A Duke University professor aims to prove that with a little tweak, traditional solar energy can be improved to produce more energy. The solution Nico Hotz envisages uses solar energy as one part of the solar-hybrid system. The hybrid option uses sunlight to heat a combination of water and methanol in a maze of glass tubes on a rooftop. A catalyst starts a reaction which produces hydrogen in a process that’s more efficient by today’s standards. The hydrogen can then be used as a power source.
Hotz compared the energy efficiency of his system to three other systems.
“The hybrid system achieved exergetic efficiencies of 28.5 percent in the summer and 18.5 percent in the winter, compared to 5 to 15 percent for the conventional systems in the summer, and 2.5 to 5 percent in the winter.”
He is currently building a system to test out the experimental theory on the ground.
The process starts with solar heating using a device that resembles the usual solar collector. It is actually 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. The mixture evaporates and then a catalytic reaction produces hydrogen which can be hived off to a fuel cell to provide electricity to a building during the day, or compressed and stored in a tank to provide power later.
“This set-up allows up to 95 percent of the sunlight to be absorbed with very little being lost as heat to the surroundings,” Hotz 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.”
As with all novel systems, real life practicability boils down to the cost. Hotz said,
“The installation costs per year including the fuel costs, and the price per amount of electricity produced, however showed that the (hybrid) solar scenarios can compete with the fossil fuel-based system to some degree. In summer, the first and third scenarios, as well as the hybrid system, are cheaper than a propane- or diesel-combusting generator.”
