08 Sep 2015
Companies feature among 11 different research projects to receive a total $24 million in funding from ARPA-E.
The US Department of Energy (DOE) has backed development of next-generation “micro” concentrated photovoltaics (CPV) technology with $24 million in funding via its Advanced Research Projects Agency (ARPA-E) – the energy equivalent of the Defense Advanced Research Projects Agency.
That support comes despite a host of CPV business failures over the past few years, the sub-sector having been decimated by the plummeting price of more conventional solar panels based on crystalline silicon or thin-film PV. Soitec, one of the few remaining commercial providers, is currently struggling to off-load its CPV division after its planned sale to a Chinese buyer fell through last month.
Where the ARPA-E projects are fundamentally different to existing commercial CPV is that they integrate concentrating technology and tracking elements within PV cells. In doing so the “micro-scale optimized solar cell arrays with integrated concentration” (MOSAIC) effort, which represents the agency’s newest development program, is aiming to cut the cost of some of the most complex and expensive elements of conventional “macro” CPV.
Late last month, President Obama and US Energy Secretary Ernest Moniz formally announced the projects at the Clean Energy Summit in Las Vegas. ARPA-E’s director Eileen Williams said at the time: “The MOSAIC program demonstrates ARPA-E’s novel approach to energy innovation. By bringing together cutting-edge advances in microfabrication, materials science and mechanical actuation, MOSAIC will create new options for solar generation and help make clean energy technologies even more affordable.”
Whether integration of concentration optics and tracking systems at the micro-scale will prove any more successful than the current macro-scale CPV technology remains to be seen, but the 11 projects to receive funding do include several high-profile laboratories – as well as commercial partners in the form of the US wings of Panasonic and Sharp, the University of Illinois John Rogers lab spin-out Semprius, and California’s Glint Photonics.
According to an ARPA-E factsheet detailing the 11 projects, the modules will typically incorporate thousands of tiny lenses to concentrate sunlight onto solar arrays.
“These micro-scale concentrated PV (micro-CPV) technologies will be integrated into ‘flat plate’ solar panels to improve their efficiency and cost,” writes the agency. “This micro-CPV approach addresses the constraints of conventional CPV, which, while highly efficient, has not been widely adopted due to its high cost, large size, and expensive solar tracking systems.”
The project teams are set to address those limitations with a variety of innovative materials, micro-scale manufacturing techniques, panel architectures, and tracking schemes.
Projects funded under the MOSAIC umbrella, which includes one Small Business Innovation Research (SBIR) award, are broadly grouped into three categories.
The first is for complete systems designed to integrate micro-CPV for sunny locations with high direct normal incident (DNI) solar radiation – the traditional target for existing CPV. However, other systems under development will be designed for less sunny regions with a lower DNI or a high level of diffuse solar radiation. The third project category looks to address “partial solutions” to specific technology challenges.
ARPA-E has awarded a total $6.5 million for the three projects working on high-DNI systems. Panasonic’s Boston Laboratory, which also works on laser technologies, is set to develop two micro-tracking sub-systems that can be mounted inside photovoltaic panels.
They will allow individual lenses to focus direct sunlight onto solar cells throughout the day, meaning that low-profile CPV systems could be positioned on rooftops. “This will deliver high efficiency concentrated solar photovoltaics without a cumbersome two-axis tilting system,” says the firm.
The Panasonic subsystems will be based on rows of lenslets tilted about their long axis, while a second axis rotates the array to keep each the optical axis of each lens parallel to the sun.
Lenslet arrays and planar light guides
Also working on high-DNI projects will be a team at Pennsylvania State University. They have received $2.9 million to work on a wide-angle planar micro-tracking cell.
“The team will use a combination of refractive and reflective plastic lenslet arrays to concentrate sunlight onto a corresponding array of micro-PV cells, which will be transfer-printed onto a transparent sheet that slides between them,” reports ARPA-E. The tracking element will be achieved by incrementally moving the middle microcell sheet laterally to follow the sun - allowing the system to operate throughout the entire day without tilting the panel.
A University of Rochester team is getting $1.5 million to develop its planar light guide system, which uses micro-optics to capture, orient, and concentrate direct sunlight onto a single PV cell, located on the edge of a module.
Said to be less than 3 mm thick, the lightweight system will be aimed at rooftops in urban areas if the development goes according to plan.
Six of the funded micro-CPV projects will work on systems and designs for areas with lower DNI that are not typically regarded as particularly suitable for CPV.
Sharing $14.8 million are university-led teams from the Massachusetts Institute of Technology (MIT), Caltech and Texas A&M, alongside Semprius and Sharp Laboratories of America – whose parent company Sharp is among the leading developers of high-efficiency multi-junction cells for CPV and satellite applications.
Semprius will work on a $2.9 million effort to make a hybrid system integrating two types of solar cells, including devices with an unprecedented six junctions to maximize efficiency.
The Durham, North Carolina, firm predicted: “The [Semprius] team will demonstrate the highest efficiency solar cells ever produced, with efficiencies projected to exceed 50 percent. Second, Semprius will redesign its standard concentrated PV (CPV) module to incorporate both ultra-high-efficiency CPV cells and medium-efficiency, low-cost, un-concentrated silicon cells.”
MIT won backing for two different projects – $3.5 million for a prismatic optical system that will split sunlight into different wavelengths, and $1.2 million to integrate wafer-level optics with silicon PV cells to better collect diffuse light.
Meanwhile Caltech researchers are getting $3 million to work on a luminescent concentrator “sheet” featuring quantum dots to convert high-energy photons into wavelengths more suited to existing PV cells. The Texas A&M team is set to develop a secondary concentrator element based on tapered waveguides.
Just one project was selected for the “partial technology solution” element of the MOSAIC program – with the team led by California’s Palo Alto Research Center (PARC). They will design and build a prototype printer said to have the potential to provide economic, high-volume manufacturing of micro-PV cell arrays.
Finally the Burlingame, California, start-up company Glint Photonics - founded by University of California, Santa Barbara-educated entrepreneur Peter Kozodoy - won the only SBIR award to feature under MOSAIC.
The firm gets $1.7 million to develop a stationary system that automatically moves a sheet of receivers within the panel to keep sunlight focused onto four-junction micro-CPV cells.
According to ARPA-E’s project factsheet this system will use a fluidic suspension mechanism for “frictionless” movement, as well as a novel drive process said to consume only a tiny fraction of the total solar energy received to ensure that the sheet remains aligned.