Standardized Method to Quantify and Compare Differences in Solar Power Production

Solar power is a potential renewable alternative to fossil fuels. However, the production of solar power is complex and affected by ever-changing aspects such as the time of day, cloud coverage, and even dust particles in the air.

Professor Mahesh Bandi, of OIST’s Nonlinear and Non-equilibrium Physics Unit, poses in front of bookcases in his office. (Image credit: OIST)

Professor Mahesh Bandi of Okinawa Institute of Science and Technology Graduate University (OIST) has jointly developed a unique, standardized method of quantifying and comparing these differences in solar power.

The latest study, reported in Physical Review Applied, may help direct the progress and performance of solar photovoltaic farms—systems that exploit the sun’s energy and turn it to electricity.

We currently have no standard to compare solar photovoltaic power fluctuations because they change depending on where they are measured. Finding that comparative basis is extremely important.

Mahesh Bandi, Professor, Nonlinear and Non-equilibrium Physics Unit, OIST

In Flux

Researchers use a quantity known as the power spectrum to examine fluctuations in solar photovoltaic power output—the energy that is produced when sunlight is changed to electricity.

This power spectrum can be used to measure the magnitude of fluctuations in the power produced by each solar plant across the globe. However, there is no standard against which to equate these distinct values across plants as the readings differ based on features such as dust in the air and cloud coverage.

Similar to the gold standard used to value currency in the 19th and 20th centuries, a standard measurement is mandatory to meaningfully evaluate energy production across plants.

To ascertain such a standard, Bandi and his collaborator, Professor Golan Bel of Ben Gurion University of the Negev in Israel, examined the clear-sky index, which measures the sun’s energy output as electromagnetic waves, without any hindrance from clouds or dust.

The scientists’ analysis of clear-sky data from 2009 exposed that this simple solar irradiance followed a pattern that relied on variations in daylight duration from one day to the next.

Bandi and Bel established that measuring the typical solar radiation at a particular location on Earth forms a dependable standard of comparison for the photovoltaic power spectrum at the same location. This is because regardless of the inconsistency of clouds and other sources of noise, geographic location has a reliable impact on photovoltaic power generation.

The subsequent step for Bandi is to examine how sources of noise such as passing clouds influence fluctuations in solar power. In due course, he anticipates this research can update engineering and policy to enhance photovoltaic power production.

We have crossed the first barrier in understanding the character of solar photovoltaic fluctuations by finding this gold standard. We now have a ruler to measure with.

Mahesh Bandi, Professor, Nonlinear and Non-equilibrium Physics Unit, OIST


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