H2Tech - Q3 2021 - 38

HYDROGEN STORAGE
TABLE 3. Range of round-trip efficiency for varying configurations
Performance
Low
Average
High
High
Maximum
Low
Average
High
Maximum
Low
Average
High
Maximum
Electrolyzer
PEM electrolyzer, %
48.5
75
75
75
82
60
70
75
90
60
75
80
90
Storage, %
97.5
98.2
99
99.8
100
Fuel cell
97.5
98.2
99
99.8
97.5
98.2
99
40
45
60
80
99.8
With waste heat recovery (CHP)
55
65
70
90
Notes
Low (60%) = Maximum de-rated average, per vendors
Average (75%) = Typical, as per Blanco and Faaij, 2018)
High (75%) = Maximum reported by vendors without heat recovery
Maximum (82%) = Maximum without heat recovery
Storage
(depth dependent)
Low = 2.5% round-trip fuel
Average = 1.8% round-trip fuel
High = 1% round-trip fuel
Maximum = Electrical compression with solar + battery
Fuel cells
Low (60%) = Lowest PEM fuel cell efficiency
Average (70%) = Median of PEM fuel cell range
High (75%) = Highest reported from vendors
Maximum = High plus 20% heat recovery (maximum reported by vendor)
Discharge limitations. Discharge cycling is constrained
by the selection of generation equipment and desired ramp
time (ramp time equals time from cold start to full power).
Fuel cells ramp up and down very quickly (sec to min, depending
on standby conditions) without meaningful degradation
of performance.
Combustion technologies are more mature and available at
scale; however, they have longer duty cycles than fuel cells. H2
has less energy content than methane, so it can do less work
instantaneously. A cold turbine firing on 100% H2
has a longer
ramping time than a comparable natural gas unit. This can be
mitigated by co-firing with natural gas during startup, but doing
so results in carbon emissions.
Combustion engine and turbine duty cycles encompass
four gross time periods:
1. Ramp-up time
2. Minimum runtime (time between
generator breaker close and reopen)
38 Q3 2021 | H2-Tech.com
3. Ramp-down time
4. Minimum downtime (time the generator
must be offline before restarting).
As an example, a gas engine with a startup ramp-up of 30
min, a minimum run time of 60 min, a ramp-down of 30 min,
and 120 min of minimum downtime would have a minimum
duty cycle of 240 min (4 hr), and would be limited to a maximum
of six starts per day.
For combustion technologies, the cost of operating and maintenance
due to frequent starts and stops is also a consideration.
Degradation and variances in capacity. Charge and discharge
capacities of HES may vary due to transient weather
conditions, progressive wear and tear, and discharge loading.
De-rating for ambient weather. There is no derating of
the electrolysis or a fuel cell facility for elevation, or within
ambient temperature of 5°C-45°C (41°F-113°F), and relative
humidity of 0% to 95% (non-condensing).
Due to changes in air density with temperature and humid23
31
45
72
32
48
55
81
PEM
fuel cell
PEM fuel cell
PEM fuel cell
PEM fuel cell
Radial turbine CCGT
Turbine gas engine
Fuel cell
Fuel cell
Generator, %
24.1
Round trip, %
11
29.5
37.8
51.5
57.7
22
28
39
47
Generation technology
Radial turbine
Simple-cycle E-class
SC aeroderivative
Combined-cycle F-class
CC H-/J-class
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