SunCones: The Sun Shines on a Stirling Concept
Zoom-Zoom Vs. Zooop-Zooop

April 3, 2007

The Sun Shines on a Stirling Concept
Gar Smith /

The Open Energy SunCone and an earlier multi-coned, inflatable configuration (inset).
Who could have guessed that a 191-year-old engine design would become the newest ally of the solar power revolution? Under a recent co-development deal, Open Energy Corporation and Infinia have joined forces to provide a novel source of cheap electricity -- and clean drinking water.

The goal is to use Open Energy Corporation's SunConeTM solar concentrators to produce steam to power Stirling engines hitched to electric generators. The result: virtually free electricity with no burning of fossil fuel and no emissions of greenhouse gases. Open Energy, which has established itself as a major supplier of SolarSave® building-integrated photovoltaic roofing materials, says its mission is "to enhance life by harnessing the power of the sun."

The SunCone, a highly reflective spun-aluminum sun-funnel designed by Los Alamos National Laboratory scientist Melvin Prueitt, manages heat-transfer efficiencies so effectively that the cone's outer shell remains cool-to-the-touch while its core reaches 700°F.

Designed to power a 3kW Stirling engine, the prototype SunCone (built by New Mexico's Hytec Engineering) stands seven feet high and measures six feet in diameter. Open Energy expects its first commercial model to be up and running by the first quarter of 2007.

Robert Stirling built his first "external combustion" engine in 1816. Unlike internal combustion motors, Stirlings have few moving parts. There is no crankshaft, only a single reciprocating piston that moves through a closed cylinder filled with helium, nitrogen or hydrogen. Applying heat (and/or cold) to either end of the engine creates a temperature differential that sets the piston pumping.

While many maverick engine designs -- Rankine, Otto, Wankel -- have been used to power automobiles (Wankel's rotary design was used in Mazda's RX-8 engine), plans to install Stirlings in Ford Pintos the 1970s were dropped after the engines experienced a "power drop" at high speeds.

But Open Energy/Infinia's goal is not velocity: it's electricity.

Sandia Labs, the government nuclear weapons facility in New Mexico, has installed the first of 20,000 solar-powered Sitrling engines. Credit: Sandia Labs / National Nuclear Security Administration
The efficiency and durability of Stirling engines has endeared them to NASA, the Pentagon and Southern California Edison (SCE), which plans to buy 20,000 Stirlings over the next 20 years to produce 500 Mw at its 4,500-acre solar farm in the Mojave Desert.

SCE's solar farm uses fields of parabolic mirrors to focus the sun's heat onto centralized Stirling engines -- a process that loses much of the heat as it's transferred through the air. Prueitt's design solves this problem by turning the solar-farm concept "outside in" -- i.e., by hoarding the heat inside the reflector.

As Open Energy President and CEO David Saltman explains: "If a parabolic reflector is 'off-sun' by one degree, 90 percent of the energy will miss the target, whereas SunCones can be 3 percent off and still capture 75 percent of the energy."

Because sunshine is concentrated inside the cone (rather than on an outside mirror) there is little chance of eye damage and no risk of a stray beam igniting a grass fire. This safety edge means that SunCones could be installed over carports and on rooftops, sites that would be too dangerous for parabolic reflectors.

Infinia CEO J.D. Sitton reports that the Stirling engines at the firm's Washington State test facility have "already achieved solid results." Infinia, which has been shipping Stirlings for more than 20 years, already has produced commercial 1kW engines for residential heating and electricity in Asia and Europe.

Mr. Saltman sees a kind of perfect storm. "All the fundamentals are in place for long-term growth -- rising fossil fuel costs, the real risks of global warming, concerns about energy security, political instability in the Middle East," he says. "Government-industry-public support for energy alternatives will drive the market for the next 20 years."

Rodrigo Prudencio of California-based Nth Power cautions that "Stirlings have great potential" but their greatest success to date has been in smaller applications. "To make them large enough and reliable enough to produce grid power will still take some progress."

But powering a traditional power grid is not Open Energy's primary focus. Mr. Saltman explains that the SunCone is being built with "standard, off-the-shelf materials" so it can be used in the Third World to generate electricity and boil saltwater to produce drinking water.

"We believe in turning that [centralized] model inside out and using distributed generation to create affordable power and clean water," Mr. Saltman says. "There are 1.5 billion people without access to electricity or fresh drinking water, so there is a tremendous opportunity globally to create small, lightweight projects" to serve this market.

Instead of prospecting among a "financially rich community of buyers," Mr. Saltman draws inspiration from philanthropists like Bill Gates, Warren Buffett and Ted Turner who have redefined the notion of "foreign aid" by creating a new form of charity driven by "intelligent capital" that solves problems while creating new markets and profits. (The Bill & Melinda Gates Foundation recently poured $7 million into water purification projects.)

Mr. Saltman believes that an array of 3kW or 5kW SunCone-powered Stirlings "could power a remote village. And resorts from the Bahamas to Baja can all benefit from affordable water desalination." Saltman says it is conceivable ("although we haven't proven it yet") that the SunCone-Stirling combo could provide power and clean water simultaneously.

Another reason the Stirling is a good match for Open Energy's global game plan: the free-piston engines can be hermetically sealed for life, making them maintenance-free once installed in the field.

Efficiency comparisons published by Sustainable Resources, Inc. show the SunCone out-performing both PV collectors and parabolic trough reflectors. More impressively, the SunCone matches the performance of parabolic mirror dish reflectors both for collection efficiency (85%) and solar-to-electric efficiency (30%). While the cost-per-square-meter-of-collection-surface was $400 for dish reflectors, SunCones were expected to harvest the same amount of energy for $138. Sustainable Resources projected that a 50-MW SunCone-Stirling array could produce electricity at a cost of $0.046/kWhr.

The Cornell Capital hedge fund has pumped $15 million into Open Energy's efforts. David Andresen, a senior banker at Cornell Capital, notes that global demand for electricity is expected to rise from 12 TerraWatts (TW) to 20TW over the next 20 years and only solar or nuclear technologies are likely to meet this demand. The way Andresen sees it, the SunCone "is the only true plug-and-play solution when it comes to solar. Every other system needs a solar installer and this bodes well for long-term play."

The California-based Cleantech Blog notes that "the big question, still unanswered, is whether solar concentrators can be the elusive technology to take Solar into 1:1 competition with grid power. The last solar technology class to wear that mantle -- thin film -- has yet to overtake the crystalline silicon market in cost or market share."

There's no question that solar concentrators represent a proven technology. A 354-MW concentrator plant built in California has been delivering reliable power to the grid for [more than] 20 years. Today, eight new 100MW-plus concentrator plants are under construction in California, Nevada, Israel, Spain and Portugal.

According to the analysts at The Fraser Domain (, electricity from these plants will be cheaper than power from natural gas plants but still more pricey than power from conventional power plants or wind power. That equation could tip in favor of solar concentrators when the Infinia/Open Energy system is added to the picture.

Thanks to the growing demand for clean, renewable energy alternatives, the modest Stirling engine and the space-age SunCone may soon achieve clean-tech celebrity status. If the SunCone prototype tests to expectations, this may be the Stirling engine's time to shine.

A shorter version of this story first appeared in the February 15 issue of Red Herring magazine.

"Zoom-Zoom" vs. Zoop-Zoop!
Gar Smith /

Not all the prizewinning EV designs are emerging from high-tech auto labs. Some of the best EVs are being created by the haute couture owners of Paris' Maison de Courréges.

During the Swinging Sixties, André Courrèges gave the world the miniskirt, the trouser suit, the Moongirl look and gogo boots. And, as far back as 1969, the French designer was using electric vehicles (Evs) as an integral part of his fashion shows. Today, as a result, some of the world's most competitive EVs are being created by the world-renowned Paris-based fashion design house -- Maison de Courrèges (

In 2002, the company renewed its interest in EVs at the Michelin Bibendum Challenge in Heidelberg, Germany. That was the year André Courrèges unveiled La Bulle (the Bubble), a bulbous vehicle capable of 110 km/h and a range of 170 kilometres -- quite a feat back in 2002. (La Bulle made its first US appearance in 2003, at the Bibendum Challenge in Sonoma, California.)

Madame Coqueline Courrèges also has become a passionate EV advocate. Coqueline has even designed her own vehicle, which she dubbed The Zoop. This high-performance three-seat EV weighs just 690 kilograms and can hit 180 km/hour. Distinguished by its bright yellow-orange canopy and matching tires, the Zoop scooped up a special award at the 2006 the Michelin Bibendum Challenge, an international design competition for sustainable mobility.

The Zoop's lightweight Lithium Polymer batteries provide an improved power density that gives the car a range of 450 kilometers. These batteries don't overheat and they recharge quickly.

The souped-up Zoop has received little publicity outside of Paris, which is odd, considering that the Courrèges are fashion-world luminaries who apprenticed under legendary fashion designer Cristóbal Balenciaga.

In 2004, André Courrèges entered the Shanghai Bibendum Challenge with a car called the EXE. A Lexan structure atop a lattice frame made it easy to convert the car from two-seater to a five-seater. The EXE used Lithium Ion batteries to accelerate from 0 to 100 km/h in 6.2 seconds. It had a top speed of 160 km/h and scored straight A's in emissions, acceleration, handling, and efficiency.

The EXE finished second overall, beating out cars from every major automotive manufacturer on the planet. Only a problem in the braking test prevented the EXE from nailing a perfect score of 4.0.

The EXE was built in the garage of the Courrèges' Paris home but the electric drive train was fashioned by AC Propulsion in San Dimas, California.

Madame Courrèges drove two EXEs in a Kyoto competition in 2005. In honor of Edouard Michelin, the late CEO of the Michelin tire empire [and a financial sponsor of the Courrèges' current-driven carriages], the EXEs sported custom-made red Michelin tires. In the event of a flat tire, the Courrèges' reportedly carried two complete sets of blue and green replacement Michelins in their van.

In September 2006, the EXE was shipped to China for the Shanghai Grand Prix, which is held on one of the finest racetracks in the world. The last drive of the day went to Edouard Michelin. With Madame Courrèges in the co-pilot seat, Michelin drove the EXE for two laps, topping 100 mph on the back straight.
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