Here's How the Solar Eclipse Impacted U.S. Power Generation (in 3 Tweets)

Yesterday, as millions of Americans stared up into the sky, grid operators were busy at work ensuring system reliability.

Why? 

Because the obscured sunlight caused by the eclipse had a significant impact on U.S. solar power generation. 

Here are three things we learned about the eclipse's impact on U.S. grid reliability and power generation. 

1. Minimal utility-scale solar capacity was in the eclipse's path of totality. 

According to the U.S. Energy Information Administration (EIA), more than 21 gigawatts (GW) were expected to be impacted by the solar eclipse on August 21.

However, as shown in the EIA's map below, minimal utility-scale solar capacity was actually located in the eclipse's path of totality, thereby limiting the eclipse's overall impact on U.S. solar power generation.

#SolarEclipse on August 21 will affect #photovoltaic generators across the country https://t.co/9VP4jepXPr #solar #PV pic.twitter.com/xtgLM3kSvn

— EIA (@EIAgov) August 7, 2017

In sum, the path of totality only impacted 17 utility-scale generators (mostly in Oregon), but hundreds of plants were at least 90 percent obscured. Despite that projected impact, the North American Electric Reliability Corporation (NERC) reported that the event would have no impact on reliability for the bulk of the power system. 

2. It briefly disrupted U.S. solar power generation. 

The solar eclipse had a definite impact on solar power generation in several key states and regions.

California experienced a significant dip in solar power output of around 3,400 megawatts (MW), which was less than the projected drop of 4,200 MW. The chart below (based on CAISO data) shows how yesterday's solar power output in California compared with the week before.

How did #Eclipse2017 affect the electric grid? Let's take a look at the @California_ISO in 8 charts.

1/ Here's realtime solar generation: pic.twitter.com/1uwEpvGAB4

— Blake Shaffer 📊 (@bcshaffer) August 21, 2017

The largest utility in North Carolina, which also boasts a notable amount of installed solar capacity, reported a 1,700 MW drop in solar output during the peak of the eclipse.

3. The U.S. power grid passed the test. 

Despite the definite drop in U.S. solar output, the power grid did not experience any reliability issues, just as NERC predicted.  

Grid operators report zero issues with #eclipse2017 (via @rtoinsider) https://t.co/L2rwJa8WJh

— Electricity Plans (@shopelectricity) August 22, 2017

Across the country, decreased air-conditioning usage (due to cooler temperatures), cloud coverage and behavior changes at both homes and businesses helped grid operators manage the drop in solar power generation. PJM Interconnection reported that such factors helped lower electricity demand by approximately 5,000 MW during the eclipse. 

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