Could a Solar-Hydrogen Economy Supply All our Energy Needs?


TreeHugger has never been a fan of the hydrogen economy; the gas is more of a battery than a fuel as it takes a lot of energy to make the stuff. We have called it nothing more than a front for the nuclear industry.

But Derek Abbott, Professor of Electrical Engineering at the University of Adelaide in Australia, makes a persuasive case that it is perhaps the most effective medium for using and storing solar energy, and explains in Physorg..

He looks at all of the technologies for making hydrogen and settles on solar thermal, driving Stirling engines.

sterling engine detail

Sterling engines in California
"The fact that there simply is 5,000 times more sun power than our consumption needs makes me very optimistic," Abbott said. "It's a fantastic resource. We have the ingenuity to send man to the moon, so we definitively have the ingenuity to tap the sun's resources."

Despite the improvements in silicon solar cells, Abbott argues that they suffer from low efficiencies and high environmental impact compared with solar thermal collectors. Solar cells require large amounts of water and arsenic; Abbott calculates that manufacturing enough solar cells to power the world would require 6 million tonnes of arsenic, while the world's supply is estimated at about 1 million tonnes. Even the overall solar cell design is fundamentally flawed, he says. Solar cell semiconductor reliability drops as temperature increases, yet large temperature differences are required to increase thermodynamic efficiency. For this reason, semiconductor technology is much better suited to lower powers and temperatures, such as pocket calculators.

On the other hand, solar thermal collectors are specifically designed to operate under hot temperatures. The idea is to use a curved mirror to focus sunlight to boil water and create steam, which is then used to power, for example, a Stirling heat engine to produce electricity. The system has already been demonstrated in California's Mojave Desert, which has been using a solar thermal system to heat oil in a closed-cycle instead of water for the past 20 years.

He then suggests hooking these up to generators and using the power to electrolyze water and make hydrogen.

"Governments should begin by setting up sizable solar farms that supplement existing grid electricity and provide enough hydrogen to power buses," Abbott said. "Enthusiasts will then buy hydrogen cars, retrofit existing cars, and refuel at bus depots. Then things will grow from there. You gotta start somewhere."

Then he goes off what I would have called the deep end by suggesting that liquid hydrogen is the most efficient way to transport the stuff, even though this requires a huge amount of energy. (See What Is The Carbon Footprint of The Space Program? for how much). No problem;

Since the sun supplies a virtually unlimited amount of energy, the solution is to factor in the non-recurring cost of extra solar collectors to provide the energy for liquefaction. His calculations show that the cost of a solar collector farm used to produce hydrogen is still lower than a nuclear station of equivalent power.

In some ways, Abbott sounds like those early nuclear proponents who said that they would provide electricity that was "too cheap to meter." But you can't help but be intrigued by his conclusion in the Physorg article:

"There is so much solar that all you have to do is invest in the non-recurring cost of more dishes to drive a solar-hydrogen economy at whatever efficiency it happens to sit at. I show in my paper that if you do this you come out cheaper than nuclear and you take up less than 8% of the world's desert area. ... So let's begin now, what are we waiting for?"

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