technology photovoltaics
in its prototype tracker systems that feature a 30 m2 array and are capable of generating about 7 kW. “The system efficiency is much more than 25 percent, which is a very good result,” says Haberland.
One of these systems is located on the edge of the University of Warwick Science Park, just a few hundred yards from the company offices. Having this so close by is invaluable for learning about how the tracking system behaves under load. However, it is not possible to gauge how well this CPV system will work in sunny climes. That’s because Coventry averages just over 4 hours of sunlight per day and has a mean maximum temperature over a year of less than 14 degrees C. In other words, it is rarely sunny, and even when the sun is out, it doesn’t beat down.
So to address the lack of suitable performance data, the company has two further test systems overseas: one in Cyprus; and another at University of Lisbon, Portugal.
“These two test fields in the sun-belt, in combination with the test field here, is good for us in making the next development step,” says Haberland.
The aim of the next step is to create the infrastructure for manufacturing, and prepare for the commercial launch of CPV systems. These will be assembled on site, using components manufactured by third parties to specifications set out by Circadian.
hoping to switch to a novel form of triple-junction cell. It has a major stake in research being carried out at Radboud University, Nijmegen, The Netherlands into the development of flexible, high-efficiency and lower-cost triple junction cells.
This effort focuses on the removal of triple junction cells from their substrates, which can then be re-used, leading to substantial cost savings. To separate the device from its substrate, a sacrificial AlAs layer is inserted beneath the solar stack and removed after growth by chemical etching. Before this processing step is applied, a 20 µm- thick copper layer is electroplated on top of the epitaxial structure to provide a highly conductive platform for the cells.
The researchers at the University of Radboud are making good progress, and can already produce cells on a 2-inch wafer. One of their next goals is to scale the process to 6- inch production. They might also look at the growth of inverted metamorphic structures, which are suited to this process and promise to enable improvements in cell conversion efficiencies of a few percent (see Compound Semiconductor October 2007, p.25).
Staying on track Circadian has employed conventional triple-junction cells 36
www.compoundsemiconductor.net July 2010
Up until recently, nearly all of the biggest deployments of CPV were at testing grounds, but genuine customer orders are just starting to trickle through. “There are signs that things are changing, and that’s good for us.”
One example of this change is the recent signing of a contract between Concentrix Solar and Chevron Technology Ventures for the deployment of a 1 MW power plant at a Chevron Mining facility in Questa, NM. And another positive sign is the recent completion of a solar power plant of that size built by SolFocus, which is providing clean power to Victor Valley College in Victorville, California.
Over the next year or so Circadian will focus on finding new premises, scaling up its manufacturing, and getting ready for market entry. Once that’s done, it should start to win orders in what should be a growing market for CPV.
“What we see – a rough estimate of course, because markets are difficult to forecast – is that in 2020 there will be about 20 GW of CPV installations in total, for both off- grid and on-grid applications,” says Haberland.
If Circadian Solar can tap into just a fraction of that business, then it should have a good future ahead of it.
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