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Another measure shown in Table 1 is
the drop in linepack over a three-hour
time period, which can be considered
as the release of stored energy.
Figure 2 presents the hourly linepack
timeseries of the NTS, GDN and
combined series. This shows a clear
seasonality for the variation in GDN
linepack with lower amounts of within-
day flexibility needed in the summer in
comparison to the winter.
This seasonality is due to the much
greater within-day changes in gas

A gas grid that transports
drop-in replacements for
fossil natural gas such as bio-
synthetic natural gas could
potentially continue to use
linepack and linepack flexibility
in a similar manner to today,
even though overall gas demand
is expected to decline Within-day linepack flexibility equivalent to just over 50 per cent of
quartile values the average linepack at 662GWh.
demand during the heating season, The quartile values of within-day The values in Table 2 show that GDNs
driven primarily by demand for space linepack flexibility are shown in provided at least 183GWh of within-day
heating and hot water. Table 2. In addition to the maximum, linepack flexibility (useable gas storage)
Larger within-day swings in demand minimum and quartile values for the for 75 per cent of the days over the
require greater within-day flexibility entire dataset, the within-day linepack heating season, and at least 243GWh for
to accommodate these, which can be flexibility values are shown for the 2 per cent of the days.
supported by linepack flexibility as well as October to March heating season. The related values for within-day
flexing gas supplies throughout the day. This gives an indication of linepack flexibility from pumped storage are at
The four pumped storage schemes in flexibility when gas demand is higher. least 10GWh for 75 per cent of the days
Britain have a total capacity of nearly Of particular note is the level of over the heating season, and at least
28GWh and use part of this capacity to within-day flexibility of the GDNs in 12GWh for 25 per cent of the days.
balance electrical supply and demand absolute terms and in percentage The initial analysis has yielded a
over a day. terms of the average level of the number of findings:
The highest three-hour reduction linepack itself. The maximum within- Firstly, the timing of variations to NTS
was -7.9GWh. day linepack flexibility was 337GWh, linepack and GDN linepack are highly

TABLE 2 MAXIMUM, MINIMUM AND QUARTILE VALUES FOR WITHIN-DAY LINEPACK FLEXIBILITY FOR ALL MONTHS, AND THE OCTOBER TO MARCH HEATING SEASON. ALL VALUES ARE MEASURED IN GWH

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