Clouds' effects on solar power

Sep 01, 2011

The U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) has produced and made available a rich data set showing what happens, second-by-second, when clouds pass over a solar power installation.

Seventeen measurement stations near Hawaii’s Honolulu International Airport on the island of Oahu collected data at 1-second intervals over the course of a year.

The data set is of great interest to utilities, developers of large-scale photovoltaic (PV) systems, forecasters, system operators, laboratories and universities.

By understanding the characteristics of cloud shadows that pass across a large PV system, utility officials can devise strategies to better manage those fluctuations so the grid isn’t adversely impacted.

The sun reliably beams down on the Earth every day, and just as reliably clouds pass by each day, shading flora and fauna, buildings and mountains, for better or worse.

What happens when those clouds pass between the sun and a large installation? How much is lost in the effort to convert the sun’s photons into electrons for electricity?

Those questions went largely unanswered until recently.

The DOE-funded study by NREL supports the Hawaii Clean Energy Initiative (HCEI), a multifaceted program to substantially increase the use of renewable energy in Hawaii. The study also includes General Electric, the Hawaiian Electric Company and the Hawaiian National Energy Institute.

The information then can be used to predict what PV outputs might be at 1-second intervals for medium-sized and large PV systems.

The collected data “allows us to set up a solar-monitoring network that simulates exactly how clouds would impact a large photovoltaic system,” said NREL Senior Scientist David Renne. “The time-synch data is 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,” Renne said. 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.

“The data has to be collected every second because PV systems respond very quickly to shadows,” Renne said. “We have to make sure we really capture the detailed ramp characteristics,” which are dips and jumps in PV output based on factors such as clouds.

The data set can model utility-scale systems up to 30 megawatts, Renne noted. “Clouds can cause pretty significant jumps or ramps over a very short period of time.” Renne said that as solar power becomes a greater part of the energy mix, those jumps can cause fluctuations in the grid, which if unmitigated can cause surges, fluctuations, and headaches for the utility operator.

Storage of the electricity generated by the sun is one way to handle those fluctuations. Another is to stabilize the grid via infrastructure and software packages.

“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.

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.

is particularly useful during hot summer days, when the demand for air conditioning is the highest. That’s also when the sun is blaring and when solar panels are producing at their peak.

The data collected for the Oahu Solar Energy Study belongs to the partners working on the HCEI, but NREL can share the knowledge about building a data set based on one-second intervals with others around the nation and the world. One year’s worth of the data can be found on NREL’s Measurement and Instrumentation Data Center (MIDC) website at .

Explore further: Morocco raises 1.7 bn euros for solar plants

Provided by National Renewable Energy Laboratory

5 /5 (2 votes)
add to favorites email to friend print save as pdf

Related Stories

NREL Updates National Solar Radiation Database

May 25, 2007

The Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) and collaborators have updated the National Solar Radiation Database, a planning tool that provides critical information about the amount of solar ...

Chevrolet harnesses sun to power volts, dealerships

Jul 29, 2011

Chevrolet is harnessing the power of the sun to install solar-powered electric charging stations for its Volts at dealerships in North America. The Green Zone initiative will generate electricity equivalent ...

Recommended for you

The state of shale

Dec 19, 2014

University of Pittsburgh researchers have shared their findings from three studies related to shale gas in a recent special issue of the journal Energy Technology, edited by Götz Veser, the Nickolas A. DeCecco Professor of Che ...

Website shines light on renewable energy resources

Dec 18, 2014

A team from the University of Arizona and eight southwestern electric utility companies have built a pioneering web portal that provides insight into renewable energy sources and how they contribute to the ...

Better software cuts computer energy use

Dec 18, 2014

An EU research project is developing tools to help software engineers create energy-efficient code, which could reduce electricity consumption at data centres by up to 50% and improve battery life in smart ...

Cook farm waste into energy

Dec 17, 2014

It takes some cooking, but turning farm waste into biofuels is now possible and makes economic sense, according to preliminary research from the University of Guelph.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.