IEEE Power & Energy Magazine - January/February 2017 - 20

table 1. Gas turbine manufacturers and
their related reciprocating engine companies.
Gas Turbine

ICEs

GE turbines

Jenbacher, Waukesha, Dresser

Rolls Royce

Bergen

Solar turbines

CAT Power

MAN Turbo

MAN

Mitsubishi Heavy Industries

when combined with capacity requirements, gas plants would
be particularly suitable. Market design and rewards for flexibility will be essential to encouraging investment in flexibility and ensure reliability.

Flexibility in Gas Supply: Gas Storage
and Gas/Electricity Market Coordination
Gas Storage
In the past, gas network flexibility appeared abundant compared to electricity systems and was largely ignored in electricity reliability assessments. The variability of varRE in the
electricity system will lead to the more flexible operation of
gas power stations, ultimately translating to diurnal variability
in gas supply, and may require that gas be stored in preparation for a ramping event in the electricity system. Compared
to electricity systems, gas systems typically offer significant
flexibility due to different storage options: line pack, underground storage, and LNG tanks.
Line pack is the volume of gas stored in pipelines and can
be used to meet abrupt diurnal changes in gas demand. It is
proportional to average system pressure. During a period of
low renewable energy output (for example, wind), gas generators may be called upon, which would lead to a large and
rapid decrease of the gas line pack. If this happens when

338
336
334
332

High Wind: 2020

330
328

Low Wind: 2020

Low Wind Case: 2020

25
Power (GW)

Base Case: 2009

10 mcm

Line Pack (mcm)

340

peak gas and electricity demand coincide, the resulting pressure drop in the gas network could limit its ability to meet
rapid changes in gas demand (including gas for power generation) and cause interruption of gas supplies to CCGTs.
Other flexibility sources (e.g., electricity imports through
interconnectors or demand-side response) would be required
to ensure reliable system operation. To mitigate such linepack shortages, coordination between gas network and electricity system operators will be increasingly important.
Modeling results for the United Kingdom's 2020 system
suggest the increasing need for coordination between gas
and electricity system operation. In a low wind scenario,
the line pack decreases strongly at times when high demand
coincides and limits the gas supply to CCGTs. As a result,
the power output from CCGTs during peak hours may drop
by almost 3 GW (Figure 5). This reduction in CCGT power
output was compensated for by the import of more expensive
electricity through the U.K./France interconnector.
Underground gas storage facilities include depleted
gas/oil fields, aquifers, and salt caverns. Depleted fields
and aquifers are typically used as seasonal storage facilities. Natural gas is injected into storage during the summer (low-demand season) and withdrawn during the winter
(high-demand season). The withdrawal rate and capacity
are often very large, but the cycling capability is limited.
Salt caverns are commonly used as fast-cycle storage due
to their ability to support several cycles of gas injection into
and gas withdrawal from storage within a year. This type
of storage is better suited to providing gas supply flexibility to electricity systems with high penetrations of varRE.
Despite the receding demand for gas in Europe, the number
of European storage facilities is increasing due to growing
flexibility requirements as well as concerns over the security of supply. The completion of currently planned projects,
mostly salt cavern facilities, will increase storage capacity
by 20% in 2020 compared to current levels.
LNG storage tanks and gasification stations are used as
peak shaving facilities that can respond rapidly to sudden

20
15
10
5
Base Case: 2009 High Wind Case: 2020

0
0

12 16 20 24 28 32 36 40 44 48
Time (h)
(a)

3.1 GW

12 16 20 24 28 32 36 40 44 48
Time (h)
(b)

figure 5. (a) The aggregate gas network line pack and (b) power generation by CCGT. (Source Qadrdan et al., 2010.)
20

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january/february 2017

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