Solar start-ups set new efficiency records

Feb 08, 2012 by Lisa Zyga report
Image credit: Semprius

(PhysOrg.com) -- Although Alta Devices and Semprius make different types of solar panels, both start-ups have been breaking records in the past few days. Santa Clara, Calif.-based Alta Devices announced that its solar panels have achieved an efficiency of 23.5%, which has been verified by the National Renewable Energy Laboratory (NREL) as the highest solar panel efficiency to date. And Semprius, based in Durham, North Carolina, has announced that its concentrated solar panels have achieved an efficiency of 33.9%. Unlike traditional solar panels, concentrated solar panels use lenses to concentrate sunlight at intensities of up to 1,000 suns.

In addition to breaking records, another thing these two types of solar panels have in common is that they’re both made of gallium arsenide (GaAs) instead of the more conventional silicon. Although GaAs is more expensive than silicon, it’s much better at absorbing . To keep costs down, both companies have developed designs that use minimal amounts of the material.

Alta has developed a manufacturing technique that fabricates about 1 micron thick, which is a fraction of the thickness of other GaAs solar cells. For comparison, the company notes that a human hair is approximately 40 microns thick. In addition to being extremely thin, the solar cells are also flexible, offering the potential to be integrated into roof and building materials, transportation products, and other devices. Last summer, Alta demonstrated that one of these solar cells could achieve an of 27.6% (some efficiency is lost when multiple cells are wired together and assembled into an entire solar panel).

Alta’s goal is to make solar panels that are cost-competitive with fossil fuels, and to do so without government subsidies. The company is pursuing the Department of Energy’s (DOE) SunShot initiative, which aims to bring solar-generated electricity down to six cents per kilowatt-hour by the end of the decade, making it competitive with coal and natural gas. The DOE predicts that, if this goal is met, solar panels would account for 15-18% of US electricity generation by 2030, up from less than 1% today.

As for Semprius’ strategy, the company’s concentrated solar panels consist of thousands of GaAs microcells the size of a pencil point that Semprius claims are the world’s smallest solar cells. The microcells are robotically stamped onto a substrate using a specialized micro-transfer printing process. The panels contain three layers of the microcells, each modified to convert a different part of the solar spectrum into electricity.

Semprius’ 33.9% efficiency, which was verified by third parties, smashes the previous record of 32.0% for high-concentration photovoltaic (HCPV) solar panels. Further, the panel is not a prototype, but is intended for commercial use. Semprius plans to open a factory in Henderson, North Carolina, this summer and to start manufacturing commercial later this year. Like Alta, the company also predicts it can eventually generate electricity at a cost competitive with fossil fuels, also without government subsidies.

Explore further: Environmentally compatible organic solar cells

More information: Alta Devices (press release), Semprius (press release)
via: IEEE Spectrum, Technology Review

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User comments : 12

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_ilbud
1 / 5 (1) Feb 08, 2012
Well that's that then theoretical maximum has been reached this is as good as it gets.
Jaeherys
5 / 5 (2) Feb 08, 2012
From wiki, "The theoretical efficiency of MJ solar cells is 86.8% for an infinite number of pn junctions, implying that more junctions increase efficiency. The maximum theoretical efficiency is 37, 50, 56, 72% for 1, 2, 3, 36 pn junctions".
Aliensarethere
1.9 / 5 (8) Feb 08, 2012
"about 1 micron thick, which is a fraction of the thickness of other GaAs solar cells."

Fraction ? Are you serious ? 10/3, 3/10, 100/100, 500/600 are all fractions.
Eikka
5 / 5 (1) Feb 08, 2012
Do concentrated solar cells have to be tracking? It seems necessary, unless they are using some kind of waveguides like tapered optical fibers.

antialias_physorg
4.3 / 5 (4) Feb 08, 2012
Do concentrated solar cells have to be tracking?

There's several ways to do it. Depending on what kind of geometry you use for the focus layer shifting it minimally with respect to the solar cell itself can be enough. You don't have to swivel the entire panel.
gwrede
4.8 / 5 (5) Feb 08, 2012
Do concentrated solar cells have to be tracking?
That's why the article picture (by Semprius, the maker of the concentrated solar cells) shows tracking solar panels.
dschlink
5 / 5 (2) Feb 08, 2012
Although you can design lensing systems that do not require tracking, they have limited acceptance angles. Even one-solar PV systems can double their annual output via tracking.
Vendicar_Decarian
2.3 / 5 (3) Feb 08, 2012
These filthy scientists are out to destroy the coal and oil industry.

They must be stopped NOW!
aroc91
5 / 5 (1) Feb 08, 2012
"about 1 micron thick, which is a fraction of the thickness of other GaAs solar cells."

Fraction ? Are you serious ? 10/3, 3/10, 100/100, 500/600 are all fractions.


Not sure if serious...
that_guy
5 / 5 (1) Feb 08, 2012
Do concentrated solar cells have to be tracking? It seems necessary, unless they are using some kind of waveguides like tapered optical fibers.

Most solar cells do not require tracking. It's just more efficient.

No matter what lens you have, it can't completely make up for the angle of attack. geometrically, a solar array can collect more light when directly facing the sun than if it is 90 degrees away from it.

OTOH, you can just use simple concentrating lenses and tracking to get the same efficiency.
------------------

I would like to point out that 6c a KW/Hour would be on par with the power production cost of an electrical plant.

Consider that they charge you 12c a KW/Hour to cover transmission losses, billing, maintenance, etc.

If solar gets down to 8 or 10c a KW/Hour, it's a great deal from the consumer point of view if you get a home installation.
djr
5 / 5 (1) Feb 08, 2012
That guy - I agree - and at $1 per watt on the panels - we are getting close. One big issue now is installation cost. We are still at a total cost of around $5 per watt. I think there is a lot of room there for more cost savings. If we can reduce the installation cost and get the total to around $3 a watt - we will see the market go crazy. Maybe have to wait a few more years - but it is coming.
RealScience
not rated yet Feb 09, 2012
Do concentrated solar cells have to be tracking? It seems necessary, unless they are using some kind of waveguides like tapered optical fibers.



Low concentration (2x-3x with lens or mirrors, ~5x with optical coupling to a refractive element) can be achieved without tracking.
Moderate concentration can be achieved by moving the receiver but not the panels.
High concentration of photons requires tracking.

However there are loopholes: luminescent concentrators absorb photons and emit lower-frequency photons in a narrow angular range, which allows them to achieve the same result as concentration without tracking.
The best example of this trade-off of photon energy versus intensity is a laser which is pumped by photons in all directions and emits lower-energy photons in one direction.

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