The difference between the amount of power produced (supply) and the amount of energy contracted or sold (demand).

Where a site consumes electricity as opposed to generating and exporting power. Import is the most common type of site.

Incumbent supplier
The energy supplier who at the time the term is used is contracted to supply energy to a consumer.

Indexed Offers
An offer from a supplier linked to the spot price published in one of the daily market reports, they ensure that the price will always equate to the average paid across the country ensuring savings over fixed prices in a falling market and vice versa in a rising market.

Infrastructure Costs
These relate mostly to the costs of providing the infrastructure required to deliver power. They include the cost of energy lost as heat as it travels from the power station down the transmission and distribution wires to you (which are called Tloss and Dloss) and charges for using the transmission and distribution networks (which are called TUoS and DUoS).

Installed Capacity
The total capacity of the generation units installed at a power station.

A material that reduces or stops the flow of electricity.

Integrated Gasification Combined Cycle (IGCC)
IGCC plants initially gasify the raw fuel input, before passing the so-called synthesis gas through a conventional combined cycle set up. IGCCs can be designed to use a range of raw fuel inputs, including coal, oil products and wastes.

Integrated Pollution Prevention and Control (IPPC)
IPPC Directive is about minimising pollution from various point sources throughout the European Union. Based on the concept of Best Available Techniques (or BAT).

Facilities which connect two electricity grid systems, gas pipelines or control areas.

A connection or link between power systems enabling them to draw on each other's capacity.

Interconnector, England - Scotland
The transmission line between England and Scotland capable of transmitting 2,200MW in one direction.

Interconnector, Northern Ireland - Irish Republic
The transmission line between Northern Ireland and the Irish Republic with a 600MW capacity.

Interconnector, Scotland - Northern Ireland
The transmission line between Scotland and Northern Ireland with a 500MW capacity.

Interconnector, UK - Belgium
A 238 km pipeline providing a strategic link between the UK and continental Europe, connecting the two gas transmission systems at Bacton in the UK and Zeebrugge in Belgium.

Interconnector, UK - France
The transmission line between the UK and France with a 2000MW capacity.

International Panel on Climate Change (IPCC)
Founded in 1988, the IPCC is a scientific intergovernmental body founded by the World Meteorological Organisation (WMO) and the United Nations Environment Programme (UNEP). It aims to provide an objective source of information about climate change to policy-makers by assessing the latest scientific, technical and socio-economic literature worldwide on the human causes of climate change.

Interruptible Service
A supply which offers lower transportation costs but where, at times of high demand, the Network Operator can shut off the gas to the supply point. See 'Firm'.

Interval Data
Interval energy data is collected by an interval meter, which, at the end of every interval period (e.g. every half hour), records how much energy was used in the previous interval period. This data is also often referred to as "interval meter data", "demand interval data", "kW interval data", "electricity interval data."

An option which has intrinsic value. A put option in in-the-money when its strike price is above the value of the underlying futures contract. A call option in in-the-money when its strike price is below the value of the underlying futures contract.

Intrinsic Value
The value to an option holder if he were to exercise an option today.

Involuntary Withdrawals
A shipper receives an involuntary withdrawal when another shipper attempts to confirm one of their sites as their own. The shipper can either object (keeping the site, normally because of an amount outstanding, or the site is still in contract), or release the site to the new shipper.

International Petroleum Exchange. A London oil futures market trading gas oil and crudes as well as options.

International Performance Measurement and Verification Protocol defines standard terms and suggests best practise for quantifying the results of energy efficiency investments and increase investment in energy and water efficiency, demand management and renewable energy projects.

ISO 14064
This is an international standard for corporate emissions reporting. It builds on the approach outlined in the Greenhouse Gas Protocol.

ISO 50001
ISO 50001 is a specification created by the International Organization for Standardization for an energy management system, which specifies requirements for establishing, implementing, maintaining and improving an energy management system, whose purpose is to enable an organization to follow a systematic approach in achieving continual improvement of energy performance, including energy efficiency, energy security, energy use and consumption