Hybrid solar system makes rooftop hydrogen
Duke University engineer Nico Hotz has proposed a hybrid solar system in which sunlight heats a combination of water and methanol in a maze of tubes on a rooftop to produce hydrogen.
The device is a series of copper tubes coated with a thin layer of aluminum and aluminum oxide and partly filled with catalytic nanoparticles. A combination of water and methanol flows through the tubes, which are sealed in a vacuum.
Once the evaporated liquid achieves higher temperatures, tiny amounts of a catalyst are added, which produces hydrogen. This combination of high temperature and added catalysts produces hydrogen very efficiently, Hotz said. The resulting hydrogen can then be immediately directed to a fuel cell to provide electricity to a building during the day, or compressed and stored in a tank to provide power later.
After two catalytic reactions, the system produced hydrogen much more efficiently than current technology without significant impurities, Hotz said. The resulting hydrogen can be stored and used on demand in fuel cells.
“This set-up allows up to 95 percent of the sunlight to be absorbed with very little being lost as heat to the surroundings,” he said. “This is crucial because it permits us to achieve temperatures of well over 200 degrees Celsius within the tubes. By comparison, a standard solar collector can only heat water between 60 and 70 degrees Celsius.”
Holtz performed a cost analysis, comparing a standard photovoltaic cell, a photocatalytic system, and the hybrid solar-methanol system. He found that the hybrid system is the least expensive solution, with a total installation cost of $7,900 if designed to fulfill the requirements in summer.
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