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How Do Solar Panels Work?

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They’re an increasingly common sight on the tops of buildings and residential properties: sometimes blindingly reflective panels that absorb sunlight and convert it into usable energy. Noted futurist Ray Kurzweil thinks we’ll all be using them by 2028. But how do solar panels work? Your basic understanding of solar panels—that they convert sunlight directly into electricity—is true. It’s called the photoelectric effect, and it was first discovered in the 1800s. Scientists learned that photovoltaic (PV) cells made of selenium were ideal for this purpose. While they later turned to the semi-conductor silicon, the idea remained the same: Up to a third of the energy found in the sun’s rays could, theoretically, be harnessed for electrical power under the most basic setup, and over 40 percent for the more expensive and complicated models. Silicon crystals by themselves aren’t necessarily great for this purpose, though. They need to be altered with boron and phosphorus and layered. The layer of boron-altered silicon has fewer electrons than it needs to form a bond, so an electron “hole” is created. The layer of phosphorus-altered silicon, meanwhile, has too many electrons. The space between is known as the P-N junction. As the sun’s photons enters the PV cells and starts dislodging electrons, the charge attempting to travel through the P-N junction gets diverted to an external circuit that can then carry the power to an inverter. You may not realize that the power generated with this method is a direct current, or DC, the same type found in batteries. To use the energy in a home or building, it needs to be converted to AC, or alternating current, the type found in outlets. And this is the role of the inverter. This kind of green energy has numerous benefits. Electricity doesn’t need to be transported by a utility company to the premises, and excess can be returned right back to the grid. If you’re thinking of installing a system, however, there are some caveats. For one, the upfront cost can be significant—around $10,000 to $13,475, depending on where you live, after tax credits. While you may be able to cut those costs with state rebate incentives or financing, it may take some time to recoup that investment. On the other hand, once installed, solar panels don’t appear to require much maintenance. Without moving parts, they’re not likely to suffer from mechanical issues, although you may need to replace the inverter at some point, which can get expensive. A site like EnergySage.com can also use your specific location to calculate how much a solar panel system might save you. So how do solar panels work? It’s one part the photoelectric effect and one part economy. If Kurzweil is correct, it won’t be long before we’ll all be well-versed in both benefits. Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.
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Why You Should Never Take Your Shoes Off On an Airplane
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What should be worn during takeoff?

Tony Luna:

If you are a frequent flyer, you may often notice that some passengers like to kick off their shoes the moment they've settled down into their seats.

As an ex-flight attendant, I'm here to tell you that it is a dangerous thing to do. Why?

Besides stinking up the whole cabin, footwear is essential during an airplane emergency, even though it is not part of the flight safety information.

During an emergency, all sorts of debris and unpleasant ground surfaces will block your way toward the exit, as well as outside the aircraft. If your feet aren't properly covered, you'll have a hard time making your way to safety.

Imagine destroying your bare feet as you run down the aisle covered with broken glass, fires, and metal shards. Kind of like John McClane in Die Hard, but worse. Ouch!

Bruce Willis stars in 'Die Hard' (1988)
20th Century Fox Home Entertainment

A mere couple of seconds delay during an emergency evacuation can be a matter of life and death, especially in an enclosed environment. Not to mention the entire aircraft will likely be engulfed in panic and chaos.

So, the next time you go on a plane trip, please keep your shoes on during takeoff, even if it is uncomfortable.

You can slip on a pair of bathroom slippers if you really need to let your toes breathe. They're pretty useless in a real emergency evacuation, but at least they're better than going barefoot.

This post originally appeared on Quora. Click here to view.

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Big Questions
Where Should You Place the Apostrophe in President's Day?
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Happy Presidents’ Day! Or is it President’s Day? Or Presidents Day? What you call the national holiday depends on where you are, who you’re honoring, and how you think we’re celebrating.

Saying "President’s Day" infers that the day belongs to a singular president, such as George Washington or Abraham Lincoln, whose birthdays are the basis for the holiday. On the other hand, referring to it as "Presidents’ Day" means that the day belongs to all of the presidents—that it’s their day collectively. Finally, calling the day "Presidents Day"—plural with no apostrophe—would indicate that we’re honoring all POTUSes past and present (yes, even Andrew Johnson), but that no one president actually owns the day.

You would think that in the nearly 140 years since "Washington’s Birthday" was declared a holiday in 1879, someone would have officially declared a way to spell the day. But in fact, even the White House itself hasn’t chosen a single variation for its style guide. They spelled it “President’s Day” here and “Presidents’ Day” here.


Wikimedia Commons // Public Domain

Maybe that indecision comes from the fact that Presidents Day isn’t even a federal holiday. The federal holiday is technically still called “Washington’s Birthday,” and states can choose to call it whatever they want. Some states, like Iowa, don’t officially acknowledge the day at all. And the location of the punctuation mark is a moot point when individual states choose to call it something else entirely, like “George Washington’s Birthday and Daisy Gatson Bates Day” in Arkansas, or “Birthdays of George Washington/Thomas Jefferson” in Alabama. (Alabama loves to split birthday celebrations, by the way; the third Monday in January celebrates both Martin Luther King, Jr., and Robert E. Lee.)

You can look to official grammar sources to declare the right way, but even they don’t agree. The AP Stylebook prefers “Presidents Day,” while Chicago Style uses “Presidents’ Day.”

The bottom line: There’s no rhyme or reason to any of it. Go with what feels right. And even then, if you’re in one of those states that has chosen to spell it “President’s Day”—Washington, for example—and you use one of the grammar book stylings instead, you’re still technically wrong.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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