Study lifts clouds over effects of solar energy on grids

A federal study at Ho­no­lulu Airport found that larger solar power systems may be able to handle cloud cover better than previously believed.

This means Hawaiian Electric Co. could accept greater amounts of solar energy into its grid without as much concern about the inconsistency of the sun’s energy.

The National Renewable Energy Laboratory set up 17 monitoring stations around the airport that collected data at one-second intervals through the course of a year. Researchers tracked how passing clouds affected the production of solar power across the test area.

One of the drawbacks to solar power is that the amount of electricity produced by grid-tied photovoltaic systems can fluctuate widely during a short period because of clouds, making it difficult for utilities to keep a steady flow of power to their customers. As a result, HECO limits the amount of solar or other renewable energy that can be connected to an individual circuit within its grid.

However, the study suggested that larger PV systems can generate more power than previously thought even when clouds are present because not all of the panels are likely to be shaded simultaneously.

"One new insight is that with very large arrays of solar panels, there is a smoothing of the fluctuation compared to the sharp spikes and plunges that can happen when a cloud passes by a single panel or small rooftop array," NREL officials said in a news release published last week.

The goal of the study is to help utility officials better understand the characteristics of cloud shadows on PV panels so they can devise strategies to manage the power fluctuations, said David Renne, NREL senior scientist.

"If they have good statistical information about cloud patterns they can design systems and wire them together along certain orientations to minimize the impact of cloud passage, and dampen those fluctuations," Renne said.

HECO welcomed the study.

"Hawaiian Electric’s goal is to integrate as much solar energy as possible while maintaining system reliability," said Peter Rosegg, HECO spokesman.

"Hawaiian Electric is also deploying sensors and gathering data throughout the islands in partnership with other utilities, UH, the military and the solar industry and we are using longer-term data such as is collected by our Sun Power for Schools installations."