US Solar, Power Grid Players Prepare for Landmark Total Solar Eclipse

Children Watching Solar Eclipse
flickr@Bob n Renee

In the stillness and the darkness, the knowledge that I was in deadly danger took to itself deeper and deeper meaning all the time; a something which was realization crept inch by inch through my veins and turned me cold.

– Mark Twain, from “A Connecticut Yankee in King Arthur’s Court”

Astronomers and astronomy buffs are polishing their lenses and tuning up their telescopes in advance of a solar eclipse that will sweep across the continental US Aug. 21. A total solar eclipse several hours in duration will occur in states from Georgia in the Southeast and pass across Wyoming and Idaho in the Mountain West, then on to Oregon in the Pacific Northwest. Neighboring states will experience a partial solar eclipse of varying degrees and duration depending on their arc length from the total solar eclipse path.

This celestial event, which occurs regularly over time, is generating broad-based public interest and curiosity, as solar eclipses have tended to do for about as long as we humans have been recording their occurrence. More substantially, the imminent solar eclipse has raised concerns regarding the impacts it will have on solar energy production across the US, where solar generation capacity soared higher over the past decade, growing at a compound growth rate of 59 percent to reach 42 gigawatts (GW) as of year-end 2016, according to the US Solar Energy Industries Association (SEIA), GTM Research and The Solar Foundation (TSF).

Power and energy industry participants spanning the entire supply chain have been meeting to hammer out preparation plans so as to ensure that electricity grids operate normally during the full and partial solar eclipses. Solar energy tech developers are contributing to the effort.

“A Happy Accident of Nature”

In an April 12 article, Skywatching Columnist Joe Rao describes a total solar eclipse as “a happy accident of nature.” That’s a far cry from the way they were viewed before the nature, configuration and movements of the sun, the moon and the earth were widely understood – scientific knowledge that only came to be somewhat widely known and understood in the late 17th century upon publication of Sir Isaac Newton’s trilogy, “Philosophiæ Naturalis Principia Mathematica” in 1687.

As Rao explains: “The sun’s 864,000-mile diameter is fully 400 times greater than that of our puny moon, which measures just about 2,160 miles. But the moon also happens to be about 400 times closer to Earth than the sun (the ratio varies as both orbits are elliptical), and as a result, when the orbital planes intersect and the distances align favorably, the new moon can appear to completely blot out the disk of the sun. On the average a total eclipse occurs somewhere on Earth about every 18 months.”

California has blazed the trail forward when it comes solar, renewable energy and clean tech in the US. Far and away, more solar power generation capacity – 18.296 GWs as of end 2016 – was producing enough emissions-free electricity to meet the needs of some 4.732 million average homes.

The California Independent Systems Operator (CAISO) is responsible for ensuring sufficient generation capacity is online at any given time so as to maintain a balance between electricity supply and demand state-wide. The state grid systems operator has been convening meetings with industry participants in preparation and releasing the results of study and analysis of the Aug. 21 solar eclipse.

US Solar, Grid Power Sector Preps for Total Solar Eclipse

CAISO August 21, 2017 Solar Eclipse Effects Table
Aug. 21 solar eclipse effects | Source: California Independent System Operator

“On Monday, August 21, 2017, a total solar eclipse will pass over the Pacific Northwest (Oregon, Idaho, Wyoming etc.). ” Amber Molley explains in CAISO’s 2015 Solar Eclipse Report. “The California Solar production areas will be affected by a partial eclipse between 9:02 AM and 11:54 AM PPT.

Forecast Grid Connect Solar Production during August 21, 2017 Eclipse
Forecast Grid Connect Solar Production during August 21, 2017 Eclipse | Source: California Independent Systems Operator

Experiencing a partial solar eclipse, from 76 percent of the sun is expected to be obscured at the higher latitudes of Northern California to approximately 62 percent in the lower latitudes of Southern California. “The reduction in solar radiation will directly affect the output of the photovoltaics (PV) generating facilities and rooftop solar,” Molley continues.

The Aug. 21 total solar eclipse will be the first time the US regulatory authorities, solar and power and energy industry players will have an opportunity to assess such an event. European solar energy producers and power grid stakeholders successfully weathered total and partial solar eclipses on March 20, 2015, however; and the data and analysis of that event is helping their US counterparts prepare.

Solar Tech Developers Pitch In

Solar energy tech developers have a vital stake in ensuring that solar energy producers are well prepared for the Aug. 21 solar eclipse. Clean Power Research’s (CPR) cloud-based SolarAnywhere software-as-a-service (SaaS) is one of a portfolio of products and services being used by solar power producers, distributed energy resource managers, utilities and grid operators to monitor, analyze, forecast and assess production and the overall performance of solar generation assets.

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CPR employees have been gathering and analyzing data regarding the Aug. 21 solar eclipse and its potential impacts, and they’re using the results to help their customers in California and across the continental US prepare for the event.

“In short, our forecasts on August 21 will factor in reduced [solar] irradiance resulting from the solar eclipse (with the variation dependent on the location of the solar generator),” SolarAnywhere lead product manager Skip Dise summarized in response to a Solar Magazine email request for information.

“Because the event will already be factored into the forecast, our customers will use the resulting forecast data for August 21st just as they would any other day.”

The predictability of the solar eclipse conveys benefits with regard to planning and taking actions to mitigate its effects, CPR points out. “In effect, the eclipse period will be akin to a steep ramp in PV output – one that could just as well be created by transient clouds. In this case, however, the utility will be more assured that this eclipse-induced ramp will be happening and can plan in advance, thus saving on short-term costs.”

Eclipse Obscuration Factors and Adjusted “Clear Sky” Models

Three Steps to Applying the Eclipse Obscuration Factor to Clear Sky Irradiance and Power Curves
Source: Clean Power Research

Associated with this, CPR is offering an eclipse Obscuration Factor (OF) that can be integrated within all its SolarAnywhere forecast products. The eclipse OF will calculate the Aug. 21 eclipse’s exact impact based on the location, capacity and configuration of the solar generator.

Applied to the clear sky output produced by SolarAnywhere, the OF results are used to modify the “clear sky” irradiance curve to reflect the new predicted shape with the solar eclipse’s forecast effects factored in. The results can then be translated into AC power output in a PV simulation model, CPR explains.

Furthermore, “CPR will utilize the eclipse-modified Clear Sky curve as the baseline on which we apply our SolarAnywhere FleetView forecasts used by utilities and utility-scale solar providers. For customers forecasting the solar eclipse’s effects across fleets of distributed PV, CPR will apply its eclipse-modified clear-sky model to the aggregate output of subsections of the distributed fleet.

“This will allow the forecast to properly account for the eclipse impact on a geographic basis, but without having to individually modify each of the hundreds-of-thousands of individual PV system clear-sky curves,” the company explains. comment