If we want to transition to a carbon free economy, renewable energy has to be pivotal – but no matter how you look at the problem, the bottom line is always the same: efficiency. Solar only generates energy when the sun is up, the same goes for wind… there’s a big reliability issue. With this in mind, an international team of researchers has come up with a new, hybrid solution. They call it hydricity.

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“The proposed hydricity concept represents a potential breakthrough solution for continuous and efficient power generation,” said Rakesh Agrawal, Purdue University’s Winthrop E. Stone Distinguished Professor in the School of Chemical Engineering, who worked with chemical engineering doctoral student Emre Gençer and other researchers.

The system

There are two ways through which we use the Sun’s energy on a large scale: through photovoltaics (the panels you see on rooftops that generate electricity) and solar thermal plants, which concentrate the Sun’s rays to generate heat and drive steam turbines. The latter option captures more energy, but is less efficient than photovoltaics; also, it only works in direct or almost direct sunlight, so you can only use it in areas that get a lot of sun.

This is where hydricity steps in. An integrated “hydricity” system would produce both steam for generating electricity and hydrogen for storing energy, using the advantages of both methods to make each other more effective. The team, from Purdue University and Switzerland’s Federal Polytechnic School of Lausanne proposed an integrated system that would produce both steam for immediate use and hydrogen for later use – making solar energy usable throughout the day, but also throughout the night. This is because the high-pressure steam generated by the system can pressurize hydrogen efficiently.

“In the round-the-clock process we produce hydrogen and electricity during daylight, store hydrogen and oxygen, and then when solar energy is not available we use hydrogen to produce electricity using a turbine-based hydrogen-power cycle,” Tawarmalani said. “Because we could operate around the clock, the steam turbines run continuously and shutdowns and restarts are not required. Furthermore, our combined process is more efficient than the standalone process that produces electricity and the one that produces and stores hydrogen.”

The figures

According to the team, hydricity can produce hydrogen at an efficiency of 50 percent and electricity at an unprecedented 46 percent efficiency, thanks to the way the high-pressure turbines can be used to run in succession of the lower-pressure ones. Over the course of a regular 24-hour day, it can reach a Sun-to-electricity efficiency of 35 percent.

To make it even more attractive, the hydrogen can also be used in transportation and industries such as chemical production.

“The concept provides an exciting opportunity to envision and create a sustainable economy to meet all the human needs including food, chemicals, transportation, heating and electricity,” said one of the researchers, Rakesh Agrawal from Purdue. “Traditionally, electricity production and hydrogen production have been studied in isolation, and what we have done is synergistically integrate these processes while also improving them.”

Journal Reference: Emre Gençer et al – Round-the-clock power supply and a sustainable economy via synergistic integration of solar thermal power and hydrogen processes. doi: 10.1073/pnas.1513488112