Concentrated PV

CPV companies acknowledge that standard tests are important so that the industry gains experience internalising the relative performance of the various PV technologies as they relate to each other. PV Insider’s Ritesh Gupta explores the maturity level of testing in the CPV sector.

Standardising the way that CPV systems are rated and evaluated is a necessary step for the maturation of the CPV industry.

There needs to be a consistent method of performance evaluation among CPV providers and the difference between CPV technology and other photovoltaic technologies must be transparent and easily understood to potential customers.

CPV companies do acknowledge the need for such differentiation. Take the case of Suncore Photovoltaics. The company highlights that it provides the only CPV system designed specifically for use on rooftops.

“As a unique offering in the field of CPV, rooftop CPV systems are typically compared with respect to more traditional forms of PV.  Standard tests are important so that the industry gains experience internalising the relative performance of the various PV technologies as they relate to each other.  Test standards for CPV help us provide a consistent metric for our technology,” says the company’s Chief Scientist, Jim Foresi.

Current Status

Soitec highlights that within the IEC organisation there is a working group defining standards for the CPV industry. This international standard series establishes IEC requirements for evaluating CPV performance. The working group and thus the standards have progressed significantly in the last couple of months.

“Just recently the draft standard IEC 62670-2, that describes an on-sun, measurement-based method for determining the energy output and Performance Ratio for CPV arrays, assemblies and power plants, was submitted to the National Committees,” says Hansjoerg Lerchenmueller, Soitec’s senior vice president product strategy, Solar Division. He says, “At Soitec we are following all the respective released and draft IEC standards.”

Typically for acceptance testing, Soitec measures the produced energy over the test period following the IEC draft standard and compares the tested energy production with the modeled energy production based on PVsyst and measured metrological data.

WG7 brings together the majority of CPV providers and is making informed decisions on how best to evaluate and test CPV products.

“We need to establish practical evaluation methods that customers can understand and that do not alienate end users by making CPV seem more complicated or scientific than it needs to,” Foresi says.  

From Abengoa Solar’s perspective, its director business development - CPV Technologies, Iñigo Viani Desplats-Redier, says, “HCPV systems have been designed to comply with applicable international standards: that includes the module (IEC62108,IEC62688, UL8703), but also the tracker, a key component that up to today has no applicable standards; therefore, we apply some codes provided by related industries and building codes.”

He adds that, “At this point, it is important to mention that we have an extensive experience base on our solar concentrated power plants, already deployed with similar tracking systems.”

He further says, “There is a current effort in defining standards and specifications for energy rating, performance and quality assurance (in line with traditional PV technologies), and aim at providing the warranties project developers are after.”

Systems

Indoor flash test systems for CPV are still in the engineering phase.  There are a few companies that offer large area flash systems; however there are still advancements in spectral control and throughput that need to occur to make them well-suited for a production environment.  On-sun testing and data translation for CPV is well-established; however this is not an approach that can be used in production.

Foresi agrees and saysindoor flash test systems for CPV are available, but they still require engineering efforts to maintain and operate. He adds that these flash test systems differ from those used in the flat-plate photovoltaic industry as CPV flash testers need to provide direct normal sunlight and good uniformity of illumination over large areas.  These flash systems are being used in production to monitor variability and deviation of module production.

A number of other tests are run at various points along the production line to ensure that produced modules meet all of the required safety and reliability standards that have been developed for CPV.

With 20 years’ experience in solar tracking systems, the team at Abengoa works with advanced design and validation tools, which are common practice in other industrial sector.

“Failure Mode Analysis, computer simulations (temperature, structural design etc.) and wind tunnel testing simulations are some of our tools in our design process,” says Abengoa’s Iñigo. “On top of that we validate a pre-serial by prototyping, followed by climatic chamber tests as well as other indoor and outdoor testing and standards certifications are used as a common practice. That includes sand blast trials, a key parameter to be controlled in some areas as the GCC.

“In order to identify source of variability and deviation of performance, statistical process control is the tool of choice and it is being integrated in all aspects of our production and deployment. We define process capabilities not only in manufacturing areas but in technology performance in the field as well.”

Other components of control in the manufacturing process includes quality compliance agreements with components suppliers in addition to achieving 100 per cent for tests for the receiver, module solar simulator; module water tightness and module isolation.

Accuracy

Two-axis tracking systems for CPV have been around for years now. Assessing how well a tracker is performing requires an assessment of system output over time and in a variety of environmental conditions.  Closed-loop feedback tracking systems help to ensure that the tracker is always optimally pointed at the sun. The rooftop market demands closed loop tracking for installation.

Rooftops cannot be relied upon to be a solid foundation, and therefore, purely open loop tracking systems will drift as a rooftop expands and contracts daily, and sags over time.  It should be noted that with closed loop tracking there is also an opportunity to have a drop in place system where the only external connections are to an inverter.

When it comes to assessing the accuracy with which a CPV system can track the sun, Soitec CPV systems claims it can ensure precise tracking with a proprietary application and algorithm which position the tracker. Astronomical positioning is used and DC power output is monitored to calculate the next optimum position for maximum power generation.