Cool Energy revamps hot-air engine for clean energy

BOULDER – During Christmas week 2005, Sam P. Weaver sat down with his father and brother in the family home in Knoxville, Tenn. to toss around ideas for clean energy technology.

Sam’s father, also named Sam, spent his career as an entrepreneur, much of it in the field of nuclear energy; brother Dan, a genetics and information systems expert. And Sam, after jobs in data storage, telecom and as an electrical engineering researcher at CU, wanted to focus on an issue that had concerned him since middle school: energy and the environment.

“Like my father, I saw this as an area that was both an opportunity and a challenge and a more rewarding way to use my time,” Weaver said.

Being a technically astute group, the holiday talk focused on an arcane topic: the Stirling hot-air engine, originally invented in the early 1800s by a Scottish minister as an alternative to internal combustion engines. The Stirling engine, Weaver explained, works by cycling gas between a hot and a cold side, which generates heat and has not-yet-realized potential in the clean energy field.

After ongoing discussions, father and sons decided to develop technology that would harness solar energy to generate not just electricity but also offset what makes up an ever-larger portion of the monthly utility bills: heat.

In March 2006, Cool Energy Inc. was founded.

For the past three years, Weaver, the company president, and his staff of now eight including five engineers, have been working on the SolarFlow System, which uses solar collectors and a hot-air engine to create heat for the home when it’s needed and electricity when it’s not.

The pilot system will be installed at CU in August for further testing and analysis, and if all goes well, the product will hit the market in 2010.

While most solar energy systems employ photovoltaic panels to capture the sun’s rays, the Cool Energy system uses solar thermal panels, which according to Weaver are a better option. “Solar thermal panels tend to be between 60 percent to 80 percent efficient at gathering heat, while solar electric panels are from 12 percent to 20 percent efficient at converting sunlight to electricity.”

The system’s other distinction is its double duty: covering both heat and electricity.

“Our market research showed that in many parts of the U.S., more than half of the energy bill is heating, particularly those homes using fuel oil or propane,” he said. Solar PV panels supply electricity, and usually just a portion of a dwelling’s total use because of roof orientation and space, which limits how much sunlight the roof gets and how many panels can fit.

“PV panels are amazing technology, but the downside is those systems only address about 40 percent of a consumer’s bill,” Weaver said. “Typical consumers use natural gas, propane or fuel oil to heat their home. And the costs of heating fuels are going up much faster than electricity.”

A solar-powered heating system has not been economically compelling because it would sit idle much of the year. “To meet heating demands of the winter would require the installation of a large number of solar thermal collectors. But come summertime, you wouldn’t have a use for the heat generated,” he said.

The Cool Energy SolarFlow System is busy year round, fulfilling whatever the energy needs of the season. The key technology is the system’s SolarHeart engine control component, which makes a critical decision: whether to use energy to generate home heat or convert it to electricity.

“The control system maximizes the value to the customer, and it does it by looking at the weather forecast,” Weaver explained. All followers of the Weather Channel know that science can predict probability, but not certainty, of sun and chill ahead. But forecasts offer enough for the system to make an informed decision about how to most efficiently use the captured energy.

While in winter and summer, energy needs are usually consistent, in spring or fall weather is more variable. If it’s January, heat is likely needed; an oppressive August day energy goes to electricity. But October or April can be a crapshoot, necessitating heat during a cloudy spell or electricity on balmier days.

The initial target market for the Cool Energy system is the Northeast where cold, gloomy days are many, and most buildings are heated with high-priced fuel oil or propane. “The payback time in New York State is as short as five or six years,” he said. Other potential users are closer to home, mountain residences also using propane for heat.

The estimated price for the system will be between $20,000 and $40,000, depending on the size and location of the home. Currently there is a federal tax credit for 30 percent of the purchase price, as well as the potential for state and local incentives.

Once the product is ready to go, Weaver plans to apply to Xcel Energy to qualify for solar rebate incentives.

The company is currently in the “prerevenue” stage. To date approximately $2.2 million has been invested in the startup, supplied by angel investors and grants from the National Science Foundation and the Colorado Governor’s Energy Office Clean Energy Fund NEED program.

Tim Bour, executive director of the Boulder Innovation Center, worked with Weaver on fine-tuning his business plan to attract potential investors. “The idea of offering an alternative to solar photovoltaic panels was very interesting and shows a great deal of potential,” Bour said.

The idea was hatched in Tennessee, but the business is headquartered here, the home of both Sam and brother Dan, who sits on the Cool Energy board. “Cool Energy is largely a technology development company. Boulder is a really good place for that, lots of engineering talent,” Weaver said.

While the final engine prototype is built in the coming months, he is finding additional investors and as a member of the Colorado Governor’s Energy Office Clean Energy Development Authority, furthering his broader mission: facilitating greater statewide use of clean energy.

Weaver is looking forward to sunny skies ahead. “I certainly think the new administration will be committed to renewable energy,” he said. “That will mean more funds for research and development, and probably more government assistance for homeowners to go solar.”


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