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Solar Startup Alta Devices Sets Efficiency Record, Works on New Cell Design

Alta Devices, which engineers solar cells with more exotic materials, has achieved a new efficiency record of 30.8 percent, the Silicon Valley startup said Monday.

The new efficiency bests the company's own former record and shows off the company's new technology that stacks two layers of semiconductors on top of each other in order to boost the cell's performance. This dual-junction design, which involves a layer of gallium arsenide and a layer of indium gallium phosphide, differs from the single-junction cell (just one layer of gallium arsenide) that it's been making.

Alta broke the world record for single-junction gallium arsenide cell when it announced it was able to achieve 28.2 percentin 2011. An efficiency record reflects the best a company can produce, but the average efficiency of what the company is making and shipping to customers is typically lower. Alta is making cells at an average efficiency of 26 percent, said Chris Norris, the company's CEO. He expects the averages to reach 27-28 percent next year.

The company's long-term target is to create multijunciton cells with 38 percent efficiency (under one sun). 

Boosting the cell efficiency is important for reducing costs and squeezing more electricity from the same-size cell. Manufacturers measure their production costs in terms of cents or dollars per watt, so a solar cell with a higher wattage will be cheaper than the one with a lower wattage. And how efficient a cell can convert sunlight into electricity affects the wattage, or the power density of the cell.

Using more efficient cells also means you can get more energy from the same-size array of solar panels. That's good news for large solar projects and rooftop systems, especially when there isn't a lot of space to spare or the price of land is high. The most common solar cells made today use silicon, and SunPower is shipping the most efficient silicon cells today, at 23 percent efficiency.  

First Solar last week said it was able to set a new world record of 18.7 percent for cadmium telluride cells.

Founded in 2007, Alta is using gallium arsenide, which is more expensive than common solar cell materials such as silicon or cadmium telluride. But gallium arsenide contains properties that make it possible to convert a higher percentage of sunlight into electricity. Gallium arsenide is one of a group of semiconductors that researchers turn to when they want to design solar cells that are suitable for space satellites. Solar cells for space are thicker and encased in a rigid protective cover to prevent breakage.

Alta, on the other hand, designs its cells to be ultra thin and flexible. The company is targeting the military, consumer electronics and automotive markets. The cells would, say, cover the wings of a drones or a charger for mobile gadgets.

"We've finally solved a real problem by generating energy that is so much higher than what's produced by traditional flexible solar cells," Norris said.

The company also is exploring the automotive market that has started, though slowly, to embed solar cells on the car's roof to run some of the onboard electronics. For hybrid or all-electric cars, the cells can generate electricity to help keep the battery cool, said Rich Kapusta, Alta's vice president of marketing. The cooling system of a battery system typically continues to run after the car is parked.

Unlike many solar startups,  Alta isn't gunning for the market that assemble cells into panels for installation on the ground or the rooftop of homes and businesses. Alta's cells are more expensive than the silicon version or other common varieties mainly because of the cost of material and the scale of its production -- the company has a 2-megawatt pilot line at its headquarters in Sunnyvale.  The military is more willing to pay a premium for high tech. The consumer electronic accessory makers would value solar cells that can pack a lot of energy into a small area, though at what price point will we see a wide adoption of solar power chargers remains to be seen.

The company plans to start shipping its dual-junction cells later this year, Norris said. The dual-juction cells will use the same equipment that makes the single junciton cells.

He is now raising what he hopes will be a $40 million round and expects to close the round this summer.

Other solar cell makers that are targeting the military and consumer electronics markets include Ascent Solar, which makes the cells with copper, indium, gallium and selenium.

Norris noted that gallium-arsenide cells are able to generate electricity indoors with the lights on. The same can be done by amorphous silicon and organic solar cells, but both aren't nearly as efficient as Alta's cells. Silicon solar cells, on the other hand, is a poor choice for indoor use (silicon cells can produce power, but the voltage is so low that the electronics connected to them wouldn't function). 

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