Applying its atmospheric expertise to solar energy, the National Center for Atmospheric Research (NCAR) is spearheading a three-year, nationwide project to create unprecedented, 36-hour forecasts of incoming energy from the Sun for solar energy power plants.

The research team is designing a prototype system to forecast sunlight and resulting power every 15 minutes over specific solar facilities, thereby enabling utilities to continuously anticipate the amount of available solar energy.

The work, funded primarily with a $4.1 million U.S. Department of Energy grant, will draw on cutting-edge research techniques at leading government labs and universities across the country, in partnership with utilities, other energy companies, and commercial forecast providers.

"It's critical for utility managers to know how much sunlight will be reaching solar energy plants in order to have confidence that they can supply sufficient power when their customers need it," says Sue Ellen Haupt, director of NCAR's Weather Systems and Assessment Program and the lead researcher on the solar energy project. "These detailed cloud and irradiance forecasts are a vital step in using more energy from the Sun."

The project takes aim at one of the greatest challenges in meteorology: accurately predicting cloud cover over specific areas. In addition to helping utilities tap solar energy more effectively, detailed cloud predictions can also improve the accuracy of shorter-term weather forecasts.

The project expands NCAR's focus on renewable energy. NCAR designed a highly detailed wind energy forecasting system with Xcel Energy that saved Xcel ratepayers an estimated $6 million in a single year. The center is also creating advanced prediction capabilities to enable wind farm developers to anticipate wind energy potential anywhere in the world.

"Improving forecasts for renewable energy from the Sun produces a major return on investment for society," says Thomas Bogdan, president of the University Corporation for Atmospheric Research, which manages NCAR on behalf of the National Science Foundation. "By helping utilities produce energy more efficiently from the Sun, we can make this market more cost competitive."

Solar energy output is affected not just by when and where clouds form, but also by the types of clouds present. The thickness and elevation of clouds have greatly differing effects on the amount of sunlight reaching the ground. Wispy cirrus clouds several miles above the surface, for example, block far less sunlight than thick, low-lying stratus clouds.

To design a system that can generate such detailed forecasts, NCAR and its partners will marshal an array of observing instruments, including lidars (which use laser-based technology to take measurements in the atmosphere); specialized computer models; and mathematical and artificial intelligence techniques. Central to the effort will be three total sky imagers in each of several locations, which will observe the entire sky, triangulate the height and depth of clouds, and trace their paths across the sky.

The team will test these advanced capabilities during different seasons in several geographically diverse U.S. locations: the Northeast, Florida, Colorado/New Mexico, and California. The goal is to ensure that the system works year round in different types of weather patterns.

Once the system is tested, the techniques will be widely disseminated for use by the energy industry and meteorologists.

"This will raise the bar for providing timely forecasts for solar power," Haupt says. "It also represents a great opportunity for providing far more detail about clouds in the everyday weather forecasts that we all rely on."