High-efficiency concentrating solar cells may soon be moving to the rooftop
For concentrating solar power (CSP) champions, placing concentrating solar cells on a rooftop must seem like a top-notch idea, one, in fact, that should have been explored long ago. Especially so, if the issue of size has been resolved, the way a Penn State team has managed, using a disruptive nanoscale solar concentration technology that could possibly alter how all rooftop renewable energy is approached.
Here is how Penn State assistant professor of electrical engineering Noel C. Giebink sees the issue:
Concentrating photovoltaic (CPV) systems leverage the cost of high efficiency multi-junction solar cells by using inexpensive optics to concentrate sunlight onto them,” said Noel C. Giebink, assistant professor of electrical engineering, Penn State. “Current CPV systems are the size of billboards and have to be pointed very accurately to track the sun throughout the day. But, you can’t put a system like this on your roof, which is where the majority of solar panels throughout the world are installed.
Giebink pointed out the falling cost of typical silicon solar cells is making them a smaller and smaller fraction of the overall cost of solar electricity, which also includes “soft” costs like permitting, wiring, installation, and maintenance, that have remained fixed over time. Improving cell efficiency from about 20% for silicon toward greater than 40% with multi-junction CPV is important because increasing the power generated by a given system reduces the overall cost of the electricity that it generates.
Should widespread manufacturing take place, it is conceivable the overall cost of manufacturing and installing rooftop solar systems would be further reduced, opening the market to a far larger customer base.
Understand that enabling CPV on rooftops in the first place was no simple task. To accomplish this, researchers combined miniaturized, gallium arsenide photovoltaic cells and 3D-printed plastic lens arrays, plus this key component: a moveable focusing mechanism to reduce the size, weight and cost of the CPV system and create something similar to a traditional solar panel that can be placed on the south-facing side of a building’s roof.
All results about this are reported in the February 5 issue of the journal Nature Communications. Funding for this research came from the US Department of Energy.
“We partnered with colleagues at the University of Illinois because they are experts at making small, very efficient multi-junction solar cells,” said Giebink, in the Penn State article. “These cells are less than 1 square millimeter, made in large, parallel batches and then an array of them is transferred onto a thin sheet of glass or plastic.”
To focus sunlight on the array of cells, the researchers embedded them between a pair of 3D-printed plastic lenslet arrays. Each lenslet in the top array acts like a small magnifying glass and is matched to a lenslet in the bottom array that functions like a concave mirror. With each tiny solar cell located in the focus of this duo, sunlight is intensified more than 200 times. Because the focal point moves with the sun over the course of a day, the middle solar cell sheet tracks by sliding laterally in between the lenslet array.
The researchers tested their prototype concentrator panel outside over the course of a day in State College, Pennsylvania. Even though the printed plastic lenses were not up to specification, they were able to demonstrate over 100 times solar concentration.
We look forward to reporting on the future development of concentrating solar cells. Rooftops around the world might become remarkable proving grounds.
Images via Penn State and Nature Communications
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