Rooftop concentrating photovoltaics beat out silicon in outdoor testing

By Warren Miller, contributing writer

The prices on solar cells keeps coming down, so it seems only a matter of time before costs are low enough for wider deployment. As the price of solar cells decreases, however, the other elements of a fully deployed system, such as installation labor, control and power conversion electronics, energy storage, and even permitting fees, are beginning to dominate the overall cost. But is there anything that we can do to improve the economics of solar power systems?

One key element in a solar power system’s deployment economics is solar converter efficiency. Concentrating photovoltaics (CPV) systems increase efficiency over traditional solar panels by concentrating sunlight and tracking the sun during the day. Unfortunately, these systems are large, cumbersome, and require a significant amount of mechanical control, which increases cost, reduces reliability, and restricts placement options. What is needed is a more compact version of a CPV system that also costs less.

Fortunately, researchers at Penn State have reported that a CPV system they have developed can improve efficiency from the 15% to 20% produced by traditional solar panels to 35% to 40%. This is done with an innovative approach to capturing and tracking sunlight. Instead of moving the entire panel system, the Penn State approach simply slides a solar cell array below a corresponding matrix of small lenses, keeping the entire panel fixed on the roof. Because of the structure of the lens matrix, the solar cells need to only be moved one centimeter to track the sun for the entire day. This dramatically reduces the cost of the mechanical element of the system, but perhaps more importantly, it also allows the same installation footprint as a traditional solar panel to be used. The lens system can concentrate sunlight more than 600 times, which contributes to the improved conversion efficiency. In fact, one area for improvement is to optimize the lenses so they don’t raise the temperature of the microcell too much, which limited the system efficiency in the field trial to only 54%. It would have operated at 73% if the overheating was eliminated.

Let the sunshine in. Image source: Giebink lab.

Many other improvements are possible, but this approach to implementing a CPV system without the traditional downsides looks promising. Are there possibilities that solar cell micro arrays and lensing matrices open up? Would it be possible to use 3D printing to inexpensively create sheets of micro lenses that can easily overlay on a similarly manufactured solar cell matrix? Perhaps micro-machines located at each lens could “crawl” the array as needed to follow the sun during the day, with no other mechanical requirements. Efficiencies of over 70% would dramatically change the economics of solar power systems. One might even say that the future’s so bright, we’ve got to wear shades.