August 2017 Solar Eclipse – Effects on Solar Generation

NASA (click to enlarge)
The contiguous United States will experience a unique event on August 21, 2017 with the advent of a total solar eclipse. The last eclipse of its kind to affect states within the US occurred in February 1979, passing over Washington, Oregon, Idaho, Montana and North Dakota. The 2017 eclipse will have a significantly greater reach; its path of totality will span coast-to-coast across the entire country, starting in Oregon and slowly arching its way southeast before ending in South Carolina at approximately 4:00 PM EDT.
In the energy realm, one of the biggest questions raised by the eclipse comes from utilities and electrical distribution companies who want to know how it will affect solar-powered generation infrastructure and to what extent. Solar-powered generation tends to find its greatest concentrations in states with aggressive renewable portfolio standards and favorable incentive programs. Where the sun shines brightest and most consistently is also a factor. This solar power potential or “light intensity” is based on the level of total hemispheric shortwave radiance in a region (see below map).

Velocity Suite Energy Map (click to enlarge)

U.S. Energy Information Administration (click to enlarge)
States with the highest levels of installed solar capacity will be the primary candidates under observation for the entirety of the event. California, the state with far-and-away the largest installed solar capacity will have a level of obscurity in the range of 50%-80%. California ISO (CAISO) started preparing itself months ago with lessons learned from Europe’s 2015 eclipse. These lessons include increased reserve margins from transmission system operators, strategic use of pump storage, and limiting planned outages. CAISO estimates a loss of approximately 5,600 MW in solar-powered generation.

CAISO (click to enlarge)
Other high-capacity states, like North Carolina and Georgia, will experience obscuration percentages around 90% or more. North Carolina plans to suspend road construction and close lanes of traffic at certain times during the event. Duke Energy, one of the largest utilities in North Carolina, will be closely monitoring the balance of energy as solar generation is reduced. Sammy Roberts, director of system operations for Duke Energy, estimates solar energy output will drop from about 2,500 megawatts to 200 megawatts in 1.5 hours. Alternative generation from sources like natural gas will ramp up to balance the grid in the meantime. To lower system stress, customers are being asked to turn off unnecessary appliances and adjust their air conditioning units.
The North American Electric Reliability Corporation’s (NERC) Wide-Area Perspective white paper on the eclipse states that advanced coordination to address ramp issues and secure non-photovoltaic resources can be readily obtained. The main challenge will be how each state deals with its forecasted non-coincident peak hourly load.
Spectators will also play a role in demand peaks. Gatherings such as the OutASight Total Solar Eclipse Festival have been organized all over the country. With so many people going outside to watch the solar eclipse, there may be a drop in load which could offset the generation shortfall.
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Linda Colelli – Energy Analyst – Power Markets