Why many in academia and industry see the future in small-sized hydrogen generators
Rooftop solar is passé. The upcoming thing is rooftop hydrogen. It is still some years away, but many in the scientific community and industry believe it is certainly happening.
Imagine a contrivance on your rooftop — an electrolyser — to which is attached a cylinder, or pipes leading to a big tank in your basement. You fill a chamber in the device with water. The next day, your cylinder or tank is full of hydrogen — a fuel for your car or the cookstove.
The problem with rooftop solar in India has had a lot to do with the intransigence of the various state-owned electricity distribution companies. The lack of an assured offtake for surplus energy generated and the low prices offered for it have hampered rooftop solar growth in India.
Storing solar electricity in batteries has been an expensive proposition, though the sharp fall in battery costs is promising. However, since the world is moving swiftly into hydrogen, there is an alternative for the batteries.
Here again, one could make use of the electricity from the rooftop solar plant to split water right on the roof to produce hydrogen; better still, there are emergent technologies that are making possible photolysis — splitting water directly using sunlight, without the interface of electricity — using photoelectrochemical cells (PEC).
Prof Aravind Kumar Chandiran, who heads the Solar Energy Research Group at IIT Madras, had announced in August the development of “a new material” (a ‘distorted hallide perovskite’) that can be used to split water under sunlight.
Prof Mohammed Qureshi of IIT Guwahati announced recently that his team developed a catalyst (cobalt-tin layered double hydroxide and bismuth vanadate) that, when used as a ‘photoanode’, can split water into hydrogen and oxygen.
Prof Qureshi told Quantum that it would be too early to comment whether this could be downsized for a rooftop plant, but many others in the academia and industry feel small-sized hydrogen generators will be ubiquitous in the future.
Even if you want to keep aside technologies for splitting water directly from sunlight and look only at conventional electrolysis, there is plenty evidence to indicate that small-scale hydrogen plants are arriving.
Size does not matter
“Fundamental physics says that these are technologies where size does not matter,” says Arne Ballantine, CEO and co-founder of Ohmium, a US-headquartered company that has started producing electrolysers from Bengaluru.
“Yes, the idea of ‘rooftop hydrogen’ becomes very, very real,” Ballantine said, adding, “We are moving past the world of chemical plants where the most efficient way to make hydrogen was with a huge installation.”
A newly set-up company called Hydrogenium Resources is talking to rooftop solar installers to put up small electrolysers alongside solar plants to produce hydrogen from surplus solar power, the company’s Executive Chairman, Umesh Sachdev, has told Quantum.
Sebastian-Justus Schmidt, Chairman of Enapter, a German company that produces electrolysers, has spoken of devices the size of a microwave oven. They can be married to a rooftop solar plant.
In a press release in February 2020, Schmidt said, “Today, we need only 4.4 kWhr of electricity to produce one cubic metre of hydrogen.”
Now, 4.4 kWhr of electricity is typically the output of a 1 kW rooftop solar plant.
Companies like the Scotland-based Pure Energy Centre and the Spain-based H2B2 already make small electrolysers.
“Demand for hydrogen is expected to grow by a factor of 1,000 or more by 2030 and decentralised systems producing the gas on-site, with no transportation cost, will make a huge difference,” Schmidt said.
Clearly, hydrogen can be produced (and consumed) by households on rooftops, or from other on-premise plants.
Ballantine is emphatic about it. “Electrochemical hydrogen generation — water electrolysis — will follow patterns of semiconductors and chips. Mini-, micro-, and nano-structuring will win again and again,” he says.
The cost factor
Of course, today the cost is an issue — one estimate pegs it at around $7.50 a kg for rooftop hydrogen, because of the electrolyser costs; but then, solar photovoltaic modules, too, were selling at over a dollar a watt-peak before they fell to a fifth in less than five years. As electrolyser manufacturing gains ground, scale will help bring down the cost.
The key enablers for rooftop hydrogen are the ‘cold-start’ and ‘rapid start-stop’ cycling capabilities,” says Chock Karuppiah, CTO at Ohmium.
On the splitting of water directly from sunlight, without using electricity, Karuppiah said photoelectrochemical systems “might look like an ideal solution”, but there are many challenges to overcome.
“The design of a single device solution needs to balance between many needs (properties of light, ionic species, electrical flows, liquid water and gaseous hydrogen). It is very hard to do that well in a single device,” Karuppiah said.
The integration of solar cells and electrolysis cells will lead to faster commercial implementation, he added.