Integrated reversible power-to-gas systems developed by researchers at Stanford University and the University of Mannheim in Germany provide a solution: hydrogen fuel cells that can be easily converted back to electricity at higher power prices.
New research shows that reversible fuel cells can be a financially viable source of backup electricity during periods of surging prices, such as Texas experienced in 2021 when winter storms knocked out natural gas-fueled power stations. As the research reveals, having the ability to change directions allows the entire system to operate closer to its maximum potential. Carbon-free hydrogen and carbon-free electricity can be produced at a lower cost this way.
Solid-oxide fuel cells
There are already commercially available reversible fuel cells that can turn hydrogen back into electricity. Traditional gas-to-power systems use expensive turbines that sit idle except when demand for electricity spikes, according to conventional wisdom, so the process isn’t cost-competitive.
The researchers found that was a much smaller problem for the newer integrated systems, which use solid-oxide fuel cells and can switch directions more easily. Even if the systems are operated to produce hydrogen most of the time, the researchers calculated, the ability to supply backup electricity during even short periods of peak demand contributes to overall profitability.
An analytical model was developed based on market conditions in Texas and Germany, where gas-to-power projects have been in operation for several years. In previous work, Reichelstein and Glenk showed that it was possible to produce hydrogen from electricity for about $3 per kilogram. That’s roughly in line with the prices that lower-volume buyers pay, though too high for large-volume customers.
The new study looks at the other side of the process, converting hydrogen back into electricity. In effect, says Reichelstein, the integrated reversible systems can help solve two problems at the same time: how to get economic value from renewable electricity when it cannot fetch a good price; and how to smooth out volatility in electricity markets. And both of those solutions help reduce carbon emissions.
A few companies already produce integrated, reversible power-to-gas systems. Hydrogen can now be produced from electricity using a single machine, as opposed to the previous system’s dual-machine setup. The hydrogen produced by these modular systems was cost-effective, but the reverse conversion was not.
Reichelstein and Glenk think that the cost effectiveness of such systems will improve as the technology matures, as happened with wind turbines and solar panels. The reversible systems can be built to almost any scale, they add, so they can be used by individual companies or small communities as well as by large urban power grids.
Over the coming years, says Glenk, reversible power-to-gas systems could bring down the cost of carbon-free hydrogen and spur its wider use as a fuel. Steel producers, for example, are actively looking at hydrogen as a substitute for coal or natural gas.
This research was funded by the German Research Foundation and the Federal Ministry of Education & Research of Germany.
