3D design increases solar cell output
MIT researchers are working on 3D solar towers that, they say, give a power output of up to 20 times that of fixed flat panels with the same base area.
The biggest boosts in power were seen just where improvements are most needed: a long way from the equator, in winter months and on cloudier days.
"I think this concept could become an important part of the future of photovoltaics," says professor Jeffrey Grossman.
The team used a computer algorithm to explore an enormous variety of possible configurations, and developed analytic software that can test each one for a range of latitudes, seasons and weather.
Then, to confirm their model's predictions, they built and tested three different arrangements of solar cells on the roof of an MIT lab for several weeks.
While energy generated by such 3-D modules costs more than that from ordinary flat panels, this is partially cancelled out by a much higher output for a given footprint. This matters, because solar cells now cost less than the associated support structures, wiring and installation, which account for about 65 percent of the total.
"Even 10 years ago, this idea wouldn't have been economically justified because the modules cost so much," Grossman says.
The system also gives a more uniform power output over the course of a day, over the seasons of the year and in cloudy conditions.
This makes power output more predictable and uniform, which could make integration with the power grid easier than with conventional systems.
The main reason for the improvement is that the 3D structures' vertical surfaces can collect much more sunlight during mornings, evenings and winters, when the sun is closer to the horizon.
Although the models showed that the biggest advantage would come from complex shapes — such as a cube where each face is dimpled inward — these would be difficult to manufacture.
However, a simple cube can produce a power output only about 10 or 15 percent less than this. The team's also had good resuts from an accordion-like tower that can be shipped flat and then unfolded for use.
The next step for the team is to study a collection of such towers, accounting for the shadows that one tower would cast on others at different times of day.
MIT isn't the first to look at 3D solar cells - Californian company Solar3D recently announced it had developed a similar system and was looking for development partners.
However, says Grossman: "our study is different in nature, since it is the first to approach the problem with a systematic and predictive analysis."