Researchers Shed New Light on Solar Cell Efficiency

The quest for more efficient solar cells is on. Currently the typical rate of conversion of sunlight into electricity is around 12% and in order to make solar power more competitive the industry works to increase this rate.

The scientific assumption is that there is a limit to the amount of energy that can be produced by a solar cell when it is hit with sunlight. Since the 1960s it is believed this limit is 33.5 percent. Five decades on and we have reached a top performance of 26 percent in the case of flat-plate, single junction solar cells, which absorb light waves above a specific frequency. Multi-junction cells could achieve higher rates of efficiency for having multiple layers and absorb multiple frequencies.

Researchers from the University of California, Berkeley recently presented a new theory about how solar cell efficiency could be increased and said the cells should resemble LEDs, that is, they should emit and absorb light. Their thesis will be presented at the Conference on Lasers and Electro Optics taking place between May 6 and 11 in San Diego, California.

Lead researcher Eli Yablonovitch said the more photons a solar cell emits, the higher its voltage, and consequently its efficiency, will be. They arrived at this conclusion while researching the reasons why solar cell efficiency has not reached its potential. They believe they have cracked it and the answer lies in the thermodynamic between absorption and emission.

They argue that designing solar cells to emit light naturally increases the voltage produced by the solar cell because the photons do not get “lost” within a cell.

Alta Devices, a company co-founded by Yablovitch, has created a prototype solar cell made of gallium arsenide (GaAs), which is used to make solar cells in satellites. The prototype achieved a record efficiency of 28.3 per cent thanks to a cell design that allowed light to escape from the cell. The reflectivity of the rear mirror was increased so that incoming photons were allowed out of the device.

The energy from the photons that come from the sun releases electrons from the cell, so they can flow freely. During this process, new photons are generated and if you allow them to escape from the cell as easily as possible, they can increase electricity generation.

The researchers expect their novel solar cell design to reach an efficiency rate of 30%. Their design is applicable to all types of solar cells.




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Solar Electric Light Fund Shines a Ray of Hope on Haiti

The Solar Electric Light Fund (SELF) has installed 100 solar-powered street lamps in Haitian refugee camps Pétionville and Caradeux. Almost two years after a 7.0 magnitude earthquake rocked Haiti taking over 700,000 lives and leaving millions homeless, the country is still struggling to rebuild its infrastructure.

Neighborhood redevelopment has accounted for the relocation of some refugees, but 23,000 still live at Pétionville, and many thousands more are in camps vulnerable to landslides, fire, flooding, and high incidents of violence. While renewable energy can’t solve all of these dilemmas, solar-powered street lamps make it possible for children to study, for dinner to be made, and for card games to be played well after the sun sets.

The Solar Electric Light Fund (SELF) has installed 100 solar-powered street lamps in Haitian refugee camps Pétionville and Caradeux. Almost two years after a 7.0 magnitude earthquake rocked Haiti taking over 700,000 lives and leaving millions homeless, the country is still struggling to rebuild its infrastructure.

Neighborhood redevelopment has accounted for the relocation of some refugees, but 23,000 still live at Pétionville, and many thousands more are in camps vulnerable to landslides, fire, flooding, and high incidents of violence. While renewable energy can’t solve all of these dilemmas, solar-powered street lamps make it possible for children to study, for dinner to be made, and for card games to be played well after the sun sets.

SELF, the Washington, DC-based nonprofit, has been using renewable energy to provide light and power to rural medical clinics in Haiti since before the quake, and they were invited to extend their platform with the help of funding from the Inter-American Development Bank.

“We believe that energy is a human right and that access to it is essential to achieving the Millennium Development Goals,” said Bob Freling, Executive Director of SELF in a press release.

As post-earthquake Haiti is slowly being rebuilt, women are more vulnerable to sexual assault and violence has increased across the country. Amnesty International has reported that women are at serious risk of sexual attack, and rape survivors continue to arrive at the office of a local women’s support group almost every day. Police surveillance hasn’t been proven to deter sexual violence, but according to SELF and J/P HRO, as soon as the street lamps went up in August, reported acts of violence (including sexual assault) declined drastically from about one a day to one a week.

Hurricane resistant, tamper-proof, and otherwise sturdy street lamps installed at the camps require minimal maintenance. The larger model streetlamp, procured from Port-au-Prince’s Green Energy Solutions, is 20 feet tall with photovoltaic modules on top and two sealed gel batteries inside a secure box connected to high-powered LED lamps.

Once the camps are dispersed, the solar street lamps will be moved to other areas. Although the lighting is temporary, its positive impact is permanent and includes diminished crime rates, more time for kids to study, increased commerce, neighborhood camaraderie, and hope for the camp’s many residents.

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