'Solid-oxide hydrogen electrolysers could be cheaper to install than alkaline or PEM in some circumstances': study
High-temperature electrolysers are already cheaper to operate but capex costs are coming down, says Clean Air Task Force report
Solid-oxide electrolysers (SOE), generally accepted as cheap to operate and cripplingly expensive to install, could be less capex-intensive to build than either alkaline or proton exchange membrane (PEM) equivalents in some circumstances, according to a new study.
The report, Solid Oxide Electrolysis: A Technology Status Assessment, published by not-for-profit Clean Air Task Force (CATF), suggested that SOE systems could be installed for as little as $917/kW including balance of plant (BOP), while at their most expensive, alkaline electrolysers could cost up to $1,000/kW, including BOP.
“Under some circumstances SOEC [solid-oxide electrolyser cells] could work out cheaper than alkaline albeit I’d argue this is more likely to happen in SOEC vs PEM,” said Gniewomir Flis, an independent hydrogen consultant and lead author on the report.
At their most expensive, PEM electrolyser systems would cost up to $2,100/kW, the report found.
SOE has been touted as an ideal solution to integrate into industrial applications such as ammonia production, as it can utilise waste heat that can increase their efficiency beyond what can currently be achieved by alkaline or PEM electrolysis, thus producing more hydrogen per kWh of input electricity.
But the cost ranges cited in the report are huge, indicating that both PEM and alkaline electrolyser systems are still broadly cheaper than SOE — which at its most expensive would cost a massive $4,000/kW including BOP.
Cost ranges for alkaline and PEM systems, however are at around $800-1,500/kW and $1,400-2,100/kW respectively.
SOE stack cost alone appears to have moved down somewhat since the International Renewable Energy Agency (Irena) last assessed electrolyser technologies in 2020 — it estimated capex on SOE stacks at around $2,000/kW, with no lower range at all, compared to CATF’s stack-only estimation of $250-2,000/kW.
So under what circumstances would SOE systems — which when paired with waste heat can operate at around 25% higher efficiency than other electrolyser technologies — be cheaper than alkaline or PEM?
For SOE systems to hit the bottom of the range, electrolyser makers would have to significantly automate and scale up manufacturing capacity, which the US’s Bloom Energy is already doing.
More generally, system costs are highly dependent on plant configuration — meaning that an SOE plant in its least efficient iteration would be cheaper to install than an alkaline or PEM plant set up to maximise efficiencies.
“Cost ranges includes several variables, such as stack and system size, efficiency, flexibility, variability in design amongst manufacturers, and even order size,” Flis explained to Hydrogen Insight. “For instance, a 10MW [alkaline] system made of two 5MW atmospheric alkaline stacks with low efficiency would be representative of the lower-end capex estimate. Conversely, a 10MW system made of twenty 500kW high-efficiency, pressurised and flexible stacks would be more capex intensive.”
“However, even here caveats apply. In the future, product standardisation and mass manufacturing might mean that in some instances a slightly smaller stack might work out cheaper even if it requires more balance of plant. But the trouble at the minute is that every electrolyser installation is essentially bespoke.”
The problem for SOE installers is that scaling up is uniquely challenging, because the system lots of balance-of-plant components to manage temperature and the use of steam.
While some of these components can be shared across a GW-scale system, much of it has to be duplicated for each “module” containing a certain megawatt-scale number of stacks, depending on the configuration on the plant.
This means that economies of scale are harder to achieve — in addition to the fact that SOE systems have not even been demonstrated at multi-MW scale yet.
And SOE systems are already large compared to PEM systems, due to the latter’s high cell density. In fact, SOE, alkaline and anion exchange membrane (AEM) systems typically have twice the physical footprint of PEM equivalents.
First Ammonia currently has one of the largest SOE-based projects in the pipeline, a massive 300MW green ammonia export project in the US using Topsoe electrolysers, and which already has a provisional offtaker, Germany’s Uniper.
But although ammonia production has been cited as a major opportunity for SOE systems, manufacturers such as Sunfire are also testing the technology in standalone hydrogen production pilot projects, as well as steelmaking, nuclear and the production of e-fuels made from renewable H2.