Concentrated solar power conversion efficiency sets new record

Solar trackers: The solar modules in this array, manufactured by Semprius, are being tested. The modules are mounted on dual-axis trackers that keep them pointed toward the sun.

Semprius, a startup that makes tiny solar cells that capture focused sunlight without the need for expensive cooling systems, announced this week that it has made the world's most efficient solar panel.

The company's solar panels use tiny solar cells made from gallium arsenide. This record-breaking solar module contains hundreds of tiny solar cells, each as wide as a line drawn by a ballpoint pen, arranged under a lens that can concentrate sunlight 1,100 times more.

Gallium arsenide absorbs sunlight much better than silicon, which is used in most solar cells, but it is also more expensive. And while concentrating solar panels use less semiconductor material, they typically require expensive optics, cooling and tracking systems to keep them pointed toward the sun. The microscopic scale of Semaprius' solar cells inherently dissipates heat better, which makes them cheaper.

The Semaprius module has another benefit: Whereas silicon solar cells absorb sunlight efficiently only in a narrow frequency band, the solar cells in this module contain three layers of gallium arsenide, each modified to convert a different part of the solar spectrum into electricity.

Testing conducted by a third party certified the efficiency of the Semprius solar panel at 33.9 percent, marking the first time a solar panel has been able to convert more than a third of the sunlight that hits the panel into electricity. Conventional silicon solar panels typically convert less than 15 percent of sunlight into electricity, and the record for silicon solar panels is 22.9 percent. Previously, the record for overall solar panels was 32 percent, Semprius said.

One-off experimental modules can achieve higher efficiencies, but Semprius' record-setting module is designed for commercial use. It was made using the same type of equipment that the company is installing in a small plant in Henderson, North Carolina, that will open this summer. "It's a good sign that these efficiencies are what our customers can expect," said Joe Carr, Semprius's CEO.

The process at Semaphore can form tens of thousands of tiny solar cells on a single gallium arsenide wafer, using chemical etching and a robotic system to transfer each layer to an inexpensive substrate. The same gallium arsenide wafer can be reused many times, which reduces costs. The approach is based on a technology that can transfer small electronic devices from wafers to other substrates, developed by John Rogers, a professor of materials science and engineering at the University of Illinois at Urbana-Champaign.

Concentrating solar panels use tracking systems to follow the sun. These systems are expensive, can be unreliable, and can't be installed on most rooftops, which limits their use. They also only work in areas with clear weather, because cloudy days can cause the output to drop far more than traditional solar cells.

But as the cost of tracking systems falls and the efficiency of multi-layered solar cells improves, concentrated photovoltaic solar power is starting to look more attractive. Large installations of this type of solar module have been increasing in recent months.

Semaprius is building its factory at a particularly difficult time for the solar industry. Oversupply and falling production costs have led to a rapid drop in solar panel prices, making it difficult for new companies to enter the market and forcing some existing manufacturers out of business.

In response to falling prices, many solar companies, including Semaphore, have focused on improving efficiency. As long as manufacturing costs continue to fall, improving efficiency will reduce the cost per watt of solar panels. More importantly, it also reduces the cost of installation and related equipment, which can account for more than half of the cost of solar power. Semaphore is also learning as much as possible from proven manufacturing technologies, which will make it easier to scale up production and reduce development costs.

Semaprius has another advantage: its partnership with Siemens. In addition to providing direct financing (Siemens owns 16% of the company), Siemens provides production experience and can build complete solar farms, and the partnership also makes it easier to obtain bank financing.

The small plant, which Semprius plans to open this summer, will be able to produce 30 megawatts of solar panels a year. Semprius expects the panels produced there will be cost-competitive for some applications, Carr said. Increasing production to 100 megawatts would bring costs down enough so that the technology could compete with cheap solar panels made in China.

Ultimately, the cost per kilowatt-hour of solar power depends on a number of factors, such as financing costs, land costs, how close transmission lines are, local labor rates, and more. But Carr argues that the solar power generated by Semaphore, at less than 10 cents per kilowatt-hour, is low enough to capture a portion of the utility market, which is the case in many areas. What's more, he says, the company can do it without government subsidies.