NEWS ANALYSIS
Materials research thrives as Concentrated Photovoltaics industry stalls
As concentrated photovoltaic businesses soldier on, research into novel III-V devices is rife. Compound Semiconductor looks at what the future holds for the industry
JUST WHEN YOU THOUGHT the CPV industry was petering out, industry developments indicate otherwise. Although commercial front-runners, such as JDSU and Amonix, are scaling down operations, and GreenVolts has folded. Organisations lower down the business chain are seeing a surge in funds.
For example, the Climate Investment Fund recently extended its $7.6 billion award for the development of concentrated solar plants in MENA nations, to include CPV development.
At the same time, IBM Research and partners have bagged $2.4 million from the Swiss Commission for Technology to build an affordable version of a novel CPV set-up – the High Concentration PhotoVoltaic Thermal (HCPVT) system – that incorporates a thermal system to capture lost heat with water. IBM reckons recovering waste heat in this way will boost overall system efficiency to an admirable 80 percent.
But it’s not just large-scale projects edging towards commercialisation that are scooping cash. Recent months have seen a flurry of research grants awarded to materials scientists and physicists keen to hone the III-V semiconductors fundamental to the efficient and affordable operation of these photovoltaics.
For example, in April last year, the UK-based Engineering and Physical Sciences Research Council (EPSRC) dished out some £500,000 to a team led by Liverpool University researchers to develop nitride-based cells for use in CPV systems.
Meanwhile, researchers from the Universities of Manchester and Salford have just won some £880,000 to conduct theoretical work on InAs, GaAs and CsSe quantum dots for solar cells.
And only last month University College London and University of Bristol researchers won £950,000, again from the EPSRC, to fabricate III-V quantum dot solar cells on silicon substrates for CPV systems. UCL researchers will pioneer MBE growth and device fabrication while Bristol colleagues will perform modelling to optimise performance.
Huiyun Liu, a key researcher from the UCL branch of this III-V QD project has seen a steady rise in the number of solar-funded projects. “[Commercial] companies have been struggling, but my research group is not,” he says.
“Our track record is in lasers, but over the last year the funding I have received has been for solar research. We have seen a dramatic shift from laser to solar research, and definitely more interest from companies.”
As Liu highlights, his latest EPSRC- funded project is also supported by the UK government owned Defence Science and Technology Laboratory (DSTL), Wales-based IQE and UK-based Sharp Laboratories of Europe.
“We’ve also been talking to the French oil company, Total. They are interested in this area as they want to develop high efficiency, low cost solar cells,” he says. “Right now III-V solar cells are too expensive, but they have this high efficiency... the [companies] that have come to us all say the same thing; it’s not making money now but we have to try.”
Next generation cells When designing III-V CPV solar cells, most researchers have adopted a multi-junction structure, connecting a number of semiconductor junctions with optimised bandgaps in series to boost efficiency.
While research into nitride-based solar cells is well underway, many existing multi-junction cell structures have been based on GaAs layers. For example US-based Spire Semiconductor claimed record peak efficiencies of 42.3 percent with its CPV InGaAs/GaAs/InGaP cells, (bandgaps of 1.89/1.42/0.94eV
The prototype HCPVT system under development uses a large parabolic dish, made from a multitude of mirror facets, which is attached to a tracking system that determines the best angle based on the position of the sun. Once aligned, the sun’s rays reflect off the mirror onto several microchannel-liquid cooled receivers with triple junction photovoltaic chips -- each 1x1 centimeter chip can convert 200-250 watts, on average, over a typical eight hour day in a sunny region. The entire receiver combines hundreds of chips and provides 25 kilowatts of electrical power. The photovoltaic chips are mounted on microstructured layers that pipe liquid coolants within a few tens of micrometers off the chip to absorb the heat and draw it away 10 times more effective than with passive air cooling. Credit: IBM-Research
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www.compoundsemiconductor.net June 2013
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