Solar Powered Engines
“A little known fact about Boeing: It’s got more solar patents than anyone else in the U.S. (14 solar thermal patents since 2002). Boeing has teamed up with solar thermal company Stirling Energy Systems to develop Boeing’s high-concentration photovoltaic solar power technology. Founded in 1996, Phoenix, Ariz.-based Stirling Energy has developed a 25 KW electric solar dish that focuses the sun rays directly onto a stirling engine. Most solar thermal technologies, by contrast, concentrate the sun’s rays onto liquid, which powers a turbine. Stirling isn’t the only company turning to stirling engines for solar power. One example is Infinia, which is backed by a gaggle of A-list Silicon Valley-ers, including Bill Gross’ Idealab and Paul Allen’s Vulcan Capital.”
“Nearly 200 years after their invention, and decades after first being proposed as a method of harnessing solar energy, 60 sun-powered Stirling engines began generating electricity outside Phoenix, Ariz., for the first time. Such engines, which harness heat to expand a gas and drive pistons, are not used widely today other than in pacemakers and long-distance robotic spacecraft. In 1996, SES bought solar Stirling design and engineering patents from companies such as McDonnell-Douglas and Boeing. SES then partnered with Sandia National Laboratories, and over the next decade tweaked and refined the technology. Stirling engines are significantly more efficient at converting sunlight into energy than most photovoltaic panels or concentrating solar power plants. Proponents of the technology point to the advantages it has over other forms of solar power – particularly concentrating solar power (CSP), which requires significant amounts of water, a challenge in desert regions of the U.S. where solar power is most attractive – while Stirling engines require none other than small amounts for cleaning the mirrors. In addition, if one engine goes down, it has minimal impact on overall production.
SES faced a manufacturing challenge in preparing its SunCatchers for mass production though. “The systems at Sandia were basically hand-built,” says Charles Andraka, a Sandia engineer. For the Phoenix site, he notes, Sandia and SES engineers built 60 units in three months. “We have to do that many in a day for the larger plants.” In order to do this, SES turned to the experts in rapid production of engines and related parts: the automotive industry. In partnership with automotive companies such as Tower Automotive and Linamar Corporation, SES managed to reduce the parts in the PCU by 60 percent (to about 650) and slash the weight of the entire system by roughly 2,250 kilograms. The new systems have been running on test sites for more than 100,000 hours. Maricopa Solar also represents just one scalable module; each multi-megawatt field will be grouped first in 60-engine units that come together to generate 1.5 MW, then those larger units are linked to each other to produce up to 9 MW. Explains Coates, “With the large 750 MW commissions, we won’t have to wait until we have 750 MW of dishes before we start producing power. This means that the utility can get the power prior to the full build-out, which can take years to complete.” This is in comparison to parabolic trough or tower CSP technology, which doesn’t generate electricity until the entire system is complete.
Solar Stirling Engine with parabolic mirror
Combined Heat and Power
“Householders could one day be producing as much electricity as all the country’s nuclear power stations combined, thanks to the revolutionary application of a device developed in the early 19th century. A new version of the device, the Stirling engine, is set to turn ordinary domestic gas boilers into miniature power stations, generating electricity whenever you switch on the central heating or hot water. It won’t make electricity meters run backwards. But for an estimated £500 extra on the price of a new boiler, the machine will generate electricity for the home for nothing, using excess heat that would otherwise escape out the flue. In Britain, a confidential report prepared for electricity companies by energy consultants EA Technology estimates that by 2025, 13m of the country’s 23m households could have their own little power station humming away in the boiler cupboard. In existing domestic gas boilers, about a third of the heat is wasted. With the latest make of Stirling engine fitted, that spare heat is used to drive a small generator. The idea of turning homes into power stations is known as “micro chp” (combined heat and power). EA Technology is championing a Stirling engine made by WhisperTech, a New Zealand company, which can generate a kilowatt of electricity – enough to power three fridges.”
Portable Power Plant
“Over the past decade, Kamen, who made a fortune as inventor of the insulin pump and other medical devices, has spent some $40 million developing Stirling engines. “We run two villages in Bangladesh on Stirlings that run on freakin’ cow dung,” says Kamen, who envisions Stirling engines powering the world’s off-the-grid villages and using the waste heat produced by the engine to purify water. “I need some killer app to put this thing into production. And one way to do that would be to create the world’s first hybrid Stirling electric car.” Which led him to install a Stirling heat engine in an electric car made by Norway’s Think. That would not only extend the Thinks range by hundreds of miles but turn the car into a mobile generator. When electricity demand peaks during the day, thousands of Thinks plugged in at office parks could feed power back to the grid so utilities could avoid having to fire up planet-warming power plants. The Stirling engine would then recharge the car’s battery for the commute home. “If you have enough Thinks out there you would literally change the architecture of the grid,” says Kamen. “The big advantage is once we’re in production with that engine, where it will really be uniquely valuable is to the 1.6 billion people on this plant who’ve never used electricity,” says Kamen. “We will become the Con Edison of every village in Asia, Africa and Central America.”
Build Yr Own
tutorial by William Gurstelle