Fake plastic trees

Solar panels are everyone’s favourite answer to our current energy crisis. They’re environmentally friendly, produce no emissions and use an abundant energy source. As it stands, they’re also horribly inefficient, they consist of scarce materials and the manufacturing process creates dangerous toxic byproducts. In other words, existing solar technology will not solve our problems.

A team at MIT is working on changing all that by tackling the problem at its roots. They’ve developed a solar cell that mimics plant photosynthesis right down to self-reparation using nano scale electronics and a system that functions at the atomic level, just like Mother Nature.

As we all know, plants use specialized cells called chloroplasts to absorb light and convert it into a useable form of chemical energy. What you may not know is that because of the destructive nature of sunlight, a plant must continually repair its cells. According to Michael Strano, MIT associate professor of chemical engineering, “In full summer sunlight, a leaf on a tree is recycling its proteins about every 45 minutes.”

While older panels saw little degradation over time, current high-efficiency and low-cost alternatives degrade from the moment they become active. The MIT researchers report that it’s not uncommon to find that “over 60 hours, the efficiency fall[s] to 10 per cent of what you initially saw.” The team has tested the newer self-repairing panel with “repeated cycles of assembly and disassembly over a 14-hour period, with no loss of efficiency.”

That’s all very good, but how does it work? The answer comes in the form of “molecular-scale tubes of graphitic carbon” more commonly known as carbon nanotubes. The nanotubes are essentially very tiny tubes composed of carbon atoms.

What makes these tiny carbon structures so special you ask? Apart from the incredibly light nature of carbon, and the tensile strength, which is “approximately five [times] higher than [that of] steel,” the nanotubes can also, under the right conditions, have “conductivities higher than that of copper” or “act as semiconductors” — silicon transistors in layman’s terms.

To harness the solar energy, the MIT researchers first created “synthetic molecules called phospholipids that form discs” on which they placed the light-sensitive reaction centers. The light would excite electrons in the reaction centres, which would in turn release electrons into the nanotubes.

The researchers explain the working process best: “The discs, carrying the reaction centres, are in a solution where they attach themselves spontaneously to carbon nanotubes. [ . . . ] The nanotubes hold the phospholipids discs in a uniform alignment so that the reaction centres can all be exposed to sunlight at once, and they also act as wires to collect and channel the flow of electrons knocked loose by the reactive molecules.”
Pretty clever, but it gets even better!

To make the system “rebuild” itself, the team added a chemical similar to the dispersant used by BP in the Gulf of Mexico oil spill earlier this year, which causes the “components to come apart into a soupy solution.” To reassemble the cells, the team “removed the [chemical] by pushing the solution through a membrane.” Once all of the chemical is through the membrane, the components return to their previous arrangements with no outside help.

The system so far is 40 per cent energy efficient, almost double the efficiency of current solar technology. It’s no surprise then that MIT is saying that solar power is “the renewable resource with the biggest potential.” If produced affordably and sustainably, the self-renewing solar cell may change the way we think about energy.