leaves_commons

Artificial Leaves

Mimicking the way planets harness energy from the sun, scientists at North Carolina State University have developed an adaptable, water-based solar cell. The leaves will provide free renewable energy pulled from radiant solar light.

Nowadays we’ve just about seen it all, from Doug Band and his work with the IRRI (International Rice Research Institute) on modified rice seeds to Todd Reichert and his Snowbird. But a large majority of new research and development in the field of technology has gone into solar/green energy.

One of the biggest issues with solar energy is the fact that it lack’s the capacity to generate enough power for large communities. Despite the recent discovery of PETE (Photon Enhanced Thermionic Emission), there will certainly continue to be a strong demand for personal solar power, similar to that of panels used to heat swimming pools.

Scientists around the world are still pursuing new methods to harness the power of the sun and turn it into electricity. In this pursuit, researchers at North Carolina State University may have found another solution. Lead author on the study and Professor of Chemical and Biomolecular Engineering at NC, Dr. Orlin Velev created artificial leaves with the thought of using solar cells to imitate nature more narrowly.

He successfully infused water-based gel with light sensitive molecules, and paired that with electrodes coated by materials (graphite or carbon nanotubes) to create these leaves. In doing so, the sun’s rays excite the molecules, yielding electricity. In nature, plant molecules are excited by the sun, which then starts the process of photosynthesis. And just to throw in a bonus, the gel permits the usage of actual chlorophyll to create the same reaction.

But the process has yet to be perfected, and therefore cannot provide actual sustainability. Dr. Velev claims that he’ll need to discover a way to mimic the self-regenerating mechanisms found in plans, and change the water-based gel to improve overall efficiency. He also goes on to state that they’re a long way from making this all practical.

Without practicality, these artificial leaves won’t be able to compete and survive in this time. But the idea is brilliant – “…this concept of biologically inspired “soft” devices for generating electricity may in the future provide an alternative for the present-day solid-state technologies.” – Dr. Orlin Velev

Contributor – Jack Lundee

Chemical engineers from MIT in Cambridge, Mass. have used single-walled carbon nanotubes (SWNTs) to make antenna-like structures that concentrate solar energy 100 times more than a regular photovoltaic cell. These antennas can capture and focus light energy, potentially allowing much smaller and more powerful solar arrays.

Caption: This fiber containing about 30 million carbon nanotubes absorbs energy from the sun as photons and then re-emits photons of lower energy, creating the fluorescence seen here. The red regions indicate highest energy intensity, and green and blue are lower intensity. Image by Geraldine Paulus.

The antennas were possible because new separation methods now allow sorting of SWNTs by their optical properties. This means that SWNTs can be used to make optically homogeneous materials that are larger than typical excitation wavelengths of interest.

The engineers, led by Michael Strano, isolated semiconducting SWNTs and dielectrophoretically spun them into largely homogeneous solid core-shell fibers that were about 10 ?m long and 5 ?m thick. The fibers each contained about 30 million SWNTs.

The engineers made light-concentrating antennas by forming a fiber with shells of successively larger-bandgap SWNTs radiating outward. These structures can boost the number of photons captured and funnel energy from light into a solar cell.

The engineers plan to test the SWNT antennas in a photovoltaic device and are working to reduce the energy loss from the current 13% to only 1%.

Research Paper: Exciton Antennae and Concentrators from Core-Shell and Corrugated Carbon Nanotube Filaments of Homogeneous Composition, Nature Materials, doi:10.1038/nmat2832

Prototype can continuously produce electricity for a week

updated 9/8/2010 11:08:34 AM E

Over time, most solar cells degrade due to prolonged exposure to the sun’s scathing rays and are rendered useless. But with a little inspiration from nature, researchers have now created a new solar material that regenerates its damaged energy-capturing packets on-demand.

A small prototype solar cell built from the self-healing material can continuously produce electricity for an entire week without losing any efficiency, the scientists report.

The team was inspired by plants in nature. The ingredients within a plant’s leaves that turn sunlight into energy aren’t actually immune to the sun’s damage. Instead, the molecules do their job (pump out sugar), get destroyed, and in less than an hour they regenerate. This process happens over and over again – enabling the leaves to produce energy at the same efficiency as they did on day one of their operation.

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“Nature has figured out how to work with solar energy,” said study lead researcher Michael Strano, a professor at the Massachusetts Institute of Technology (MIT). “It makes a dynamic cell that can constantly repair itself.”

Today’s solar materials, which range from the rigid-silicon panels found on rooftops to the flexible, organic kind that can be coated like paint onto surfaces, all degrade over time when exposed to sun and oxygen. The result of this damage is that the material’s ability to turn sunlight into electricity decreases over time.

Strano and his team have built what they call a “dynamic” solar cell. The light-capturing material is a mixture of several chemicals, including a photosensitive protein, a fatty substance called a phospholipid and carbon nanotubes .

The team found that when they added soapy liquid to the mix, the components of the material break apart and form a soupy solution. In this form, the material can’t produce electricity. However, when put into a special bag with tiny holes that only let the soapy molecules – called surfactants – leak out, the “disordered mess” turns into “a very structured, very ordered material” – one that can turn sunlight into electricity.

This process of adding and removing the surfactant can be repeated over and over again, allowing the mixture to constantly regenerate its electricity-producing structure.

There’s still a lot to do before this technology could be used in homes and buildings to produce electricity. For one, the initial efficiency — a measure of how much of the sun’s light the panel can convert into electricity  – of the new system is much lower than today’s solar panels.

The researchers see this research as a “first step” in developing a solar cell capable of regeneration, Strano said.

Strano and his team detail their research online Sept. 5 in Nature Chemistry.