The Question

These Solar Cells Use Nearly Every Frequency Of Sunlight

In 1979, President Jimmy Carter made history when he installed the White House's first-ever solar panels. At the dedication, he was feeling pretty optimistic, saying,"In the year 2000 this solar water heater behind me, which is being dedicated today, will still be here supplying cheap, efficient energy." His prediction fell short. Two years later, Ronald Reagan had them removed shortly after taking office. Even had Reagan not taken them down, the solar panels of the '70s can't hold a candle to those created today.

One common criticism of solar power is that it just isn't efficient — nearly 40 years after those presidential panels, most solar cells can only convert about a quarter of the sunlight they absorb into electricity. But a new design is challenging the status quo by absorbing nearly every frequency of sunlight.

Stacked solar cell

Like Panning For Gold, But For Sunlight

The new design, which came out of George Washington University, has vastly improved previous kinds of solar panels and nearly doubled their efficiency. But if you look at the numbers, you could be forgiven for feeling a little underwhelmed. After all, turning 44.5 percent of all available sunlight into electricity is certainly better than only 25 percent, but it's not exactly something to write home about. Except, it kind of is. After all, plants took over the world on almost nothing but solar energy, and they absorb light at only about 3–6 percent efficiency. It comes down to the fact that there's a lot of sunlight, and if we can harness even half of it, we'll be doing pretty great.

But how did the researchers make such a giant leap forward? Basically, the new design is a series of different types of cells that capture different types of light, like a gang of prospectors panning for gold in the mountains. The first one has a sieve with big holes in it to capture all of the biggest nuggets (the ultraviolet light) while letting the dirt and smaller chunks of gold through. The next prospector's sieve has slightly finer holes, capturing some of the gold that the first let through — let's say that's indigo light. The next has even smaller holes to capture blue light, and the next gets green, all the way up through the warmer colors and then to invisible infrared. By the time the "water" has passed through every "sieve," pretty much everything has been pulled out of it. Afterwards, they all go back to camp for a solar-powered jamboree.

Solar Panels Have Got The Blues

If you've seen a lot of solar panels, you may have noticed that quite a few of them are blue. But why would that be? If you think about it, black absorbs more light than blue does, so shouldn't black be the preferred color? It basically comes down to this: black solar panels are more efficient, but blue solar panels are cheaper. But unfortunately, even the black ones leave a lot of light on the table.

About half of all the light that makes it to Earth is infrared light, and most solar panels work exclusively in the visible spectrum. That's what makes this design so revolutionary — because it encompasses the entire spectrum of light, the only waste comes from inefficiency in converting that light to electricity. And that's a problem that's only going to improve in time.

As for the White House, President Obama had solar panels reinstalled in 2010. The new system generates 19,700 kilowatt hours of electricity a year, almost enough to power two average American homes.

Solar Power

Written by Reuben Westmaas August 18, 2017

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