Challenges and Opportunities in Concentrating Photovoltaic Research
Figure 3: Curtain Wall – A Building-integrated Photovoltaic Application of a Pythagoras Solar Photovoltaic Glass Unit33
expected to bring breakthroughs that should help commercialise CPV systems technology in the near future.
Medium concentrators use silicon solar cells, which might get heated during the day – this can drastically reduce their performance. Usually the medium concentration PV (MCPV) systems have large aluminium cooling fins attached to the back of each panel to dissipate the excess thermal heat. The Skyline X14 (see Figure 4) is a working example of the MCPV system.34
The system consists of a reflective surface that
Figure 4: Representation of a Medium Concentrator Photovoltaic System – Skyline X14 System34
HGS Architecture HGS array HGS panel
concentrates sunlight onto the silicon solar cells. The temperature of these cells tends to rise due to the concentrated light and hence aluminium fins are used on their back to dissipate the heat generated. Slightly special solar cells are used in this system, compared with those used in a PV system. These cells tend to have a lower temperature dependency on their overall efficiency compared with conventional solar cells. The systems are tracked along the sun’s trajectory by means of a single- or double-axis tracker.
High Concentration Photovoltaics
High concentration PV (HCPV) systems are used for power generation and have a concentration factor greater than 100×. A few notable systems include the Concentrix Solar,35 and Opel, Inc., SolFocus.40
Amonix,36,37 Reflective rack Arima EcoEnergy,38 Emcore39 Using a higher concentration reduces the HGS = high gain solar. Figure 5: High Concentrating Photovoltaic Systems41 AB
consumption of the solar cell material significantly. If we have a HCPV system of 500× concentration, then a 1 cm2 solar cell area can produce the same electricity as a 500 cm2 simple PV system. However, this shifts emphasis onto the solar cell, which needs to be capable of working under this high concentration. Figure 5 shows some of the installed technologies using HCPV systems. HCPV systems usually have two-axis tracking to capture the maximum amount of available solar radiation. The high energy output from these systems and a minimal area of solar cells makes this technology competitive with utility power generation. The three types of concentrating systems are compared in Table 1.
Application of Concentrating Photovoltaic Systems CPV systems are finding their use in several applications, including power generation, desalination and BIPV applications, such as facades, sky lighting and wall curtains. The use of CPV systems in BIPV and power generation is still the most important application. Recently a
Amonix Emcore
a concentration ratio of 2.37. Other technologies in this category include the luminescent concentrators.10–12,31
developed and that is gaining in popularity is Pythagoras Solar32
A recent system that has been (see
Figure 3), which is claimed to have four times the concentration of other building-integrated photovoltaic (BIPV) systems.
Medium Concentration Photovoltaics
Medium concentration systems have a concentration ranging between 10 and 100×. These systems primarily employ a Fresnel lens, mirrors and parabolic or V-troughs. There is a slight disparity in classifying medium-type concentrators because some companies extend the range of medium concentrators to 150×. Having a higher concentration factor demands more space and therefore, they are only suitable for outdoor applications. Several types of concentrators have been developed by researchers and companies. For a recent review of the majority of CPV systems using a Fresnel lens, see Xie et al.3 concluded that these concentrators are the most promising and are
who 20
huge power-cum-desalination plant able to produce 30,000 m3 of pure water per day working on HCPV technology with a concentration ratio of 1,500× was announced in the Kingdom of Saudi Arabia.42
Several huge
power plants working on CPV technology are also being announced.41 With these figures continuing to grow, CPV technology seems promising.
Solar Cells for Concentrating Photovoltaic Systems The solar cell design plays a key role in enhancing the performance of the entire CPV system. Depending on the concentration ratio, application and the type of concentrator, different types of solar cells are used for
MODERN ENERGY REVIEW – VOLUME 3 ISSUE 2
Low concentration photovoltaic systems are usually simple in their design, manufacture and operation.
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