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Economy 7 is the name of a differential tariff provided by United Kingdom electricity suppliers that uses base load generation to provide cheap off-peak electricity during the night.
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Houses using the Economy 7 tariff require a special electricity meter which provides two different readings - one for electricity used during the day, priced higher, and the other for the night, priced lower. The night (off-peak) period lasts for a total of seven hours, hence the name; however it may or may not be a continuous period, as it may alternate between the two prices during the night.
The first mention of Economy 7 is in 1978: "A new off-peak tariff known as the 'Economy 7' tariff was introduced in October [1978]. It featured a seven-hour night rate some 20 per cent cheaper than most night-time tariffs, made possible by economies in the night-time operation of the system." In more recent years the difference between day and night rates has become much larger, with typically over 50% reduction (though dependent on the supplier). Choice of the Economy 7 tariff results in either or both of an increased standing (fixed) charge or increased daytime rate. (Also known as "White Meter", mainly in Scotland, with appropriately white-cased meters.)
Timing and switchover
The night storage heaters and hot water boilers are generally on a separate circuit which is only switched on when the night rate is activated, although any electrical appliance on an ordinary circuit during this period also runs at the lower rate of billing, such as a dishwasher or washing machine set to start using a timing device. Some such machines have timers built-in partly for this purpose. In newer houses, a digital meter automatically switches to record both ranges. The wiring in the house is rarely different for Economy 7. Many consumers will however choose to set devices such as storage heaters and water heaters to turn on during the hours of Economy 7 to save money. Few houses now have devices controlled solely by the timer on the electricity meter itself.
The specific times when Economy 7 applies vary between different regions, seasons, and sometimes individual meters. For example, the seven-hour period might start at 1.30am during British Summer Time and 12:30am during Greenwich Mean Time (winter). Some regions use radio teleswitching to control consumers' systems and vary the timing. This uses data superimposed on the 198 kHz BBC Radio 4 long-wave signal.
Pricing
Electricity supply in the United Kingdom is deregulated and the several providers offer different tariffs, much as telephone or internet service providers do. Economy 7 can offer some consumers savings, but a careful analysis should be done. For example, if the price is double the normal tariff during the 'day' period, and half the normal during the 'night' period, then to break even the consumer would need to use over 2/3 of their energy during the 'night' period. Typically this holds true when heating/water is electric rather than gas, or if the supply is used to charge an electric vehicle overnight. An Economy 7 tariff can end up costing significantly more than a standard tariff without restructuring current energy usage.