Linepack ‘Park and Loan’ Quantity - Influencing Factors
Review Group 291 – July 2010
Summary
 Pre-assessment of available quantity for park and loan is complex.
 Competing needs for flexibility and contingency impact on the
operating range of linepack.
 This motivates discretionary release, with appropriate incentive.
Operational Range of Linepack Flexibility
Maximum operating pressures
Demand / supply pattern
Linepack
Flexibility
NTS set-up
Flexibility + contingency
Contractually agreed pressures
day
System Flexibility
 NTS has historically been built to transport gas efficiently, based on flat
supply and demand, within a range of operating pressures.
 System flexibility is inherently a “by-product” of operating the NTS within a
range of pressure limits.
 Current “limits” of flexibility entirely dependent on the daily NTS setup and
the supply/demand pattern and therefore quite complex to define and
model outer-boundary and maxima of available flexibility.
 National Grid is incentivised to minimise day-on-day linepack changes but
has no incentive on within-day linepack ‘release’ or ‘use’
Flow Pattern Volatility – “Time of flight”
The ability to profile energy within day across a number of entry/exit points
whilst maintaining an energy balance in aggregate across the day.
 Supply patterns responding to demand and market changes.
 Plant issues and Portfolio balancing.
 Price-responsive supplies and demands.
Supply B
Supply A
50km
200km
Offtake
Flows from Supply A switch to Supply B.
Linepack levels at Offtake will drop due to
the inherent lag of flow from Supply B taking
time to reach the Offtake
Single Entry/Exit Point Flexibility
The ability to profile an entry or exit flow above and below a flat rate.
 DN offtake profiles.
 Power station changes driven by electricity market interaction.
 Storage and interconnector within-day switching.
Flow
 Within-day entry flow fluctuations driven by demand changes and
nomination changes.
Average flow
(1/24th rate)
Removing
Linepack from
NTS
Example: DN Offtake
Flows vary within day due
to domestic demand
Replenishing
Linepack to
NTS
Time
Flow
(2) NTS Flow, Pressure & Flexibility
Replenishing
Linepack to
NTS
Removing
Linepack from
NTS
DN Offtake
Flow profile
varying about the
1/24th rate
Average flow
(1/24th rate)
Increasing
Linepack
Usage
Time
Minimum pressure at
point where depletion of
linepack ceases
Min Daily
Pressure
Pressure
Max Daily
Pressure
Finite limit of flexibility
linked to compression/
flow rates required to
return to start of day
pressure
Increases the
severity of NTS
pressure drop
Time
06:00
Start of Day
22:00
06:00
Example Day – 9th January (Actual Data)
Within day linepack movement - 9th January 2010
360
355
345
340
335
06
:0
0
04
:0
0
T
G
M
02
:0
0
00
:0
0
22
:0
0
20
:0
0
18
:0
0
16
:0
0
14
:0
0
12
:0
0
10
:0
0
08
:0
0
330
06
:0
0
mcm
350
Operational Range of Linepack Flexibility
Maximum operating pressures
 Compressor trip risk
Linepack
Flexibility
Contractually agreed pressures
day
Operational Range of Linepack Flexibility
Maximum operating pressures
 Compressor trip risk
 Within-day exit flexibility
Linepack
Flexibility
Contractually agreed pressures
day
Operational Range of Linepack Flexibility
Maximum operating pressures
 Compressor trip risk
 Within-day exit flexibility
Linepack
 Within day entry flexibility
Flexibility
Contractually agreed pressures
day
Date
01/03/10
01/02/10
01/01/10
01/12/09
01/11/09
01/10/09
01/09/09
01/08/09
01/07/09
01/06/09
01/05/09
01/04/09
01/03/09
01/02/09
01/01/09
01/12/08
01/11/08
01/10/08
MCM
Within-day Linepack Utilisation
Within-day Max-Min Range of NTS Linepack
30
25
30 day rolling average
20
15
10
5
0
Operational Range of Linepack Flexibility
Maximum operating pressures
 Compressor trip risk
 Within-day exit flexibility
Linepack
Flexibility
 Within day entry flexibility
 Information uncertainty,
EOD imbalance
Contractually agreed pressures
day
01/06/2010
01/04/2010
01/02/2010
01/12/2009
01/10/2009
01/08/2009
01/06/2009
01/04/2009
01/02/2009
01/12/2008
01/10/2008
01/08/2008
01/06/2008
01/04/2008
mcm
Day-to-day linepack change
Closing Linepack minus Opening Linepack, 01-Apr-08 to 06-Jun-10
12
9
6
3
0
-3
-6
-9
-12
Within-day PCLP swings
Predicted Closing Linepack (PCLP)
Daily Range of Hourly PCLP: Monthly Maximum and Average
80
70
60
mcm
50
40
30
20
10
monthly maximum
Apr-10
Feb-10
Dec-09
Oct-09
Aug-09
Jun-09
Apr-09
Feb-09
Dec-08
Oct-08
Aug-08
Jun-08
Apr-08
Feb-08
Dec-07
Oct-07
Aug-07
Jun-07
Apr-07
Feb-07
Dec-06
Oct-06
Aug-06
Jun-06
Apr-06
0
monthly average
PCLP = Opening linepack
+ System Inputs (Daily Flow Nominations and Storage Flow Nominations)
– System Demand (Offtake Profile Notifications)
This graph shows ranges of hourly PCLP values during the gas day.
Operational Range of Linepack Flexibility
Maximum operating pressures
 Compressor trip risk
 Within-day exit flexibility
Linepack
Flexibility
 Within day entry flexibility
 Information uncertainty,
EOD imbalance
 Supply loss risk
Contractually agreed pressures
day
Example Day – 4th January (Supply Loss)
Within day linepack movement - 4th January 2010
350
345
335
330
325
320
0
0
06
:0
G
M
0
02
:0
04
:0
T
0
00
:0
0
22
:0
0
20
:0
0
18
:0
0
16
:0
0
14
:0
0
12
:0
0
10
:0
0
08
:0
0
315
06
:0
mcm
340
4th January - Continued
Within day linepack movement - 4th January 2010
350
345
335
330
325
320
315
06
:0
0
08
:0
0
10
:0
0
12
:0
0
14
:0
0
16
:0
0
18
:0
0
20
:0
0
22
:0
0
00
:0
02
0
:0
0
G
M
T
04
:0
0
06
:0
0
mcm
340
Actual Linepack
Linepack based on a Average profile
Operational Range of Linepack Flexibility
Maximum operating pressures
 Compressor trip risk
 Within-day exit flexibility
Linepack
Flexibility
 Inter-Day Linepack ‘park and loan’
 Within-day entry flexibility
 Information uncertainty,
EOD imbalance
 Supply loss risk
Contractually agreed pressures
day
Release volume
 Competing requirements for flexibility and contingency, and varying
conditions day to day, determines the release will be discretionary if
the quantity is to be maximised.
 The risks and rewards inherent in linepack release leads to an
incentivised regime.