Amonix, Solar Junction Plot CPV Efficiency Gains, Lower Costs

Last October Solar Junction topped 44 percent efficiency with its multijunction solar cells. Amonix set the top market for a CPV module in May 2012 at 33.5 percent, using ~40 percent efficient cells supplied by Spectrolab. Putting the two together will push the end efficiency significantly higher, they believe, which is the key to reducing total system costs over time. And that is CPV's real selling point over other solar PV technologies: despite higher upfront costs, it makes up for that with lower LCOE over the system's lifetime.

This new agreement lets the companies formally open their process IP playbooks and determine how much more efficiency their combined technology would achieve, and where those refinements can be made. Most areas of CPV are pretty well maximized, explained Pat McCullough, Amonix's CEO: cell/module architecture, thermal diffusion, tracking systems, and general geometry. "We think it's managing the recipe and their process to make and tune the cell," he said, "and maybe optimize the optics to fuller utilize the cell's capability."

Amonix also likes that Solar Junction's target sunlight concentration is around the same that it uses (900-1000×), which they believe is the optimal level balancing cost, efficiency, and long-term reliability, McCullough said. Higher levels of concentration (up to 2000x) is not cost-effective, and lower levels of concentration don't squeeze out enough efficiency per surface area.

As the current CPV leader in active CPV installations, Amonix feels a duty to "facilitate development of all cell companies and work with the best ones," McCullough said. A robust cell industry should foster an efficiency arms-race among CPV cell providers, which will ultimately raise the efficiency bar and ultimately improve the economics and pricing for the entire CPV system.

Some small gains can be made in terms of materials, optics, or in ramping economies-of-scale and standardizing processes. But the real gains will come from continuing to raise conversion efficiency, where CPV has a lot more headroom than other solar PV technologies, points out Ed Cahill from Lux Research. Higher conversion efficiency means more output in a given surface area, and that reduces the cost of everything else, from modules to tracking systems to operations/maintenance. Ratcheting CPV module efficiency from 30 percent to a projected 35 percent by 2017, he says, would chop a current $2.95/W down to $2.29/W. Other solar PV technologies are now around, or slightly below, $2/W — but "we don't have to get all the way down to where silicon is," he says, "just close enough where it's worthwhile."

Lead image: Bar graph and ladder, via Shutterstock