flow flexibility capacity joint office 7 th december 2006

Flow Flexibility Capacity

Joint Office

7th December 2006

Effect of Within Day Demand Change

Shipper DN NTSActual demand is below expectationShippers are long and system is in imbalance

Actual demand is below expectationNational Balance depends upon DNs hitting end of day stockHence need to reduce offtake from NTS

Actual demand is below expectationDNs pass imbalance onto NTSNational Balance is achieved by selling gas off the system/shippers informed of imbalance

Consider situation where demand is falling:

Therefore imbalance should be resolved by flow change not by use of NTS storage


Offtake

Rate

Time 22:00 06:00

Planned Flow Rate at start of day

Flexibility utilisation = cumulative offtake to 22:00 – (2/3) of daily flow


Offtake

Rate

Time 22:00 06:00


Actual Flow Rate

Change of flow to meet change of demand forecast increases flow flex utilisation

The following example demonstrates the effect of a demand change at 22:00;22:00 was chosen for the sake of clarity


Offtake

Rate

Time 22:00 06:00


Actual Flow Rate



Average Flow Rate


Offtake

Rate

Time 22:00 06:00


Actual Flow Rate



Average Flow Rate

Flexibility utilisation

Impacts

DNs must ensure that their bookings of flow flex allow for this effect.

This artificially inflates the volume of storage required by a DN

Whilst the flow flex apparently taken has no impact on NTS storage the NTS cannot simply oversell flow flex as they would then be unable to

deliver if the DNs chose to use their allocation of flow flex to meet true diurnal demand

DN investment will be required to provide additional storage that is unnecessary

If a DN runs out of flow flex, they will have an incentive to keep within their flow flex limit by increasing their end of day stock

This hides the imbalance from the NTS, undermining both the “national” and “daily” elements of the balance

When demand has been under-forecast the opposite effect occurs with the apparent consumption of flow flex being understated

Thus NTS storage could be over-stretched without the connected parties having broken their flow flex limits

Flow Flex Utilisation Correction

Presently:

flow flex = flow (06:00 to 22:00) – 16/24 (end of day flow)

•But can correct for within day demand change:

Real flow flex utilisation = metered flow flex – correction

Where correction = demand change * correction factor

•Overruns triggered if real flow flex utilisation > booked flow flex

Flow Flex Utilisation Correction Factors

Time ofForecast Change

Coversion of Forecast Change

to Flow Flex

Hours Action

Pre 2200

Hours Action

Post 2200 Total Hours Action

0600 0.00% 16 8 240700 -1.45% 15 8 230800 -3.03% 14 8 220900 -4.76% 13 8 211000 -6.67% 12 8 201100 -8.77% 11 8 191200 -11.11% 10 8 181300 -13.73% 9 8 171400 -16.67% 8 8 161500 -20.00% 7 8 151600 -23.81% 6 8 141700 -28.21% 5 8 131800 -33.33% 4 8 121900 -39.39% 3 8 112000 -46.67% 2 8 102100 -55.56% 1 8 92200 -66.67% 0 8 82300 -66.67% 0 7 70000 -66.67% 0 6 60100 -66.67% 0 5 50200 -66.67% 0 4 40300 -66.67% 0 3 30400 -66.67% 0 2 2

0500 -66.67% 0 1 1

Example

Time Demand Change (mcm)

Correction factor

Flow flex correction (mcm)

10:00 37.5-35.9 = 1.6 0.0667 0.11

13:00 35.9 – 35.9 = 0 0.137 0

16:00 35.9 – 36.1 = -0.2 0.238 -0.0476

21:00 36.1 – 35.7 = 0.4 0.555 0.222

Total 0.281

The following example shows how a falling demand throughout the day would result in a flow flex correction of 0.281 mcm representing 8%of the LDZ flow flex requirements

Advantages of Correcting for Within Day Demand Change

•Reveal real NTS diurnal support required by DNs

•Avoids undermining NTS balance

•No incentive for DNs to hide imbalance

•Provide certainty to DNs when booking flow flexibility

•Reduce costs of DNs investing to provide storage

flow flexibility capacity joint office 7 th december 2006

Documents