# Technical

# Should WPS be located outside the cabinet?

While the WPS is intended to be placed outside the cabinet, if required, the WPS can be integrated into an enclosure on a project-to-project basis.

# Are there any equipment (besides cabinet and Water Purification System) that will be necessary integrate inside a container?

For every 6-7 Electrolyzers, a WTM should be added into the container as well.

# Regarding electrical installation inside a container, what do I need for the auxiliary services (light, socket, etc.) and power for cabinets and fan?

There should be enough lighting to work on the Electrolyzers. Also, one socket per Electrolyzer (3 kW), one socket per Dryer (400 W), one for every WTM (70 W) plus one for the WPS (80 W). All works on 230 V AC. The sockets should be evenly distributed over the phases.

# Does the container need to meet some special conditions in relation to the structure (insulation panels) or fire-resistant conditions?

Generally no, but is application dependent. Temperature within container must be maintained between 5 – 45°C.

# What flow should the ventilation system supply for each Electrolyzer?

Fans for air flow ventilation should supply 50m3/h and only supply 800m3/h on specific moments for each Electrolyzer.

# What is the energy content of hydrogen?

The energy content of hydrogen is described in the (lower and higher) heating value. The lower heating value of hydrogen can be expressed as 33.33 kWh/kg or 2.78 kWh/Nm3. The higher heating value of hydrogen is 39.41 kWh/kg or 3.28 kWh/Nm3. A practical medium value to keep in mind is 3 kWh/Nm3.

The energy content of 1 Nm3 hydrogen gas is equivalent to 0.34 L gasoline, 1 L liquid hydrogen is equivalent to 0.27 L gasoline, 1 kg hydrogen is equivalent to 2.75 kg gasoline (based on lower heating value).

# How much does hydrogen weight?

The weight of hydrogen is 0.08988 g/L. The EL2.1 is producing 0.5 Nm3/hr (500 NL/hr) or 0.04494 kg/hr. One EL2.1 module produces in 24 hours 12 Nm3 of hydrogen gas which will weighs >1kg (1.0785kg). At the normal output pressure of the EL2.1 with 35 bar, 1 kg of hydrogen occupies a volume of 0.343m3 (343 L).

A full tank of hydrogen for a passenger vehicle contains about 5 kg of hydrogen gas (stored at 700 bar) and can drive for over 500 km.

# When stored in a tank, what are the losses over time through leakage? Does hydrogen, like for example diesel, have an “expiry date”?

When properly stored, there are no losses. While diesel and all other Hydrocarbon based fuels has an expiry date of around a year, hydrogen does not and can be stored for years.

# What is the lifetime of an Enapter Electrolyzer?

Based on the degradation data we have for our systems we expect a lifetime of the stacks of >30,000 hours.

# What is the lifetime of an Enapter Dryer?

The material that is absorbing the water from the stream of hydrogen can be fully regenerated. Over time, mechanical processes and pressure changes can degrade the drying material, which will reduce the effectiveness of the Dryer. This is expected only after many years of operation.

# Can CO2 contamination negatively affect the lifetime of the Electrolyzer?

CO2 contamination is not a problem in our Electrolyzer, as our system design avoids potential interaction with the surrounding air. But, even if there would be CO2, they would only reduce the pH of the AEM, but this is reversible and would not contribute to explicit degradation of the membrane.

# What happens at the end of the Electrolyzer lifetime?

At the end of the stack lifetime, we will take the Electrolyzer back and recycle it. The cost will have come down so much that it won’t be viable to replace the stack, it will probably be easier to replace the Electrolyzer.

# Do I need a compressor for the AEM Electrolyzer?

No, the Electrolyzer produces hydrogen gas pre-compressed at 35 bar, which is sufficient for most stationary storage projects. Only if very large amounts of hydrogen is stored, or hydrogen is produced for mobility (hydrogen vehicles), then a compressor is needed to reach higher pressures.

# Is Nitrogen used during the process?

No, our Electrolyzers do not use Nitrogen.

# How many connections does the Electrolyzer has?

Our Electrolyzers only have the following connections:

  1. Electrical power input.

  2. Clean water input.

  3. Hydrogen output.

  4. Oxygen vent.

  5. Hydrogen purge to safe area (for releasing the internal pressure).

# What effect do frequent start/stop cycles and ramping have on the longevity or system performance of the Electrolyzer?

The Electrolyzer is intended to be operated intermittently, as it can happen from renewable energy sources. However, like with most electrochemical systems, it is better to avoid cycling the system on and off very frequently, as this can accelerate the degradation of system performance. Meanwhile, normal use with several on-off cycles per day does not affect the system negatively.

In industrial or in-process use cases with frequent changes in the hydrogen consumption rate, we recommend installing a buffer tank (at least 50L) to hold some hydrogen and to avoid switching the Electrolyzers on and off every few minutes.

To help with the control of the devices for these constant consumption use cases, it is also possible to regulate hydrogen production to keep the outlet pressure stable at a given set point with the use of the Enapter gateway running rule-based controls; this also minimizes system cycling.

There are no specific prescriptions for the shutdown procedure, the system does this automatically. One thing to note is that after every shutdown, the system will release the internal working pressure (hydrogen at 30-35 bar) and purge a small amount of hydrogen gas from the purge line.

# What is the duration of starting the Electrolyzer until it is fully functional, in other words, what’s the warm up time?

The ramp up time of the AEM Electrolyzer depends on the electrolyte temperature (the ramp up is slower at cooler temperatures and quicker in warm temperatures). Typically, the system will start with a hydration period of 60 seconds, and then ramp up to the nominal production rate with the following values:

  • Warm-up time (time taken for the EL to heat up): The electrolyte working temperature in the AEM Electrolyzer is 55°C. The Electrolyzer can usually reach a heating ratio of 1 °C/min, at 55°C reaches maximum efficiency. For example, if we start the machine with an electrolyte temperature of 25°C it will take about 30 min to be fully operational and perform at its maximum efficiency.

  • Ramp up time (time to reach nominal production rate): Usually, the 500 NL/hr production rate is reached in about 2/3 of the total warm-up time (the warm up time is 30 min, so if you start at 25, you will need 20 min to reach max production rate)

  • Build pressure time: When the system starts and the Electrolyzer starts to heat up, the hydrogen production starts immediately, and the maximum production rate is reached later. With standard set-points, the pressure is completely built in 1/6 of the total warm up time (if you start at 25 °C, then the warm-up time is 30, so you need 5 min to build pressure)

# How constant is the output current or how sensitive does the Electrolyzer reacts to the fluctuations in the input power?

The PSU (Power Supply Unit) in the Electrolyzer needs an input voltage of 200-240 Vac. The Electrolyzer works in this range and the production rate can be varied flexibly. If the input voltage falls below the minimum voltage, the Electrolyzer switches off. If the available input current fluctuates, this information can be processed via the intelligent EMS and the production rate of the Electrolyzer can be adjusted accordingly.

# Is a hydrogen storage tank required to operate the AEM Electrolyzer safely?

Enapter provides the Electrolyzer system for hydrogen generation from electrical energy and water. Each Enapter Electrolyzer module generates a stream of hydrogen at a rate of 500 NL/hr which is released at 35 bar. The Electrolyzer is intended to be operated intermittently, as it can happen from renewable energy sources. However, like with most electrochemical systems, it is better to avoid cycling the system on and off very frequently, as this can accelerate the system performance to degrade. Normal use with several on-off cycles per day is no problem. The storage system, or immediate use case of the hydrogen output gas is outside Enapter’s standard scope of delivery and normally taken care of by the system integrator or end customer. In industrial or in-process use cases with very frequent changes in the hydrogen consumption rate, our customers normally install a buffer tank (~50L) to hold some hydrogen and to avoid switching the Electrolyzers on and off every few minutes.

# Is it possible to add a manual regulator for stack current and voltage and circulation pump flow control?

No, these functions are regulated by the balance of plant within the Electrolyzer module and cannot be individually controlled to protect the system from bad operation conditions. However, you can set the desired production rate set point via the control interface.

# What is the surface area of the membrane?

We don’t provide such information outside of an NDA, as it is part of Enapter’s intellectual property. The internal specifications of the stack and other components within the Electrolyzer are not relevant to the purpose of the product, which is to produce hydrogen gas from electricity and water.

# What is the hydrogen yield for the AEM Electrolyzer?

Enapter has standardized the AEM Electrolyzer into a fully stackable and flexible product: The EL2.1. Each module yields 500 NL/hr or 0.5 Nm3/hr of hydrogen gas output at 35 bar and with a purity of ~99.9% (optional >99.999% with a Dryer module). Multiple units of the EL2.1 Electrolyzers can be easily combined into one larger system.

# What is the efficiency of the Electrolyzer?

With the EL2.1, we need 4.4 kWh to produce 1 Nm³ of hydrogen. That means it takes 48.9 kWh to produce 1kg of hydrogen (compressed at 35 bar and with a purity of ~99.9%). 1 kg of hydrogen contains 33.33 kWh (using the lower heating value), i.e. our Electrolyzer already has an efficiency of 68%. System efficiencies (not stack efficiencies) need to be compared.

# What is the Electrolyzer cell DC voltage range?

Please understand that we don’t normally provide such information outside of an NDA, as it is part of Enapter’s intellectual property. The internal specifications of the cells, stack and other components within the Electrolyzer are not relevant to the purpose of the product, which is to produce hydrogen gas from electricity and water.

# What is the operative power consumption of the AEM Electrolyzer?

The operative power consumption at standard conditions of the EL2.1 is 2.2 kW. The peak power consumption (max power draw at any time) is 2.8 kW and should be considered for sizing of electrical safety devices and wiring. You can find the standard specifications in the data-sheet.

# What is the Electrolyzer cell minimum voltage?

Please understand that we don’t normally provide such information outside of an NDA, as it is part of Enapter’s intellectual property. The internal specifications of the cells, stack and other components within the Electrolyzer are not relevant to the purpose of the product, which is to produce hydrogen gas from electricity and water.

# What is the single Electrolyzer chamber voltage range?

Please understand that we don’t normally provide such information outside of an NDA, as it is part of Enapter’s intellectual property. The internal specifications of the cells, stack and other components within the Electrolyzer are not relevant to the purpose of the product, which is to produce hydrogen gas from electricity and water.

# What is the electrolytic cell DC current range?

Please understand that we don’t normally provide such information outside of an NDA, as it is part of Enapter’s intellectual property. The internal specifications of the cells, stack and other components within the Electrolyzer are not relevant to the purpose of the product, which is to produce hydrogen gas from electricity and water.

# How the hydrogen is pressurized inside the Electrolyzer?

Our cell allows for differential pressure when hydrogen is produced, it accumulates on the cathode side and fills the space before the back-pressure valve. Once the pressure reaches a set point (30 bar), hydrogen will start to flow from the hydrogen outlet of the Electrolyzer. The Electrolyzer will then continue to operate until the external pressure on the outlet reaches 35 bar, which is the point at which the Electrolyzer shuts down in “max pressure” mode.

# What is the pressure on the hydrogen side?

Hydrogen gas is produced at 35 bar (3.5 MPa).

# Is the hydrogen delivered in a continuous mode at 35 bar pressure?

The hydrogen is produced at 30-35 bar in stack and will flow into an external tank or pipeline until the pressure on the outlet reaches 35 bar. As long as the Electrolyzer production rate can match the consumption, the pressure in the external tank can be held constant.

# What is the pressure of the oxygen produced?

The pressure on the oxygen side is at atmosphere (0.1 MPa).

# What is the composition of the oxygen that the Electrolyzer produces?

Our oxygen content, though it hasn’t been formally characterized, is primarily O2 with a high relative humidity and trace amounts of atmospheric gases plus about 2% H2. Any KOH/K2CO2 (potassium carbonate) will be solved or exist only in trace amounts of ppm concentration within water droplets that are on the outlet line.

# What maintenance is required on the AEM Electrolyzer?

The only regular maintenance needed is draining and refilling electrolyte once a year. The Electrolyzer operates with a slightly alkaline solution (1% KOH) which makes it safe and easy to handle. The electrolyte is filled into the Electrolyzer during the initial installation and is not consumed. Only water needs to be supplied to the Electrolyzer during operation, no KOH needs to be refilled. As part of the yearly maintenance of the Electrolyzer, we recommend replacing the electrolyte solution, which can be done by a technician in about 15 minutes.

# What is the water content at hydrogen side outlet?

The water content in the hydrogen gas produced is ~1,000 ppm. Adding the optional Dryer removes trace amounts to >10 ppm (at -60˙C dewpoint) up to about 3 ppm (at -70˙C dewpoint) on average.

# What is the maximum differential pressure between hydrogen and oxygen side?

The differential pressure in normal operation is up to 35 bar (3.5 MPa), the maximum allowed before safety devices are triggered is 40 bar (4 MPa).

# What is the connection type and size at oxygen outlet?

The EL2.1 uses 10 mm Push Fit Quick Connectors made by John Guest for the oxygen vent outlet.

# What is the connection type and size of the water inlet?

The EL2.1 uses 8 mm Push Fit Quick Connectors made by John Guest for the refiling inlet.

# What are the connection type and size at hydrogen outlet?

The EL2.1 has the following water and gas connections: Water in, Hydrogen out, Hydrogen purge, oxygen vent, maintenance drain

# What is the water input quality requirement for the Electrolyzer?

The AEM Electrolyzer is highly resilient to water input and can be fed with purified rainwater or tap water. Simple and cheap reverse osmosis processes with resin filters can provide the required water quality. The water input to the Electrolyzer needs to be desalinated and have a conductivity of <20 microS/cm. It is not possible to use saltwater in the Electrolyzer.

# Are water purifier and water tank integrated in the cabinet? If not, should I install water tank and water purifier outside the cabinet by myself? What is the function of the water tank in the system?

The function of our water tank in the cabinet is to provide some autonomy in case the water supply is interrupted. It is optional. We can offer a water purifier and water tank; however you can use any water supply system you like.

# What is the required water input pressure?

Water input pressure: 0.75-4 bar.

# Do I need a water purification unit to feed the Electrolyzer? What is the maintenance associated with this?

If a water purification unit is needed, we will resell a water purifier that uses reverse osmosis filters and resins to clean up tap water and supply it to the Electrolyzer. The maintenance consists of filter/resin replacements and will depend on the input water quality and the amount of water consumed. As long as the water purity requirements of our Electrolyzers are met, you can use any water purification system you like.

# Can the unit be easily automatically started/stopped while in standby mode?

Yes, the unit can be controlled automatically to start/stop based on some logic rules or manual inputs via the Enapter monitoring and control system. It can also be controlled via a Modbus interface. you can also press the button on the front of the machine.

# What are the dimensions of the Electrolyzer?

The EL2.1 dimensions are 482 x 594 x 310 mm. The EL 2.1 is rack-mountable in a standard 19” cabinet.

You can find all the standard specifications of the EL 2.1 on the data-sheet.

# What is the weight of the Electrolyzer (kg)?

The EL2.1 weighs approximately 50 kg, so you must take care to handle it in a safe manner. The EL 2.1 is rack-mountable in a standard 19” cabinet. You can find all the standard specifications of the EL 2.1 on the data-sheet.

# What is the oxygen content (%) of untreated hydrogen at electrolytic cell outlet?

It is <1 ppm.

# What is the hydrogen content (%) of untreated oxygen at electrolytic cell outlet?

The hydrogen content of the oxygen is <2.5%, well below ignition thresholds.

# What happens to the oxygen? Is it released back into the atmosphere? As it is also explosive are there any safety measures needed such as a dispersal unit?

There are two vent lines from the Electrolyzer which needs to be released to the atmosphere in a safe area without any ignition sources:

  1. The oxygen vent, where oxygen streams out at atmospheric pressure continuously during hydrogen generation.

  2. The hydrogen purge, where some hydrogen is vented out to release the pressure after a system shutdown.

# Can I collect the discarded oxygen through the vent into a tank?

The flow rate of the oxygen at nominal production is 250 NL/hr. The oxygen contains quite a lot of humidity, around 2% hydrogen depending on operating conditions, and potentially trace amounts of KOH and amines (as we make no attempts to filter/purify). The oxygen vent is at atmosphere and needs to be kept open. If the vent is blocked or flow is restricted, the pressure on the oxygen part of the Electrolyzer can build up and damage the system.

# Are power electronics with a DC-DC conversion available?

We hope to have a feasible and cost-effective solution in the future. For now, unfortunately it is not available, and we only have the standard AC power supply option.

# What is the DC power consumption value per cubic meter of hydrogen (kwh/m3H2)?

It is 4.4-4.95 kWh/Nm3 H2. However, we do not have a DC-powered version of the EL2.1. The standard power connection is 200 – 240 Vac, 50 – 60 Hz.

# Are power electronics with a DC-DC conversion available?

We hope to have a feasible and cost-effective solution in the future. For now, unfortunately it is not available, and we only have the standard AC power supply option.

# What is the current density?

Please understand that we don’t normally provide such information outside of an NDA, as it is part of Enapter’s intellectual property. The internal specifications of the cells, stack and other components within the Electrolyzer are not relevant to the purpose of the product, which is to produce hydrogen gas from electricity and water.

# What is the electrolytic cell rated operating temperature in degree Celsius and degree Fahrenheit?

The rated operating temperature is 55 °C and 131 °F.

# What is the ambient temperature for the operation of the EL2.1?

Our system operates at an ambient temperature of 5-45°C. The cabinet that we offer is passive and has no cooling or filters integrated. The airflow for the cooling of the systems is blown for each module individually from front to back, the cabinet allows accordingly undisturbed air flow through the front and rear door. An additional cooling cycle is not necessary. If our Electrolyzers are installed in locations with ambient temperatures outside of 5-45 ° C, or in locations with condensing humidity, the system integrator must take this into account when selecting the cabinet and, accordingly, use heating, cooling, filters, etc.

# What is the calorific value from electrolytic cell (Joule/h)?

We do not have exact measurements, the estimated value is 1840-3750 kJ/h.

# What is the threshold power of the Electrolyzer to run?

20% of nominal power.

# What is the waste heat of the Electrolyzer?

The EL2.1 is air-cooled, which means there is waste heat, which is around 400 watts. We are currently working on a water-cooled variant so that we can make better use of the waste heat.

# Can the EL2.1 handle fluctuating input voltages/currents due to ramp-up & ramp-down and cloud movements?

The EL2.1 behaves like a standard AC-powered device, it contains a commercial power supply. It does not have the intelligence to detect by itself the available or fluctuating input. If at any time, the Electrolyzer tries to draw more power than available, I would expect that the AC voltage will drop, and the Electrolyzer power supply will cut out.

However, the production rate of the Electrolyzer (and thereby its power consumption) can be controlled from 20-100%. At start-up, the Electrolyzer always goes to maximum production rate to build up the internal pressure as quickly as possible. After a few minutes, the production rate can then be ramped down. This means that up to 2.8kW (peak consumption at worst conditions in cold temperatures and with all fans and pumps running) of power should be available at start-up.

The simplest way to add the intelligence needed would be a small battery buffer somewhere in the system (even just 1kWh can be enough). If full, it can support start-up of the Electrolyzer, if it starts to be drained, that information could be used to ramp down the Electrolyzer (any excess would then recharge the battery). Enapter’s monitoring and control system is designed to be expandable beyond basic Electrolyzer control to perform this kind of jobs.

# What is the technology of the Enapter Dryer?

The Enapter Dryer raises the output purity of hydrogen gas from the AEM Electrolyzer to >99.999% in molar fraction. It is hybrid temperature/pressure swing adsorption system that comprises of two cartridges filled with a highly adsorbent material. One cartridge will be catching the humidity from the hydrogen gas stream of the Electrolyzer, while the other cartridge is heated and regenerated with a small reverse stream of hydrogen gas (about 1% of the output of the Electrolyzer). This reverse stream of hydrogen gas will carry out the water caught by the Dryer and be released into the atmosphere from the purge output of the Dryer. All of this is completely automatic, and the system is fully integrated in the Enapter EMS, so we can monitor the states of the Dryer, temperatures and pressures of the system. The drying process gets the purity level to 99.999% in molar mass. We have two models of the Dryer one with 2 cartridges that dries up to 1,000 NL/h, and one with 4 cartridges that dries up to 2,000 NL/h.

# What is the hydrogen dew point without Dryer?

The dew point without Dryer is -20 degree Celsius.

# Does the Dryer have a sensor in the unit to monitor the humidity of the hydrogen produced?

We do not have any sensors to monitor the humidity of hydrogen produced on a continuous basis. We measure the dew-point (below -70deg C) of a system during the final acceptance test in our factory. Alternatively, for applications such as hydrogen refueling stations, our customers would install their own hydrogen purity measurement equipment, particularly if there are dangers from contamination from an additional compressor system.

# What are the installation requirements for the system (location, set off distances from adjacent walls, electrical outlet, ventilation, ambient temperature, siting location, indoor/outdoor, non-hazardous/non-classified area)

The Electrolyzer is designed for indoor installation, by itself it doesn’t have protection from the elements. The installation of the EL2.1 can be done in most standard 19” racks/cabinets by the system integrator so depending on the type of enclosure it can be installed anywhere. If Enapter is tasked with the integration into a cabinet, we currently use IP20 cabinets from Rittal. On the customer site, the installation of these cabinets requires 1.5m of empty space in front of the cabinet for working access and 0.5m of empty space behind the cabinet to allow for airflow (the Electrolyzer is air-cooled and requires unrestricted airflow from front to back). All piping and electrical connections are in the front of the machine. This means the system needs to be accessible from the front. There is no need to have a minimum distance on the sides, top, or bottom, so this makes it very easy to build systems containing many Electrolyzers stacked together. The customer must provide the correct power, and hydrogen, water connections and vent lines to the cabinet/Electrolyzer, if our cabinet is used, the connections are at the bottom on the back of the cabinet.

# What is the oxygen and water content of the hydrogen when it comes out of the Dryer?

Our Electrolyzers produce hydrogen with a purity of approximate 99.9% by default. This means you still have a water content of about <1000 ppm. If purity levels of 99.999% is required, the Enapter Dryer is used. This reduces the water content to <10 ppm. Contamination with air is minimum, oxygen is <1 ppm. Further substances are not found in our hydrogen.

# Is it plausible to use Enapter's Dryer with a non-Enapter Electrolyzer?

Unfortunately, this is not plausible. It would take quite some effort to individually adjust the operating parameters according to their requirements. Additionally, we wouldn’t be able to offer any guarantee on the system itself or the hydrogen output purity, as we have never tested it with any other source of hydrogen as our own Electrolyzers.

# Is there a problem with catalyst poisoning or agglomeration?

In fact, we don’t have any significant issues with either of these topics for our catalysts. We are not aware that we face any challenges from catalyst agglomeration. We suppose that the interface between membrane/catalyst/electrode is very strong and stable. Similarly, we don’t have any problems with catalyst poisoning when the input water quality is according to the requirements. Our system is extremely robust, also because the electrolyte (low concentration 1% KOH in water) is circulating only on the anode. This key design feature of the AEM electrolyser is protected by our core patent.

# What is the partial load range of the device and how does the overall efficiency (LHV/P absorbed) behave in such range?

The system can operate from 20-100% of the nominal production rate. The power required at different production rates can be estimated with the following graph:

Loadcurve


1: Heating Ventilation and Air Conditioning