Technology News - September 8, 2004

Nano-PV set to accelerate solar-energy use

A selection of what innovators are calling the “next generation of photovoltaic technologies” is expected to be commercially available within the next few years, sending the traditionally high costs of solar energy spiraling down. Nanotechnology is the key to the new solar-cell architecture, which promises to transform everyday polymers, like those used in consumer goods ranging from car windows to computer cases, into flexible energy producers.

The first photovoltaic (PV) devices were constructed of crystalline silicon, and the second generation relied on amorphous silicon thin-film coatings. The nano-PV technologies of the third generation do away with both the conductive materials and the glass substrate. Instead, they rely upon coating or mixing “printable” and flexible polymer substrates with electrically conductive nanomaterials.

Research into the perfect coating material is now heading in several directions, with an array of nanoscale semiconductors under investigation. Some predict that these cells will be produced in simple laboratory vats instead of the high-maintenance clean rooms or vacuum chambers used for current solar PV fabrication. Add rapid roll-to-roll printing and low-temperature processing capabilities that replace the energy-intensive batch manufacturing requirements of current PV devices, and the high cost of solar energy starts to come down to earth. Today’s average price of crystalline silicon PV rooftop solar modules, at $5–10 per watt for installed modules, is 4–8 times the cost of grid-fed electricity, depending on a host of local factors. “Ours will be an entire order of magnitude cheaper than current PV,” insists Martin Roscheisen, CEO of Nanosolar, a start-up company based in Palo Alto, Ca. Nanosolar is on track to begin producing nano-PV building modules by 2006.

But cost is immaterial if performance lags behind current standards. Researchers must continue to inch conversion efficiency rates upward to reach, and even surpass, the standard 12–18% efficiency rate at which today’s conventional solar arrays convert sunlight into electricity.

Earlier this year, scientists at Siemens announced that they had achieved 10% efficiency, a new record, for converting light into electricity when they used nanomaterials that combine nanoscale buckyballs with electrically conducting polymers. And just this past May, researchers at the Los Alamos National Laboratory identified a way to use lead selenium nanocrystals to potentially double the energy output of a solar cell by making each photon move two electrons.

General Electric and Hitachi have also boosted efficiency rates in the laboratory using a variety of nano-sized particles and flexible substrates. Yet the strongest commercialization push is coming from three well-funded start-ups: Konarka, Nanosolar, and Nanosys—all recent recipients of multimillion-dollar grants from the U.S. Defense Advanced Research Projects Agency (DARPA), the central research and development organization for the U.S. Department of Defense (DOD).

Konarka was cofounded by Alan Heeger, a Nobel laureate in physics and professor of materials at the University of California, Santa Barbara, who developed some of the original conducting polymers using fullerene composites. With an impressive lineup of scientific advisors, including a second Nobel laureate, the company is developing a hybrid solar cell that combines nanocrystalline titanium dioxide with conducting polymers.

Konarka cofounder and CEO Howard Burke reports that the company is testing various product applications for consumer electronics and military devices at its pilot manufacturing facility in Lowell, Mass. However, he remains mum about specifics and whether the tests have reached the company’s stated efficiency goal of 10%. In a late-breaking development, Konarka just announced it has acquired the organic photovoltaic research efforts of Siemens.

Northern California-based Nanosolar and Nanosys are both concentrating solely on building materials that will produce electricity. Nanosys has licensed a portfolio of patents originally developed at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory under A. Paul Alivisatos, a chemistry professor at the University of California, Berkeley. Experimenting with the crystallization of various cadmium compounds, one of Alivisatos’ graduate students unintentionally increased branching, enabling easier movement of electrons along the surface. Nanosys will remain an R&D company but has licensed its technology to Matsushita Electric Works, which hopes to begin selling solar rooftop tiles to the Asian construction market by 2007.

Nanosolar is the only one of the three start-ups that has a target launch date and timeline for a specific product. SolarPly are 10 X 14-foot thin-film solar-cell modules that use a proprietary substrate coated with quantum-dot-based semiconductor paint with an output of 110 volts of power at a conversion-efficiency rate “pushing towards conventional PV,” reports Roscheisen, who declined to be more specific. As the flagship product undergoes testing at the Palo Alto headquarters, Roscheisen expects to begin shipping in 2005 to select test customers. He anticipates commercial availability in 2006 at a fivefold decrease in the current cost of PV. By bringing the cost down to less than $2 per watt of electricity, Nanosolar expects that its products will be able to compete with the cost of grid-fed electricity, especially during peak loads in sunny climates where electricity rates soar from air-conditioner use.

Despite some promising advances, Roscheisen concedes that the biggest hurdle could be proving SolarPly’s durability and longevity to buyers who are used to 25-year guarantees on conventional rooftop PV solar cells. The jury is still out, especially given that previous thin-film amorphous silicon solar cells revealed unexpected degradation rates that were not identified in the laboratory. “We’re putting the panels through accelerated lifetime field testing, and most of the longevity data will be available next year,” says Roscheisen.

In the meantime, thanks to overseas demand and grid-tied applications to shave off-peak power costs, the solar industry is growing at a breakneck pace. “Solar generation capacity has grown by an average of more than 30% annually over the past 5 years—growth rates more commonly seen in the high-tech worlds of personal computers and the Internet than the more staid energy sector,” says Joel Makower, cofounder and principal of Clean Edge, a clean-energy research and consulting firm based in Oakland, Ca.

Nevertheless, a host of skeptics will only appreciate nano-assembled solar-cell devices when they see them. “The solar field is littered with failures when it comes to deploying new technology into a mass-manufacturing setting,” insists Chris Tilley, president and CFO of Prevalent Power, a major supplier of solar installations on the west coast. “Plus, the costs of mainstream PV panels are continually going down as the economies of scale improve and companies initiate robotic manufacturing,” he concludes. —JEANNE TROMBLY