Key Takeaways about From Water to Watts: Electrolyzers & Fuel Cells are the muscle behind the Hydrogen Revolution

• Electrolyzers can produce hydrogen from water and electricity
• Hydrolyzers can store hydrogen
• Fuel cells can produce electricity from hydrogen
• Proton exchange membrane (PEM) devices can react quickly to input variations and are thus most suitable to renewable energy applications

Introduction

For many years now, we’ve been told about the “hydrogen revolution”, touting how hydrogen, the smallest element in the universe, will be the key to low cost, pollution free energy for the whole world to enjoy with no ecological side effects. There are two problems with this story:

The first is that hydrogen may well serve as an energy storage medium, but not as an energy source. The reason is simple – hydrogen is so very reactive, so ready to disgorge its energy, that very little of it exists on the Earth’s surface in elemental form. It is very typically found combined with oxygen in the form of water.

The other is that hydrogen is very difficult and expensive to store either in the form of compressed gas, or, worse in solid form – this is rocket fuel we’re talking about!

In this report, we’ll describe how to isolate hydrogen via electrolyzers, how to store it via metal hydrides, and how to use fuel cells to obtain electricity.

• Electrolyzers, when powered by electricity, (hopefully electricity supplied by solar or wind), will break down water into its components of water and oxygen – now you’ve got the hydrogen. 2H20 → 2H2 + O2.
• So if storing hydrogen as a gas or in solid form is impractical, how can it be saved if not needed immediately? That’s where metal hydrides come in. We described this important technology in a previous article, for those who want more background. Suffice it to say that hydrogen storage via metal hydrides is safe and long lasting over years with a minimum of special care required – almost like a non-polluting lump of coal.
• When hydrogen and oxygen are presented to a fuel cell, the elements are allowed to combine. This process yields energy, in the form of electricity. The equation is the exact opposite of the electrolyzer’s equation. O2 + 2H2 → 2H2O

So let’s start the story with electrolyzers.

Types of Electrolyzers

There are three major types of electrolyzers. They are alike in that each variation is fed by electricity and water, and renders electricity, oxygen and water as outputs.

Proton Exchange Membrane (PEM) Electrolyzer

PEM electrolyzers employ solid polymer membranes as electrolytes to allow protons (H+ ions), to pass, while blocking the pathway of gasses.

PEM Electrolyzer. Image source: Biologic

They respond very quickly to unpredictable changes in voltage input. For this reason, they are the preferred type to work with variable renewable energy (VRE)  sources. A major drawback is high cost, as they require expensive platinum and iridium as catalysts 

Alkaline Electrolyzers (AEL)

The name comes from the fact that these devices employ a liquid alkaline solution, typically potassium hydroxide as its electrolyte, allowing hydroxide ions (OH+) to migrate from cathode to anode.

The major advantage of this mature technology is low cost. Because startup time is slow, it isn’t suitable for direct employment with VRE. But, it is a good choice for hydrogen production when steady state electrical input is employed.

Solid Oxide Electrolysis Cells (SOEC)

These units employ solid ceramic material as its electrolyte. They operate at very high temperature, up to 1000℃, with the water input supplied as steam. Like AEL electrolyzers, they don’t work well with variable electrical input.

They are best suited for applications where waste heat from other processes is available to supply the high input temperature required as input. As such, overall efficiency is excellent. 

Accelera’s PEM Electrolyzers

Accelera offers its HyLYZER 500 and HyLyzer 1000 PEM electrolyzers. These units offer a choice of 1.25, 2.25 and 5 MW outputs.

Accelera[2] specializes in PEM units because of their “Dynamic operation. PEM technology enables operation across a wide load range and responds rapidly to changes in power input. This flexibility allows systems to adjust quickly to varying energy demands”. Also cited is their compatibility with “Renewable integration. PEM electrolyzers are ideally suited for integration with intermittent renewable energy sources such as wind and solar. Their responsiveness supports grid balancing and frequency regulation. 

Multiple 5 MW Hydrolyzer 1000 are modular, and can be combined for greater power outputs. The company has deployed a 35 MW system for hydrogen production at a facility in Niagara Falls, NY. Accelera also boasts a deployment of an array of 20 HyLYZER 1000s to supply a full 100 MW system for BP Lingen’s green hydrogen project in Germany.

Hydrogen Storage

The most practical way to store hydrogen is in the form of metal hydrides. As mentioned, this process is covered in detail in our previous article entitled “Metal Hydrides: Green Hydrogen Storage for Real-World Energy.”

Now that we’ve described how to generate and store hydrogen, the final step in this narrative is to describe how to use that hydrogen to generate electricity. That is done via fuel cells.

Types of Fuel Cells

For large scale systems, multiple individual fuel cells, described as stacks, are electrically and mechanically combined to reach the size needed. Additionally, because the hydrogen, now once again in gaseous form, is presented to the fuel cell system under high pressure, a comprehensive control system is required for safe and efficient operation.

PEM Fuel Cells

Once again, proton exchange membranes allow for good efficiency even with a varying input, in this case the output is hydrogen gas, not electricity. This factor makes them a great choice for renewable energy applications.

A further advantage is that PEM fuel cells operate at comparably low temperatures. This factor makes them prime candidates for large trucks, locomotives and maritime use cases.

Solid Oxide Fuel Cells (SOFC)

A disadvantage is that these devices must operate at temperatures up to 1000℃. But, this high heat has certain advantages in some industrial applications. A great advantage is efficiencies in the range of 75%.

Molten Carbonate Fuel Cells (MCFC)

Another high temperature technology, MCFCs operate in the range of 600℃. As in the case of SOFCs, MCFC’s can also serve to convert natural gas or biogas into hydrogen as an added benefit. Efficiency is also in the 75% range.

HDF Energy’s Renewstable Hydrogen Power Plant

As described by HDF Energy[1],”In many parts of the world, weak or isolated electric grids struggle to meet high energy demands, relying on polluting fossil fuels. While wind and solar offer carbon-free and cost-effective benefits, their intermittency causes grid instability when overused.”  The company goes on to state that their Renewstable power plant serves to “competently integrate intermittent renewable energy sources with substantial on-site energy storage in the form of green hydrogen.”  

Renewstable. Image source: HDF Energy

The diagram above illustrates the complete cycle. First, renewable energy is generated. Batteries, which as of late 2025 can only store a limited amount of energy for short periods of time, are used for short term needs. Electolyzers produce hydrogen, which in this case is stored as gas, which is a lot less precarious when the gas doesn’t need to be transported. When power is need, it is generated via the company’s PEM electrolyzer. 

The basic HDF FC 1500 fuel cell can generate 1.5 MW of electrical power. Multiple units can be combined for greater power. Specifications are described in the company’s data sheet.

Wrapping Up

The hydrogen revolution is real, but its actual manifestations are quite different then the popular perception. Hydrogen is not a source of energy, rather a way of storing it. Storing it as a gas is possible (but problematic) at fixed locations, but transporting it is best done via metal hydrides.

The process involves electrolyzers fed by electricity to liberate the hydrogen from water. It can be combined into metal hydrides for storage or even for transport. Finally, the hydrogen can be liberated from the metal hydrides to power fuel cells to produce electricity.

There are many factors to consider, but the consensus seems to be that this “fully cycle” offers efficiency of about 40%.

Electrolyzer types include:

• Proton Exchange Membrane (PEM) Electrolyzer
• Alkaline Electrolyzers (AEL)
• Solid Oxide Electrolysis Cells (SOEC)

Only the first type, with its speedy response, is well suited for work with renewable energy.

Major Fuel cell types:

• PEM Fuel Cells
• Solid Oxide Fuel Cells (SOFC)
• Molten Carbonate Fuel Cells (MCFC)

Again, only the PEM variety works well with changing hydrogen inputs. The other two are somewhat more efficient.

Challenges and Opportunities

This article centers on what we describe as the full cycle, most relevant for producing electricity from VRE (Variable renewable energy).  The most pressing challenge, of course, is improving the efficiency of that full cycle conversion up beyond from the present 40% consensus.

There are many utility scale solar power plants that died on the vine because there is no will to expand the national power grid. But, unlike gaseous or solid hydrogen, metal hydrides are solid and stable, and can be transported by truck or rail, and the full cycle produces almost no pollution of any kind. Because there are many sunny climes in America where land is cheap, why not produce metal hydrides and transport them to regional fuel cell depots that can be located close to existing power grid nexuses?

There are an almost limitless number of use cases for all or part of the full cycle. For instance, industry has a voracious need for hydrogen in numerous processes. These include the hydrogen needed to produce ammonia, a fertilizer responsible for feeding untold hundreds of millions of people. Producing this hydrogen from steam methane reforming of natural gas, the most common present method, is a grotesquely dirty process, which could be eliminated through the use of electrolyzers. 

The list goes on and on.