CPV Technologies in the US and Globally
Research on concentrating photovoltaics began in earnest in the 1970s, but development of the technology has been slow. In the last few years, however, cell costs have come down and a renewed interest in CPV has emerged with several new companies developing CPV products. It is only within the last couple of years that CPV has started to reach commercial viability, although the technology is still in the early commercial stages. Most of the companies working on CPV technologies are young companies, though some larger companies are interested in CPV. Many established companies that focused on making high efficiency cells for space applications are now developing products for terrestrial CPV systems.
CPV Companies
Over time several companies have worked on CPV technologies, although few of them have persisted to produce commercial products. Recently, many more companies have formed or entered the market, and are at various stages of product commercialization. Most of the companies are start-ups, and over time some have become more established, and established companies are adding CPV to their existing business.
The technologies fall into three general categories: low concentration, medium concentration, and high concentration. SolFocus (http://www.solfocus.com/) provides an example of a high concentration CPV technology. Other companies also targeting this market tend to use a 500 suns concentrator although the surveyed companies are split between the use of reflective surfaces and refractive lenses.
The following list, which is in no particular order, includes both companies with technology very similar to SolFocus, as well as other companies who may not be considered direct competitors. The nature of emerging markets means that the companies involved are evolving. Therefore, this list is subject to change, and is not intended to be exhaustive.
Reflective
  • GreenVolts
  • SolTec
  • Cool Earth Solar
Refractive
  • Concentrix
  • Amonix
  • Opel Solar
  • Energy Innovations (Sunflower)
Some may also be familiar with solar thermal systems, which make use of solar energy to create heat to generate power through turbines. However, many still do not see solar energy as viable alternatives to produce electricity due to high start-up costs and other issues related to the manufacture and use of photovoltaic panels.
A new technology is emerging that will change all that. Called concentrated or concentrating photovoltaic (CPV) technology, the system makes use of lenses or mirrors to concentrate solar energy onto tiny solar cells that are highly efficient in converting solar energy into electricity. Such arrangement is meant to address the number one problem with the use solar PV systems – the expensive silicon-based solar panel.
Although many journals have already reported significant claims on how effective this technology is on a laboratory setting, the challenge remains on whether this technology will be viable in the commercial market. “Because no standardized product has been rolled out and tested at large volume, banks are extremely unwilling to provide debt for projects using CPV equipment — even if they were cheaper than crystalline silicon,” wrote Jenny Chase, manager of Solar Insight at Bloomberg New Energy Finance, in an email. “This is a huge nontechnical barrier to market penetration — difficult to overcome without a strong strategic partner to back the product with warranty and brand name.”
CPV panel efficiency considers the panels as a whole and is much lower than cell efficiency. Efficient CPV panels can reach 25%, which is typically twice the efficiency of traditional PV cells. As this efficiency increases the cost for harnessing solar energy decreases resulting to less raw materials required, lower manufacturing costs and reduced land utilization.
Some of the additional benefits that can be realized with the use of concentrated photovoltaic solar panel technologies include:
  • Dual Land Use: CPV panels are mounted on elevated tracking systems which can allow utilization of the land underneath for planting crops.
  • 95% Recyclable: unlike traditional PV panels, CPVs use glass and aluminum as their two main materials which can then be recycled. Useful life of solar panels is typically 30 years.
  • Auto Industry Model: the manufacture of CPV panels makes use of automated manufacturing systems similar to the very stringent auto industry. This manufacturability makes it more cost-effective than traditional solar panels.
General overview of CPV applications
Because CPV systems require that the light incident on the reflector has a direct trajectory from the sun, rather than being scattered by clouds before reaching the optical input, their preferred range of deployment targets regions with a Direct Normal Insolation (DNI)1 of 6 kWh/m2/day or higher. In the USA , these regions are located in the Southwest. CPV systems track the sun on dual-axis trackers in order to collect DNI. Due to tracking, CPV systems will generation more energy than a fixed tilt system. The design approach to CPV is to outweigh the additional costs with the increased energy output.
Reliability in the solar industry boils down to lifetime in the field and degradation. CPV technologies have a higher bar to hurdle in terms of reliability, as compared to flat plate PV technologies. One major reason for this hurdle is the concentration factor which increases the need for thermal management and proper tracking. Some other phenomena to consider include organics accumulating on the inside of the glass and optical losses. In a sense CPV technologies must pass all the qualification testing for a standard flat plate, plus additional testing.
Volatility of Direct Normal Insolation (Inter-Annual Variability)
Direct normal insolation (DNI), the solar resource which arrives directly from the sun and is the only useful input for most concentrating technologies, will be more volatile than global insolation, which includes DNI and scattered light. During periods of heavy clouds, no DNI is available since all solar energy is scattered or reflected back into space. Aerosols in the atmosphere reduce DNI by scattering solar energy into diffuse insolation. Because global insolation includes direct and diffuse insolation, the variability from year to year is less affected by clouds or haze. DNI, however, is significantly affected by clouds and haze, the occurrence of which varies from year to year.
SolFocus and Palo Alto Water
The system at Palo Alto Water consists of several trackers, one of which is a SF- 1100. The systems are located in Palo Alto , California , in the San Francisco Bay Area. The SF-1100 array has been operating since June of 2009, and had produced over 250 kWh by the end of September 2009. The performance was assessed when all energy, DNI and temperature data were accurately recorded, which was 82 percent of the daylight hours between June and September [1].
The figure below shows the cumulative average daily production of the system through the end of September 2009.
Figure 1-1. Palo Alto Water Production to date. Figure 1-1. Palo Alto Water Production to date.
Performance ratio is a measure of the system’s ability to convert sunlight to power. While its definition is not uniformly accepted across the industry, it is generally the ratio of the actual energy received at the AC tie point, to the estimated energy at the DC feed. This means that modeling errors, DC losses, inverter efficiencies and AC losses will all affect the performance ratio, which is commonly found between 80% and 95%. Figure 1-2 below shows the performance ratio of the system over time.
Figure  1.2 PAW Performance Ratio. Figure 1.2 PAW Performance Ratio.
The following figure, Figure 1-3, shows SolFocus’ performance ratio analysis. The performance ratio of the system between June 1 and September 29 was stated to be 89.6 percent, while SolFocus found this to be 90.0 percent. The difference in performance ratio values is a result of the time step chosen and DNI filtering as described above. The system performance appeared reasonable and in line with expectations.
Figure 1-3. PAW Performance Ratio Calculated by SolFocus. Figure 1-3. PAW Performance Ratio Calculated by SolFocus.
Key Findings
The SF-1100 tracker at PAW performed as expected. The performance ratio appears reasonable and the production profiles are as expected. As expected, sunny days have a smooth production profile with a quick ramp up and down as the sun rises and sets. Also as expected with CPV systems, the SF- 1100 is significantly affected by cloudy days as the technology relies on DNI.
SolFocus design strategy appears to have been well implemented. Their technology can be manufactured with relatively low technology processes, is simple to install, appears reliable, and is high performance. The acceptance angle of the product allows for flexibility in both manufacturing and operation of the product, and should support strong field performance.
SolFocus has developed a quality control organization and quality assurance process, and Black & Veatch believes that SolFocus will be able to achieve a high level of quality and consistency in its product. SolFocus has a comprehensive testing process for each component and for the completed subsystems, such as modules and trackers.
SolFocus relies on a number of contract manufacturers and has a skilled and experienced team managing its supply chain. SolFocus has detailed processes and procedures for qualifying and monitoring its suppliers.
Author Bio
Michael Vargas is the founder and principal consultant of Atlas Project Support. Mr. Vargas has more than 10 years of construction and energy accounting and utilization experience, and is a Certified Business Energy Professional through the AEE, a California Energy Commission Certified Energy Plans Examiner, LEED Green Associate and GBCI Advisory Panel Member. . Mr. Vargas also holds a BSBA from SDSU, MBA and MPM from Keller Graduate School and is currently pursuing his Doctorate of Business Administration at Alliant International. For more information contact Michael at mvargas@myatlasproject.com or via the web at www.myatlasproject.com.
 
[1] The system was down for 3% of the time for test engineering and marketing reasons. Energy data was unavailable from 6/29 until 7/2 due to data logging issues, and reliable DNI information was unavailable from 8/8 until 8/20 due to localized dirt on the NIP. These data points were not included in the analysis.