POWER April 2015 - 74

GENERATION TECHNOLOGIES
4. Best fits. This modification of the duck
pond chart shows where simple cycle plants
(red) and combined cycle generation (blue) are
best fits. In the area between, the best technology
depends upon plant-specific circumstances.
Source: Siemens
27
25
23
21
19
17
15
13
12
11
10
9
8
7
6
5
4
Less than
10%
2015
2013
10%-20%
capacity
factor
5. Typical daily operation at SCC5-8000H in Irsching, Germany. This plant
starts quickly in the morning, follows demand during the day, shuts down in the evening, and
repeats the pattern the next day. Source: Siemens
Reliable plant startup
More than 20%
capacity factor
250
200
150
100
50
The driver is economics. Driven by the
levelized cost of electricity, simple cycles
are typically dispatched <10% and combined
cycles are typically more advantageous over
20% dispatch. The grey area in between depends
on the actual plant configuration and
conditions.
Transferring these criteria to the duck
pond, you can see in Figure 4 the area showing
where simple cycles make the best economic
choice. Combined cycles are a better
choice for the rest of the pond if they can
meet the fluctuating demand-and analysis
and history shows that they can. (Ed.: For
studies suggesting other potential solutions
that may be part of the picture, see " California
Plans for Even More Renewable Power in
Its Future " at powermag.com.)
Flexible Combined Cycles for Load
Following
Combined cycles, especially modern flexible
combined cycles like Siemens Flex-Plant are
capable of meeting large, fast load changes.
Modern combined cycles are getting so fast
that they can exceed simple cycles in flexibility
and benefit to the grid.
Siemens Flex-Plants, for example, can
start fast and ramp up quickly, offering full
gas turbine power in less than 15 minutes and
full combined cycle power in about 30 minutes.
They also offer high-efficiency operation
over a wide range of available output and
can quickly load follow over this available
range. The higher efficiency of combined
cycles also means they are dispatched and
operating more often, and are therefore able
to provide frequency support for the grid.
A good example of a flexible combined
cycle is the Siemens H-Class power plant
74
On grid control
Fast, controlled
ramp up & down
April 8, 2013
April 9, 2013
0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12 21:36 0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12 21:36 0:00 2:24
Time
6. Winter renewables scenario. This chart simulates a winter day on the Huntington
Beach grid. Source: Ventyx Inc.
35
30
25
20
15
10
5
1
Demand
Net demand
Wind
Solar
Simple cycle
Combined cycle
Hydro
Gas-fired steam turbine
Cogen
Hour
24
Biomass/geothermal
Coal-fired steam turbine
Nuclear
7. Combined cycle contribution. This chart is a simulation of the ramping support
from combined cycle power plants on the Huntington Beach grid. Source: Ventyx Inc.
Combined cycles:
12
10
8
6
4
2
1
that has been operating since 2012 in Irsching,
Germany. Figure 5 shows an example
of the plant operation as it starts quickly in
the morning, follows demand during the day,
shuts down in the evening, and repeats this
pattern the next day.
www.powermag.com
Ramp rate of >2,500 MW/hr
Hour
24
With Siemens Flex-Plants there is no need
to trade efficiency for flexibility. This plant
exceeds 60% net combined cycle efficiency
and can add 500 MW of generation to the
grid in 30 minutes. Operating Flex-Plants
in the U.S. include Lodi Energy Center in
POWER | April 2015
Net load (GW)
Generation (GW)
Generation (GW)
MW

http://www.powermag.com http://www.powermag.com

POWER April 2015

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