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A solar panel is a solar panel is a solar panel, right? Not exactly. They’re kind
of like cars. While all cars have wheels, a steering wheel, and pedals to control it,
there are a wide variety of engines, horse power, types of tires and brakes that all
impact how efficient the car is and handles the road. The same is true for solar panels.
There are different materials and technologies that can have a profound impact on the amount
of energy generated and the cost. And the past year or so has had some really interesting
advancements that will have a big impact. Plus, what if I told you it might be possible
to harvest power from shadows?
I’m Matt Ferrell ... welcome to Undecided.
The cost of solar power has been dropping dramatically over the past decade, while at
the same time solar panel efficiency has been rising. If you look back to 1977, the cost
per watt of solar energy was around $77, but today it's around $0.13. And it's continuing
to drop. It’s worth taking a quick look at how solar evolved to give the latest developments
some context. There's a much longer history than you might have realized.
The photoelectric effect was first observed in 1839 and the first patent was awarded to
William Coblentz in 1913. But it wasn’t until the 1950’s that solar power started
to become a real thing. In 1954 Bell Labs invented the first practical silicon solar
cell, which had an efficiency around 6%. Solar cell efficiency is how much of the collected
sunlight the cell is able to convert into electricity. In 1957, Hoffman Electronics
was able to increase that efficiency to 8%, and then to 10% by 1959. By the time we get
into the early 1960’s solar cells had achieved about 14% efficiency.
Today, most solar panels are somewhere between 15% and 20% efficient. With some of the higher
efficiency models that you can buy being in the low 20% range. The LG panels (LG365 Q1C-A5)
I had installed on my roof are 21.1% efficient. And SunPower has a panel that’s almost 23%
efficient. So commercially available solar cells have gone from about 10% efficiency
in 1959 to 23% efficiency today. That's 60 years to more than double the efficiency.
Beyond efficiency of solar panels, it's also important to understand the materials used
to create them. The primary material used in solar panels today is silicon, which can
be formed in three ways: mono-crystalline, polycrystalline, and thin-film panels.
Mono-crystalline solar panels have the highest efficiency with current ratings between 15-22.2%,
and a lifespan around 25-30 years. To make a mono-crystalline, or single crystal solar
cell, silicon is formed into bars and then cut into wafers. The single crystal structure
gives the electrons more room to move and creates a better flow of electricity.
Polycrystalline solar panels have average efficiencies between 12-18% with a 23-27 year
lifespan. They’re also made from silicon, but instead of cutting bars of single crystal
wafers, manufacturers melt many fragments of silicon together to form the wafers. The
mixture of many kinds of crystals gives the electrons less room to move, so it’s not
as efficient. But the benefit is the price because they’re cheaper to produce.
And finally there’s thin-film, which is the least efficient between 9-14%, and a lifespan
closer to 20 years. Instead of forming thicker, rigid wafers, this is a very thin layer that
can be applied to plastic to create flexible solar panels. These are typically only seen
in large scale installations where space isn’t a premium, or you need to mold a cell to the
shape of something, like an RV or boat.
So are we stuck at 23% efficient solar panels? No, but it’s not far off from the theoretical
maximum efficiency of a single material. It’s referred to as the Shockley-Queisser limit
and for silicon panels it’s around 30%.
But, the good news is we aren't limited to silicon. There's been growing research around
perovskite, which is a class of man-made compounds that share the same crystalline structure
as the calcium titanium oxide mineral with the same name. What makes perovskite an enticing
silicon alternative is that the structure makes them highly effective at converting
light photons into usable electricity. They're capable of beating traditional mono and polycrystalline
silicon solar cell efficiency, and since they're from a man-made compound, manufacturing costs
should be lower. Perovskite cells can be made through a process called "solution processing,"
which is very similar to the printing of newspapers ... you can use inkjet printers to deposit
materials on plastic sheets. So perovskite solar cells are another form of thin-film
solar, but with much higher efficiency. And unlike silicon, you don't have to heat it
to thousands of degrees to form it.
But there are challenges around perovskite, which includes shorter lifespan, durability
and toxicity. Perovskites are more sensitive to air and moisture, which can dramatically
shorten their lifespan. But this may not be a showstopper since solar cells are already
sealed inside of plastic and glass for protection. However if these are going to catch on they'll
need to match the 20-25 year warranty that most silicon based solar panels come with
today. As for toxicity, many of the formulations include lead, which could become problematic
if not handled and recycled properly. All challenges that can be dealt with, including
different formulations, but it's worth making a note of.
In the time that scientists have been researching perovskite solar cells, the efficiency has
gone from 3.8% in 2009 to 25.2% this year in single-junction, or single layer architectures.
If you compare that to silicon's efficiency increase since the 1970's, when the National
Renewable Energy Laboratory (NREL) started tracking this data, it's a dramatic achievement.
Today's most efficient panels, like my LG panels, are where researchers were in the
lab almost 20-30 years ago. The fact that perovskite has advanced so far so quickly
is promising.
But it doesn't stop there. There's been a lot of work around layering multiple solar
technologies to do more together than they can on their own. This is called multi-junction
solar. Each layer is designed to absorb a different wavelength of the incoming sunlight,
so collectively they can capture more energy. There are a couple of companies combining
silicon and perovskite tandem layers to do just that.
A San Francisco start-up, Swift Solar, and Oxford PV are both using a thin layer of perovskite
film along with a more standard silicon solar cell with promising results. The silicon absorbs
the red band of the visible light spectrum and the perovskite absorbs the blue spectrum.
Oxford PV has reached a 28% efficiency and thinks they'll be able to break the 30% milestone.
They aren't available on the market yet, but they are actively setting up a mass production
line with the help from Meyer Burger, one of the largest suppliers of photovoltaic manufacturing
equipment, and they're expecting to have that complete by the end of this year. At launch
they're expecting to have a 400 watt, 60-cell module available, with a 500 watt version
down the line. For comparison my solar panels are 365 watts.
But the biggest breakthrough is from the National Renewable Energy Laboratory (NREL). They've
fabricated a solar cell in the lab with an efficiency of 47.1%, which set a record this
year. Now, this was in a lab and used concentrated illumination, but even under “one-sun illumination,”
which simulates more real world conditions, it achieved 39.2% efficiency.
How they did it is pretty clever. This is another multi-junction cell, but instead of
two tandem layers, it's a six junction solar cell, which basically means they’re layering
six different solar technology layers. In total there are 140 layers of the six different
solar materials ... and all combined are still less than 1/3 the thickness of a human hair.
As amazing as that is, it's still in the lab and not ready for mass manufacturing. This
is helping to establish what's possible on the high end and shows a path forward for
companies and other researchers, and it proves that we should be able to go well beyond the
30% efficiency limit of a single material.
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And finally a little bit of crazy science fiction level technology, and one that I wouldn't
expect to see anytime soon, but if researchers can build on this ... it's kind of crazy.
What if you could generate power from shadows and not just light? Researchers from National
University of Singapore have developed a prototype of a device called the Shadow Effect Energy
Generator (SEG), which generates power from ... you guessed it ... shadows. The way the
technology works is by generating and harvesting a small amount of electricity from the difference
in contrast between the shadow and illuminated sections of the device. If the device is in
full shadow or full light, it's not generating a voltage, but the closer you get to 50% coverage
the more voltage it produces. The working prototype generates about 1.2 V, which is
enough energy to power a digital watch in their demonstration.
This type of technology could take advantage of passing shadows like trees or clouds on
a solar panel. Today if a solar panel gets partially obstructed, it stops producing energy.
A solar panel equipped with this could turn that tree's shadow into power. It could also
be put to use as collectors inside a house, which are full of passing shadows all the
time. They can also double as a sensor and log shadows passing over it, which could be
used in applications with smart home devices. Again, this one is a long way off from anything
practical -- it's still very much in the lab -- but it's a very unique concept worth thinking
about.
Now jump into the comments and let me know what you think and if you've been holding
out on solar until something like these breakthroughs come to market. And as always a special thank
you to all of my Patrons. If you liked this video be sure to check out one of the ones
I have linked right here. Be sure to subscribe if you think I’ve earned it. And as always,
thanks so much for watching, I’ll see you in the next one.