The East Coast of the US experienced up to 5 percent lower than average levels of solar irradiance in 2014, negatively impacting overall performance of solar sites in the region. Concurrently, the West Coast enjoyed irradiance levels up to 10 percent higher than average, widening the productivity gap between projects in the country’s two areas of highest solar development.
The disparity is seen clearly in the 2014 Solar Performance Maps of the United States, which have just been released by the environmental and industrial measurement company Vaisala.
Although it is widely accepted that the solar resource of the East Coast does not match of the West, the Atlantic Coast has a large volume of operational capacity. This means it is critically important for project developers and operators in the region to understand the reasons behind a below-average energy output and whether it is due to malfunctioning equipment or weather variability.
The Vaisala 2014 study illustrates the impact of short-term, month-to-month weather variations on performance at US solar projects and places them into a long-term context. This reveals frequent and significant deviations from long-term average irradiance conditions and highlights the clear requirement to analyse the effect of solar resource variability on both over and underperformance. The study shows that weather patterns during 2014 had an adverse effect on a large number of installations along the Atlantic Coast from Florida to Massachusetts, as well as Texas, while the bulk of projects in California and the Southwest saw an uptick in solar irradiance that may have increased overall 2014 production at many sites. However, these annual variations only offer a high-level view of project performance. Vaisala also conducted a monthly analysis that gives a much more robust understanding of how specific weather conditions affected solar production throughout the year.
“The fact that California, for instance, had higher than average irradiance over the course of the year doesn't tell the whole story” said Gwendalyn Bender, Energy Assessment Product Manager at Vaisala. “We actually have many clients with projects in California coming to us with concerns about last year's production numbers. As seen in our study, monthly low solar irradiance anomalies had a significant impact on generation, even in the West.”
The summer of 2014, for instance, was the coolest summer since 2009 and the ninth wettest summer on record within the continental US, with cloudy conditions leading to below average solar irradiance. This meant underwhelming solar performance in many regions where there are large numbers of operating projects, and negative media attention for solar projects recently put online - such as Ivanpah, Agua Caliente, Solana, and Topaz.
While the summer was disappointing, it was not the only or the most extreme anomaly of 2014. January, October, and December also saw atypical conditions where solar irradiance was more than 10 percent above or below average for much of the country.
Routinely evaluating resource variability is critical for understanding in the short-term whether a solar project is performing as it should be, based on the available resource. This allows both distributed and utility-scale generators to effectively deploy maintenance and repair crews when problems, such as inverter issues or heavy snow on panels, lower production when resource data clearly show the sun was shining.
Anomaly analysis is also crucial for viewing recent performance from a long-term perspective as it allows operators to understand whether recent conditions (low or high irradiance, heavy snowfall, etc.) foretell what can be expected throughout a project's lifetime or if it is out of the ordinary. For example, in Texas, where there is growing interest in solar and already a few operational projects, it is useful for developers and operators to understand that this past December's solar irradiance was extraordinarily low compared to previous years due to unusually foggy conditions.
Vaisala specialises in solar measurement, project assessment, and energy forecasting. It acquired 3TIER in 2013, a company that developed the first high-resolution, global solar dataset. Vaisala has also helped to secure over $5.5 billion in project financing worldwide.
Image by Vaisala
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