By Susan Kraemer

The new awards, under the Full-Spectrum Optimized Conversion and Utilization of Sunlight (FOCUS) program, might spin-off a new form of CSP that can work in diffuse light. Or perhaps to a solar drone able to approach the sun and not lose power in the heat.

“We're supposed to really swing for the fences,” ARPA E Acting Director Cheryl Martin told EENews TV in March. “We ask all the bright minds across America to come up with ideas on how to get that. And we'll select maybe 10 to 12 ideas going after that same objective.”

Once a project has received ARPA E funding, milestones must be met every quarter over the three-year funding period, where ARPA E meets with the awardees to look at how they are doing.

Arizona State University (ASU), with an award of $2,640,122, will develop a curved mirror - as if for CSP - but made of solar cells so that it can collect both direct and diffuse light.

“ARPA E were looking for proposals for how to goose the efficiency of CSP by adding photovoltaics. FOCUS is all about how to make CSP more competitive by combining higher efficiency conversion,” says University of Arizona telescope optics genius, Dr. Roger Angel.

His team at the University of Arizona is providing support to the ASU researchers led by Zach Holman, assistant professor in the School of Electrical, Computer and Energy Engineering.

A prescient conversation

Last year, Angel had discussed with CSP Today a possible marriage between CSP and CPV.

“If you can take everything that CSP has learned about tracking and mirrors, but simply switch what happens at the focus to CPV, then maybe you have a chance to get the best of both worlds,” he said last year. 

“What interests me is actually an area midway between CSP and CPV – in the sense that in the past CSP people have been using big mirrors and CPV have used little optics - so one thing that my group and my company REhnu is doing is looking at the bridge between those two.”

Angel is no stranger to such “bright minds” awards. From producing the $25 million dollar astronomy telescope that took four years to build, when we spoke last year, he was meeting milestones set by the DOE Sunshot program in devising a way to turn out a perfect parabolic mirror every twenty seconds at a cost of $85 each in his lab.

The FOCUS award that he is supporting at ASU will entail making a curved mirror too, but using PV cells in the mirror, so that it can also capture diffuse light.

Expands geographic reach of CSP

“Even in Tucson, where you have pretty high DNI, there’s still enough cloud about that if you can make use of that as well, that’s good. About 25 to 30 percent of the total light energy in Tucson is cloudy: diffuse, not direct,” Angel points out.

“So this widens the reach, because you can be more effective in higher cloud regions. It also increases the efficiency, because you’re actually making use of that light.”

He sees room for improvement in CSP efficiency. “There’s a skeleton in the closet; CSP doesn’t make use of all the light that is available,” he says.

“CSP completely misses 25 to 30 percent of the energy that PV panels can use because it’s not direct incidence from the sun, but diffuse light from the rest of the sky. The biggest component of diffuse light is from clouds; that’s why PV works in Germany.”

Endorsement of CSP-CPV

One firm is already commercially straddling this intersection between CSP and CPV: Cogenra is one of the 12 recipients of the FOCUS awards.

“We see this award and the FOCUS program as an endorsement of the path we had taken; to design a high-efficiency PV system that can also capture the heat for additional stored on-demand solar power,” says Dr. Mani Thothadri, VP of Product Management at Cogenra.

The ARPA E award of $1,996,127 to Cogenra will help advance their state-of-the-art CPV system, the T14. It produces electricity with concentrated PV, but is able to also capture heat at up to 120 °C in its parabolic mirror trough.

“It’s basically the next generation version of our T14,” says Thothadri. “We will be working to drive the up temperature that we collect at, to almost 300 degrees Celsius.” In part this will be done by shielding the PV from the high temperatures.

“Traditionally the difficulty has been operating photovoltaics at very high temperatures, and making them operate efficiently at these very high temperatures,” says Thothadri. “Up till now we used silicon-based cells.”

Silicon can handle this temperature, but performance degrades at half a percent every degree Celsius above STC. Newer hetero-junction cells that are now coming out have a much better temperature performance at 120 °C, but ARPA E is looking for performance at even higher temperatures still for these crossover applications.

High temperature operation

Several of the FOCUS awards are looking for PV to withstand temperatures as high as 400 °C. Double-Focus Hybrid Solar Energy System with Full Spectrum Utilization’ – will extend Cogenra’s existing low temperature storage solution to higher temperature CSP operation.

Cogenra’s high-efficiency PV cells will generate electricity and IR wavelengths will be harnessed to generate high-temperature heat, which can be stored and converted to electricity on-demand with a steam turbine.
“We will be working on spectral filtering optics,” Thothadri says. “So that in a cost-effective way we can avoid putting PV into the 300 °C temperature regimes. We capture the PV at a much lower temperature, but use a kind of spectral splitting”

Launched only in 2009 with funding by the Obama administration, ARPA E is already starting to see signs of success, with 24 startups formed from early-stage technologies like those receiving funding.

Solar industry insiders have previously commented that “the ARPA E folks are very sophisticated; industry professionals both in CSP and in PV.” And clearly not afraid to make far-out bets.

Many former awardees have gone on to partner with other agencies or other DOE programs to build pilot projects needed for commercial viability. Private financing now runs at around 6 to 1 in commercial investment versus DOE funding.

“You're managing risk across a whole bunch of projects in an area of high importance, and so we know they won't all work,” Martin said. “Science will get in the way. But it's actually, I think, a really effective way of getting a lot of thought in an area.”

To comment on this article, please contact the author, Susan Kraemer.