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December 16, 2011

3-D Photovoltaics Could Revolutionize Solar Power

Technology Review - Engineers say replacing flat panels with three dimensional structures can significantly change the economics of solar power generation.

Marco Bernardi and pals at the Massachusetts Institute of Technology in Cambridge say there is a simple fix that could dramatically increase the performance of photovoltaics. Instead of two dimensional flat panels, Bernadi and co suggest using three dimensional structures.

They've simulated the performance of various shapes and tested several of these on the roof of a building at MIT. Their results indicate that 3D structures can increase the amount of energy that can be generated by a given footprint by as much as 20 times. These structures can also double the number of useful peak hours of generation and reduce seasonal variation to boot.

Arxiv - Solar Energy Generation in Three-Dimensions (45 pages)




These structures needn't be complex. A simple cube, open at the top and covered inside and out with photovoltaic cells, can generate as much 3.8 times the power of a flat panel with the same footprint. By comparison, a solar tracking mount produces an increases of only up to 1.8 times.

The ultimate test for this idea is in the economics, of course. A cube has a much higher surface area than a flat panel and is more expensive to produce in the first place. But Bernadi and co say the extra power it generates more than compensates up for this.

If the numbers work out as these guys say, 3D structures could significantly change the photovoltaics market. Bernadi and co suggest their 3D structures could be shipped as flat packages that easily "pop up" into 3D structures when assembled.

Optimizing the conversion of solar energy to electricity is central to the World’s
future energy economy. Flat photovoltaic panels are commonly deployed in residential
and commercial rooftop installations without sun tracking systems and using simple
installation guidelines to optimize solar energy collection. Large-scale solar energy generation plants use bulky and expensive sun trackers to avoid cosine losses from photovoltaic panels or to concentrate sunlight with mirrors onto heating fluids. However, none of these systems take advantage of the three-dimensional nature of our biosphere, so that solar energy collection largely occurs on flat structures in contrast with what is commonly observed in Nature. Here we formulate, solve computationally and study experimentally the problem of collecting solar energy in three-dimensions. We demonstrate that absorbers and reflectors can be combined in the absence of sun tracking to build three-dimensional photovoltaic (3DPV) structures that can generate measured energy densities (energy per base area, kWh/m2) higher by a factor of 2 – 20 than flat PV panels, double the number of useful peak hours and reduce the seasonal and latitude variation of solar energy generation, with even higher benefits in case of cloudy weather. For example, a simple cube open at the top can increase the annual energy density generation by a factor (depending on the latitude) of 2 – 3.8 compared to a flat horizontal panel, versus an increase by a factor of 1.3 – 1.8 achieved from a flat panel using dualaxis tracking. 3D photovoltaic structures show the potential to create new schemes for PV installation using self-supporting 3D shapes, while their increased energy density could facilitate the use of cheaper thin film materials. The paradigm of 3DPV opens new avenues towards Terawatt-scale solar energy generation.

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