By Andy Jensen, News Writing Student
Students fixed their eyes on the 6-inch engine, with no apparent power source, silently spinning away in the palm of engineering professor Greg Holland’s hand.
“This looks like a perpetual motion device,” Holland said. “It is a Stirling engine, powered using only the heat from my hand.”
Holland gave a lecture on alternative energy April 9 to a class of journalism students.
“One of the things I see a lot of is the misuse of the term ‘alternative energy,’” he said.
Alternative energy is a broad term, which covers both energy to power homes and vehicles, as well as renewable sources of energy, Holland said.
“Something doesn’t have to be renewable in order to be an alternative energy source,” he said.
As examples, Holland pointed out that coal and gasoline were once considered alternative energy sources.
He said he thinks alternative energy is a complex issue right now, as the world is looking for the next big source of energy. But it must have fewer, or none, of the drawbacks the current sources have.
“There is no ‘good’ source of energy,” he said. “You can find drawbacks to any source.”
Solar power requires large mines for rare materials to build the panels. Wind power needs giant turbines that are visible for miles, and some people do not want to see them.
“I don’t know why people feel that way,” said Holland. “[Wind turbines] are very elegant machines.”
Holland said he is a fan of the Stirling engine.
Originally conceived almost 200 years ago, the device is named after its inventor, Robert Stirling.
The engine uses pressure from hot expanding air to move a piston connected to a wheel, he said.
The wheel rotates and pulls a cooler piston, drawing hot air to the cooler area where the temperature and pressure come down.
Holland said when the air has cooled sufficiently, the pressure cannot hold the piston against gravity, so it moves down forcing air into the hot side to start the process again.
He said it is a simple design that helps address most of the negatives of other forms of alternative energy.
“It could be centralized in one location, or distributed,” Holland said. “It’s quiet. Everyone could have one in their back yard.
“It can also run off of biomass.”
This means a Stirling engine could be used to make energy from natural gas, ethanol, or even warm compost or garbage.
“That temperature differential is the driving force for heat transfer,” Holland said. “You can run a Stirling engine off just the temperature difference between the ground and the air.”
Today, Stirling Energy Systems is building 20,000 of the engines for use in concentrated solar dishes in “the largest solar power project in the world,” according to its website.
Each dish works in tandem with a Stirling engine to produce enough power for 12 average homes.
Power company Southern California Edison has agreed to buy all the power generated by the alternative source when the project is complete.
Holland teaches Engineering 1000 Special Projects in which students build Stirling engines as a group project.
For more information on the Stirling engine and other alternative energy sources, visit Holland’s website at www.occc.edu/gholland.
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