# Technical Integration

# 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.

# 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 Electrolysers. Also, one socket per Electrolyser (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 Electrolyser?

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

# 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 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.

# What happens at the end of the Electrolyser lifetime?

At the end of the stack lifetime, we will take the Electrolyser 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 Electrolyser.

# Do I need a compressor for the AEM Electrolyser?

No, the Electrolyser 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 a hydrogen storage tank required to operate the AEM Electrolyser safely?

Enapter provides the Electrolyser system for hydrogen generation from electrical energy and water. Each Enapter Electrolyser module generates a stream of hydrogen at a rate of 500 NL/hr which is released at 35 bar. The Electrolyser 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 Electrolysers 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 Electrolyser 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.

# 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 Electrolyser production rate can match the consumption, the pressure in the external tank can be held constant.

# What is the composition of the oxygen that the Electrolyser 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.

# 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.

# Do I need a water purification unit to feed the Electrolyser? 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 Electrolyser. 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 Electrolysers are met, you can use any water purification system you like.

# What are the dimensions of the Electrolyser?

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 hydrogen content (%) of untreated oxygen at electrolytic cell outlet?

The hydrogen content of the oxygen is around 2%, well below ignition thresholds.

# 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 Electrolyser 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 technology of the Enapter Dryer?

The Enapter Dryer raises the output purity of hydrogen gas from the AEM Electrolyser 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 Electrolyser, while the other cartridge is heated and regenerated with a small reverse stream of hydrogen gas (about 1% of the output of the Electrolyser). 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 -15deg C.

# 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 Electrolyser 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 Electrolyser 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 Electrolysers stacked together. The customer must provide the correct power, and hydrogen, water connections and vent lines to the cabinet/Electrolyser, 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 Electrolysers 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 Electrolyser?

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 Electrolysers.

# 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.

# Which fuel cell, storage tank and compressor should I use?

The fuel cell manufacturer should be rack mountable modules. Some 2.5 and 5 kW can be found with a good performance and can be integrated in the Enapter EMS. Just take into account that some does not have separate purge; the generated water and impurities are removed from the anode by exhausting a small amount of hydrogen to the coolant air stream. This might require more ventilation for the hydrogen system.

For stationary storage, steel vessels are a good option as they are cheaper than the light-weight composite cylinders for transportation and are a good solution for low pressure storage (60 bar and less).

As for the compressors, there are options. Membrane compressors ensure no oil carry-over into the hydrogen and supposedly have longer lifetime as well as less maintenance and repair. This comes at cost: upfront-costs are much higher than those of piston compressors. For piston-compressors, many companies from Italy and USA have the cheapest offers. When looking for a silent compressor, the electro-chemical compressor might be an option).

Please bear in mind, that although we know about some prices of compressors, we currently do not have any experience with either compressor of the companies mentioned. For example, we do neither know about the reliability and uptime of the compressor nor about the operating and maintenance costs.

# Do you sell any spare parts?

Due to its modular nature, the easiest way to fix a unit is to simply drop in a replacement module and send a broken system back to our factory for repair. As a system integration partner, we would encourage you to keep a stock of spare modules on hand in order to be able to quickly and efficiently service your customer sites and avoid extended downtimes for the shipment of modules back and forth. During the warranty period (2 years with our remote monitoring system enabled), all repairs covered under the warranty are free of charge.

# Which piping and tubes should I use for connecting modules?

For the water piping we use John Guest components as they are easy to source and cheap, but it is no requirement to stick with this brand. The hydrogen piping must be stainless steel, we use Swagelok tube fittings, as they are easier to tighten than thread fittings. From the water trap (on floor of container) a vent line with an inner diameter of 10 mm or more must go up into a safety area, different from the safety area the purge line goes into (could be at two opposite sides of the container for example).

# Can the EL 2.1 handle fluctuating input power?

The EL2.1 behaves like a standard AC-powered appliance, 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 Electrolyser tries to draw more power than available, the AC voltage will drop, and the Electrolyser power supply will cut out.

However, during operation the production rate of the Electrolyser (and thereby its power consumption) can be dynamically controlled between 300 NL/h up to the maximum nominal production rate of your system (500 NL/h * number of EL 2.1). Using data from other devices and sensors, the Enapter EMS can be set up to automatically control the production rate.

# Do I need the WTM (Water Tank Module)?

The short answer: No, the WTM is not needed, as long as you can guarantee the good quality of the supply of purified, pressurized water to the Electrolyser.

The long answer: We have studied the occurrence of a sudden deterioration of the output water quality of the Water Purification System (WPS) after some time of operation that was observed in the field and in our factory when directly connected to the EL without a clean water buffer tank. The WPS Enapter we are currently using and supplying doesn’t have an active output water quality monitoring and flushing system and is prone to failure with frequent start and stops. Therefore, Enapter recommends the use of the WTM to act as a buffer and helps to avoid frequent start and stops, preserving the water quality and the water filtration cartridges. Our data indicates the risk factor to be carbonates / CO2 in the refill water that can quickly degrade the electrolyte solution in the Electrolyser. Depending on the filtering system, they are normally caught by the resin filter, but then they tend to be released massively out of a resin filter as it gets exhausted and catches the stronger ions instead. This can be easy to miss without continuous and careful monitoring. When the Electrolyser stack performance suffers, it is too late, and the electrolyte needs to be replaced in addition to the water filters.

# What is the electrical isolation level of the EL2.1?

In our Electrolyser, we use AC-DC power transformers that provide the isolation between the AC power input and all the subsystems in contact with the electrolyte.

# What is the DEPR connection on the Dryer 2.1?

It’s a new bulkhead connector that is usually closed to hold the pressure inside the Dryer 2.1. It is only used to open the internal piping of the dryer before transport to ensure no hydrogen is contained within the device.

Having this “depressurisation connector” is an improvement that makes it easier to ship the unit to all places around the world. In the Dryer 2.1, it is now easy to completely remove all hydrogen contained in the internal piping between the check valves before shipment.

# How many Electrolysers can refill a single WTM? And how many a WTM + WPS?

Only with one Water Tank Module, up to 9 electrolyzers can be fed simultaneously since the limitations are mainly volumetric. The calculation was carried out in the worst condition where the WTM has a medium level of water (about to trigger the refilling process) and all the electrolyzers need to be fed at the same time. In the case of having a WTM attached to Enapter's WPS, the same situation as above is considered, but in this case, once the WTM goes below medium level, the automatic refilling is triggered and the WPS starts refilling the WTM while it refills the Electrolysers, so more volume will be available until the WTM reaches the low level volume and the pump stops. In this situation, up to 16 Electrolysers can be refilled.

# What effect does low water supply pressure have on the Electrolyser unit and does it affect feed pump?

The electrolyzer has a pressure sensor at the water supply inlet that works connected to a solenoid valve which opens at 0.45 barg and closes again at 5 barg to prevent overpressure in the water line. When the water pressure is below 0.45 barg, a warning is displayed announcing low water pressure in the system, and the solenoid valve remains closed until the pressure rises to at least 0.45 barg. The circulation pump inside the electrolyzer will not be affected at all since it has an operating time between the medium level where refilling is required and low level of the tank when the Electrolyser stops for lack of water.

# Is there a relief valve/vent for high H2 pressure in the Electrolyser? Does this use the H2 vent?

Yes, the electrolyzer has two ways to ensure that there are no over pressures within the system. The first is a pressure switch calibrated between 39 and 41 barg. This activates the opening of a solenoid valve connected directly to the hydrogen purge line; it will also send the stop command to the Electrolyser. Additionally, the system has a check valve calibrated at 42 barg, which is also connected to the purge line in case everything else fails.

1: Heating Ventilation and Air Conditioning