Explanation of the various categories

Historic Demand Data
Description of contents
This document explains what is included in the historic demand data files published
on the National grid website:
The page contains two data files “DemandData_Historic.csv” and “DemandData_Update.csv”; combined these
provide a complete set of historic demand data since the beginning of British Electricity Trading and
Transmission Arrangements (BETTA) in April 2005.
The larger file “DemandData_Historic.csv” contains data from April 2005 up to the latest completed settlement
month. It is updated each month, usually during the second week of the month. The file contains all the data
fields described in the section below.
The smaller file “DemandData_Update.csv” gives an update to the larger data set to include the latest
operational data where available. This file contains a subset of the data items below; these are indo,
england_wales, embedded_wind and embedded_solar. The file is updated daily, usually prior to mid-day.
Data Item
Initial National Demand Outturn (INDO) - as published on BM Reports. It is equivalent to
the Great Britain generation requirement and is comparable to the National Demand
forecast. The figures exclude station load, pump storage pumping and interconnector
INDO is calculated as a sum of generation based on National Grid operational
generation metering. The list of generators that are included in the sum is published
separately in the accompanying BMU List.xls file.
England and Wales Demand - as INDO above but on an England and Wales basis.
Embedded Wind Generation - an estimate of the UK’s wind generation from wind farms
which do not have Transmission System metering installed. These wind farms are
embedded in the distribution network and invisible to National Grid. Their effect is to
suppress the electricity demand during periods of high wind. The true output of these
generators is not known but is modelled based on actual weather and capacity data.
Note that embedded wind farms which do have Transmission System metering are not
included in this total.
For future dates a forecast value is shown. This is equivalent to the data that feeds into
the National Demand forecast published on BM Reports. This is updated daily.
Embedded Solar Generation – as embedded wind generation above, but for solar
Non-BM Short-Term Operating Reserve – operating reserve for units that are not
included in the INDO generator definition. This can be in the form of generation or
demand reduction.
I014 Demand - the demand as derived from Settlement data. This is done using metered
generation from the I014 file. The list of generators used is identical to that used for
INDO above. Note that the demand includes station load and is therefore higher than
INDO. Station load is 500MW in BST and 600MW in GMT.
Total Gross System Demand (TGSD) - the total demand on the Transmission System; it
includes station load, pump storage pumping and interconnector exports. The data is
derived from Settlement data similarly to the I014 Demand above.
Pump Storage Pumping – the demand due to pumping at hydro pump storage units; the
-ve signifies pumping load.
Interconnector Flow – the flow on the respective interconnector. -ve signifies export
power out from GB; +ve signifies import power into GB.
If you have any questions or feedback please contact:
Nikhil Madani
Email: nkhil.madani@nationalgrid.com
Jack Barber
Email: jack.barber@nationalgrid.com