China Power System Transformation |
Power system transformation and flexibility |
For the short timescales in this report, the focus is on system frequency.24 Any imbalance between supply and demand results in frequency deviation, denoting either supply surplus or deficit. System frequency is one of the critical considerations in determining appropriate technical and regulatory options, particularly as the share of VRE increases.
For longer-term flexibility, the issue of uncertainty in the future resource mix is also relevant since it is related to ongoing investment. One important consideration is that the non-VRE mix should be sufficiently robust to accommodate an uncertain VRE penetration rate, which may differ from the plan.
In addition to technical aspects, unlocking flexibility requires action in additional areas as discussed in the next section.
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Table 5. |
Different timescales of power system flexibility |
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Flexibility |
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Ultra-short- |
Very |
Short- |
Medium- |
Long- |
Very long- |
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type |
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term |
short-term |
term |
term |
term |
term |
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flexibility/ |
flexibility |
flexibility |
flexibility |
flexibility |
flexibility |
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stability |
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Timescale |
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Subseconds |
Seconds to |
Minutes to |
Hours to |
Days to |
Months to |
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to seconds |
minutes |
hours |
days |
months |
years |
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Issue |
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Ensuring |
Ensuring |
Meeting |
Determining |
Addressing |
Balancing |
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system |
short-term |
more |
operation |
longer |
seasonal and |
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stability |
frequency |
frequent, |
schedule of |
periods of |
inter-annual |
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(voltage and |
control at |
rapid and |
the available |
surplus or |
availability of |
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frequency |
high shares |
less |
generation |
deficit of |
variable |
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stability) at |
of variable |
predictable |
resources to |
variable |
generation with |
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high shares of |
generation |
changes in |
meet system |
generation, |
power demand |
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non- |
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the supply- |
conditions in |
mainly |
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synchronous |
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demand |
hourand |
driven by |
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generation |
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balance; |
day-ahead |
presence of |
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system |
time frame |
a specific |
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regulation |
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weather |
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system |
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Has |
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Dynamic |
Primary |
AGC, ED, |
ED for hour- |
UC, |
Hydro-thermal |
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relevance for |
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stability |
and |
balancing |
ahead, UC |
scheduling, |
co-ordination, |
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following |
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(inertia |
secondary |
real-time |
for day- |
adequacy |
adequacy, |
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areas of |
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response, grid |
frequency |
market, |
ahead time |
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power system |
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system |
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strength) |
response, |
regulation |
frame |
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planning |
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operation |
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which |
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and planning |
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include |
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AGC |
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Notes: AGC = automatic generation control; ED = economic dispatch; UC = unit commitment.
Source: IEA (2018a), Status of Power System Transformation 2018: Advanced Power Plant Flexibility.
Layers of system flexibility
The flexibility of a power system can be determined according to three different aspects (adapted from IRENA, IEA and REN21, 2018):
technical options available (the hardware and infrastructure, or the “what”)
24 Voltage control aspects are not covered in detail.
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