sentences:  The motivation for dual-tariff arrangements was the lower night-time demand.Dual tariffs made possible the use of low-cost night-time electrical power in applications such as the maintaining of 'heat banks' which served to 'smooth out' the daily demand, and reduce the number of turbines that needed to be turned off overnight, thereby improving the utilisation and profitability of the generation and transmission facilities.The metering capabilities of the 1960s grid meant technological limitations on the degree to which price signals could be propagated through the system.