MW, operation start year: 1977) on June 29. However, since the facility had been in operation for 45 years, it took time to repair several problems due to aging, and operation was not resumed until 10:45 on June 30, the following day. There are many large-scale thermal power plants in Japan that have been in operation for more than 40 years.
Similar problems occurred at nuclear power plants. At the unit 3 of the Takahama Nuclear Power Plant (capacity: 870MW, operation start year: 1985) by Kansai Electric Power, damaged heat-transfer tubes in the steam generator were found during a routine inspection that began on March 1. As of July 1, Kansai Electric Power has not announced when the plant will resume operation. One of the causes of the damage was cited that the plant has been in operation for a long period of time. The average age of nuclear power plants in Japan is over 30 years, and the possibility of similar damage is increasing. France, which heavily relies on nuclear power generation, is experiencing a series of problems associated with aging facilities this year, resulting in a significant reduction in supply. Reliance on old equipment and technology is concerning in terms of reliable operation.
In developed countries in Europe, many distributed renewable energy power plants, mainly solar and wind, are installed to minimize the impact of troubles and manage supply and demand flexibly. The measures to increase the flexibility of the power system are being enhanced by batteries, demand response, and the import and export of electricity through international interconnections.
Japan has a much larger capacity of pumped hydro than developed countries in Europe. Inter-regional interconnections play an important role as the international interconnections in Europe. Further expansion of interconnections, batteries and demand response in addition to renewable energy generation facilities will fundamentally solve the tight supply and demand issue. Lastly but not least, energy efficiency and saving energy measures must be promoted throughout the country to curb electricity demand.
Renewables to Strengthen Energy Security in Europe and Japan (July 2022)