Economy 7
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Economy 7 is the name of a tariff provided by United Kingdom electricity suppliers that uses base load generation to provide cheap night-time electricity.
Electricity is charged at a cheaper rate during the off-peak night time - specifically, a 7-hour period, hence the name. To take advantage of Economy 7, boilers and night storage heaters are often automatically switched on during this period rather than during the day. Additionally, it is cheaper to operate appliances such as washing machines and dishwashers during this period. As an example tariff from October 2006, Ecotricity charges 22.03 UK pence per kilowatt hour for the first 728 kilowatt hours of day usage, 12.13 UK pence for subsequent day use and 4.63 UK pence for night time electricity.
A drawback of economy 7 is that the day rate is higher than the standard 24 hour tariff (15.78 pence per kilowatt hour for the first 728 units and 11.47 pence after that). Consequently a house needs to have at least 20% of its consumption at night to save money.
Houses using the Economy 7 tariff require a special electricity meter which provides two different readings - one for the day period and one for the night period. The wiring in the house does not need to be altered. For example, the night storage radiators are not on a special circuit attached only to the night meter, but rather are on the ordinary circuit. Thus to save money the appliances require the intelligence to turn themselves on and off at the right times. Thus an ordinary electric fan heater plugged into a study and run at 6am still gains the savings.
The specific times when Economy 7 applies vary between different regions and at different times of year. The seven-hour period typically starts at around midnight, but may start as early as 10.30pm or as late as 1.30am, and may or may not be continuous. Npower (UK), for example, has the period running from 1am to 8am.
