D

Daily Contract Quantity (DCQ)
The quantity of gas to be supplied daily to a site (sales contract) or to a terminal (supply contract).

Daily Meter (DM)
A supply point whose annual quantity (consumption) is greater than 58,600,000kWh (2,000,000 therms per annum), will have a mandatory DM meter fitted.

Dark Spread
A form of analysis used to compare coal prices with electricity prices by converting the coal price to MWh and subtracting it from the electricity price during a period taking power station efficiency into consideration, a negative dark spread indicates that it is more beneficial to sell coal than to produce and sell electricity.

Data Aggregator (DA)
A company responsible for putting a consumers' electricity consumption data into a format agreed by and for suppliers.

Data Collector (DC)
The organisation responsible for collecting and distributing details of the electricity consumed at half-hourly metered supply points.

Data Flow(s)
Data related to a specific supply point - generally pertaining to a change of supplier, Meter Operator (MOp), measurement or profile class - which passes between suppliers and meter operators of distribution companies enabling contractual details to be registered.

Data Logger
A device used to record meter readings and automatically transmit them to the meter reading agency.

Day Ahead
A physical contract for next day delivery.

Day Rate
Expressed in pence per kilowatt hour (kWh), the rate charged for consumption during those hours defined by the supplier as 'day'.

Decay
Disintegration of atomic nuclei resulting in the emission of alpha or beta particles (usually with gamma radiation). Also the exponential decrease in radioactivity of a material as nuclear disintegrations take place and more stable nuclei are formed.

Declared Net Capacity (DNC)
The highest generation of electricity (assuming that the source of power is available continuously) being maintained indefinitely without causing damage to the plant, minus the capacity consumed by the plant.

Deemed Contract
A contract that is deemed to apply when a customer begins a new supply at a property and has not signed a written contract for its supply. These contracts have a defaulted rate for supply until a customer requests a fixed price for a fixed period.

Default tariff
A rate of charge applicable to business energy consumers who fail to enter into a contract for the supply of energy or who fails to renew a contract before the end date of a current contract, default tariffs can 35% or more higher than a negotiated contract rate.

Degree Days
A measurement of the coldness of the weather (heating degree days) or is heat (cooling degree days)based on the extent to which the daily mean temperature falls above or below a specified base temperature. Used for calculations relating to the effect of outside air temperature on building energy consumption.

Delivery Facility Operators
Those who process natural gas at terminals around the coast of Britain before delivering it to 'Public Gas Transporters'.

Delta
The variable referring to the sensitivity of an option's value to a change in price in the underlying commodity.

Demand
The requirement for power at a supply point.

Demand Side Management (DSM)
Action by consumers of energy to control and alter their usage, typically in response to price signals and also through formal arrangements with suppliers and network operators.

Demand-Side Management
The planning, implementation, and monitoring of activities designed to encourage consumers to modify patterns of energy usage, including the timing and level of electricity demand.

Depleted Uranium
Depleted uranium means the by-product residues from the uranium enrichment process in which the concentration of the isotope U235 is less than that occurring in natural uranium.

Derivative
A market where the value of the contract being traded is derived from an underlying commodity. These markets typically involve forward purchases of sales and can take the form  of futures markets or over-the-counter swaps and options.

Differential (spreads)
The difference between two prices. A significant percentage of all oil transactions are effected on the basis of differentials rather than outright flat prices.

Direct Current (DC)
An electrical current that flows only in one direction in a circuit. Batteries and fuel cells produce direct current.

Discount
An amount agreed between buyer and seller to be subtracted from an existing benchmark.

Display Energy Certificate (DEC)
DECs are designed to promote the improvement of the energy performance of buildings. They are based upon actual energy usage of a building and increase transparency about the energy efficiency of public buildings.

Distributed and Microgeneration
This is when electricity is generated for local distribution and is not connected directly to the National Grid. Microgeneration is typically used to describe smaller scale generating technology. Both of these types of generation have a role to play in the country's energy mix, although it is important to be realistic about the overall size of the contribution - they may not be the best economic or most environmentally friendly solution in every case.

Distributed or Embedded generation
Electricity generation by plant connected to a (localised) distribution system rather than to a transmission system.

Distribution company
See Distribution Network Operator - the company which owns the local distribution electricity system, charges for use of the system (DUoS) are passed onto the client via the supplier.

Distribution Losses (Dloss)
Charges for the loss of distributing power through the wires.

Distribution system
The local wires, transformers, substations and other equipment used to distribute and deliver energy to end-users.

Distribution use of system charges (DUoS)
Charges passed on by the Distribution Company to cover the cost of passing electricity through the local network.

Domestic / Non Domestic Supply
A Supply Point with an AQ of 73,200kWh (2500 therms) or less, is deemed as a domestic site. (This does not mean the user is necessarily residential). A supply point with an AQ of over 73,00kWh is deemed as non-domestic.

DRC - Data Retrieval Centre
The centre that remotely interrogates the meters, and sends the information up to the Data Aggregator.

Dynamic Hedging
The constant readjustment of hedging positions to reflect changes in the relative prices of the underlying commodity and the various derivative instruments in the portfolio.