San Diego's New CPV Solar Giant

Located on the tailings site of Chevron Mining Inc's (CMI) molybdenum mine in Questa, New Mexico, some 2000 metres above sea level in an area of the US noted for its high levels of Direct Normal Irradiance (DNI), its developers say the project will demonstrate the technology as well as a practical use of previously impacted land. Electricity produced from the installation will be sold to the Kit Carson Electric Cooperative, through a power purchase agreement.

Covering some 20 acres (8 ha) the site has 173 CPV modules, each of which has an area of about 18 by 21 feet (35 m²) and is pole mounted on dual axis trackers supplied by a major manufacturer. The Concentrix technology uses Fresnel lenses to concentrate sunlight almost 500 times onto high efficiency multi-junction PV cells. With this technology, Soitec claims to achieve AC system efficiencies of 25% and more, significantly higher than currently available conventional solar PV technology, and as a result, cost reductions of 10%-20% could be reached, depending on the location of the installation, it says.

Concentrix CPV modules at the 1 MW Questa installation (Source: Chevron)

Hansjoerg Lerchenmueller, founder of Concentrix and now senior VP Customer Group at Soitec, explains to REW that the system uses a relatively simple architecture, with a Fresnel lens and no secondary optics, and while this does make for ease of manufacture, it also implies a low acceptance angle, hence the need for extremely accurate tracking. Lerchenmueller adds that by developing the inverter system too, in a single unit the company has combined the three functions of DC/AC conversion; tracker control, in which the system achieves very high accuracy using system output as a controlling input; and output monitoring, remotely or otherwise.

'The "sweet spot" for CPV is really 20-200 MW, where there is a real commercial gain' says Lerchenmueller, adding that the Chevron plant is a 'very, very important milestone'. 'This is a real power plant,' he says. 'We have been installing power plants since 2008 and we are making tremendous progress both in terms of power plant efficiency and installation time, which fell dramatically with the 170-unit system.'

Through 2008 and 2009 the company had installed systems in Seville and Puertollano, Spain, of 100, 200 and 300 kW, he adds. In 2010 the company installed overall close to 2 MW of capacity with projects or demo installations in more than 10 countries including the US, Spain, South Africa, Italy, Egypt, Jordan and France. 'We have demonstrable longevity on the field, with three years' experience and no evidence of performance degradation in that time,' says Lerchenmueller, adding that the modules have an anticipated 25-year operational lifespan. 'We're really at the point where we can take off at the real power plant level,' he concludes. Soitec achieved International Electrotechnical Commission (IEC) certification 62108 for its CX-75 module in January 2010.

Large Scale Development

With the project at Questa underway, and perhaps more significant in terms of the roll-out of the technology, Soitec also recently announced that its CPV technology had been selected by Tenaska Solar Ventures for a 150 MW power plant near San Diego, California.

Imperial Solar Energy Center (ISEC) West will be constructed on a 1057 acre (427 ha) site in Southern California's western Imperial County. Delivery of the CPV systems to the ISEC West plant is due to begin in early 2013 and is expected to be completed in 2015.

Furthermore, to support the project, Soitec revealed plans to build a new manufacturing facility in the region that will be able to produce some 200 MW of modules annually once fully ramped up. Modules from this factory will be used to supply ISEC West as well as other utility-scale solar power projects throughout the Southwest US and elsewhere. The factory location is anticipated to be announced in summer 2011, with completion expected within 18 months of the start of construction. Currently, Soitec operates a fully automated industrial production line for Concentrix technology modules with an annual production capacity of 25 MW, located in Freiburg, Germany.

Utility group San Diego Gas & Electric (SDG&E) has already signed a 25-year power-purchase agreement with a subsidiary of CSOLAR Development, LLC, a renewable energy company managed by Tenaska Solar Ventures that will develop and operate the plant, for the output from the ISEC West plant.

Chevron's molybdenum mine tailings site in New Mexico offers an ideal climate for CPV generation

Commenting on the development of local transmission infrastructure and its impact on renewable energy projects in the region, James Avery, SDG&E's senior vice president of power supply, said: 'The start of construction of the Sunrise Powerlink has triggered a wave of proposed new utility-scale solar and wind projects in the Imperial Valley region.'

The ISEC West project has applied for a US DOE loan guarantee. Upon receipt of the guarantee and closing of its agreement with Tenaska, Soitec will implement capacity investments to construct its San Diego area factory and pursue options for related financing, it says in a statement.

In April 2011, SDG&E announced the signing of three further contracts with Soitec for CPV power plants with a combined capacity of 30 MW. As with ISEC West, the modules will again be manufactured in the new factory. Soitec's delivery of the CPV systems for these three new solar energy facilities in San Diego County will begin in 2013 and finish in 2014, given relevant approvals from the California Public Utilities Commission. No loan guarantee is required for these projects.

Dave Fiorelli, president of Tenaska's Development Group, adds: 'The ISEC West solar power plant will demonstrate Concentrix CPV scalability, and commercial viability of this innovative technology for utility scale deployment.'

CPV's Geographical Advantage

CPV systems are typically more efficient than conventional solar systems at locations with both high ambient temperatures and dry weather conditions. Because of the very low temperature coefficient of its solar cells, a CPV system's performance is much less affected by temperature than other photovoltaic technologies. Another key advantage of CPV technology is the very low levels of water required for operations, essentially used in cleaning only, a crucial consideration for the water-constrained regions to which it is suited, such as the Imperial Valley, which is some 150 miles (230 km) from the coast.

Indeed, such technology is expected to work best in areas with higher DNI like northern New Mexico and southern California, as well as in north and southern Africa, the Middle East, and much of China and India. Certainly, in 2010 Soitec announced that it had joined the Desertec Industrial Initiative (Dii) as Associated Partner and Medgrid as a founding member, in the expectation that the decision will pave the way to utility-scale CPV projects in the Middle East and North Africa (MENA).

Soitec, which produces high-performance materials for the semiconductor industry, including substrates for SOI (Silicon-on-Insulator) and CPV systems, among other applications, acquired Concentrix Solar GmbH in late 2009, valuing the company at some €55 million. With the acquisition of Concentrix Solar, originally a 2005 spinout from the Fraunhofer ISE, Soitec also signed a strategic technology alliance with both the Fraunhofer ISE and the research institute CEA-Leti. This agreement included a long-term licence agreement related to the manufacturing of concentrator cells. They plan to jointly develop the next generation of very high efficiency CPV solar cells based on Soitec's proprietary technologies, significantly improving CPV system performance.

Lerchenmueller explains the company's push to improve efficiency with Soitec's Smart Cut technology. 'By peeling off thin layers of semiconductor materials and mechanical stacking of the layers we are less restricted in the selection of the semiconductor materials and get to less defects,' he says. 'We have 28% module efficiency currently and expect to achieve 30% this year, and more still in coming years. On the cell level we are aiming for 50%.'

In October last year, Soitec also concluded a global alliance with Johnson Controls for the development and construction of utility-scale solar energy facilities. Under the terms of the alliance, Johnson Controls will build, operate, maintain and provide lifecycle support for solar installations using Concentrix CPV technology.

Lerchenmueller sums up: 'The key future market is utility-scale, not MW- but GW-scale. We're going to need a lot of inexpensive renewable energy over the coming years. To achieve that we need to go to where there is lots of sun and we need to go for big economies of scale.' He estimates this 'sweet spot' will be a market worth some $2 billion annually.