New study measures effect of clouds on PV

As photovoltaic (PV) systems continue to grow in size, they’re better able to withstand the negative effects of cloud-cover, suggests new research from the Sandia National Laboratories.

The lab recently said that it has developed a new method of monitoring how cloud cover affects large PV systems with a photodiode sensor network.

“What we’re really trying to do is provide scientific basis for decisions related to how much PV can be integrated into a utility’s grid,” said Joshua Stein, a principal member of technical staff at Sandia.

The lab conducted an initial test of the new measurement system on the Hawaiian island of Lana’i, which is home to the 1.2 MW La Ola Solar Farm about 3,000 residents.

“It probably represents the highest amount of photovoltaic penetration anywhere in the world,” Stein said. “Any problems integrating PV into the Lana’i grid may foreshadow possible challenges for many PV plants planned for the mainland.”

The island is isolated from other grid-tied electricity and must generate all its own electricity. At peak, it uses 4.7 MW of electricity, and more than a quarter of its generation is provided by the PV array, according to Sandia. The conditions made it an ideal candidate for the study. PV reacts instantaneously to changes in light, and generation is greatly reduced when PV cells are shaded by cloud cover.

“When they’re proposing a 100 MW PV array for a utility, they’re going to want to know second to second the high frequency variability of the PV plant, so they can balance the load,” with other forms of generation, Stein said. “I perceive that it’s one barrier to more large-scale solar on the grid. And many utilities have put a limit on how many PV plants they can put on the grid because of the variability.”

“The sensor network allows us to develop models for variability of very large PV plants,” Stein said. “The point is that as [PV plants] get larger, and they cover larger areas, the variability decreases.”