This document explains the basic concepts of electricity demand and supply and the mechanisms for stable power system operation.
Electric power supply and demand literally refers to electricity demand and supply, indicating the amount of electricity we need and the amount actually generated and provided. Due to electricity's characteristic of being difficult to store in large quantities, maintaining constant balance between demand and supply is extremely important. Therefore, electric power companies predict electricity consumption in advance and adjust generation according to predictions.
To ensure stable electricity supply, it is necessary to secure more electricity than the anticipated maximum demand to prepare for emergencies such as sudden demand increases due to rapid temperature changes or supply reductions due to equipment troubles. This extra capacity is called "supply reserve capacity," and the ratio of supply reserve capacity to maximum demand is called the "reserve ratio." A minimum reserve ratio of 3% is required for stable electricity supply, and falling below this increases blackout risk.
Meanwhile, electric power companies use the "electricity usage rate" indicator in "electricity forecasts" published for the general public. This shows the ratio of maximum demand used to supply capacity including reserve capacity, and when electricity usage rates exceed 100%, there is risk of blackouts. Therefore, 92% or above to below 97% is classified as "severe," and 97% or above as "extremely severe," with staged alerts calling for conservation cooperation.
This article was published on August 5, 2025, as part of the "Economic Terms You Should Know" series on the Ministry of Economy, Trade and Industry (METI) Journal ONLINE, providing easy-to-understand explanations of basic power system mechanisms for the general public.
The article is evaluated as providing foundational knowledge for understanding how the stability of electricity supply, essential for daily life, is maintained through systematic mechanisms.