1. Place your chosen image here. The four corners must just cover the arrow tips. For covers, the three pictures should be the same size and in a straight line. Linepack ‘Park and Loan’ - Estimated Volume UNC Transmission Workgroup, 11 February 2011

2. Estimated release volume  We previously indicated:  Decision to release and volume released at discretion of National Grid.  Potential range of park and loan between 2 and 10mcm.  After further analysis we now estimate:  Release park and/or loan on 60% to 80% of days.  Most often net volume of release between 2mcm and 6mcm.

3. Estimated Release Volume (2)  More uncertainty at early release times.  More certainty later in gas day, but limited time for physical rate increase/decrease.  Likely to release both park and loan at same time, depending on operational conditions.  Minority of days with zero release - for example following recent supply loss, and uncertainty over subsequent reliability of this supply.

4. Uncertainty of physical imbalance  Uncertainty reduces during the gas day.  Current incentive to ensure closing linepack (CLP) is close to opening linepack (OLP), whilst minimising effect on market. Target change = 2.8mcm.  In 2010, achieved average difference of 2.0mcm.  Projected closing linepack (PCLP) is increasingly accurate during gas day, demonstrating increasing certainty of physical imbalance.  Of course late changes can occur.  The following graphs illustrate this.

5. Increasing accuracy of PCLP, in 2010

6. Increasing certainty

7. Increasing certainty (2)

8. Example of late change