3TIER US Solar Performance Maps Show Substantial Variability

“The 2011 study shows that some areas experienced above or below normal irradiance levels at extremes of +/-30-40%,” said Dr. Mark Stoelinga, senior scientist at 3TIER. “In comparing the results of 3TIER’s 2010 solar performance study, this summer’s irradiance anomalies, both positive and negative, were much stronger than last summer. This shows us that high amounts of variance, even in peak production months, are not unusual.”

Solar irradiance variances caused by weather anomalies have a substantial impact on the economic performance of a solar power project. Prior to development, comprehensive solar assessments that include long-term, site-specific resource context can be used to quantify and manage the risk of variability. However, solar plants already in operation also need to put current over or under production into long-term context to reconcile performance.

“3TIER’s solar performance reconciliation service enables stakeholders to assess financial risk on an ongoing basis,” said Gwendalyn Bender, head of solar product development at 3TIER. “Our continually updated dataset allows us to help clients identify whether project under or over performance was the result of resource variability or some other aspect of the project not operating efficiently. Delivered monthly across any number of sites, this information enables ongoing portfolio analysis at both existing and proposed sites.”

Findings from the 2011 three-month study include:

June: This month saw the most significant, widespread irradiance anomalies of the summer, highlighted by a broad area extending from Texas and Oklahoma to the Carolinas experiencing direct normal irradiance (DNI) values ranging from 15%-40% above normal. This was caused by a high-pressure pattern that also produced hot, dry, drought conditions and wildfires in Texas. Meanwhile, DNI values ranging from 15%-30% below normal were seen in the West Coast, interior Pacific Northwest, and Upper Midwest. In the West this was due to an upper-level trough that has been in place since January causing cool, cloudy weather.

July: Positive anomalies over Texas and Oklahoma persisted in July, but were less noted than in June, with DNI values ranging from 10%-20% above normal. Farther east, the Deep South transitioned to a below average irradiance regime connected to wet weather along the Gulf Coast. Along the East Coast, positive anomaly shifted north to the mid-Atlantic and New England. The lingering trough in the Northwest continued along with below average DNI values, although parts of California and the Northern Rockies transitioned to normal or above normal irradiance.

August: This month the breakdown of the persistent upper-level trough over the Northwest finally occurred, yielding above normal DNI values, particularly in the interior Pacific Northwest where DNI ranged from 10%-20% above normal. However, the ridge over the eastern part of the country persisted, maintaining hot, dry weather and DNI levels 20%-30% above normal over Texas and the Ohio Valley. The Gulf Coast transitioned to dryer weather, yielding well above normal DNI. Meanwhile in Florida and the Northeast, Tropical Storm Emily and Hurricane Irene contributed to DNI values 10%-20% below normal.

3TIER’s solar performance analysis is based on its global solar dataset, which provides continuous, hourly records of irradiance for 12+ years at any location in the world and is updated monthly for most locations. 3TIER used this dataset to determine long-term average irradiance based on conditions from 1997-2010 and to calculate conditions for the summer of 2011. The resulting maps illustrate departures from the long-term average that range from -20% to +20%.
 
For more information on 3TIER, long-term solar assessment, and solar performance reconciliation, visit www.3tier.com or register here for our webinar on Thursday, October 13.

###

ABOUT 3TIER

3TIER helps the global energy market manage renewable energy risk. A pioneer in wind, solar, and hydro generation risk analysis, 3TIER uses weather science to frame the risk of weather-driven variability – anywhere on earth, across all time horizons. With offices serving North America, Europe, India, Latin America, and the Pacific Rim, 3TIER has global reach with products and services spanning renewable energy project feasibility, energy marketing, and asset management. For more information, visit www.3tier.com.