How Much Solar Power Will We Lose During the August Solar Eclipse?

On August 21, 2017 there will be a total solar eclipse that spans the continental United States from Georgia to Oregon. During the event, the Moon will pass between the Sun and the Earth and cast a shadow, completely blocking the Sun’s light for nearly 3 minutes and partially obscure it for over an hour. Such events have long been seen as portents of doom in many mythologies and blamed on hungry frogs, wolves, or even vengeful deities devouring the Sun. Animals often begin to behave as if night has fallen and there can be a noticeable drop in temperature.

Such spectacular events happen, of course, due to a total cosmic coincidence. The Moon is much smaller than the Sun (roughly 400 times smaller) but it is nearly 400 times closer on average. Thus both celestial objects appear ~1/2 a degree in size on the sky from our perspective.

There is some variation in the Earth-Moon and Earth-Sun distance, so annular solar eclipses also occur, where the Moon passes between the Sun and the Earth but does not entirely obscure the Sun revealing a glowing ring.  Depending on your viewing angle, you may also only see a partial eclipse while other observes on Earth have a face-on, total eclipse view.

Total solar eclipses, like the one occurring in August in the US, happen once every 1.5 years somewhere on the globe, and so are not really all that rare. However, the August eclipse will be the first total solar eclipse visible from the US in 38 years. Thus, campsites and hotels spanning the eclipse’s path of totality are filling up fast. Check out NASA’s infographics page for a map on what locations in the US will see the eclipse in totality versus only partially.

How much solar power will we lose?

While ancient civilizations may have considered total solar eclipses to be a bad omen and thus prepared for them accordingly, humans today are now making a different kind of preparation: how much solar power will we lose?

Although Californians will only experience a partial solar eclipse, the impact is predicted to be largest there since they provide nearly half of the solar electricity generating capacity in the US. And although the eclipse is only partial, roughly 68% of the Sun will be obscured in Southern California and up to 76% obscuration in Northern California. The California Independent System Operator, which provides access to the state’s power grid, predicts that contributions to the solar power grid will fall by 70 megawatts per minute or 6,000 megawatts during the total duration of the eclipse which is enough to power a large city.

Although still far behind California, North Carolina, which will also experience the eclipse in close to totality, is fourth on the list of largest state contributions to the solar power grid. Utility operators in both states are preparing by coordinating with industry to temporarily ease up on demand while also reserving spare energy from gas and hydroelectric power plants.

Solar power is on the rise.

Another sign that solar power is on the rise is the news this week that Tesla solar roof tiles, solar panels designed to look like standard roofing, have already sold out well into 2018. They became available for preorder with a $1,000 deposit in late 2016 but given their high cost – a predicted $21.85 per square foot according to Tesla – critics were hesitant in predictions of their popularity. You can estimate the cost savings that such solar tiles would provide for your address, based on the size of your roof and the amount of sunlight your corner of the world gets, thanks to an interactive tool from Google Project Sunroof.

We will have more coverage of the total solar eclipse here at Everyday Einstein in August, but please remember it’s never a good idea to stare directly at the Sun, even during an eclipse. If you want to participate in this potentially once in a lifetime event (at a given location), start looking for your own special eclipse viewing glasses now!

Until next time, this is Sabrina Stierwalt with Everyday Einstein’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com. 

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