Printed solar cells the size of a ballpoint pen tip are tiny, but mighty

ORIGINAL: Smart Planet

By Kirsten Korosec

December 15, 2011, 11:07 AM PST

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Startup Semprius took the transfer-printing technology it originally developed for flexible electronics and applied it to solar cells. What did they create in return? Tiny solar cells — each a dot the size of a ballpoint pen tip — able to convert 41 percent of solar energy into electricity using low-cost lenses to concentrate the sun more than 1,000 times.

The Energy Department’s National Renewable Energy Lab announced Wednesday it had recently validated the 41 percent efficiency of the company’s solar cells. Semprius was selected by the DOE and NREL as one of its PV Incubator (now called SunShot) companies. The startup, which began at the University of Illinois, has piqued the interest and investment dollars of venture capitalists and power gear giant Siemens. Last June, Siemens took its partnership with Semprius considerably further and bought a 16-percent stake in the company.

How it works

Semprius makes solar concentrating photovoltaics — a clean-energy mashup of solar panels and solar thermal tech — that uses mirrors and lenses to concentrate light from the sun onto super-efficient cells.

Semprius makes the array of gallium arsenide-based micro cells by growing a semiconductor on a substrate and then using a machine to rapidly transfer it to a wafer. Layers are added to create a triple-junction solar cell. This patented micro-transfer printing process allows thousands of cells to be stamped at once.

The triple-junction cells are tiny and occupy only one-one thousandth of the entire solar module area. Lenses are then used to concentrate light on the tiny solar cells.

Each solar cell’s tiny footprint and the low-cost lenses allow modules to pack more power in a smaller space. And by using lots of small cells, unwanted waste heat is distributed more easily over the cell’s structure and eliminates the need for expensive thermal management hardware, according to the NREL. The upshot? Semprius execs say it can slash manufacturing costs by 50 percent.

Solar concentrating PV does have its drawbacks. The technology tends to have more parts than traditional PV, which can add to the cost of building and maintaining a large-scale project. In other words, there’s room for companies like Semprius to use innovation to reduce costs of CPV.

A few CPV solar companies have had success. For example, California-based Amonix is supplying a concentrating PV system for a 30-megawatt solar farm near Alamosa. Its system, which is manufactured in the U.S., powers a 5-megawatt powe plant owned by NextEra Energy in New Mexico. The company also received $4.5 million from the DOE to develop a new dual axis tracking system as part of the agency’s SunShot program, which aims to cut solar costs to $1 per watt.

Photo: NREL

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