戦前日本において定額制電灯料金が主流を占めた理由は、生産原価中固定費が大部分を占める水力発電が主電源であったこと、電力メーターが高価であったこと、需要家の電力使用時間帯が類似しておりロードカーブの形状が相似していたことであった。しかし定額制には電力を濫費する傾向が出やすく、器具を随時増加させることが困難であり、電力の用途が徐々に多様化してくると不都合になってきた。こうして１９２０年代前半から従量制料金が導入され始め、その割合は全国で２９％、市部では４９％まで上昇した。
In Japan before World War 2, the reason of fix-rate electric light charge being used by majority, was because of the main usage of hydroelectric power of which the fixed fee was of major portion in the production cost , the high price of meters, and also the similarity of the load curve of electricity users' using period.
However, under the fix-rate system easily came the result of overcharge, and it was also difficult to increase the instruments as occasion demands, and finally with the gradually diverse usage of electric power, the system had become inconvenient. With such situation, from the first half of 1920, volume-charging system was introduced, and the usage ratio ascended to 29% throughout the nation and 49% in cities.
