Experts highlight that HCPV is at the beginning of the learning curve with a big potential for improvement

One of the key elements of a CPV system is the optical system that focuses a large area of sunlight onto each cell.

CPV solar arrays utilise 2-axis sun tracking systems to capture more of the available sun energy. The high energy output from a more efficient system, and the savings in costly semiconductor area make the application of CPV technology economically advantageous.


The proponents of this technology are counting on the fact that as Concentrator PV arrays advance their projected learning curve in terms of high volume manufacturing and increased cell efficiency, this technology will continue to dramatically reduce the cost of generating electricity from solar energy.

According to Gustavo Nofuentes, Professor of Electronic Engineering applied to PV- IDEA Group - University of Jan, Spain, the complexity of the required highly precise tracking system, brought together with maintenance procedures, has traditionally prevented the implementation of CPV small arrays, which would not benefit from the potential cost reduction that is inherent in larger CPV systems.

"Despite these considerations, some smaller and flatter designs are becoming available in the present market. Anyway, the potential for achieving cost reductions through scale justifies the expenditure in complex tracking systems in a life-cycle cost approach," said Nofuentes, speaking to CPVToday.com ahead of 2nd Concentrated Photovoltaic Summit, to be held on 28-29 April in Toledo, Spain.

Advantages of concentrating

The use of concentration allows substitution of cost-effective materials such as lenses and mirrors.

The focus is on concentrating the sunlight onto a very small, highly efficient multi-junction solar cell by using optical lenses and mirrors. Besides reducing the consumption of PV materials, the concentrator approach allows for entering the domain of highly efficient multi-junction cells.

One of the main advantage is related to cost. Area for area, optics in a concentrator system are less expensive than the photovoltaic cell. The basic concept is that if the amount of cell area per unit can be reduced, then the overall cost of the system will drop.

It is pointed out that under 500-sun concentration, 1 cm2 of solar cell area produces the same electricity as 500 cm2 would, without concentration. This is particularly significant when considering the inherent efficiency advantage of the multi-junction technology over Silicon solar cells.

The other main advantage is related to manufacturability and reliability. Concentrating systems are mechanical assemblies, and can make use of inexpensive, field-proven materials and manufacturing techniques, such as are used in the automotive and disk drive industries. By using common materials such as glass and aluminum for the bulk of a system, and much less solar cell material, concentrator systems are less susceptible to supply constraints of specialised materials such as PV cells, making the technology highly scalable to large volumes of production.

There are two main types of concentrating optical systems - refractive types that use Fresnel lenses, and reflective systems that use one or more mirrors.

Fresnel Lenses are refractive optical elements where the local slope of the surface is decoupled from the global shape of the lens.

Companies like Concentrator Optics GmbH offer the design, prototyping, testing and manufacturing of Fresnel lens parquets exceeding an area of 1 m. (In September last year, Capricorn Venture Partners, a pan-European manager of venture capital funds, had invested in Concentrator Optics to help the German company in building a manufacturing plant to produce solar Fresnel lenses up to a capacity of 100 MW in Marburg. That time it was indicated that the market for solar Fresnel lenses is estimated to reach 200 million in 2011).

It is believed that Fresnel Lenses offer a degree of freedom needed for a prescribed irradiance distribution on the target.

The reflective lens uses an array of concave, spaced apart reflectors inclined at relatively sharp angles with respect to the incident sunlight. Each element in the array is designed to reflect the corresponding portion of the incident radiation downward through the space between itself and an adjacent reflector and direct it to a common focus.

Challenges

Over the years, it has been acknowledged that the requirement of higher concentrations puts excessive pressure on the lens design since the concentrating ability of Fresnel lenses is constrained by the fundamental limits of refractive optics. As a result, further advancements of Fresnel lens technology are typically relying on secondary concentrators which reduce the overall optical efficiency while the performance still remains capped at lower than desired concentration levels.


According to Juan Carlos Miano and Pablo Bentez from LPI, who are going to present on `How new optical concepts & designs affect efficiency', scheduled as part of of 2nd Concentrated Photovoltaic Summit, to be held on 28-29 April in Toledo, Spain, point out that the time evolution of efficiencies and cost shows that HCPV is at the beginning of the learning curve with a big potential for improvements.

The duo from LPI, an optical design, prototyping and manufacturing firm, believe that for HCPV to succeed, there is requirement of high efficiency, sufficient high concentration and as much tolerance as possible; the best Efficiency-Concentration-Tolerance is being achieved by Advanced Optics; Scaling-up HCPV will need the synergy with present high- throughput low-cost industries (such as automotive or solid state lighting).

Going forward, the start-up companies also believe that by bridging the gaps of knowledge by exchanging of academic research results and experiences in the field, they can move closer to understanding the issues in the forerun of the first commercial concentrating photovoltaic power plants.


2nd Concentrated Photovoltaic Summit

A session, titled `How new optical concepts & designs affect efficiency', will be conducted as part of the 2nd Concentrated Photovoltaic Summit , to be held on 28-29 April in Toledo, Spain.

For more information, click here: http://www.cpvtoday.com/eu09/programme.shtml or contact Beln Gallego by email belen@cpvtoday.com

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