Photo credit: Saving Oahu's Solar LLC
The US Dept. of Energy’s National Renewable Energy Laboratory (NREL) has produced and made publicly available a data set that shows in greater than ever detail the effect of clouds passing over a solar PV power installation. The data set captures second-by-second over the course of one year the effects of clouds passing over 17 measurement stations near Hawaii’s International Airport on Oahu.
The extremely granular nature of the data set can provide utilities, solar PV system operators and project developers, researchers, forecasters and others empirical data in heretofore unobtainable detail on the effects clouds have on the power output and overall performance of solar PV installations. This can in turn enable them to construct models that can help them forecast electrical power output based on varying cloud conditions and help manage fluctuations in the flow of electricity.
‘What happens when clouds pass between the sun and a large solar PV installation?’ and ‘How much is lost in the effort to convert the sun’s photons into electrons for electricity?’ were questions that remain largely unanswered until recently, NREL points out in a press release. The information in the NREL data set can be used to predict probable PV power outputs at 1-second intervals for medium- and large-scale installations.
Smoothing out fluctuations in voltage are critical to ensuring stable, grid-quality flows of electricity. Solar PV system operators can stabilize electricity flows by storing electricity or by using infrastructure and software packages, according to NREL.
“Clouds can cause pretty significant jumps or ramps over a very short period of time,” NREL senior scientist David Renne noted, adding that as solar power becomes a bigger part of the energy mix, such jumps can cause fluctuations in the grid, which can cause surges, fluctuations, and headaches for the utility operator if unmitigated.
Researchers from NREL’s Solar Radiation Research Laboratory designed the equipment so that a global positioning satellite system can be used to provide concurrent 1-second measurements for each of the 17 stations, a degree of precision necessary as solar PV systems respond quickly to shadows, Renne explained.
Funded by the DoE in support of the Hawaii Clean Energy Initiative (HCEI), the measurement system and data set enabled the NREL team “to set up a solar-monitoring network that simulates exactly how clouds would impact a large photovoltaic system,” that can be used to model solar PV systems’ output for installations as large as 30 megawatts (MW), Renne said.
“The time-synch data are unique. All 17 stations make a 1-second measurement at exactly the same time. This allows the array to ‘see’ clouds moving through and simulates how a PV system might behave. Each of the 17 measurement stations measure the solar energy in the sun’s visible spectrum that reaches a horizontal surface at ground level.”
In addition, very large arrays of solar PV panels smooth out fluctuations caused by cloud shadows to a greater degree than is the case for single panels of small rooftop arrays, the research team found.
The data was collected for the Oahu Solar Energy Study, the partners of which include HCEI, General Electric, the Hawaiian Electric Company and the Hawaiian National Energy Institute.
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