The lack of low cost, large scale energy storage systems is a big
problem for solar power. Today, the typical solar cell can only store
energy for only a few microseconds. As a result, customers equipped with
solar panels will for the foreseeable future remain dependent on the
electric power grid. This is why so many green energy gurus consider hybrid systems
combining solar and storage to be the mother of all disruptive
technologies.
A new study
by chemists at the University of California, Los Angeles (UCLA)
suggests that rather than combining solar and storage, it may be easier
to design solar cells that can do double duty as batteries. The study, which was published in the most recent issue of the journal Science, describes a process for designing solar cells is capable of storing electricity for as long as several weeks at a time.
The solar cells, which are made from plastic rather than silicon,
mimic a mechanism used by plants to generate energy through
photosynthesis.
“Biology does a very good job of creating energy from sunlight,” said
Sarah Tolbert, a UCLA professor of chemistry and one of the senior
authors of the research. “Plants do this through photosynthesis with
extremely high efficiency.” The new technology has two basic elements: a polymer donor and a
nanoscale fullerene acceptor. The polymer donor absorbs sunlight and
passes electrons to the fullerene acceptor, which generates electricity.
Here is a great analogy used by UCLA’s press release to explain how the system works:
The plastic materials, called organic photovoltaics, are typically organized like a plate of cooked pasta — a disorganized mass of long, skinny polymer ‘spaghetti’ with random fullerene ‘meatballs.’ But this arrangement makes it difficult to get current out of the cell because the electrons sometimes hop back to the polymer spaghetti and are lost. . . . The UCLA technology arranges the elements like small bundles of uncooked spaghetti with precisely placed meatballs. Some fullerene meatballs are designed to sit inside the spaghetti bundles, but others are forced to stay on the outside. The fullerenes inside the structure take electrons from the polymers and toss them to the outside fullerene, which can effectively keep the electrons away from the polymer for weeks. In the new system, the materials self-assemble just by being placed in close proximity.
“In photosynthesis, plants that are exposed to sunlight use carefully
organized nanoscale structures within their cells to rapidly separate
charges — pulling electrons away from the positively charged molecule
that is left behind, and keeping positive and negative charges
separated,” said Tolbert. “That separation is the key to making the
process so efficient.”
http://www.forbes.com/sites/williampentland/2015/06/23/biomimicry-could-lead-to-solar-cells-that-store-energy-for-several-weeks-new-study-says/2/?ss=energy