Published on April 14th, 2020 | by Tina Casey0
US Scientists Create New Solar Cell That Blows Past Theoretical Limit, But Why?
April 14th, 2020 by Tina Casey
The National Renewable Laboratory just nailed down bragging rights to the world’s most efficient solar cell to date. The new PV device sails past the theoretical limit of 33% and gets pretty close to the 50% range, clocking in at an impressive 47.1%. The downside is that high-performance devices like these have an irritating tendency to price themselves out of the marketplace. They get stuck in outer space and other niche areas. Nevertheless, high performance could pay off in the sparkling green future, even though the cost of garden-variety solar is already low and falling.
A New Record For Solar Cell Efficiency
Before we get to the sparkling green economy of the future, let’s take a quick look at that new photovoltaic research from NREL.
For those of you new to the topic, the basic idea is that the right combination of materials can improve the ability of a solar cell to convert solar energy to electricity.
So far, silicon has proved to be the gold standard for solar cell efficiency. The 33% limit is based on single-junction solar cells, which use only silicon.
By switching up materials, adding more junctions, and performing some impressive feats of engineering in between, you can push past that limit.
Some triple-junction solar cells, for example, can surpass 45% under concentrated sunlight.
The new NREL solar cell is a six-junction affair of the III-V variety (“III-V” refers to the position of light absorbing elements on the periodic table).
You can get all the details from the research paper, published in the journal Nature Energy under the title, “Six-junction III-V solar cells with 47.1% conversion efficiency under 143 suns concentration,” but if you only have time for the plain-language version, the basic idea is that each of the six junctions capture different parts of the solar spectrum.
Through the magic of modern engineering and nanotechnology, the new solar cell consists of about 140 layers of the various materials, but it is narrower than a hair.
If that sounds rather pricey, it probably is. NREL has been working on bringing the cost of III-V solar cells down, but they are typically used in space and other niche applications where small is good and money is not an obstacle.
Expensive Solar Cell Meets Concentrating Solar Power
As for more ordinary applications in everyday life, that could be in the cards.
The research team points out that their new solar cell hit the record-setting mark of 47.1% under concentrated light. Under the equivalent of just one sun, it *only* racks up a conversion efficiency of 39.2%.
That rate of 39.2% may seem somewhat less impressive but it’s still nothing to sneeze at. In fact, 39.2% sets a new world record for one-sun conversion efficiency, which the NREL team bragging rights to a solar cell efficiency twofer for the same device.
More to the point, the difference in conversion efficiency between one sun and concentrated light suggests that there may be an economical way to deploy six junction III-V cells in the mass market.
If you’re guessing our old friend concentrating solar power could be the linchpin, run right out and buy yourself a cigar.
“One way to reduce cost is to reduce the required area, and you can do that by using a mirror to capture the light and focus the light down to a point,” explains NREL scientist Ryan France, who co-authored the new study.
Loosely speaking, the idea is to use a big field of relatively inexpensive mirrors to balance out the cost of a small field of ultra-efficient solar cells.
How small? According to France, you could end up using a fraction of semiconductor material compared to a conventional silicon solar cell, on the order of 1/100 or even 1/1,000.
Whatever Happened To Concentrating Solar Power?
If all goes according to plan, that would be sweet vindication for concentrating solar power fans.
The US Department of energy showcased CSP during the Obama administration, but back then the technology was relatively slow to prove itself in the marketplace.
In recent years, though, concentrating solar has really taken off. The current focus is on thermal energy plus energy storage, but the potential for adding a photovoltaic angle could give the CSP industry yet another avenue of solar energy to pursue.
On the thermal side, the Energy Department has ramped up its interest in concentrating solar power in recent years with a particular focus on the high-temperature solar area. Microsoft’s Bill Gates has also dipped a toe in the high-temperature CSP field, in his new guise as a high tech energy investor.
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Photo: “Scientists John Geisz (left) and Ryan France fabricated a solar cell that is nearly 50% efficient‘” by Dennis Schroeder, NREL.