Oppføringer av Daniel Janzen

Maritime Energy Density

At the core of energy transition in the Maritime industry is a physics problem, namely Energy Density


What is Energy Density?

Energy Density can be measured in two ways:

 Volume: How much energy exists within a specific space

 Weight: How much energy exists within a specific weight

Many times we confuse ourselves by speaking about one of them while forgetting about the other, and more often we forget about how one category may impact the other ie: large volume energies require large storage containers…which are often heavy. When we speak of energy density in maritime applications, both weight and volume can be challenges. At the end of the day, many types of shipping are measured on how many units of cargo they can carry and this can be impacted by the weight or volume of the energy system on board.

Why is this a challenge for the maritime industry?

As you can see in the figure above, the traditional fuels used by the maritime industry are very volume dense, meaning you can get a lot of energy into a small space. The fuels of the future; primarily Ammonia, Liquid Hydrogen (LH2) and Compressed Hydrogen (CH2 350/700 Bar) are quite the opposite, these are gravimetrically dense energies. Batteries are also a useful energy carrier – and often the cheapest overall solution when they are feasible. From the figure you can also see that batteries have low volumetrically & gravimetrically energy density, which means that you need large and heavy batteries to have sufficient energy. This limits the application of batteries to short sea applications (and of course as an energy buffer in all others). 

How does energy efficiency play a roll in this?

Energy efficiency is important because it is the multiplier different energies go through when they are actually used on board. What this means is energy densities are measured in theoretical energy contained per unit (volume or weight), however when the energy is consumed on board it is not the theoretical energy density that matters but the overall system efficiency. If energy has a high density but low efficiency it’s ‘Actual’ or ‘In Use’ energy density is much lower. Batteries shine strongly here because they have high efficiency and therefore are not penalized as severely as other energy carriers.

We’ve put together an interactive figure that displays the energy density for several conventional fuels such as MGO, and Diesel, and some of the new fuels proposed for use in maritime such as Liquid Hydrogen (LH2) or Ammonia. As a twist, we have added the option to see what these energy densities look like on board when the energy is actually utilized (in a combustion engine or fuel cell, etc). Just click the box under Energy Density: Theory or Reality and select «Reality».

Beyond the density of the energy itself, system (Balance of Plant) weights and volumes are important but require design and operational specifications to compare these appropriately. Beyond energy and system densities are a number of key issues to be considered such as safety, cost, and fuel availability.

If you have a maritime project you’d like to explore zero emissions on, we’re always looking to take on projects and offer advisory where we can add value

Do you want to learn more about electrolyser technologies? Check out our technology series: part 1, part 2 and part 3.

Technology: Electrolysers – part 3

Electrolyser technology

The last part of the electrolyser series is a comparison between Alkaline (ALK), Polymer Electrolyte Membrane (PEM) and Solid Oxide electrolysers (SOEL),  explaining the advantages and disadvantages with the different technologies.

Did you miss the previous parts in the electrolyser series? Read them here: part 1 and part 2.

Maturity and costs

The alkaline electrolysis stacks have been available on a MW-scale for a long time, and a scale-up of PEM has been realized the last few years, largely driven by the drive to run electrolysis from Variable Renewable Energy (VRE) and to reduce plant footprint. Alkaline stacks are available up to 6 MW and PEM stacks up to 2MW. The SOEL is still in laboratory scale with up to 10kW. 

Alkaline electrolysers have the lowest cost per kW. In commercial scale plants (2 MW +), Alkaline electrolyser plants have a capital cost of $ 800 – 1 000 /kW. PEM electrolysers come in at an overall higher capital cost at 1 400 – 1 700/kW. The price difference between Alkaline and PEM electrolysers is largely explained by the maturity of the technology and the use of precious metals in PEM electrolysers. There is an uncertainty regarding the investments cost due to the pre-commercial status for SOEL.

Renewable energy applications

Usage of intermittent power sources requires flexibility. A State-of-the-art PEM electrolyser can operate more flexibly than current Alkaline technology, and these characteristics are suited for variable renewable energy. Historically, the alkaline electrolyser was designed for stationary applications with grid connections and must be adapted to the new flexibility requirements.

Advancements in Alkaline technology, specifically ‘Pressurized’ Alkaline electroysers have made them once again suitable for variable renewable energy if the system components are engineered to operate with an intermittent power supply. 

While PEM electrolyers offer best in class use of intermittent power sources, both PEM and (pressurized) alkaline electrolysers can offer fast load dynamics when they are in operating temperature and is suited for grid stabilizing.

Figure 1 compares parameters regarding the different electrolyser technologies:


The development of PEM has been driven by energy storage application. PEM has short startups, especially from cold. Alkaline electrolysers have a slower start-up taking up to an hour. The SOEL has a cold start-up time up to several hours and needs a high energy consumption (in the form of heat) to maintain a temperature that allows a short start-up time. 

One of the most significant issues with start-ups is when shut downs extend for a extended period of time resulting in the need to purge the equipment using nitrogen. This can increase the start-up time signficantly beyond normal start-up periods. Nitrogen purge requirements however largely differ from manufacturer to manufacturer.


The production rate for PEM can be varied over the full load at 0-100%, but the alkaline electrolyser typically has a load limit of 20% meaning it cannot operationally drop below 20% of the nominal load. It is worth noting that some alkaline electrolysers can offer higher flexibility such as pressurized alkaline. The SOEL has the ability of co-electrolysis of CO2 and steam to produce syngas containing H2 and CO2 for synthesis of fuels. It is also possible to have the reversible operation. This allows operating range from -100 to 100%. However, SOEL is still at the research stage based on single-cell or short-stack tests and any capabilities such as this may not be realized on a commercial stage.

A lower operating limit and the number of stops permitted by the manufacturers are limitations for the commercial Alkaline electrolysers. Reducing the electrolysers’ lower operation limit and improving the response times are key aspects in development.


The outlet pressure of each of an electrolyser can influence the overall production facility and maintenance requirements. While the alkaline typically offers low outlet pressure of only 2 – 3 bar, SOEL has a slightly higher output pressure around 5 bar, and the PEM offers the highest outlet pressure in the range of 20 – 30 bar.


Alkaline electrolysers offer the longest lifetime, some have been in regular operation for 30+ years. Typically, cell stacks need replacement after 80 000 operational hours. PEM electrolysers also offer long times, however, degrade faster than their Alkaline counterparts requiring stack replacement after 40 – 50 000 hours. Finally, SOEL offers little to no lifetime with a ~8 000 hours lifetime – this is due to very high temperature used in the process causing material breakdown.


Solid Oxide Electrolysis is the most electrical efficient with electricity consumption around 42 kWh/kg, however this comes with the requirement that very high excess heat is available and therefore the true efficiency is significantly higher. Alkaline electrolysers have the highest overall efficiency with energy consumption around 52 kWh/kg produced. Meanwhile, PEM electrolysers have the lowest overall efficiency at 59 kWh/kg produced.

A caveat to the ‘efficiency’ discussion: PEM electrolysers are better suited than ALK electrolysers for operation under pressure due to smaller cell surfaces. It is more efficient to have a higher pressure inside the stack. The PEM electrolysers have a higher power consumption but the result is a higher output pressure. Given that the hydrogen is to be compressed later for distribution  or storage then the additional energy consumption from the PEM electrolyser is not entirely wasted.



Do you have a project you want to realise and need more information? Please contact us at greensight@greensight.no. This is the last part in the electrolyser series. Read the previous parts here: part 1 and part 2. 

Technology: Electrolysers – part 2

Electrolyser technology

Alkaline, PEM and Solid Oxide electrolysers produce hydrogen using different technologies. In this part of the technology series, we will present application areas for electrolysers and hydrogen. We will also present the suitability of the technologies to each application.

Did you miss «Technology: Electrolysers – part 1»? Read it here. You can read part 3 here.

Hydrogen is a potential key factor to address the energy transition, and water electrolysis is the cleanest and most sustainable way to produce hydrogen. If hydrogen is produced from renewable energy sources, e.g. solar or wind power, it is a zero-emission energy carrier. Hydrogen can be used in sectors that are difficult to decarbonize through electrification.

Electrolysers can produce Hydrogen that can be used in:

  • Transport
  • Off Grid
  • Grid Balancing
  • Industry 

In the following paragraphs we will discuss some of the application areas for electrolysers in general.


This is the rather obvious application electrolysers can be used for. Hydrogen can be used not only for light-duty vehicles such as the Toyota Mirai, but also heavy-duty vehicles such as the Nikola Tre. Hydrogen can be used beyond these areas of transport in applications such as trains & maritime. Airbus is even looking to fuel a plane with hydrogen!

How an electrolyser can help electrify & decarbonize the transport sector is by producing hydrogen from water & electricity which when used in transport is a zero emission fuel. Hydrogen for transport can be produced locally at the dispenser or centralized and then distributed & dispensed in compressed or liquid form.

Illustration of Electrolysis/Hydrogen use in transport:


Off-grid production and use of Hydrogen as a solution is possible with electrolysers. Here, we must consider fluctuations in the electrolyser operating conditions when using Variable Renewable Energy (VRE) such as wind or solar power.

Another configuration is an off-grid solution combining electrolysers, storage and fuel cells. This solution can be used to supply energy to remote areas with no connection to the electricity grid. Normally in these situations you want to have a short-term storage based on batteries, and a long-term storage based on hydrogen. However, the round trip efficiency is low, and the investment cost is high compared to alternatives like pumped hydro and battery storage.

Illustration of Electrolysis/Hydrogen direct use in an off-grid Scenario:

Illustration of Electrolysis/Hydrogen in a micro electricity grid:

Grid Balancing*

Electrolysers are systems that can typically be turned on and off and ramped up and down in unilization levels which can increase or decrease it’s electricity consumption and thereby providing grid balancing services. Grid balancing has been given an asterix(*) because it is a service that can be provided but it unlikely justifies the case on its own. Here it is possible to have multiple benefits at the same time. Electrolysis can be used to balance the grid by only taking the surplus electricity from the grid when it is available. This way the system is always in balance and no excess electricity production from VRE is wasted.

The hydrogen that is produced from the electrolyser for grid balancing can be added back into the grid as electricity through use in turbines or fuel cells as described in the Off-Grid application or used in transport or industrial applications.

Illustration of Electrolysis/Hydrogen use in grid balancing:


Within industrial applications hydrogen is mostly used as an «ingredient» in a chemical process, rather than an energy carrier (or “source”). For instant when making ammonia (which in the next step can be used to make fertilizers) hydrogen is added to a chemical process that combines hydrogen with nitrogen into ammonia, NH3. In smelters hydrogen can replace carbon (typically from coal) as a reductant in the chemical process of removing the Oxygen from the oxidised metal-ore (the reduction process). In that case the resulting product of the reduction process is the pure metal and clean water (vapor) instead of CO2.

Hydrogen can also be made into other energy carriers, based on hydrocarbons, like methanol, jet fuel, diesel etc. This is called “Power-to-X” meaning that electricity (the “power”) can be turned into different fuels (the “X”) by first making hydrogen in an electrolyser and then adding carbon (for instance from CO2 in the air) into the preferred hydrocarbon fuel. This process will “re-use” carbon/CO2, but not eliminate it.

Illustration of Electrolysis/Hydrogen use in industry:


Suitability of Different Electrolyser Technologies

While many hydrogen users do not care what the source of Hydrogen is, it is important to note that there are certain attributes to each electrolyser technology that make it more suitable within certain applications.

In the case of Transport for instance there is no noticeable difference between the suitability of the technology however economic conditions or electricity sources may dictate that one is better than the other.

In the case of Off Grid and Grid Balancing, there are clear differences in the suitability of different electrolysers due to technological limitations.

In the case of Industry, we have the same scenario as with Transport where there is no noticable difference in the suitability however specific conditions may dictate one is more suitable than another.

The suitability of the different electrolyser technologies: Alkaline (ALK), Proton Exchange Membrane (PEM) and Solid Oxide Electrolyser (SOEL) to the applications is summarised in the illustration below:

In part 3, we will compare between the different electrolyser technologies and highlight the trade-offs between each other, their perfect applications and actual economic implications.

Do you want more details regarding the applications for the different electrolyser technologies?  Contact us at greensight@greensight.no. Did you miss «Technology: electrolysers – part 1»? Read it here.


Technology: Electrolysers – part 1

Electrolyser technology

Hydrogen has many colours and can be produced with a broad range of technologies. Green hydrogen is produced by water electrolysis with renewable electricity. Water electrolysis is the cleanest and most sustainable way to produce hydrogen. The next weeks we will discuss the different electrolyser technologies.

We will discuss the technologies in three parts:

Electrolysis is the electrochemical process splitting water into hydrogen and oxygen by supplying electrical (or thermal) energy given by the equation:There are currently three main technologies for electrolysis:

  • Alkaline Electrolyser
  • Proton Exchange Membrane Electrolyser
  • Solid Oxide Electrolyser


The alkaline electrolyser (ALK) is a mature technology. In an alkaline electrolyser, the electrolyte is usually a 25-30% aqueous KOH-solution and is operated at 60-90˚C. The electrodes are immersed in the liquid electrolyte, separated by a separator that only allows transport of ionic charges. Historically, the separator was made of asbestos, but is currently made of Zirfon PERL.

When a direct current is applied to the water, the water molecule is split into oxygen and hydrogen. The electrolyte let the ions be transported between the electrodes. The purity is 99,5-99,9% for the hydrogen.

The electrolysis reactions: 

Alk redoks reaksjon


Alkaline cell

Conceptual set-up of an alkaline cell. Source: The International Journal of Energy


Proton exchange membrane (PEM) systems are based on the solid polymer electrolyte concept for water electrolysis introduced in the 1960s.  The PEM electrolysers that are commercially available today, are more flexible and tend to have smaller footprint than the alkaline electrolysers. 

A proton exchange membrane separates the two half-cells, and the electrodes are usually directly mounted on the membrane. The membrane only allows transportation of hydrogen ions. It is necessary to use noble metal catalysts like iridium for the anode and platinum for the cathode. Water is supplied at the anode. The cell temperature of a PEM cell is 50-80˚C. 

The electrolysis reactions are as follow:

PEM redoks-reaksjon

The resulting purity is higher than for alkaline and is typically greater than 99,99% H2. PEM has a compact module design because of the solid electrolyte and has a high current density operation compared to alkaline.

pem electrolyser technology
Source: Wood Mackenzie, U.S. Department of Energy


Electrolysis of water can be performed at high temperature using steam. A Solide Oxide Electrolyser (SOEL) is a high-temperature electrolyser that perform a solid oxide electrolysis and operates at temperatures of 700-900˚C. The technology is currently immature and has only been tested at laboratory scale. High temperature operation results in higher electrical efficiencies than alkaline and PEM, but it has challenges in material stability and also depend on waste heat. The high temperature steam is either supplied by an external heat source or by an electrical heater, therefore the applicability of SOEL is limited to specific instances (more in part 2)

SOEL use a solid ion-conducting ceramic as the electrolyte and comprise of three layers. Yttria-stabilized zirconia is often used as electrolyte.

The half reduction equations:

Solid oxide cell

Conceptual set-up of a solid oxide electrolyser cell. Source: International Journal of Hydrogen Energy


Part 2 will discuss the applications for the different technologies. Part 3 compares the different electrolyser technologies.

Do you have a project you want to realise and need more information? Please contact us at greensight@greensight.no. You can sign up for our  newsletter here. Read more blogposts here

Greensight Hydrogen Economics Tool – profitable hydrogen business models.

hydrogen economics tool

Understanding how to get the most out of investments in zero emission solutions is maybe more important than ever, and our Hydrogen Economics Tool has you covered.

Greensight continue to work with hydrogen and forecasting production costs as industries, markets, and technologies develop and change.

We have developed Greensight Hydrogen Economics Tool for use in calculating hydrogen production prices and required sales prices to realize real business models that are profitable and sustainable.


What this tool does:

The Hydrogen Economics Tool enables us to calculate, visualize, and evaluate hydrogen production prices from a total value chain aspect using specific inputs relevant to the case analysed. The tool works for hydrogen in both compressed and liquefied states and for on-site or distributed use.’

How it works:

Specific data inputs relevant to the project such as required hydrogen outputs in the short and longer term, technical aspects, equipment costs, operating costs and electricity prices are gathered together into a techno-economic model.
The model calculates the specified results such as cash flow, ROI, payback period, cost per kg H2 by category and displays it in both numerical and graphical representations for further analysis.

What this tool enables:

Feasibility Analysis:

The tool enables fast feasibility analysis of different hydrogen production plants so that business’ can identify best opportunities available today and to strategize to develop opportunities for tomorrow.

Detailed analysis:

The tool enables detailed results on each aspect of the hydrogen production value chain allowing decision makers to identify and focus their efforts on the aspects that are both influenceable and important in order to realize the best results.


The tool enables directly comparable results and analysis of different investments, production plant setups.


Often hydrogen calculations are done with rules of thumb; such as electricity is 80% of the cost of hydrogen or maintenance is 5% of the initial capital cost. The Hydrogen Economics Tool uses specific real-world inputs to simulate actual results on specific cases.


The tool has add-inns to integrate sale of excess heat and oxygen from the electrolysers.


Who can benefit from the use of this tool?


Hydrogen consumers (current or prospective) who are looking to understand the cost of producing hydrogen for their own use or for use in negotiations with hydrogen suppliers.

Hydrogen producers who want to understand the true cost of hydrogen production and investigate different business cases and understand trade-offs between investments in different designs.

Energy producers who have VRE (Variable Renewable Energy) and want to take control of the variability of electricity production through the use of hydrogen to optimize time of electricity production.

Interested in learning more about our Hydrogen Economics Tool? Chat with us now or send us an email, we would love to hear from you!  Email: greensight@greensight.no


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Investments in publicly traded hydrogen companies is charging up

Over the past 6 months the market capitalization of publicly traded hydrogen focused companies have more than doubled.

What is causing this recent increase in market capitalization and share prices?