Over the weekend, the New York Times noted that the solar power
“craze” is partly responsible for Wall Street’s recent good times. The
Times used the example of solar giant SolarCity, which has seen a
sevenfold increase in its share price to $59.27 since it went public,
but this could just be starters for the US solar industry. An
international research team based at North Carolina State University has
come up with a simple way to increase the efficiency of organic solar
cells by more than 30 percent, leading to lower costs and a much bigger
market.
That’s great news for companies like SolarCity. The company – another brainchild of Tesla creator Elon Musk
– packages and installs solar systems, so it’s not subject to the kind
of downward global pricing pressures that doomed US manufacturers like
Solyndra.
In fact, down works good for SolarCity’s business model.
Solar cells account for about half the cost of a fully installed and
connected solar system, so a major drop in the cost of solar cells will
have a significant impact on overall costs. That gives SolarCity and
other solar packagers another opportunity to offer their systems at more
competitive prices, and nudge conventional fuels out of the market.
A New Solar Cell Efficiency Breakthrough
With that in mind, let’s take a look at that NCSU solar cell efficiency breakthrough, which was just published in the journal Advanced Materials.
The research applies to organic solar cells,
which refers to a relatively new class of solar cells based on polymers
(loosely speaking, plastic). Organic solar cells are less efficient
than silicon, which is still the gold standard, but they make up for it
with the potential for a broader range of applications and a low cost
manufacturing process.
The key to the breakthrough is the creation
of a new low cost polymer by NCSU’s partner in the project, the Chinese
Academy of Sciences. Called PBT-OP, the new polymer is made from two
readily available monomers and a third monomer that can be synthesized
with relative ease (monomers are identical molecules that can be bonded
together into long chains as polymers).
The new polymer skips over
a key hurdle for lowering the cost of organic solar cells, which is the
use of fluorine. Typically, in organic solar cells a fluorine atom is
needed in the polymer’s “molecular backbone” in order to increase
efficiency, but that is a complicated processes and it introduces
significant manufacturing costs.
PBT-OP has the fluorine advantage
without the fluorine. To get a handle on that, all you need to know is
that organic solar cells consist of an electron acceptor material and an
electron donor material, each with its own molecular orbit.
The
trick is to find the ideal difference between the highest occupied
molecular orbit of the acceptor and lowest unoccupied molecular orbit of
the polymer.
Once you get that nailed down, what you’ve done is
to create a kind of super-efficient electrical highway, in which
excitons (the energy particles created when a solar cell absorbs light)
travel as quickly as possible within the interface of the donor and
acceptor domains. That means you minimize the loss of energy that occurs
in a conventional organic solar cell.
NCSU physicist Harald Ade breaks it down:
The possible drawback in changing the molecular structure of these materials is that you may enhance one aspect of the solar cell but inadvertently create unintended consequences in devices that defeat the initial intent. In this case, we have found a chemically easy way to change the electronic structure and enhance device efficiency by capturing a lager fraction of the light’s energy, without changing the material’s ability to absorb, create and transport energy.
Thank
you, Harald. Now let’s also thank the U.S. Department of Energy, which
funded the research project in partnership with the Chinese Ministry of
Science and Technology.
SolarCity And Tesla
Now let’s get back to that SolarCity/Tesla connection. Tesla Motors co-founder and CEO Elon Musk is best known for his innovation in the electric vehicle field, which seamlessly marries EV charging stations with onboard technology in the form of Tesla Motors’s Supercharger network, and he is also the Chairman of SolarCity.
Tesla has been introducing Supercharger stations powered at least partly by on site solar installations in the form of canopies, so it’s no surprise that SolarCity is providing the installations.
SolarCity is also the force behind solar-powered home EV charging stations and SolarStrong, which involves $1 billion worth of rooftop solar panels for military housing. Los Angeles Air Force Base and Fort Bliss are two examples, with Los Angeles being particularly interesting because the base has also been introducing electric vehicles.
Given
SolarCity’s track record with thin-film solar cells and the
solar/mobility connection with Tesla Motors we’re thinking that it won’t
be long before both companies cook up new applications for organic
solar cells as the cost of the technology continues to drop.
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