Scientists at MIT have created a breakthrough solution to one of the biggest problems facing solar cells by mimicking the world's best harvesters of solar energy:  plants.

Over time, sunlight breaks down the materials in solar cells, leading to a gradual degradation of devices aiming to harvest the energy in that light.  Plants don't have this problem because the chloroplasts in plant cells constantly breakdown and reassemble their light-capturing molecules -- essentially constantly creating brand new molecules.

The scientists have developed self-assembling solar cells that can be broken down and reassembled quickly by the subtraction or addition of a surfactant (similar to the dispersants used on the oil spill).  MIT News describe the system as being made up of:

"synthetic molecules called phospholipids that form disks; these disks provide structural support for other molecules that actually respond to light, in structures called reaction centers, which release electrons when struck by particles of light. The disks, carrying the reaction centers, are in a solution where they attach themselves spontaneously to carbon nanotubes. The nanotubes hold the phospholipid disks in a uniform alignment so that the reaction centers can all be exposed to sunlight at once and they also act as wires to collect and channel the flow of electrons..."

When the surfactant is added, all of the components come apart.  When it's removed, the components spontaneously reassemble into a "rejuvenated" photocell.  After repeated tests where the cell is dis- and reassembled, there was no loss of efficiency.  The individual molecules have an efficiency of about 40 percent, around double current solar cells, but testing has been at low concentrations of these molecules, so the overall efficiency of the device was also low.

The scientists think that the individual molecules could theoretically hit 100 percent efficiency.  They are currently working to increase the concentration of the device and up the overall efficiency to something much greater.

via  MIT News

The State of California has granted approval for a new solar thermal power plant. The 250-megawatt Beacon Solar Energy Project is the first solar thermal power plant to be licensed in the United States in nearly 20 years. Commercial operation is expected to start by the third quarter of 2011.

Several other solar projects are also in the pipeline and seeking approval by the end of the year, including the Brightsource 400 MW solar tower. More than 4 GW of other solar thermal projects are also pending with the state.

Beacon Solar will be an array of solar focusing parabolic troughs spread over a 2,012 acre site in Kern County, California. The approval process required a solution to local residents' objections to the great amount of water the project would require. The final agreement will have the project use recycled water from a nearby community instead of drawing directly from the local aquifer. The project expects to use nearly 1600 acre feet (1.97 million cubic meters) of water annually.

The state of California has mandated that 20% of its electrical power come from renewables by 2010. While it does not look like that target is going to be met, the approval of several hundred megawatts of solar thermal power will help get the state closer to that goal.