Even clean energy can get dirty

Dust: it’s enemy number one for solar photovoltaic panels (PV) in the sunny, warm areas with the most potential for solar power. That’s because it takes less than a tablespoon of dust per square meter to reduce the electrical output of a typical PV panel by 40 percent.

“In Arizona,” says Professor Malay Mazumder of Boston University, “dust is deposited each month at about four times that amount. Deposition rates are even higher in the Middle East, Australia and India.”

Few home owners in the Southwest want to climb up on their roof several times a month to hose off the light-blocking dust. Utility-sized PV installations are hand-washed or use mechanical sprayers — but either way is costly. In the desert there’s the additional problem of increasing water use in an arid land — one that is likely to grow drier as the climate changes.

The solution to this problem (or at least a solution) comes from the U.S. space program — which is fitting, given that PV panels were pioneered by NASA in the 1960s and ’70s to power satellites and, most recently, rovers on Mars.

At the 240th National Meeting of the American Chemical Society (ACS) last weekend, Dr. Mazumder reported on advances in bringing the same technology used to clean dust from the Mars rovers down to Earth.

The trick to cleaning PV panels without water is to incorporate an Electrodynamic Screen (EDS) like the one on the Mars rovers. An EDS is a thin, electrically sensitive layer on the surface of the panel. When enough dust accumulates on the EDS, a sensor triggers a small electric pulse which repels the dust.

NASA first developed the idea for an “electric curtain” in 1967. In 2003, NASA’s Electrostatics and Surface Physics Laboratory (ESPL) worked with researchers at the University of Arkansas at Little Rock (where Dr. Mazumder then taught) to design and build an EDS for the Mars rovers. (The ESPL website has a short video showing test modules working under space conditions.)

Mazumder reports that the EDS developed by his lab can remove 90 percent of dust particles from a square meter of PV paneling in two minutes using just 10 watts.

Mazunder said the Earth-version of the EDS should be commercially available within a year.

Not all PV panels may require EDS technology, says Alan Bernheimer, a spokesman for First Solar, the world’s largest manufacturer of thin-film PV.

“Theoretically it would be possible to apply this technology to thin film solar modules,” Bernheimer wrote in an Email. “First Solar’s advanced thin film technology, however, is productive in diffuse and lower light conditions, such as those caused by dust.”

While even thin-film panels eventually need to be cleaned, Bernheimer said First Solar has no plans to adopt the EDS technology.

For traditional silicon-based PV manufacturers, however, the development of waterless cleaning technologies is likely to be seen as a milestone on the road to renewable, sustainable, energy.

You can read a 2008 paper about EDS technology co-written by Prof. Mazumder here (PDF).

Ohio's new Wyandot Solar Farm

The second largest utility-scale solar plant east of the Mississippi River opened Thursday and is now generating enough electricity to power an estimated 1,500 homes in north-central Ohio. The 12MW Wyandot Solar Farm uses 160,000 thin-film solar panels set on 84-acres of former farmland.

The panels were produced by First Solar at its Perrysburg, Ohio, manufacturing plant, which was recently expanded.

The thin-film technology is cheaper to produce than silicon-crystal based photovoltaic panels, but is less efficient at converting sunlight into electricity. PSEG Solar Source, the Newark, NJ-based company that owns the solar plant, decided the trade-off was worthwhile, according to spokesman, Curt Judy.

Location of new Ohio power plant

“The thin-film technology is also very well suited at capturing lower radiance or low sunlight which we tend to see in the winter months,” Judy told local television station NBC channel 4 out of Columbus.

Ohio’s Renewable Portfolio Standard (RPS) requires utilities to obtain a minimum of 12.5 percent of electrical generation from renewable sources, including solar, by 2025.

Energy Independence Day, July 3, 2010

With the economy and job-growth stagnant, oil still spewing from the BP well-head into the Gulf of Mexico as a toxic reminder of our addiction to fossil fuels, President Obama couldn’t have picked a better time to announce a major solar power initiative than today, July 3rd — only hours away from Independence Day.

The president labeled his weekly radio address “A Solar Recovery,” reflecting the emphasis on pocket-book voting in this election year. Personally, I wish Obama would have gone with “Energy Independence Day,” putting the spotlight on the larger, long-term prize. But I guess that explains why I’m a journalist and he’s The President of the United States of America.

“We’re accelerating the transition to a clean energy economy and doubling our use of renewable energy sources like wind and solar power…” the president said and then announced a new commitment to solar power of $2 billion.

Solana Solar Generating Station

The bulk of the money will be used to build the world’s largest solar power plant, a 280-MW station in southwestern Arizona. The Solana generating plant, said Obama, “will be the first large-scale solar plant in the U.S. to actually store the energy it generates for later use — even at night.”

Solana (Spanish for “sunny place”) will be built and operated by Abengoa, headquartered in Seville, Spain. The plant will use concentrating solar power (CSP) technology, which uses heat generated by sunlight to produce electricity. Most Americans are more familiar with photovoltaic (PV) solar panels used mostly on rooftops to generate electricity.

Electricity generated by Solana will be purchased by Arizona Public Service, the state’s largest utility, and used to supply electric power to an estimated 70,000 homes.

“This is very encouraging news,” Pat Dinkel, VP for power marketing and resource planning at APS, told The Sun today. “We know there are a lot of steps remaining before our customers can benefit from Solana’s generation but this action brings that goal a step closer.”

Abengoa’s Fred Morse thanked Arizona Congresswoman Gabrielle Giffords (D-Tucson), a leading solar advocate in Washington.

“Congresswoman Giffords played an instrumental role to make this project a reality,” said Morse. “She understands the importance of creating jobs in Arizona and the ripple effects that this project will create throughout the Arizona economy. Solana will bring Arizona one step closer to becoming the solar capital of the nation.”

The Solana project has been in the works for at least three years. With the federal loan guarantee, construction on the plant may begin yet this year.

Secretary Chu: U.S. leadership in the global green economy

Abound Solar's PV Panel

Secretary of Energy Steven Chu touted the second part of today’s announcement — $400 million to Abound Solar Manufacturing to produce a new form of PV cells. Plants in Longmont, Colorado, and Tipton, Indiana will manufacture Cadmium-Telluride panels, a technology developed at Colorado State University, the National Renewable Energy Laboratory (NREL) and the National Science Foundation.

The Indiana plant was originally built for a Chrysler auto parts supplier, but because of the recession, it had never been occupied. By 2013, Abound hopes to be manufacturing 840 MW worth of solar panels a year at the two plants.

“By supporting new cutting-edge solar manufacturing technologies,” said Chu, “we are advancing a diverse renewable energy portfolio while helping to position the U.S. at the forefront of the global green economy.”

Jobs for Arizona & New Mexico, too

The Solana plant will need nearly a million specially-made mirrors to reflect and concentrate the Arizona sunlight, and miles of tubing to carry the super-heated liquid used in the CSP process. A mirror factory is planned for the Phoenix area, and the tubes will come from neighboring New Mexico, where a factory owned by Schott Solar is currently operating well-below capacity.

Solana Solar Generating Station

The Solana plant will cover 3,000 acres of former farmland. While CSP that uses water for cooling is controversial, especially in the desert, the power plant will use less water than the farm that had been at the same location. According to Rep. Gabrielle Giffords office, Solana will use slightly more than 10 percent of the water drawn by the farm.

Solana generates electricity without producing greenhouse gasses — eliminating an estimated 470,000 tons of GHG a year.

Some 3,200 giant parabolic collectors will track the sun throughout the day at Solana. Each collector is 25-feet wide, 20-feet high and the length of 1.5 football fields. Some of the heat generated by the collectors will be stored as molten salt, allowing the plant to generate electricity for six hours after sunset.

• Watch the video of the President’s address
• Solana on the APS Website
• Representative Gabrielle Giffords
• Abound Solar
• Abengoa white paper on trough technology (pdf)