A Danish chemical catalyst company has announced plans to construct a 500MW factory to manufacture solid oxide electrolysers (SOEs) that could reduce the cost of green hydrogen by as much as 20% compared to the more common alkaline and PEM electrolysers, Recharge has learned.

Haldor Topsoe’s automated factory is set to be the world’s first large-scale SOE plant when it becomes operational in 2023, as well as one of the planet’s biggest electrolyser manufacturing facilities.

SOEs differ from alkaline and PEM electrolysers because they use high-temperature heat to increase the efficiency of the water electrolysis process (see panel below).

“With Topsoe’s SOE electrolyser, more than 90% of the renewable electricity that enters the electrolyser is preserved in the green hydrogen it produces,” says chief executive Roeland Baan. “This is significantly more efficient that the other available technologies in the market.”

By comparison, hydrogen produced by PEM and alkaline electrolysers only contain about 70% of the energy used to produce it.

Tore Jeppesen, senior vice-president of business development at Haldor Topsoe, tells Recharge that the company’s SOEs need up to 30% less electricity than PEM and alkaline technology to produce the same amount of hydrogen when low-temperature heat is fed into the system from an external source. The fact that heat coming out of the high-temperature stack is re-used also helps improve efficiency.

“You can say half of that is the higher efficiency of the process compared to PEM and alkaline. And the other half is where you can substitute electricity with heat input,” he explains.

Jeppesen adds that the price of the electricity used in the electrolysis process accounts for about two thirds or 75% of the cost of the hydrogen produced. So a 30% reduction in the amount of electricity required, results, roughly speaking, in a 20% cut of the price of green hydrogen.

“We firmly believe that we are, on a capex level, [on] equal terms with low-temperature electrolysers and the opex is cheaper due to the lower electricity requirement.”

So if SOEs are much better than alkaline or PEM technologies, why are other electrolyser manufacturers sticking with those?

“That’s a good question I ask myself sometimes,” said Jeppesen. “I think it's just the history involved in this. I mean, it is more difficult to make a high-temperature process. We’ve been working on [SOE] for many, many years.”

Haldor Topsoe — which specialises in designing catalyst-based process plants for many industries — first began work with solid oxide materials in the 1980s, first on solid oxide fuel cells, and then exclusively on electrolysis since the start of 2015,” Jeppesen tells Recharge.

“We’ve done loads of development work, demonstrators at client sites. We’ve just not been all that vocal about it.”

The new factory will produce modules of just under 1MW and could be expanded to 5GW if and when demand increases.

“We think we have a fantastic product and if you look at the early client engagement we have currently, we certainly feel that is a realistic target,” says Jeppesen.

The three main types of electrolyser

Alkaline (ALK)

This technology has been around since the 1920s and was widely used, particularly in the chemicals industry, before the natural-gas boom of the 1970s made steam methane reforming cheaper.

It is, however, the lowest-cost and most efficient form of electrolyser, particularly when powered by baseload sources. The electrolyte (electricity-conducting medium) is a solution of water and potassium hydroxide.

Proton exchange membrane (PEM)

This relatively new technology is said to be more expensive and slightly less efficient than ALK electrolysers, but is rapidly catching up on both fronts.

PEM has several potential advantages, which has led the technology to play a leading role in green hydrogen pilots — it can ramp up quickly and is highly efficient at low loads, meaning it is far better suited to the variable energy input supplied by wind and solar power. It also uses pure water as its electrolyte, so recovery and recycling of potassium hydroxide is not required; it can output hydrogen at higher pressures, therefore requiring less energy for compression; and it takes up around half the space of comparable ALK systems.

The downsides are that the technology is more expensive, requiring expensive platinum- and iridium-coated electrodes and ultra-thin specialty-plastic membranes — and is said to have a shorter lifespan than ALK electrolysers.

Solid oxide electrolysis (SOE)

This technology uses solid oxides or ceramics as its electrolyte, with high-temperature steam (rather than water) being separated into hydrogen and oxygen.

It operates at higher efficiencies than ALK or PEM, but requires a heat source, so would be perfect for use with clean electricity generation that produces waste heat, such as nuclear, concentrating solar power and geothermal. Low-temperature heat from industrial processes will work equally well.