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BNL cloud study aims to boost solar power

When Paul Kalb looks up at the sky, he sees more than just clouds. The environmental scientist sees what he calls "the gray scale" -- wispy puffs dimming the horizon -- that makes harvesting the sun for power on a grand scale a challenge for any country dedicated to expanding renewable energy sources.

"Clouds will always impede the sun's energy," said Kalb, who heads the environmental sciences division at Brookhaven National Laboratory in Upton. Just how much, he adds, "depends on their degree and frequency."

Now Kalb and a team of 10 researchers, engineers and technicians at the Brookhaven Lab are tracking those puffy configurations, in real time, as part of a national effort to help forecast sunlight and its resulting power.

The efforts are aimed at helping utility companies and other solar generators anticipate drops and surges in energy production due to cloud cover. A more-precise "solar forecast" could save utilities and other power operators billions in energy costs by making it easier to know when to tap the sun's power.

Brookhaven's team will track clouds every 15 minutes over the Long Island Solar Farm, a 200-acre, 32-megawatt array on the lab's property. The largest solar facility east of the Mississippi River, it generates enough renewable energy to power 4,500 households on Long Island. The farm is one of several such facilities, from Florida to California, serving as test sites.

Spearheaded by the National Center for Atmospheric Research, the effort aims to design a model to predict how clouds and other atmospheric particles that hamper solar energy can move and change shape in the sky -- one of the most difficult measurements for meteorologists to make.

The three-year project, primarily funded by a $4.1 million grant from the U.S. Energy Department, involves universities, utilities, independent systems operators, commercial forecast providers and government labs, like Brookhaven.

"The whole idea is to forecast drops and surges in solar energy," said Sue Ellen Haupt, the NCAR researcher leading the nationwide effort. "We need to know when the variability will occur so the utilities can integrate the power into the grid."

Once a solar forecasting model is tested, the techniques will be widely disseminated for use by the energy industry and meteorologists, Haupt said.

The Brookhaven team will play a central role in providing basic building blocks of data for the forecasts through state-of-the-art imaging technology.

"They have tons of instrumentation there, and the Brookhaven folks are experts in deploying it," Haupt said.

The most important instrument Kalb's team will deploy is the Total Sky Imager, a fish-eye lens digital camera. The device will take a 360-degree snapshot of the clouds every 15 minutes, so that researchers can track their rate of movement, thus predicting when the clouds will loom over the farm's solar panels.

Brookhaven's system will also feature computer software to identify the clouds -- tracking not just their distance but also their density.

Already, the team has stationed three sky imagers, each about the size of an overhead projector, in strategic areas throughout the solar farm to provide different views of the sky. The team will measure the clouds from the three angles in order to figure out their height. Researchers will also measure the amount of solar energy available, using a network of 60 "pyronometers," or sun sensors.

"It's a huge opportunity to use this generating facility as a learning tool," Kalb said. "We're learning how well these systems can work in the Northeast, how to develop tools to make solar energy more useful."

Jan Kleissl, a top researcher in solar forecasting from the University of California, San Diego, describes the NCAR project as "groundbreaking."

Kleissl said it's the first time sky imaging will be paired with satellite images and computer-algorithm software to predict a cloud's movement down to its tiniest particles.

While solar forecasting is not in high demand by utilities today, Kleissl predicts: "In one or two years, these forecasts will mean big money for utilities and power operators. They will be very valuable."

The project, which kicks off next week in Boulder, Colo., could pave the way for building up solar power as a renewable energy source in the United States.

"It's an exciting opportunity to really push the development of renewable energy," Haupt said.

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