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What is Concentrator Photovoltaics (CPV)?

Concentrator photovoltaics (CPV) or also called “concentration photovoltaics” is a type of photovoltaic (PV) technology that generates electricity coming from solar energy.

For generating electricity CPV uses lenses or curved mirrors to focus sunlight onto small, high-quality multi-junction (MJ), and highly efficient solar cells. Also, CPV systems sometimes use a cooling system and solar trackers to increase its efficiency. Which the conventional photovoltaic system doesn’t have.

These multi-junction (MJ) solar cells use a variety of solar cells wherein each solar cell is stacked on top of one another. Each of these stacked solar cells is being tuned to a specific wavelength of light to maximize the efficiency conversion of incoming light into electricity. To gain a higher efficiency of the solar cells, a wider solar spectrum conversion into electricity is needed. Take not that conventional single-layer silicon solar cells will never be as efficient as of that multi-junction semiconductors. 

Additionally, today most multi-junction concentrator solar cells composed of 3 solar cells but scientists are currently on work with 4 and 5 junction solar cells to achieve even higher solar cells efficiencies. It was also announced that by the year 2020, we will be able to use almost 50 percent efficiency of the multi-junction solar cells in CPV systems.

Originally, multi-junction solar cells were designed to apply in space science, and until today they are still used for that purpose. In the early 2000s, scientists also started applying these multi-junction solar cells for terrestrial concentrator solar applications.

Whereas, it was forecasted that PV systems that utilize high-concentration photovoltaics (HCPV) have a big potential to become prominent and competitive in the next few decades. These photovoltaics also possess the highest efficiency of all existing photovoltaic technologies, while the smaller photovoltaic array can also minimize the system costs balance. However, concentration PV is not currently used in the PV rooftop system and is also way far common compare to the conventional PV systems. 

Additionally, high-concentration PV still competes with concentrated solar power or CSP. These PV technologies are both ideal for areas with high direct normal irradiance, such as the Golden Banana in Southern Europe and the Sun Belt region in the United States. People are often confused with the CPV and CSP, despite being naturally different technologies even from the time these two were made and launched.

To avoid confusion, CPV is using a photovoltaic effect to directly produce electricity from sunlight, whereas CSP which is often called “concentrated solar thermal” is directly using the heat coming from the radiation of the sun to make steam to make a turbine works, then it can produce electricity using a generator. 

History of Concentrator Photovoltaics (CPV)

Mid-1970s when researches about concentrator photovoltaics began, originally provoked by the energy shock from the Mid-east oil embargo. Most of the early works for the CPV began in the Sandia National Laboratories in Albuquerque, New Mexico. It was also the site where the first modern-like CPV system was produced, a few decades before the initial works. Additionally, the first photovoltaic technology they produced is the linear-trough concentrator system that uses an acrylic Fresnel lens point focus which focuses on the two-axis and water-cooled silicon cells. 

In 1979, The Ramon Areces Project exhibited the use of silicon-on-glass Fresnel lenses and cell cooling with a passive heat sink at the Technical University of Madrid under the Institute of Solar Energy. Whereas, Sandia/Martin Marietta constructed the 350 kW SOLERAS project in Saudi Arabia in 1981. 

Throughout the year 1980s and 1990s, researches and development for the CPV continued without less industry interest. While improvements in the efficiency of the cells were eventually recognized as crucial and one of the keys to making the PV technology more even economical. However, the Si-based cell technologies improvements that were used by concentrators and flat PV did not succeed in favouring the system-level economics of the concentrator PV. 

Moreover, the introduction of III-V Multi-junction solar cells started in the early 2000s and has provided a clear differentiator. The efficiency of a multi-junction cell has improved from 34 percent (3-junctions) to 46 percent in 4-junctions. In addition, since the year 2010, a large number of multi-MW CPV projects have been commissioned all over the world.

How does CPV work?

Concentrator photovoltaics (CPV) work by using optics that help in focusing the solar energy on a small high-efficiency multi-junction (MJ) solar cells. These multi-junction solar cells were originally designed for space applications and used until today. It was in the early 2000s when scientists began using multi-junction solar cells for terrestrial concentrator solar applications. The small solar cells are being paired to less expensive optics which are made from acrylic or glass allowing a reduction in the amount of expensive semiconductor material while the superior performance is being retained, using high-efficiency multi-junction solar cells. With that, solar modules are highly efficient which generates electricity at a lower cost compared to the traditional silicon solar panels.

Moreover, CPV systems significantly produce an increased in temperatures on the surface material of the PV, so the energy being used should be allocated equally in all areas of the cell to avoid local overheating because it can damage the PV materials. Also, some kinds of cooling must be considered since the thermodynamic efficiency of the photovoltaic conversion is lower at elevated temperatures. You can use either an active or passive cooling procedure. Also, the high-concentration cells need high-capacity heat sinks to avoid the destruction of PV material during the thermal process. As to CPV cells with low and smaller concentration ratios, it is not necessary to use active cooling procedure since it can only reach moderate temperature. 

Types of Concentrator Photovoltaics (CPV)

Low Concentration PV

Low concentration PV systems have a solar concentration of 2 to 100 suns. In a low CPV, the flow of heat is usually low enough that the cells do not require active cooling. In fact, after modelling and experimenting with the standard solar modules it has been discovered that no tracking or even cooling modifications are required if the concentration level is low. 

Besides, low-concentration PV systems are often using a simple booster reflector, which helps in increasing the solar electric output by over 30 percent compared to non-concentrator PV systems. Based on experimental results from LCPV systems in Canada, the energy gains over 40 percent using the prismatic glass while 45 percent were gained using the traditional crystalline silicon photovoltaic modules.

Medium Concentration PV

The medium concentration Pv ranges its concentrations from 100 to 300 suns, and these CPV systems require either an active or passive cooling and two-axis solar tracking which makes the PV material more complex than the low concentrator PV.

High Concentration PV

High concentration photovoltaics short for HCPV are PV systems that utilize concentrating optics which consists of fresnel lenses or the so-called dish reflectors. These concentrate sunlight to 1,000 suns or more intensities. The solar cells of higher concentrator PV need high-capacity of heat sinks to avoid thermal destruction as well as to manage life expectancy and temperature-related electrical performance. To further aggravate the concentrated cooling design, the heat sink must use passive cooling, or else, there will be a reduction in the overall conversion efficiency of power needed for the active cooling.

Advantages and Disadvantages of CPV

Advantages

Has a greater potential for efficiency increase in the next few years and could lead to greater improvements in land area use.
Waste heat can be possible to use for large mirror systems with active cooling
Smaller cell sizes can hamper the large fluctuations in module price due to semiconductor price variations 
Has two-axis tracking that can significantly increase the production of energy throughout the day
Can withstand high efficiencies under direct normal irradiance
No cooling water needed for passive cooling
Low energy payback time
Low cost per watt of manufacturing capital
Low-temperature coefficient
High potential for cost reduction
Less PV material
Modular – kW to GW scale

Disadvantages

Strong cost decrease of competing technologies for electricity production
Tracking systems is complex as sufficient accuracy and reliability are required. 
It can only function properly under direct beam radiation
It can only be used in regions with high DNI
CPV cannot be installed on rooftops, easily
Lack of technology standardization
Require regular cleaning to reduce soiling losses (depending on the site)
The power output of Multi-junction solar cells is more sensitive to shifts in radiation spectra 
Bankability and some issues on perception 
The formation of hot spots is possible due to concentrated sunlight
LCPV can only utilize a fraction of diffuse radiation while HCPV cannot utilize at all
Optical losses

CPV's Potential

Concentrator Photovoltaic technology is expected to grow and to expand on the market in the near future. The cost-effectiveness of CPV technology is related to some smaller-scale solar cells that have cheaper PV semiconductor material and is used to convert the concentrated light into electricity. Besides, the optics being added to the system are made from glass which are usually affordable compared to the cells themselves. 

Reviews about Concentrator Photovoltaics (CPV)

Concentrated PV Technology

HCPVT – High Concentrating Photovoltaic Thermal Systems

Concentrated Solar Power (CSP) – Murray Power and Generation

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Archived news

The concentrated photovoltaic (CPV) market has beenlong on promise and short on results.  But there have been a few hopeful signs of late.

Kleiner Perkins saw fit to invest $130 million into CPV systems vendor Amonix.  And shortly after that fund raise, Cogentrix announced a 30 megawatt project with Amonix.  That’s easily the largest CPV project in the history of CPV.

SolFocus recently said that it would have 10 megawatts in the ground by the end of the year.

Concentrix Solar, German-based CPV vendor, funded by Good Energies and recently purchased by Soitec, just announced the opening of a U.S. office and a CEClisting.

And today we saw JDSU, the optical networking, laser and coatings expert, announce that theywere entering the CPV market as a chip supplier.  The firm has a marketcapitalization of $2.1 billion.

One of the chicken-and-eggproblems that has plagued CPV is the cost and supply of thetriple-junction compound semiconductor solar cell that performs theactual photovoltaic conversion.  The low-volume supply chain for thesechips has depended on somewhat dysfunctional suppliers Emcore and Spectrolab.   Emcore has a history of losing money, questionable management and flirting with entering the CPV system business.  Spectrolab makes a quality product but both of these firms, with a culture of supplyingthe space and satellite market, have found the transition to commercialmanufacturing a bit of a cultural stretch.

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