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Eclipsing Solar Generation: Lessons Learned from the 2015 European Eclipse

Roberto Rodriguez Labastida — June 8, 2017

The United States will experience a solar eclipse at 10 a.m. PST on August 21, 2017. This will be the first total solar eclipse in 26 years—and the first since the solar PV industry expanded and PV became a meaningful source of electricity in certain US markets (especially in the California Independent System Operator, or CAISO, territory). The eclipse’s route is expected to skirt the states with the most solar installations, influencing generation in states such as California and North Carolina.

Globally, this will be the second time a region faces this challenge. On March 20, 2015, a total solar eclipse passed through Northern Europe (and partially in the southern part of the continent) between 9:40 a.m. and 12:00 p.m. CET. My colleagues at Ecofys did a presentation at the time to explain the effects the eclipse could have on the German grid. Back then, Germany had a total generation capacity of about 190 GW, 39 GW (20.5%) of which were solar.

At the time, the Ecofys team projected that PV power generation could drop by up to 13 GW for more than 1 hour in Germany and by up to 34 GW across Europe for a few minutes. That would represent 2-3 times the magnitude of variation due to other natural events like sudden storms.

Projected Trajectories of the 2017 and 2024 Total Solar Eclipses

(Source: Xavier M. Jubier)

Prior Knowledge Maps the Way

The nature of solar resources means that the effects can vary significantly depending on the local weather. The day of the 2015 event had cloudier weather conditions than originally forecast, which led to a less severe reduction in PV generation. Those areas that did have clear skies were affected significantly, but European energy markets managed to cope. Some of lessons from the eclipse included:

  • The hourly day-ahead market was mostly unaffected by the eclipse. German transmission system operators (TSOs) successfully marketed the PV in a first step at the hourly market and in a second step at the quarter-hour market.
  • In case of high demand or supply, there is a de facto quarter-hour market (over-the-counter and power exchange) in Germany, Austria, and Switzerland that can provide significant contributions for intra-quarter-hourly compensation. This solution is a fine-tune balancing done by the TSO.
  • The quarter-hour market showed big spreads. A European coupling of quarter-hour markets should contribute to increased liquidity of the market and reduce these spreads. At the same time, the quarter-hour trading should be combined with the hourly market.

The main challenge is how to balance the power system against this dynamically changing generation backdrop. This requires flexibility in the power fleet and significant amounts of reserve control over a short period of time. To tackle this challenge, the European Network of Transmission System Operators for Electricity (ENTSO-E) put in place the framework below to reduce the effects of future eclipses that the US regional transmission organizations/independent system operators (RTOs/ISOs) can use as a guideline:

  • Develop a plan to disconnect part of the installed utility-scale PV generation in advance of the eclipse and establish the amount and timeframe for disconnection and reconnection.
  • Detail the steps necessary to reconnect PV systems to the grid.
  • Add backup generation and/or interconnectors to allow transfers to fulfill load in the absence of PV generation.
  • Establish a clear description of the installed PV capacity and its capabilities to improve the accuracy of forecast studies.
  • Enable real-time measurement of distributed PV generation so operational strategy can be adapted in real-time.

The Effect of the 2015 European Solar Eclipse in the German Market

(Source: Energy Charts)

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