IMPROVING EFFICIENCY

Most solar panels are placed flat on rooftops because they are designed to harness solar energy when the sun is directly overhead. However, when the angle of the sun’s rays hitting the panel changes, traditional panels quickly become less efficient.

To get around this inefficiency, scientists have been experimenting with a variety of new solar cell technologies, including nanoscale 3D structures to trap light and increase the amount of solar energy absorbed. However in a new study in Energy and Environmental Science, a team of MIT researchers has taken a different approach by changing the shape of the solar panels. The researchers were able to develop a 3D shape that allows for 20 times greater power output.

By exploring a variety of 3D configurations using a computer algorithm and testing these under differing latitudes, seasons, and weather, they were able to build three different 3D modules for solar panels. These were then tested on the MIT lab building, with the researchers measuring their performance. These 3D configurations resulted in a boost in power output ranging from double to more than 20 times that of a flat solar panel with the same base area.

By going vertical, the panels were able to collect more sunlight when the sun is closer to the horizon, generating a more uniform output over time. This uniformity held even when seasons changed and even when parts of the panels were blocked by clouds or shadows.

Despite the increase in cost of production of the 3D modules, the researchers believe that its higher energy output would help offset this additional cost. In addition, its usage would also ensure that the electrical supply from solar power sources are more predictable and allow solar power plants to be integrated further to the electrical grid.

SHAPING PERFORMANCE

To determine the needed shapes for the panels, the team turned to computer modeling to analyze the performance of each shape. Initially, this modeling showed that complex shapes, such as a cube with each face dimpled inward, would offer a 10 to 15 percent increase in power output compared to a simple cube. The problem here however is that the complex shapes make printing much more difficult.

In their rooftop tests, the team studied both simpler cube modules as well as more complex accordion-like shapes that could be shipped flat for unfolding on site. The accordion-like tower was the tallest of the tested structures. A potential use for this would be installation in parking lots as charging stations for electric vehicles.

The tests also illustrate the benefits of the fall in the cost of solar cells in recent years. Without such a fall, the researchers would be hard pressed to justify developing the more complex shapes of the panels. “Even 10 years ago, this idea wouldn’t have been economically justified because the modules cost so much,” Jeffrey Grossman who led the study says. But now, he adds, “the cost for silicon cells is a fraction of the total cost, a trend that will continue downward in the near future.”

The researchers plan to test and study a collection of solar towers to figure if an individual tower’s shadows will have an effect on the overall power output. While they still need to figure an optimum power collecting strategy for these 3D modules, it’s another step forward for developing renewable energy.