Valley filling includes building the load during off-peak hours
This proves to be particularly interesting in cases whereas the long term marginal production costs are less than the selling price of electricity. Under these conditions, adding loads at a reasonable rate helps to reduce the whole cost price of electricity. For example, one of the ways of increasing the energy consumption during off-peak hours (valley filling) is to design buildings along with thermal storage facilities (e.g., water heating and /or space heating), that could produce demand during off-peak hours or to offer special rates (tariff clauses) favoring load increases during off-peak hours only. For instance, power utilities encourage customers to switch on their water heating appliances during off peak hours.