the wind/hydrogen demonstration system at utsira in norway ......the wind/hydrogen demonstration...
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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 5 ( 2 0 1 0 ) 1 8 4 1 – 1 8 5 2
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The wind/hydrogen demonstration system at Utsira inNorway: Evaluation of system performance using operationaldata and updated hydrogen energy system modeling tools
Øystein Ulleberg a,*, Torgeir Nakken b, Arnaud Ete c
a Institute for Energy Technology, P.O. Box 40, NO-2027 Kjeller, Norwayb StatoilHydro Research Centre, NO-3908 Porsgrunn, Norwayc University of Strathclyde, Energy Systems Research Unit, Glasgow, Scotland G1 1XJ, UK
a r t i c l e i n f o
Article history:
Received 15 May 2009
Received in revised form
23 October 2009
Accepted 25 October 2009
Available online 15 January 2010
Keywords:
Wind
Hydrogen storage system
Water electrolysis
Stand-alone power system
Demonstration plant
Operational experience
System simulation
TRNSYS
HYDROGEMS
* Corresponding author.E-mail address: [email protected] (Ø
0360-3199/$ – see front matter ª 2009 Profesdoi:10.1016/j.ijhydene.2009.10.077
a b s t r a c t
An autonomous wind/hydrogen energy demonstration system located at the island of
Utsira in Norway was officially launched by Norsk Hydro (now StatoilHydro) and Enercon
in July 2004. The main components in the system installed are a wind turbine (600 kW),
water electrolyzer (10 Nm3/h), hydrogen gas storage (2400 Nm3, 200 bar), hydrogen engine
(55 kW), and a PEM fuel cell (10 kW). The system gives 2–3 days of full energy autonomy for
10 households on the island, and is the first of its kind in the world. A significant amount of
operational experience and data has been collected over the past 4 years. The main
objective with this study was to evaluate the operation of the Utsira plant using a set of
updated hydrogen energy system modeling tools (HYDROGEMS). Operational data (10-min
data) was used to calibrate the model parameters and fine-tune the set-up of a system
simulation. The hourly operation of the plant was simulated for a representative month
(March 2007), using only measured wind speed (m/s) and average power demand (kW) as
the input variables, and the results compared well to measured data. The operation for
a specific year (2005) was also simulated, and the performance of several alternative
system designs was evaluated. A thorough discussion on issues related to the design and
operation of wind/hydrogen energy systems is also provided, including specific recom-
mendations for improvements to the Utsira plant. This paper shows how important it is to
improve the hydrogen system efficiency in order to achieve a fully (100%) autonomous
wind/hydrogen power system.
ª 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
1. Introduction hydrogen technology in remote areas is the notion that
Hydrogen can be used to store variable renewable energy,
such as solar and wind energy [1,2]. Previous studies [3–6]
show that there is a potential market for wind/hydrogen
energy systems in remote areas and/or weak grids, specifi-
cally for (1) Stand-alone power systems and (2) Hydrogen
vehicle fueling stations. The main motivation for applying
. Ulleberg).sor T. Nejat Veziroglu. Pu
locally produced renewable hydrogen will be able to
compete with traditional fossil fuels (e.g., diesel) sooner
here than in more densely populated areas. The situation
today is that remote communities are already experiencing
relatively high fuel costs. Remote areas with favorable
winds are therefore logical targets for wind energy based
hydrogen systems.
blished by Elsevier Ltd. All rights reserved.
Nomenclature
Acronyms:
AC, DC alternating current, direct current
BOP balance of plant
CO2, H2 Carbon dioxide, Hydrogen
EES engineering equation solver
FC fuel cell
HHV higher heating value
HYDROGEMS HYDROGen Energy ModelS
IFE Institute for energy technology
IGBT insulated-gate bipolar transistor
NiCd nickel cadmium
PEM proton exchange membrane
R&D research & development
RE renewable energy
SAPS stand-alone power systems
TRNSYS TRaNsient SYstem simulation program
WECS wind energy conversion system
Symbols & Units:
P power, kW
v speed, m/s
h hour
kVA kilovolt–Ampere
kW, MW kilowatt, Megawatt
ms millisecond
m2 square meters
Nm3 normal cubic meters
V euro
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Several wind/hydrogen concepts and system designs have
been studied over the past decade [4–9], and a few physical
installations have been made [3,7,10–19]. An overview of the
most known wind/hydrogen demonstration systems and pilot
plants installed around the world the last decade is provided
in Table 1. Most of the installations listed here are small-scale
systems based on wind turbines with only few kWs and a DC-
busbar stabilized by a battery bank. The most notable excep-
tion is the autonomous wind/hydrogen system at the island of
Utsira (Norway), which provides power to 10 households via
a local AC mini-grid [12,18]. Another relatively large system is
the DC-based system serving the West Beacon Farm in
Table 1 – Overview of wind/hydrogen-systems installedworld-wide, 2000–2008.
Yeara Location Name of project Refs.
2000 ENEA Research
Centre, Casaccia, Italy
Prototype wind/electrolyzer
testing system
[7]
2001 University of Quebec,
Trois-Rivieres, Canada
Renewable energy
systems based on hydrogen
for remote applications
[10]
2004 Utsira Island, Norway Demonstration of
autonomous
wind/hydrogen-systems
for remote areas
[12,18]
2004 West Beacon Farm,
Loughorough, UK
HARI–Hydrogen and
Renewables Integration
[13]
2005 Unst, Shetland
Islands, UK
PURE–Promoting Unst
Renewable Energy
[3]
2006 IFE, Kjeller, Norway Development of a
field-ready small-
scale wind-hydrogen
energy system
[16,17]
2006 NREL, Golden,
Colorado, USA
Wind-to-hydrogen
(Wind2H2)
demonstration project
[14,15]
2007 Pico Truncado,
Argentina
Wind/hydrogen
demonstration plant
[11]
2007 Keratea, Greece RES2H2 wind-hydrogen
pilot plant, with H2-storage
in metal hydrides
[20]
a Approximate year of commissioning.
Loughborough (UK) [13], which has a hydrogen storage
capacity of about 2850 Nm3, slightly larger than the 2400 Nm3
installed at Utsira. Most of the systems listed in Table 1 were
based on commercially available alkaline electrolyzers with
rated hydrogen production capacities and operating pressures
in the range of 0.2–10 Nm3/h and 7–20 bar, respectively. The
exceptions were the prototype PEM-electrolyzer at IFE
(0.3 Nm3/h and 15 bar) [16] and the prototype high-pressure
alkaline electrolyzer in the PURE-project (3.6 Nm3/h and
55 bar) [19]. In comparison, the hydrogen pressure and
production capacity for the alkaline electrolyzer installed at
Utsira was 12 bar and 10 Nm3/h.
The overall motivation for the Utsira project is to demon-
strate how renewable energy and hydrogen systems can
provide safe and efficient power supply to communities in
remote areas. The main goal for the project is to perform
a full-scale demonstration and testing of a wind/hydrogen
energy system [12]. After several years with concept devel-
opment, system design, and project planning undertaken by
several partners [21,22], the decision to build the Utsira plant
was made in April 2003. The installations in place were mainly
realized by Norsk Hydro (now StatoilHydro) and Enercon, the
two main partners in the project. The Utsira plant was inau-
gurated in July 2004, is still in operation, and continues to play
an important part in StatoilHydro’s R&D on hydrogen tech-
nology [23]. A significant amount of operational data and
experience has been collected since the commissioning of all
of the systems during the winter 2004/2005 [18]. The main
objective of this study is to evaluate the energy performance
of the Utsira plant using actual operational data and an
updated set of hydrogen energy system modeling tools. A
thorough discussion on issues related to the design and
operation of wind/hydrogen energy systems is also provided,
including specific recommendations for improvements to the
Utsira plant.
2. System description
The Utsira wind/hydrogen energy demonstration plant is
located at the island of Utsira, ca. 20 km off the west coast of
Haugesund in Norway. This island was picked because of its
Fig. 1 – Photo of the Utsira wind/hydrogen demonstration plant (Ulleberg, 2005).
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excellent wind conditions and small, but representative,
electrical power demand. The island also provides a great
opportunity to test autonomous renewable energy mini-grid
power systems, as back-up power from the main land is only
available through a subsea cable.
A photo and a schematic of the Utsira system are given in
Figs. 1 and 2, respectively. Two 600 kW wind turbines are
installed on the site, but only one of the wind turbines is
dedicated to the demonstration plant. The main components
in the hydrogen system are a 10 Nm3/h alkaline electrolyzer
(12 bar), an 11 Nm3/h hydrogen compressor (12–200 bar, 2-
stage, diaphragm), a 2400 Nm3 hydrogen gas storage (200 bar),
and a 55 kW hydrogen engine generator system (genset). A
10 kW PEM fuel cell is also part of the system, but this is
currently not in use. The characteristics of the main compo-
nents are summarized in Table 2, some of these are discussed
in more detail below. A more detailed description on how the
system is connected electrically is also provided below.
2.1. Local grid and customer connection
The components in the autonomous power system at Utsira
(Fig. 1) are electrically connected at 400 V and 50 Hz. A sepa-
rate transformer (315 kVA, 22/0.4 kV) is connected to a 1.5 km
long cable that transmits power from the autonomous system
to the customer substation. Here 10 households are connected
to the customer substation at 230 V, which is the standard
voltage level in Norway. The customer substation also
includes a 22 kV busbar circuit breaker to enable fast switch-
ing of the customers from autonomous power system mode to
grid-connected mode. This feature was added to safeguard
against power failure, and to simplify service, maintenance,
and modifications on the demonstration plant. Since the
circuit breaker could also be used in case of an emergency
(e.g., power failure), the requirement for redundancy in the
autonomous system was minimized [12]. The system at Utsira
is capable of 2–3 days of full energy autonomy for 10 house-
holds located on the island.
2.2. Wind turbines and grid stabilizing equipment
Two wind turbines (Enercon E-40), each with a maximum
power output of 600 kW, have been installed on the site
(Fig. 1), but only one of these is dedicated to the autonomous
power system. The wind turbine is connected to the autono-
mous system via a separate 300 kW one-directional inverter,
which draws electricity from the wind turbine DC-circuit and
feeds this to the autonomous system. (The other wind turbine
feeds power directly into the local grid, and is not part of the
autonomous system). In practice, this means that there is
a cut-off in power from the wind turbine at 300 kW, and
surplus power can be fed to the local grid (in parallel to the
other wind turbine). Grid stabilizing equipment was required
for the autonomous system, as this was connected to a weak
grid. The grid stabilizing equipment installed consists of
a flywheel (5 kWh) for frequency control, a master synchro-
nous machine (100 kVA) for voltage control and short circuit
power, and a NiCd battery (34 kWh, 100 kW) for redundancy.
2.3. Hydrogen genset and fuel cell
The hydrogen engine generator (genset) was a diesel engine
genset rebuilt for using hydrogen as fuel. Its rated power
capacity (55 kW) is sufficient to supply the customers
without relying on the fuel cell. The hydrogen genset was
designed for black start and parallel operation with the fuel
cell. It also provides voltage control and inertia to the
autonomous system. One of the most challenging tasks in
this part of the project was to find a fuel cell stack supplier
to take responsibility for the overall fuel cell system inte-
gration. The fuel cell system had to comply with strict
requirements for autonomous power system and tough
10 Houses
∼=
H2-engine
Wind Turbine
~
~
H2-storage
Water
Electrolyzer
H2-Compressor
Rectifier
Flywheel
Battery
Low Voltage Mini-Grid
Fuel
Cell
∼=
Sync. Machine
Inverter
Auxiliaries:
Feed water & cooling pumps, gas drier,deoxidizer, ventilation, fans, heating, lighting
Fig. 2 – System schematic of the wind/hydrogen demonstration plant installed at Utsira.
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climatic conditions on the site. A manufacturer was even-
tually found, and the fuel cell system was integrated inside
a heated container. The fuel cell system was also designed
to be capable of black start.
3. Operational data and system performance
Over the past 3 years a significant amount of data from stand-
alone operation has been collected from the system at Utsira.
This particular study was based on operational data (10-min
averages) measured at Utsira in the period of 1–30 March 2007
(Fig. 3). The top plots in Fig. 3 show the wind power production
Table 2 – Main components installed at the Utsira wind/hydrogen demonstration plant.
Systemcomponent
Ratedcapacity
Supplier/manufacturer
Wind turbine 600 kW Enercon, Germany
Hydrogen engine 55 kW Continental, Belgium
Fuel cell 10 kW IRD, Denmark
Electrolyzer 10 Nm3/h, 50 kW Hydrogen
Technologies,a
Norway
Hydrogen compressor 5.5 kW Andreas Hofer,
Germany
Hydrogen storage 2400 Nm3,
200 bar (12 m3)
Martin Larsson,
Sweden
Flywheel 5 kWh Enercon
Battery 50 kWh Enercon
Master synchronous
machine
100 kVA Enercon
a Hydrogen Technologies AS (previously Norsk Hydrogen Electro-
lyzers AS) is fully owned by StatoilHydro.
and user load power demand, while the bottom plots show the
power produced by the hydrogen engine genset and power
consumed by electrolyzer (including auxiliaries and
compressor) versus pressure in the hydrogen storage. A
decrease in the hydrogen pressure from 145 bar to 33 bar from
1 to 30 March can be observed; the pressure increases up to
165 bar during a period with high levels of wind energy (Fig. 3,
period 1), before it decreases at times with less wind energy.
Data from March 2007 shows that 100% stand-alone oper-
ation is achieved ca. 65% of the time. This is slightly better
than the long-term performance, which on average gives
stand-alone operation about 50% of the time. A closer look at
the data (March 2007, hour 420–720) shows that the electro-
lyzer frequently needed to operate on grid-electricity in order
to produce extra hydrogen and level out the hydrogen storage
pressure, which otherwise would have decreased very rapidly.
A significant part of the work in the Utsira project has been
dedicated to the development of the power conditioning
system. A flywheel, a synchronous generator, and a battery
system ensure that the voltage and frequency on the local
mini-grid (the 10 households and the balance of plant for the
hydrogen system) is kept within standard limits and toler-
ances. The performance of the power system at Utsira is best
illustrated by taking a closer look at data for a shorter time
period (5 March 2007).
The on/off-switching of the electrolyzer and hydrogen
engine genset, as a function of the net available power (wind
power–user load) is illustrated in some more detail in Fig. 4: (1)
The master control system is programmed to switch on the
electrolyzer only during time of excess power (wind-load). (2)
Once the excess power on the grid goes below a critical low
point, the electrolyzer is switched off (2a) and the H2-engine
genset is switched on (2b). (3) Short term increases in power is
used to charge the flywheel. (4) Short term decreases in power
is covered by stored energy in the flywheel. The flywheel is
constantly being charged and discharged, which explains the
Fig. 3 – Operational data (10-min averages) from Utsira, 1–30 March 2007. (Top: Power produced by wind generator versus
power supplied to users (mini-grid). Bottom: Power from hydrogen engine generator versus power required by water
electrolyzer).
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sometimes highly cyclic behavior of the power (e.g., Fig. 4, hour
101–107). (5) In more prolonged periods of excess power the
battery gets fully charged. (6) If this period of excess power
continues and the battery is fully charged, the H2-engine genset
is switched off, and the electrolyzer is switched on again.
The stand-alone power system at Utsira has been working
properly for the past 3 years. The exception was the fuel cell
system, which right from the start gave technical difficulties.
First, there was an incident where glycol-cooling liquid
leaked into and damaged several cells. These cells were
replaced and the glycol was exchanged with water. Next, the
fuel cell voltage monitoring system had to be replaced
because its gold coating had been damaged during the
assembly procedure. Finally, when the fuel cell was con-
nected to the stand-alone grid, the power electronics and
control system frequently detected a ‘‘grid failure’’ alarm
that caused the system to shut down. However, the main
problem with the fuel cell was that the stack itself degraded
rapidly, independent of being in operation or not. Hence, very
few real operation hours on the fuel cell (<100 h) was
achieved. Lately, after more than 3 years of steady and reli-
able operation, the hydrogen engine has also run into some
technical problems, and is no longer operational. The pistons
on the engine have been damaged beyond repair, and a new
engine will be put in place. The damage on the pistons in the
engine may have been caused by hydrogen leakage and
consequent reactions with the lubricating oil and/or by water
resulting from the combustion emulsifying the oil. Both
effects would result in increased friction and wear in the
engine. Hence, the operation of the Utsira plant over the past
few years show that both the fuel cell and hydrogen engine
have their technical challenges that must be overcome. A
new hydrogen engine will be ordered and will be installed as
soon as possible. A new fuel cell is also being considered.
4. Modeling tools
Over the past decade a number of different wind/hydrogen
concepts have been investigated using various modeling and
Fig. 4 – Operational data (10-min averages) measured at Utsira on 5 March 2007.
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system simulation tools [2,8,16,24–26]. Below is a brief descrip-
tion of the simulation tools used in this particular study.
4.1. Simulation and modeling tools
The system simulations in this study were performed with
TRNSYS [27] and a set of hydrogen energy models (HYDRO-
GEMS) specifically developed for TRNSYS16 [26]. The
HYDROGEMS-library consists of the following component
models: Wind energy conversion systems (WECS), photovol-
taic systems (PV), water electrolysis (advanced alkaline,
adaptable to PEM), fuel cells (PEM and alkaline), hydrogen gas
storage, metal hydride hydrogen storage, hydrogen
compressor, secondary batteries (lead–acid), power condi-
tioning equipment, and diesel engine generator (multi-fuels,
including hydrogen). The source code for all of these models,
except the metalhydride model and alkaline fuelcellmodel, are
available for registered TRNSYS16 users. IFE has also
developed a duplicate HYDROGEMS library for EES (www.
fchart.com) based on the exact same source code as that
developed for TRNSYS, but these are only made available
through collaborative R&D projects. The main objective with
the EES-models is to perform more detailed component and
sub-system modeling, and to verify and calibrate more
advanced models based on experimental data. Both simu-
lations platforms, TRNSYS and EES, where used in this
study.
The HYDROGEMS component models are based on ther-
modynamics, electrochemistry, and applied physics (e.g.,
electrical, mechanical and heat and mass transfer engi-
neering). As a result the models are fairly physical and
generic, but in order to make the models suitable for energy
system simulations some simplifications have been made.
This is done by using empirical relationships for current–
voltage characteristics (IU-curves) for solar cells or electro-
chemical cells (e.g., fuel cells, batteries, electrolyzers), power
curves for wind turbines, efficiency curves for electronic
equipment (e.g., AC/DC-inverters), etc. Typical system model
parameters are: (i) Component sizes (e.g., cell areas), (ii)
System sizes (e.g., number of cells in series or parallel per
module), and (iii) Limits (e.g., min/max of voltages, currents,
temperatures etc.). Typical forcing functions required for
renewable energy system simulations are wind speed (m/s),
solar radiation (W/m2), current (A) or power (W) demand,
while typical variables calculated by the models are temper-
ature (�C), pressure (bar), current (A), voltage (V), and flow rate
(Nm3/h). The empirical parts of the models are designed so
that it is possible to find default parameters and/or calibrate
coefficients based on data found in literature (e.g., product
data sheets, papers and articles). It is a challenge to calibrate
model parameters and coefficients. Hence, access to actual
data from the hydrogen demonstration systems being
modeled is essential to ensure the validity of the models [28].
HYDROGEMS have been used to evaluate several other
hydrogen installations around the world [29].
4.2. Model updates and modifications
Modeling and characterization of the electrolyzer system,
including its complete balance of plant (BOP), and hydrogen
engine genset was performed in this study (Fig. 5). The
energy efficiency calculations for the electrolyzer and
hydrogen genset were both based on the higher heating value
(HHV) for hydrogen. The models were calibrated based on
actual system performance data collected from the operation
of the plant in March 2007 and additional component
performance data (e.g., energy efficiency and fuel consump-
tion curves) and general technical specifications from the
suppliers of the equipment.
The overall hydrogen production system efficiency at
maximum production was around 53%, while the electrolyzer
stack efficiency at these conditions was around 73%. At
maximum hydrogen production the total power consumption
of the hydrogen production system was about 65 kW. The
electrolyzer (stack) consumed about 73% of this power
consumption, while the auxiliaries (feed water pump, drier,
deoxidizer, cooling water pump etc.), rectifier/transformer,
and hydrogen compressor each contributed to about 9% of the
total power consumption (at maximum capacity). It should be
noted here that the electrolyzer installed at Utsira can operate
Fig. 5 – Characterization of electrolyzer and hydrogen engine generator systems. (Plots are generated using via calibrated
simulation models).
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at 50–100% of its rated capacity, but in practice it seldom
operated down to 50% of its capacity (Fig. 3).
The maximum hydrogen engine genset efficiency was
around 20% (Fig. 5), but on average this efficiency was around
17–18%, due to frequent part-load operation (Fig. 3).
5. System simulations
A set of wind/hydrogen system simulations (in TRNSYS) were
performed using calibrated models (HYDROGEMS) for the
wind turbine, electrolyzer system, and hydrogen engine gen-
set. Annual simulations of the Utsira plant (reference system)
and three alternative wind/hydrogen system designs were
performed, based on hourly wind speed (m/s) and power
demand (kW) measured at the site in 2005 (Fig. 6).
A monthly simulation (March 2007) of the reference
system confirms that it is not possible to achieve 100% stand-
alone operation with the existing system design at Utsira
(Fig. 6, plot 1). In the first alternative design a hydrogen
storage with a much larger capacity (7200 Nm3 instead of
2400 Nm3) was investigated. The results show a negative
total hydrogen mass balance (i.e., pressure decrease) for the
given time period (Fig. 6, plot 2). A similar result is found if
the H2-engine genset is replaced by a fuel cell with twice the
efficiency (Fig. 6, plot 3). However, if these two alternative
system design changes are made simultaneously (i.e., fuel
cell system with a larger H2-storage), the hydrogen mass
balance is positive for the given time period (Fig. 6, plot 4).
These results indicate that full autonomy can only be ach-
ieved by improving the overall efficiency of the hydrogen
production system (electrolyzer), by increasing the hydrogen
storage size, and/or by increasing power generating effi-
ciency of the unit (e.g., by switching from hydrogen engines
to fuel cells). This was then investigated in some more detail
for a complete year (see simulations based on 2005 input data
described below).
The hourly annual performance of alternative system
configurations that have the potential to reach full (100%)
energy autonomy was also simulated, and cost-estimated
based on the general cost functions listed in Table 3. A
comparison of the performance of two alternative system
configurations, one based on a fuel cell (with an efficiency of
50%) and the other on a hydrogen engine (with an efficiency of
25%), is shown in Fig. 7. It is important to point out here that
Fig. 7 does not show the techno-economic optimal system
configuration, but merely shows two alternative designs at
approximately the same overall system cost. The results show
that at system with a fuel cell requires a relatively small
electrolyzer (10 Nm3/h) and hydrogen storage (4800 Nm3)
compared to a system with a hydrogen engine, which requires
a relatively large electrolyzer (20 Nm3/h) and hydrogen storage
(11000 Nm3). Further economic analysis (not shown here)
show that the total investment costs for the main components
in these two alternative systems are both in the same order,
ca. 1 million V if based on the specifications in Table 3. In
summary, for the case of Utsira, a wind/hydrogen system
based on a fuel cell will be more compact and efficient (but
also slightly more costly) than a system based on a hydrogen
engine, which will be more bulky and less efficient (but
slightly less costly).
6. Discussion
6.1. Specific design issues and operational experience
Several important experiences have been gained from the
planning, building, and operation of the Utsira plant. First of
all, it is important to have a well-defined design basis and
operational philosophy, taking into consideration climate,
signal quality, communication (control and regulation), and
all system interfaces. Since wind/hydrogen energy systems
are not plug-and-play, but still fall into the category of R&D, it
Fig. 6 – Wind/hydrogen system simulation results using input data from Utsira (March 2007).
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is particularly important to select the right project partners,
preferably a few with technical expertise. In order for a project
of this nature ever to be realized, it is also important to have
a strong focus on safety, health, and the environment. Finally,
great care should be made in the selection of the site for the
installation. An appropriate location has the following
features: Good to excellent wind conditions, small but repre-
sentative load, back-up systems in place, not too remote,
a supporting community, and access to service personnel.
Some of these points are discussed in more detail below.
Utsira has a typical North Sea offshore climate with high
winds, strong waves, salty air, and temperatures down to
below zero (freezing). High waves, particularly during winter,
made it difficult to transport the largest components out to the
site. Since some of the components had long delivery times, it
became extremely important to plan with these weather
conditions in mind. The electronic equipment and housings
were all prepared for a saline environment, and the fuel cell
and electrolyzer containers were heated to avoid freezing.
The Utsira mini-grid (i.e., the stand-alone power system
created for 10 households on the island) mainly includes
inverters based on IGBT-technology, but some conventional
inverters were also installed. The influence these inverters
have on the (weak) grid needed to be carefully considered.
Variations in signal quality (voltage and frequency) in the mini-
grid at Utsira were observed in the beginning of the project.
Table 3 – General cost functions for wind and hydrogentechnologies [4].
Component Lifetime(years)
Capital Costs(V/kW or V/m3)
O&M Costs(% of Captial Costs)
Wind turbine 20 800 V/kW 1.5
Electrolyzer 20 2000 V/kW 2.0
H2-compressor 12 5000 V/kW 1.5
H2-engine 10 1000 V/kW 2.0
Fuel cell 10 2500 V/kW 2.0
H2-storage 20 4500 V/m3 2.5
Reactive power, resonance, over-harmonics can occur, and
must be dealt with. The power supply for the electrolyzer
installed at Utsira was one source for such problems. In
general, all equipment should be kept as simple and robust as
possible, and redundancy should be considered. Due to the
uncertainty in future wind power production and customer
power demand, a slightly oversized installation should also be
considered. However, as always, there is a trade off to be made
between plant availability and overall system cost.
The Utsira plant was designed to be remotely operated, and
a system for self-testing and automatic remote resetting of
individual components after shutdowns was therefore put in
place. Remote resetting for all of the components was not
possible to achieve from the start of the project, due to limi-
tations in the available technology (equipment was not
designed for remote operation). The key lesson learned here is
that it is important to specify or choose equipment with a high
degree of fail-safe and remote operation. Remote operation is
a necessity for safe operation. Suppliers of equipment often
have proprietary control systems. Nevertheless, communica-
tion and interfaces between components should be described
and standardized. This applies especially for the hydrogen
part of the plant.
Safety was prioritized in the design of the Utsira plant. It
would be detrimental to the development of hydrogen as an
energy carrier if a serious accident would occur in such
a highly profiled demonstration project. The Utsira plant,
which is compact and complex and contains explosive zones
and advanced equipment, regularly receives many unskilled
visitors. Safety has therefore been given the highest priority,
and there have been no accidents. The key for achieving this is
proper training of operators and other personnel, good
working instructions for all parts of the system, and clear
distribution of responsibility at the site.
Finally, it is important that these first wind/hydrogen
demonstrations systems that serve as the main power system
for real users is working without problems; to keep the
customers satisfied and positive is important for the public
acceptance of hydrogen. At Utsira the customers can, in case
Fig. 7 – Wind/hydrogen system simulation based on input data from Utsira for a complete year (2005). Comparison of two
alternative system configurations: fuel cell versus hydrogen engine.
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of failures or testing in the stand-alone mini-grid, be con-
nected back to the regular local grid (1 MW subsea cable to the
main land). This electrical configuration is working well. The
installation of a ‘‘dummy load’’ has also proven to be useful, as
this can be used to emulate the power demand during testing
of the system before it is connected back onto the mini-grid.
6.2. General system design issues
Hybrid hydrogen energy systems and refueling stations have
the potential to be both energy and cost efficient. The
discharge of hydrogen through a dispenser for a hydrogen
vehicle (preferably a fuel cell vehicle) increases the run-time
of the wind/electrolyzer system without having to invest in an
excessively large hydrogen storage system [30].
Techno-economic studies of wind/hydrogen mini-grid
systems based on today’s compressed hydrogen gas storages
(200 bar) and hydrogen internal combustion engines or fuel
cells (ICE and FC conversion efficiencies of 20 % or 40 %,
respectively), show that it is realistic to have a hydrogen
storage system capable of storing wind energy for about 1–2
weeks [6]. The exact size of the hydrogen storage will depend
on the wind energy profile and the load profile, as well as the
choice of hydrogen to power conversion device.
In general, renewable energy hydrogen systems should be
designed with input from several energy sources in order to
reduce the need for large and costly hydrogen energy storage.
However, if a hydrogen system is based only on wind energy,
it is particularly important to pick a location with steady and
good wind energy resources. Previous studies have demon-
strated that the need for seasonal storage of energy (weeks to
months) is more dependent on the annual wind speed profile,
than the average wind speeds [21].
For systems located in cold climates and high latitudes,
such as remote islands in the Nordic region, there is often
a positive correlation between the wind energy input and the
user load (thermal loads usually increase with increasing
wind speeds). Unfortunately, this correlation is normally not
so perfect that it can completely offset the need for some
kind of seasonal storage of electricity in the form of
hydrogen. Furthermore, if part of the electric load is used for
heating purposes the mismatch between the load and wind
energy input is even higher. (This is often the case for
communities in remote areas with limited access to other
heat sources, e.g., locally produced biomass). Hence,
designing fully autonomous RE/H2-power systems (e.g.,
systems with FC-power> 100 kWel) will always be
demanding, even though it is theoretically possible. In prac-
tice, full autonomy is most realistically achieved in smaller
RE/H2-power systems (e.g., systems with FC-power< 2 kWel)
that have insignificant heating/cooling demands and are
based on renewable energy sources with relatively small
seasonal variations, as such systems do normally do not
require large hydrogen storages [2].
6.3. Electrolyzer operation
Previous RE/H2-studies and experiments performed at IFE
[16,28,31] show how important it is to install a water electro-
lyzer with a quick response to varying power input (load-
following), particularly in wind energy based systems. The
more wind energy that can be captured, the more hydrogen
can be produced. Ideally, the electrolyzer should operate
continuously, and be able to operate down to only a few
percent of its rated capacity. Most existing commercial alka-
line electrolyzers today only allow for operation down to
25–50% of their rated capacity. In practice, this means that the
electrolyzer must be shut down when the input power is lower
than this limit (normally 25–50% of its rated capacity). This is
a severe disadvantage because once the electrolyzer has been
switched off, it takes a while (30–60 min) before it can be
switched on again (due to purging with nitrogen). Hence, the
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 5 ( 2 0 1 0 ) 1 8 4 1 – 1 8 5 21850
possibility to produce hydrogen during this period of time (if
the wind picks up again) is lost.
Results from the testing of a new and advanced large-scale
(MW) high pressure (30 bar) alkaline electrolyzers from Sta-
toilHydro Hydrogen Technologies [23] show that this tech-
nology should be able to handle down to 5–10% of it’s rated
capacity with a regulation speed of 200 ms [32]. This new
alkaline electrolyzer has a cell electrode area of 0.8 m2,
making it particularly suitable for larger plants with high
hydrogen production needs and large amounts of excess wind
energy available (MW range). If such an electrolyzer was to be
used in a smaller system, such as Utsira, only a few cells
would be required to produce the required amount of
hydrogen (10 Nm3/h). However, the voltage across a stack
based on only a few cells in series would be very low, and not
suitable for dynamic power conversion between the wind
energy generator and electrolyzer, as an AC/DC-inverter with
a very large voltage difference would be required. Hence, an
electrolyzer with smaller cells (allowing for more cells to be
placed in series) should be used instead. The high-pressure
alkaline electrolyzer described above can be down-scaled, but
there are also other options.
PEM-electrolyzers, with their inherent simplicity and
potential for quick startup and wide operational window
(5–100% of rated capacity), may prove to be more suitable for
wind/hydrogen-systems than advanced alkaline electrolyzers
[31]. This would particularly be true for systems based on
small to medium range (50–250 kW) electrolyzers. The most
suitable approach here would be to connect PEM-electrolyzer
stacks with electrode areas from 0.25 to 0.50 m2 in series and/
or parallel in order to achieve the proper voltage level (as close
as possible to the nominal operating voltage on the AC-bus-
bar, e.g., 400 V). The main disadvantage with the PEM-elec-
trolyzers is the uncertainty about the lifetime of the PEM.
6.4. Hydrogen pressure
Increasing the pressure in the hydrogen storage from 200 bar
to 450 bar, or even 700 bar, would increase the overall energy
density of the hydrogen storage, thus making it possible to
store more wind energy on the same footprint. However, high-
pressure hydrogen storage systems are likely to be more costly
than low-pressure systems, both from an investment and an
operational point of view. The increase in investment costs
will mainly be associated with the need for stronger storage
tanks (thicker steel walls and/or use of composite materials),
while the increase in operational cost will mainly be associ-
ated with the increased energy consumption for compression
of hydrogen. There are also likely to be extra costs associated
with the required safety system, although this depends on the
type of system installed.
There are two basic techniques to produce high-pressure
hydrogen gas: (1) Low-pressure electrolysis with a large
compression stage or (2) High-pressure electrolysis without
compression. Theoretical comparisons of these two hydrogen
production techniques have shown that high-pressure elec-
trolysis without a compressor is slightly more efficient (ca. 5%
more efficient) than low-pressure electrolysis followed by
a compressor [33].
Practical trade-off studies on high-pressure alkaline elec-
trolyzer systems show that high-pressure electrolysis might
be difficult to achieve, as increasing the operating pressure of
the electrolyzer is likely to come at a relatively high cost [34].
These increased costs are related to increased material and
system engineering cost associated with pressurizing the
electrolyzer stack itself, as well as extra costs associated with
the required safety and control systems.
In conclusion, it seems to make most sense to operate the
electrolyzers at lower pressures (ca. 10–40 bar), followed by
a hydrogen compressor. The optimal hydrogen storage pres-
sure will be a trade-off between extra investment cost of the
hydrogen storage on one side, and the increased investment
and operating cost associated with the hydrogen compressor
on the other side.
7. Conclusions and recommendations
The autonomous wind/hydrogen system at Utsira has
demonstrated that it is possible to supply remote area
communities with wind power using hydrogen as the energy
storage medium. However, further technical improvements
and cost reductions need to be made before wind/hydrogen-
systems can compete with existing commercial solutions, for
example wind/diesel hybrid power systems. Several areas of
improvements have been identified.
In general, the overall wind energy utilization must be
increased (at Utsira only 20% of the wind energy is utilized).
This can best be achieved by installing more suitable and
efficient electrolyzers that allow for continuous and dynamic
operation (load-following electrolyzers). Analysis of the
operational data from Utsira confirms that more efficient
electrolyzer systems (entire balance of plant, including
hydrogen compression) need to be developed. New and more
efficient and dynamic electrolyzers are currently being
developed in Norway.
The surplus wind energy should also be used to meet local
heating demands, both at the plant and in the households. In
addition, one could consider to utilize the hydrogen produced
(and possibly the oxygen) for other purposes (e.g., for trans-
portation). A more sophisticated wind energy forecasting and
load management system could also be implemented,
particularly if more complexity is added to the system (e.g.,
multi-purpose hybrid systems).
The hydrogen storage installed at the Utsira plant allows
for only 2–3 days of autonomous operation. A larger electro-
lyzer and hydrogen storage could improve this, but would lead
to a larger and more costly system. Another alternative would
be to improve the hydrogen–electricity conversion efficiency
by replacing the internal combustion engine with a fuel cell,
but this would lead to an equally costly system, as demon-
strated in this study. Hence, more compact hydrogen storage
systems and/or more robust and less costly fuel cell systems
need to be developed before wind/hydrogen-systems can be
technically and economically viable. Meanwhile, hybrid
system solutions based on more than one energy source (e.g.,
wind, solar, and bioenergy, depending on the location) should
be developed. The use of a diesel engine genset for back-up
power (redundancy) and/or to cover a small part (e.g., 5–10%)
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of the annual load could also be an option, particularly for
systems located in areas where natural resources are scarce.
Fortunately, there are a few general trends that could make
renewable energy hydrogen system concepts similar to the
one at Utsira cost-effective in the not too distant future: The
introduction of ‘‘green’’ incentives (e.g., green certificates and
CO2-tax), increases in oil and gas prices, and capital appreci-
ation of green image and security of supply. All of these
factors justify and motivate the construction and further
development of full-scale demonstration system such as the
wind/hydrogen plant at Utsira. It is believed that such
demonstrations will help improve public awareness and
acceptance, improve cost competitiveness of renewable
energy, and reduce market barriers for new energy and tech-
nology solutions in general, and hydrogen technology in
particular.
Acknowledgments
The authors would like to acknowledge the long-term efforts
made by former colleagues in Norsk Hydro, and new
colleagues in StatoilHydro, in the design, building, and oper-
ation of the Utsira plant. The technical collaboration with
Enercon, the financial contributions made by the Research
Council of Norway and Enova, the public acceptance at Utsira,
and the scientific input from IFE and other research institu-
tions in Norway is also greatly appreciated.
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