High-level waste (HLW) is highly radioactive material arising from nuclear fission. It can be recovered from reprocessing spent fuel, though some countries regard spent fuel itself as HLW. It requires very careful handling, storage and disposal. Low-level waste (LLW)is mildly radioactive material usually disposed of by incineration and burial.

Waste Residue
The portion of the waste stream (domestic and commercial) that cannot currently be recovered or recycled.

Watt (W)
The conventional unit which measures the rate of flow of energy. One watt amounts to one joule per second.

Wattless Unit
See Reactive power (kVArh)

WC - Whole Current
Whole Current meters require site shutdown when being installed.

Working days next week.

Week (1 to 52)
Refers to a specific week of the current year commencing on a Monday.

Whole Current Metering
Metering that is 100 amp and below.

Wind power
The conversion of energy in the wind into electrical power. The wind hits the blades of the wind turbine, which rotates like a giant propeller and powers the generator. Wind farms can be sited on land or at sea, with those offshore able to take advantage of the much stronger and consistent winds found off our coast.

Wind Turbine
A term used for a wind energy conversion device that produces electricity. These typically have between one and three blades.

The winter period, normally November to March inclusive.

Within Day
Within the current day.

Wobbe Index
The gross calorific value of natural gas divided by the square root of the Relative Density.