U.S. 2015 Solar Plant Underperformance: Operational Issues or Just Bad Weather?

Solar panels on a utility-scale solar project
Naomi Stringfield
Mar 12, 2016
Renewable Energy

Did your plant underperform expectations last year? If so, you may currently be under pressure to evaluate and fix any of a mirade of possible equipment or operational issues. While it's likely some instances of low production are due to equipment, others may simply be caused by a lack of solar resource due to cloudy weather. If your project came online last year in the U.S., it is much more likely that the low output was caused by the latter.

2015 was a wetter than normal year for much of the United States, which was good for states struggling with drought but not so good for the solar industry. For example, Texas and the surrounding area was hit particularly hard in three of the last four quarters, having significantly cloudier conditions than normal. Last year 300MW of new solar projects were expected to come online in Texas. Without factoring in the affect of this year's weather and its deviation from long-term conditions, many of those projects may have been flagged as "underperforming expectations." A difficult start for an industry trying to get established in a new region.

2015 US Solar Performance

Click here to view our 2015 U.S. Solar Performance quarterly maps and 12-month climate analysis.​

"There was more storm activity than normal this past year," said Dr. Louise Leahy, Solar Resource Analyst at Vaisala. "Disturbances in the normal upper-level flow patterns in the first half of the year and the onset of a strong El Niño in the second half created particularly wet conditions in the central and western United States."

The Northeast did see a nice break from last year's storms with higher than average irradiance for much of the year and the Northwest experienced exceptionally high irradiance conditions.

The onset of a major El Niño event caught significant media attention due to its impact on the wind industry. Reduced power production at many wind farms in the central United States was blamed on lower than average wind speeds caused by the same storm patterns that affected irradiance in the region. While the full effect of El Niño will not be experienced until the first half of 2016, it is clearly already having an effect on the renewable energy industry.

When it comes to solar plants, these weather patterns have a direct impact on power production. Vaisala's solar performance maps are a good reminder of why it is critical to weather-adjust power performance at solar plants with on-site measurements or a regular weather data feed. Accounting for the weather should be the first step in assessing whether a solar plant is performing as expected. This is particularly important for plants coming online without a benchmark of long-term irradiance variability. In these cases, knowing when solar conditions were well above or below normal can save a lot of effort in chasing down equipment problems that simply don't exist.

Understanding how these climate patterns impact performance at your solar plant is critical for reconciling recent performance and identifying the true cause of over or underperformance. From a fleet perspective across a group of power generation assets, building a climate resilient portfolio means paying attention to how weather patterns can vary in different geographies and building a portfolio to balance their effects on power production. This might mean building projects in different areas of the country or building some solar and some wind projects in the same geography.

Gwendalyn Bender

Gwendalyn Bender

Gwendalyn Bender
Solar Product and Production Manager

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