The way ecocute works is that it heats water at times when electricity is cheap and stores it in a highly insulated tank. So if you’re having a soak in the evening, it’s cheaper to use the water that is already preheated at cheaper rates and stored, than to reheat it again using the expensive to peak time rates.

My rates are 36yen from 6am to 10pm and 19yen on the other end.

Re-reading my earlier post, I should’ve said cost and not energy.