Bringing Solar Home?

Energy solutions for less

Solar panels began appearing on random rooftops in suburbia several decades ago, but the solar revolution has been slow to catch on. Although the power of the sun is plentiful, safe, and clean, the rise of solar energy as a major component in the world's energy portfolio has faced some major challenges. Scientists have wrestled with questions about how to capture sunlight most efficiently, how to store that energy, and how to draw upon those stores as needed.

Beyond the basic science that can make solar energy work, there is another fundamental issue that must be addressed before solar power can be considered a major player in the energy industry: affordability. For solar energy to make a difference, it must be competitive with the cost of traditional energy sources.

In the years since the first photovoltaic panels began adorning the homes of well-intentioned environmentalists, the science of solar energy has been answering these challenges slowly but steadily. Two firms blazing the trail are lead by Purdue engineers. In Santa Monica, California, SolarReserve, headed up by president and chief executive officer Terry Murphy (BSAAE '80) and chief operating officer and head of development Kevin Smith (BSME '79), has designed a way to generate utility-scale power using so-called concentrated solar thermal energy. Jim Miller (BSAAE '86) is applying his broad experience with supply-chain logistics and aerospace engineering to the promising market of solar energy with his Silicon Valley-based firm, Sierra Crest Consulting. These industry experts are convinced that the dawn of solar energy is finally on the horizon.

The secret is in the salt

In the vast, sunny expanse of the Mojave Desert outside Barstow, California, stands a towering achievement in solar energy science. It's a tower, called Solar Two, encircled by hundreds of heliostats that reflect and concentrate sunlight onto the tower's receiver—solar capture technology that has been around for a long while. But SolarReserve, partnering with a group of scientists from Hamilton Sundstrand Rocketdyne, has found a way to store that energy efficiently and disburse it on demand—a breakthrough in solar know-how.

"We're turning the sun into the solution," says Murphy. "Our facilities are engineered by the same team at Rocketdyne that built the Space Station power systems, the space shuttle main engines, and the Apollo moon rocket propulsion systems. The molten salt power tower was thoroughly validated by the Department of Energy at the Solar Two pilot plant, and it's ready for worldwide deployment."

Murphy explains the technological nitty gritty. Solar energy captured by the receiver is transferred as heat to molten salt, which is then stored in large insulated tanks. The stored energy is converted into steam on demand, which turns turbines to create electricity. "The secret sauce, if you will, is salt," he says. The molten salt is a mixture of sodium and potassium nitrate, which in solid form can be used as garden fertilizer. This environmentally friendly material has a high boiling point and can achieve temperatures over 1000° F and still remain a liquid.

"The inherent storage capacity of concentrated solar thermal energy means we can actually match demand," says Murphy. "We can operate through the haze and with clouds, because we have decoupled the power gathering from the power generation," he explains, "so you don't have that intermittency that comes with wind or rooftop photovoltaic solar."

With photovoltaic cells, by contrast, cloud cover can slash operational efficiency from 100 percent to zero percent. The new technology improves on that tremendously. Over the course of the day, the energy loss in the salt storage tanks is minimal—less than one percent. "With the storage of energy in the salt, we can produce electricity 24/7," Smith states. "We can collect as much energy as possible during the day, and when the sun goes down, we can still produce power."

SolarReserve plans to build 30 to 40 commercial power plants worldwide over the next 10 years. The first will be constructed in Spain and is scheduled to go online in 2012. "I would have liked to see the first one in the U.S.," says Smith, "but Spain simply has the more fruitful market."

Smith describes a frustrating irony about the Spanish location: the plant they build in Spain will work around the clock to produce an impressive 50 mW of power, but the same plant, were it to be constructed in the ideally sunny U.S. desert southwest, could produce 150 mW of power to be dispatched on demand over 10 hours. The economic implications of this contrast demonstrate Spain's commitment to green energy. They also illustrate how much more cost effective this technology would be if deployed at home in the United States. "We're confident that the new administration will have a more aggressive renewable energy policy," Smith says.

Toward "grid parity"

One thin dime. That's the maximum price per kilowatt hour it can cost for any alternative energy industry to compete with traditional petrochemical-based energy. "‘Grid parity' is the holy grail of all alternative fuels," says Miller. He estimates the cost of producing solar energy today to be between 25 and 40 cents per kilowatt hour. "It's not competitive now," Miller admits. "But by 2010 or 2012, it will be. Technological advances are occurring at a rapid pace now," he says.

The kind of advances he is seeing in the field, plus the "incredible" investment that businesses and venture capitalists are starting to pour into the solar industry, are the two complementary factors that encouraged him to start Sierra Crest Consulting. A Purdue aerospace engineering graduate with master's degrees in mechanical engineering and business from Massachusetts Institute of Technology, Miller's career has woven together science and business very effectively. Now he has his sights set on the solar industry.

"I see a lot of opportunity in supply-chain management of the solar energy industry," he says. His firm helps commercialize solar-energy by evaluating technologies and products. They help clients find funding, determine cost competitiveness, reduce costs, decide where to build facilities, and expand their scale capabilities.

Miller notes how far the industry has come. "The solar industry used to consist of two kinds of people: zealots, who were building solar panels in their garages, and technologists, who were people with advanced degrees fleshing out the science of solar. Neither group could build a company able to compete and achieve grid parity," he says.

Now, with increased pressure to find alternatives to fossil fuels and the science to back up the promise of solar energy, venture capitalists with "clean tech" portfolios want in. "And they are in it to win," says Miller. He sees solar becoming an important American business with a great potential for growth. Solar energy now provides less than one percent of the nation's power, but Miller predicts it could be supplying up to 15 percent of the national energy demand by 2020.

Beyond the crucial utility-scale solar advances being pioneered by companies like SolarReserve, Miller also points to exciting and effective new applications for solar energy. Solar panels are becoming more aesthetically pleasing and cheaper for homeowners to install. The technology is now even being incorporated into individual roof shingles. Capturing ambient heat in attics and off roofs to heat water is becoming a possibility, too. What's more, large commercial buildings are beginning to lease their rooftops for solar panel installation. Big-box stores in the near future could even generate enough of their own energy to be able to unplug from the grid and become energy independent.

Solar energy is clearly on the rise. "What used to be a young, immature industry has almost reached the tipping point," Miller says, "and there's no turning back now."

-Gina Vozenilek