A means of improving the connections between stacked solar cells — one capable of increasing the overall efficiency of solar energy devices, while also reducing associated costs — was recently devised by researchers at North Carolina State University. The new technique makes it possible for stacked solar cells to operate at solar concentrations of up to 70,000 suns worth of energy while still maintaining an optimal level of efficiency — rather than losing a larger and larger proportion of voltage as waste heat, as would otherwise be the case. The researchers think that this should help to reduce the cost of solar energy production.
For some background — stacked solar cells are simply a collection of multiple solar cells that are assembled on top of each another — they’re currently the most efficient type of solar cell on the market, reaching conversion efficiencies as high as 45%. In order for them to be effective, though, they need to be designed so that the connecting junctions in between these stacked cells don’t absorb any of the sunlight — in other words you need to make sure that the connections don’t siphon some of the voltage that the cells produce. The energy that is siphoned off ends up being “wasted” as waste heat.
“We have discovered that by inserting a very thin film of gallium arsenide into the connecting junction of stacked cells we can virtually eliminate voltage loss without blocking any of the solar energy,” states Dr. Salah Bedair, a professor of electrical engineering at NC State and senior author of a paper describing the work.
The press release from North Carolina State University has more:
This work is important because photovoltaic energy companies are interested in using lenses to concentrate solar energy, from one sun (no lens) to 4,000 suns or more. But if the solar energy is significantly intensified — to 700 suns or more — the connecting junctions used in existing stacked cells begin losing voltage. And the more intense the solar energy, the more voltage those junctions lose — thereby reducing the conversion efficiency.
“Now we have created a connecting junction that loses almost no voltage, even when the stacked solar cell is exposed to 70,000 suns of solar energy,” Bedair explains. “And that is more than sufficient for practical purposes, since concentrating lenses are unlikely to create more than 4,000 or 5,000 suns worth of energy. This discovery means that solar cell manufacturers can now create stacked cells that can handle these high-intensity solar energies without losing voltage at the connecting junctions, thus potentially improving conversion efficiency.”
“This should reduce overall costs for the energy industry because, rather than creating large, expensive solar cells, you can use much smaller cells that produce just as much electricity by absorbing intensified solar energy from concentrating lenses. And concentrating lenses are relatively inexpensive,” Bedair concludes.
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