A new 3-D configuration for photovoltaic cells can generate 20 times more power than standard fixed flat panels with the same base area. Research has focused on improving the performance of solar cells and bringing down their cost, but little attention has been paid to the best way to arrange those cells. Photovoltaic (PV) cells typically are placed flat on rooftops or other structures, or to motorized structures that keep the cells pointed toward the sun as it crosses the sky. Now, researchers at MIT have built cubes and towers that extend the solar cells upward in 3-D configurations. “I think this concept could become an important part of the future of photovoltaics,” said Jeffrey Grossman, the Carl Richard Soderberg Career Development associate professor of power engineering at MIT. Two small-scale versions of 3-D photovoltaic arrays were among those tested by Jeffrey Grossman and his team on an MIT rooftop to measure their actual electrical output throughout the day. (Image: Allegra Boverman) The team initially used a computer algorithm to explore a variety of possible configurations. The analytical software tested the 3-D configurations under a variety of latitudes, seasons and weather conditions. To confirm their model’s predictions, the team built and tested three arrangements of solar cells on the MIT laboratory’s roof for several weeks. The 3-D installations analyzed by the team included simpler cubic and more complex accordio-like shapes. A distinct advantage of the 3-D structures they studied was that the devices could gather slanting sunlight better than flat panels in locations far from the equator, during morning and evening hours, and during the winter, said Marco Bernardi, a graduate student at MIT. Although the cost to mount the PV cells in a 3-D configuration is more expensive than placing them in a simple flat panel, the expense is offset by the extra power generated per unit of mounting area, the researchers say. The configurations would provide “much more uniform power output over the course of a day, over the seasons of the year and in the face of blockage from clouds or shadows,” they argue. The time is ripe for innovation, Grossman said, because the cost of PV cells has dropped in recent years. And as that cost continues to decline more quickly than the costs of accompanying support structures, wiring and installation, the advantages of 3-D systems will grow accordingly. “Even 10 years ago, this idea wouldn’t have been economically justified because the modules cost so much,” he noted. That is changing. Today, “the cost for silicon cells is a fraction of the total cost, a trend that will continue downward in the near future,” Grossman said. Although the team has tested only individual modules, they plan to study multitower installations, taking into account how each tower will cast shadows on others at different times of the day. The idea of 3-D photovoltaic installations is not a new one, Grossman said, but “our study is different in nature, since it is the first to approach the problem with a systematic and predictive analysis.” The results were published in Energy and Environmental Science. For more information, visit: www.mit.edu
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