Concentrated PV

While LCPV producers strive to match the costs of their technology to flat-plate PV and reduce the amount of silicon used in panels, HCPV companies are looking for ways to drive down upfront costs brought about by the use of components such as dual-axis trackers and multi-junction cells.

By Heba Hashem

Attractiveness scale

Both LCPV and HCPV are finding their way into new markets, albeit in different applications. Last year, Soitec opened an HCPV manufacturing facility in San Diego, while Semprius launched its first HCPV production plant in North Carolina.

“We completed our pilot production line and began shipping commercially. We also set the record for production module efficiency at 33.9%, and we completed the development and testing of several commercial-scale systems ranging from 14kW to 24.5kW each,” Russel Kanjorski, vice president of business development at Semprius tells PV Insider.

“Finally, we announced our first commercial-scale project with Aerojet Rocketdyne (formerly Pratt & Whitney Rocketdyne) which will be completed in early 2014,” he adds.

HCPV pioneer Amonix is also making tremendous advancements, having recently demonstrated an NREL-verified 35% outdoor rated CPV module, which surpasses its own previous record of 34.2%.

According to Kanjorski, HCPV modules are best suited for commercial- and utility-scale applications in high-DNI regions, where their energy yield has advantages versus other technologies are most pronounced, and where the delivered LCOE is the most attractive.

Amonix founder and chief technology officer, Vahan Garboushian, shares a similar view: “Utility-scale applications in high-DNI and very hot environments [would be better served by HCPV)],” he tells PV Insider.

LCPV does stand out with several advantages, such as its ability to reach high efficiencies even with diffuse irradiance, and its utilisation of less expensive and widely proven silicon solar cells.

“LCPV will perform better in any location that has less than absolutely perfectly clear skies. This is because of the capability to capture a good part of the diffuse light. In addition, because of the relative costs, modules utilizing Banyan’s optics will yield a lower cost of electricity than HCPV in virtually any location,” explains Rusty Schmit, president and CEO of Banyan Energy.

But HCPV is already catching up. “HCPV inculcates two axis tracking for low diffuse environments, and it has one third temperature coefficient than silicon has, thereby producing higher energy than silicon-based systems,” notes Garboushian.

He points out that there are several issues associated with LCPV: “Single axis LCPV is not as efficient as flat-plate single-axis, and significant amount of the diffuse is still lost - only some is concentrated. Optical efficiency of some LCPV reflective systems is even lower than flat plate.” Leveraging the silicon industry, he adds, is not a clear advantage as the cells are custom made both in geometry and design.

The efficiency race

Today, HCPV has succeeded in reaching a cell efficiency of nearly 40% and going towards 50%. At the same time, a 15% improvement is forecasted in HCPV module and optical losses, resulting in more than 40% in overall system efficiency improvement, according to Garbousian.

In comparison, LCPV cell efficiency currently ranges from 22% to 24%, with about 10% improvement expected in the near future.  This is because of the limitation of first and second generation solar cells, and the theoretical limit to the maximum efficiency that can be reached with a single junction cell.

Innovations to solve this issue are now emerging. Banyan’s proprietary OptiWave technology promises to increase the electrical output of each solar cell by 5 to 10 times; reducing the number of cells in each module by 80-90%. This should enable LCPV manufacturers to produce modules with high power output using a fraction of the amount of cells.

OptiWave’s concentration range of 5 to 10 times also results in an economic advantage over lower 2 to 3 times-concentration products – without any significant heating problems that 20-times-and-above concentrators have, as Schmit reveals.

“The optics have a much lower profile than any other 5-10-times concentration system because of the unique waveguide technology. This enables the finished module to have the same size and shape – including depth – as a standard flat module, so the installation can be performed using the same methods and hardware that are used with standard modules,” says Schmit. This means that system designers would not have to do anything differently than they would with standard modules.

Essentially, Banyan’s optics are added on to a standard laminate, so the product can be easily incorporated into a standard module production line. At the end of the production, just prior to framing, the optics are incorporated, giving manufacturers the flexibility to produce either standard modules or modules using Banyan’s technology.

Most importantly, no significant capital investment is required for specialised equipment, says Schmit. “Because the optics are added to standard laminate, the reliability is already proven. The bankability will be readily demonstrated.”

Banyan’s business model is to license and provide the optics to module manufacturers, rather than produce the module itself. “This enables economies of scale to be achieved almost immediately, and bankability is much easier with the backing of large manufacturers”. The company has already begun field testing modules and shipping samples to customers, and reliability has proven to be quite good so far.

“I have been working in the PV industry since 1980, and my first job was on a development project for a 70X concentrator at Motorola. After a year of that, I was convinced that concentration of any kind was too complicated to capture any significant market share. That opinion did not change until I was introduced to Banyan’s technology,” explains Schmit.

LCPV progress

Other firms in the LCPV arena are also witnessing considerable growth. Last May, LCPV manufacturer Solaria Corporation established operations in China, where it has several megawatt-size solar plants under construction, and where it is currently promoting its STS-AZ Azimuth Tracking System – a ground mounted, single-axis vertical tracker that enhances PV energy production.

The STS-AZ is the same system installed at the U.S. Army’s White Sands Missile Range in New Mexico, which in January became the world’s largest LCPV project at 4.1 MW. Solaria is now constructing more than 1,000 MW of PV tracking projects globally.

HCPV progress

Meanwhile, HCPV firms are balancing their higher costs and restriction to high-DNI climates with their superior cell efficiency, fast installation turnaround, and lower land usage that results in more kWh per acre.

For example, Amonix HCPV modules – the largest in the world at 10kW each – are designed to allow non-sophisticated manufacturing for 80% of the system, where difficult field alignment is brought to the automated and controlled environment of the factory.

The company’s module is the only one to have been deployed in volumes above several megawatts, with nearly 80 MW of Amonix systems installed in the U.S. and Spain, including the world’s largest HCPV plant in Alamosa, Colorado – a 30 MW project developed, owned, and operated by Cogentrix Energy.

When it comes to cost reductions in HCPV, some of the factors enabling Semprius to drive down expenses include the substrate reuse of expensive semiconductor source wafers; the use of thin-module design cutting material; and the high concentration (1,111x) that reduces semiconductor use and cell costs. In addition, low-cost, high-performance optics, and standard, low-cost manufacturing borrowed from the microelectronics industry are contributing to its cost savings.

Semprius uses the world’s smallest solar cell to create modules with significant cost and performance advantages, due to the company’s proprietary micro-transfer printing process.

Other HCPV leaders are also making remarkable progress. In recent weeks, Isofoton’s modules and cells were certified as European-made by LCIE Bureau Veritas, placing the HCPV manufacturer among the first companies worldwide to obtain this certification. This qualifies the Spanish company’s products to benefit from the 10% French feed-in-tariff approved in January 2013.

And while LCPV manufacturer Solaria is expanding into China, Chinese HCPV producer Suntrix plans to expand into North and South America.

Suntrix produces ground-mounted HCPV systems for utility-scale projects, and is the only HCPV supplier that has the technology to produce the Fresnel lens in-house.

“Our modules have a wider acceptance angle, which allows the panels to perform correctly even if the tracker is shaking because of the wind. Another advantage is brought by the industrialized process of construction. SMC panels with uniform molds limit human intervention and any possible errors,” explains Andrea Antronaco, international marketing manager at Suntrix.

“An LCPV panel is still silicon-based”, he says. “Not only will it age faster and lose performance over the years, but excessive heat on an LCPV panel from external temperature and from the concentration itself will lead to heat drop effect so the panel will lose efficiency. On an HCPV panel, the increase of the temperature will result in a farther less drop in efficiency.”

Overcoming challenges

The question remains: what issues will HCPV and LCPV have to overcome to increase their market share?

“LCPV manufacturers must demonstrate low cost and reliability to be accepted in the market. Most LCPV technologies have a difficult time to do this because the cost is demonstrably higher, and/or the system is more complex and ‘different’ than a standard system – especially parabolic trough technologies,” Schmit highlights.

In the meantime, HCPV manufacturers will have to continue lowering costs and increasing efficiency – a major lever to reduce module and system costs – while scaling rapidly. “On the mere technological side, lots can be done by improving optics and cell efficiency, which have a wide space for improvement,” says Antronaco.

As wide apart as the two technologies may be in their concentration levels, proving bankability and raising cell efficiency seem to be the main challenges. But with a few players dominating each market, competition is likely to remain intense until major advancements are made.